The invention relates to an electric turbine bypass fan and compressor for hybrid propulsion.
Optimization of thermal power in turbine engines starts with the optimization of the thermodynamic cycle scheme, i.e. the thermodynamic relations of cycle media in the process of power production. In accordance with Camas Rule of Thermodynamics, it involves the introduction of fuel heat input at maximum possible temperature, compression and expansion, at maximum compressor and turbine efficiency, along with the release of non-convertible heat to ambient temperature at minimum loss.
Gas turbine engines, and the devices that are powered by gas turbine engines, are limited in overall design and performance by mechanical, material, and thermodynamic laws. They are further constricted by the design limitations of the three elements that make up the baseline design of gas turbine engines: the compressor, the combustor and the turbine. In turbines for aircraft, these three engine sections are contained inside of the outer turbine casing and are centered on a load bearing drive shaft that connects the turbine (on the portion of the drive shaft) with the compressor (on the forward portion of the drive shaft). Typically the drive shaft is a twin or triple spool design, consisting of two or three concentric rotating shafts nested one inside the other. The different spools allow the turbine assembly and the compressor assembly, each of which is connected to one of the spools of the drive shaft, to rotate at different speeds: the turbine is optimized to run at one particular speed for combustion and thrust processes, and the compressor is optimized at a different speed to more efficiently compress incoming air at the inlet face. The difference in speeds of the spools Is typically accomplished by reduction gears.
The compressor assembly consists of several compressor stages, each of which is made up of a rotor and a diffuser. The rotor is a series of rotating airfoil blades, or fans (attached to the shaft), which converge the air, i.e., compressing the volume of air on the intake side of the blade into a smaller volume of air at exit. Adjacent to each rotor is a diffuser. The diffuser is a fixed, non-rotating disc of airfoil stators that expands the volume of the incoming high pressure air, now at higher velocity after exiting the adjacent rotor, by having the air pass from a narrow opening on the intake side of the diffuser into a gradually enlarging chamber that slows and lowers the pressure of the air. Each compressor stage is made up of a compressor rotor and a diffuser disc. There are as many stages of the compressor as are required to get the air to the required air temperature and compression ratio (in high performance aircraft turbines usually in between 40:1 to 65:1 dependent on combuster design, flight and speed envelope and turbine thrust requirements) prior to entering the combustor.
In the combustor, the higher pressure and higher temperature air mixes in a swirl of hot liquid fuel and ignites to form a controllable flame front. The flame front expands as it combusts, rotating and driving turbine blades as the flame front exits the engine. The turbine assembly consists of several sets of rotating turbine blades connected to the drive shaft and angled so that the thrust of the flame front causes the blades to rotate. The turbine blades, being connected to the drive shaft, cause the drive shaft to rotate and thus the compressor blades to rotate.
Turbomachinary design must be optimized in terms of flow efficiency, high temperature blade cooling methods, rotor speed, and turbine compressor driving connections on the basis of sound rotor dynamics. Many technical specialties are interwoven in a design; e.g., axial flow air compressors involve the intersection of thermodynamics, aerodynamics, structures, materials, manufacturing processes, and controls. Typically, selection of rotational speed is complex in current turbomachinary designs using drive shafts. It largely depends on the balance of the requirements of the three major components on the common shaft—the by-pass fan, compressor, and turbine. Because of requirements for differential compression and associated rotational speeds, the drive shaft is multi-segmented with one shaft running inside another. In an electric turbine by-pass fan and compressor system, eliminating the drive shaft leads to a more refined approach to differential staging of the fan to the compressor, and the interrelation of thermodynamics and efficiencies with interstages in multi-axial compressor designs.
The overall layout of multiple compression stages in turbomachines is driven by the objective of maximizing the performance of the first transonic turbine stage and its associated impact on subsequent turbine stages and their efficiences of power extraction from the combusting gases. Electric turbo compressor-compounding eliminates the mechanical coupling to the engine crankshaft, thereby eliminating the need for a crankshaft forward of the combustor. This provides additional flexibility in packaging the thermodynamic cycle scheme and its design in the turbine. The compressor-compounding also provides more control flexibility in that the amount of power extracted can be varied, allowing for control of engine thermodynamics, pressure ratio, fuel consumption, mass airflow, entropy and endothermic reactions and nitrogen oxide (NOX) and carbon dioxide (CO2) formation. Moreover, the compressor-compounding can be operated as a ring-generator with embedded systems controls for switching and generate large amounts of power for other electric payloads on an airframe.
Pressure Ratio compressibility is to be matched to multiple design point operating conditions. Because the compressor of the present invention has one or more rotor stages (compressor and diffuser), each being driven by one or more electric ring motors, the compressor rotor stages are designed and tuned more precisely to the compression ratio to be attained within the turbine design operating characteristics, thrust requirements and flight envelope. This allows for optimal aerodynamic design and efficiencies of the rotor stages in the compressor and subsequently the possibility of fewer stages needed to achieve the required compression ratios for operation of the turbine. The result is a significant potential in weight savings. Because each compressor rotor may be driven independently and at different speeds, the engine may be used more efficiently at different stages of the flight envelope.
The impact of the present invention, its innovation and the unique aspect it can impose on current turbomachinary layout design, thermodynamic cycles, and thermal efficiencies, which can improve power production, is dramatic.
It is an object of the invention to design and tune the compressor rotor stages more precisely to the compression ratio to be attained within the turbine design operating characteristics, thrust requirements and flight envelope.
It is another object of the invention to provide optimal aerodynamic design and efficiencies of the rotor stages in the compressor. Another object of the present invention is to achieve significant weight savings for operation of the turbine.
An additional object of the present invention is to use the engine more efficiently at different stages of the flight envelope. Still another object of the invention is to provide conductive pathways to power the ring motor magnetics via the generator location.
Yet another object is to provide a novel and unique configuration of forming electrical conductive pathways in rotational turbomachinary components.
Another object is to reduce the number of rotor/diffuser compressor stages.
The present invention is shown in the appended drawing figures of which:
a s a graph depicting the pressure and velocity profiles through an electrical multi-stage axial compressor.
For the purposes of promoting an understanding of the principles of the Invention, reference will now be made to the embodiments of the present invention illustrated in the drawing figures briefly described above. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated device, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates.
The key operations of the electric by-pass fan and electric turbocompressor-compounding compressor turbine system are that they are disengaged or engaged electrically, so that combustion cycles, compressor ratios, compressor cooling, thrust, and electric generation can be arranged and optimized for high thermodynamic and combustion efficiencies across the entire flight envelope, regardless of altitude, air density, temperature and other operating constraints.
Compared to current turbine engine systems for aerospace applications, the electric by-pass fan and/or electric turbocompressor-compounding system is designed to operate at ideal compression, combustion and burn efficiencies, and at higher temperatures, throughout a broader range of operation, from low subsonic (Mach 0.3) to high supersonic (Mach 2.8+) flight speeds. This is due to the magnetic, thermodynamic, mechanical and electric technologies that enable electric compression and by-pass fan operation.
The pressure ratio compressibility can be matched to multiple design point operating conditions. The electric by-pass fan has one or more low-bypass fans and/or electric compressor stages making up a compound compression system. The air flows into the electric by-pass fan and/or the electric compressor in an axial direction through a series of rotating rotor blades, and stationary stator vanes that are concentric with the axis of rotation. The flow path in the axial electric ring by-pass fan and the electric multi compressor stages (turbocompressor-compounding system) decreases in cross-sectional area in the direction of flow. The decrease in cross-sectional area is in proportion to the increased density of the air as the compression progresses from stage to stage
The preferred embodiment of the present invention has one or more stages comprising a compressor and diffuser. Each stage is driven by one or more electric ring motors. The compressor rotor stages are designed and tuned more precisely to the compression ratio to be attained within the turbine design operating characteristics, thrust requirements and flight envelope. They are independent form one another, which offers greater flexibility in the generation of compression, maximum pressure ratio attained, aerothermodynamic generation heating ratios, and high endothermic and entropic combustion and fuel burn oxidation optimization, ultimately being passed on in the combustion cycle to a highly efficient fuel burn. This allows specifically for optimal aerodynamic design and efficiencies of the rotor stages in the compressor, and accordingly, the possibility of fewer stages needed (hence potential significant weight savings) to achieve the required compression ratios for operation of the turbine. Because each compressor rotor can be driven independently and at different speeds, the engine may be used more efficiently at different stages of the flight envelope as a combustion turbine machine.
The use of a compressor stage enables the compressor rotor to generate higher torque than a shaft driven compressor rotor (wherein the compressor fan rotors are being driven from the tip of the blade at the circumference of the rotor rather than from the root or hub, and the leverage moments required to overcome mechanical loading are in an order of magnitude less) and enables the compressor stage to optimized typically constrained design variables, including those set forth below;
In thermodynamics a gas turbine engine is presented using the Brayton cycle 100, as shown in
Mathematical expressions will allow the definition of a particular performance and then determine the optimum component characteristics for a compressor meeting specific flight conditions at a given mission. The ideal cycle analysis addresses only the thermodynamics of airflow within the compressor and fan. It does not describe the details of the components and the intricate aerodynamics and efficiencies that occur during operation. Results of the various components are in the form of mathematical equations defining performance (e.g. pressure ratios, temperature ratios, entropic equations)
b is a depiction of gas turbine engine station numbering with compressor defined. The Brayton cycle depicted in
A. Mathematical Notation for an Electric Multistage Ringmotor Compressor and Fan:
Stagnation properties, TT & PT, are more easily measured quantities than static properties (T and p). Thus, it is standard convention to express the performance of various components in terms of stagnation pressure and temperature ratios:
For an electrical ring motor compressor and fan ideal assumptions are proposed:
B. Ideal Cycle Analysis Example: Turbojet Engine:
a l depicts a schematic with appropriate component notations, compressor defined.
Methodology:
Determine thrust by finding uexit/uo in terms of qo so as to create a power balance defining the relation of turbine parameters to compressor parameters, and therefore an energy balance across the compressor, relating the compressor temperature rise to the fuel flow rate and fuel energy usage and content in the combustor. The goal is to exhibit a larger compressor temperature rise through conservation of energy mass flow and reduction of aerodynamic losses due to increased thermal efficiency by fuel consumption reduction with a shaftless electric compressor concept.
The expressions for thrust and I of a turbojet are provided:
T={dot over (m)}┌(1+f)u−un┐+(p−pn)A
where f is the fuel/air mass flow ratio
With algebra manipulation of these expressions into more useful forms an expression for the exit velocity is written for the compressor (this does not account for aerodynamic drag reduction and benefit due to magnetically levitated induction air bearings in the electric ring motor compressor stage(s) nor eddy current reduction at the interface of integral distal blade and ring interfaces):
and noting that:
Thus with further algebraic manipulation:
T
T
=T
0θ0τcτ0τt (**)
This expresses the exit temperature at the last stage of a multistage compressor as a function of the inlet temperature, the Mach number, and the temperature changes across each compressor component stage. This expression will be used again later and thus marked with a double asterisk (**).
The pressure at the exit of the compressor is written in a similar manner:
Equate this to the expression for the temperature (**)
Label it (***) to be used later in developing the following expression:
Continue on the path to the expression for u7/uo or uexit/uo
Next tc, compression is written in terms of tt, temperature by noting that they are related by the condition that the power used by the compressor is equal to the power extracted by the turbine. This assumes an adiabatic condition of enthalpy of mass flow, temperature, and velocity across the combustor (between the compressor/fan and the turbine) and electromagnetic power consumption for the compressor ring motor drive and levitation coils is equated to with power production (including losses and power conditioning) from either turbine ring generators or MHD drive using alkaline seeded exhaust in the electric compressor concept. The burner temperature ratio is expressed in terms of the exit temperature of the burner, (TT4 or more specifically qt=TT4/To) as this is the hottest point in the engine, and is a frequent benchmark used for judging various designs.
The steady flow energy equation demonstrates that:
{dot over (m)}Δh
T
={dot over (q)}−{dot over (w)},
Assuming that the compressor and turbine are adiabatic, then: {dot over (m)}ΔhT=−rate of power density energy generation work done by the system=rate of power density energy consumption done on the system Since the turbine generator is connected through a magnetic flux of density “D” and an electromagnetic magnitude confined circumferentially to the turbine machine casing surrounding the compbustor, between the electric compressor/fan and turbine generator
{dot over (m)}C
p(TT
assuming {dot over (m)} and Cp are the same.
This can be rewritten as:
This is the first step relating the temperature rise across the turbine to that across the compressor with electromagnetics constant (equated to mechanical systems, not accounting for energy efficiency gains due to aerodynamic drag reduction and friction reduction for example, from magnetically levitated bearings).
Temperature Rise Across the Combustor with Change in Compression
The following step denotes the writing of an equation which represents the temperature rise across the combustor in ratio with the change in compression/change in temperature and in terms of qt=TT4/To. The equation represents the ideal where by in compression Delta T is minimized, and this is most accomplished with a multistage, electric ringmotor compressor, where conservation of energy is maximized, enthalpy decay is minimized by the two largest variables against degrading performance; aerodynamic drag and mechanical friction. Magnetic air bearings (Maglev) address this, and it is unique to this invention. The equation follows:
and for an engine with an afterburner
Now substituting the expressions for tb, and tt into an expression for u7/u0, and then into the first expression that was first written for thrust, results produce:
Specific Thrust for a Turbojet
This provides an expression for thrust in terms of design parameters for compression, combustion, Mach number, temperature and ultimately an optimized flight condition:
With algebra
Another form of this equation is:
The next step involves re-writing the equation for specific impulse, enthalpy rise, Mach number and fuel flow/heating value ratio in terms of these same parameters. This is done by beginning with writing the First Law across the combustor to relate the fuel flow rate and heating value of the fuel to the total enthalpy rise.
The specific impulse thus becomes:
Specific Impulse for an ideal turbojet where I is expressed in terms of the design parameters of Mach number, mass flow, compression, temperature, change in enthalpy rise, fuel flow/heating value ratio and physical constants, as depiced in
Similarly, the overall efficiency, hoverall is
The ideal thermal efficiency is:
and the propulsive efficiency can be found from hprop=hoverall/hthermat
Magnetic Drag
For electrodynamic suspension, magnetic drag losses are proportional to the weight of the induction ringmotor machine and are inversely proportional to travel velocity. The generally accepted form of the drag equation is given by equations 2 and 3 of 3.0b for high velocities. Here Fy is the ringmotor weight, or vehicle weight in the case of a tracked Maglev vehicle, n is the total number of coils in magnets, I is the current in each coil, h is the height of levitation, t is the thickness of the conductive track, and s is the conductivity of the track. This is depicted in
For a single stage tracked, magnetically levitated ringmotor compressor stage of mass 1040 lbs., polytropic efficiency of 0.90, 5000 SHP with mass flow rate of 24 lbs./sec. (assumes a five stage multiaxial compressor design, the magnetic drag energy consumption is estimated at 1.043 MW while the aerodynamic drag energy consumption is estimated at 5.4 MW operating at 0.2 atm (20 kPa). Aerodynamic drag dominates the energy consumption for electric compressor ringmotor concepts, however close gap tolerance to maintain high energy density from high shear pressure gap performance (16.0-20.5 lbs./sq. in.) offsets the losses of magnetic and aerodynamic drag bringing them close to match (not as seen in mechanically driven designs), and overall efficiencies are higher than in current art of multiaxial mechanically driven compressors. Lower weight and no mechanical drag from drive shafts adds further advantage and offsets magnetic drag which in overall design offers the potential of lot lower horse power to drag ratios. Further, higher mass flow rates may be tolerated, along with higher stage loading due to rim driven high torque design, consequently higher stage pressures are achievable.
Lastly, compressor area, and subsequent stage diameter design optimization is critical In defining further performance advantages as magnetic drag reduces with diameter and raise in shear pressure to achieve high energy level densities. Analysis such as this can be used to define feasible pressure versus velocity profiles such as that shaded in
Energy Exchange with Moving Blades (Compressor)
So far we have only looked at the thermodynamic results of compressors and turbines (p's and t's). Here we will look in more detail at how the components of a gas turbine compressor produces the thermodynamic results in terms of pressure and temperature, and compare thermodynamic mathematical expressions with current art, as compared with the new art of the invention. In a compression machine it is only possible to change the total enthalpy of the fluid with an unsteady process (e.g. moving blades). The amount of energy required to instill an enthalpy change, Delta E, must be analyzed with steady flow equations and design tools at this preliminary level as are known in thermodynamics and propulsion dynamics and considering improvements in the power equation of the comoporession machine in question via evaluation of steady flow in and out of a component compressor as shown in
The Euler turbine equation relates the power added to or removed from the flow, to characteristics of a rotating blade row. The equation is based on the concepts of conservation of angular momentum and conservation of energy. A representative model of the blade row describing representative vectors and metrics:
Applying conservation of angular momentum, we note that the torque, T, must be equal to the time rate of change of angular momentum in a streamtube (blade row representative of a rotor stage of the compressor) that flows through the device
T={dot over (m)}(vcrc ybrb)
This is true whether the blade row is rotating or not. Sign matters (i.e. angular momentum is a vector—positive means it is spinning in one direction, negative means it is spinning in the other direction). Dependent on definition and design, there can be positive and negative torques, and positive and negative angular momentum. In
P=Tω=ω{dot over (m)}(vcrc−vbrc)
If torque and angular velocity are of like sign, work Is being done on the fluid (a compressor). If torque and angular velocity are of opposite sign work is being extracted from the fluid (a turbine). Here is another approach to the same idea:
If the tangential velocity increases across a blade row (where positive tangential velocity is defined in the same direction as the rotor motion) then work is added to the flow (a compressor).
If the tangential velocity decreases across a blade row (where positive tangential velocity is defined in the same direction as the rotor motion) then work is removed from the flow (a turbine).
From the steady flow energy equation:
{dot over (q)}−{dot over (w)}
s
={dot over (m)}Δh
t with
{dot over (q)}=0 and −{dot over (w)}=P
P=m|h
T
−h
T
}
Then equating this expression of conservation of energy with our expression from conservation of angular momentum, we arrive at:
h
T
−h
R
=ω(rcvc−rbvb)
or for a perfect gas with Cp=constant
C
p(−TT
The Euler Turbomachinary Equation relates the temperature ratio (and hence the pressure ratio) across a compressor to the rotational speed and the change in momentum per unit mass. The velocities used in this equation are what are denoted as absolute frame velocities (as opposed to relative frame velocities).
When angular momentum increases across a blade row, then TTc>TTb and work was done on the fluid (a compressor).
When angular momentum decreases across a blade row, then TTc<TTb and work was done by the fluid (a turbine).
An axial compressor is typically made up of many alternating rows of rotating and stationary blades called rotors and stators, respectively, as shown. The first stationary row (which comes in front of the rotor) is typically called the inlet guide vanes or IGV. Each successive rotor-stator pair is called a compressor stage. Hence compressors with many blade rows are termed multistage compressors.
One way to understand the workings of a compressor is to consider energy exchanges. An approximate picture of this is done using the Bernoulli Equation, where PT is the stagnation pressure, a measure of the total energy carried in the flow, p is the static pressure, a measure of the internal energy, and the velocity terms are a measure of the kinetic energy associated with each component of velocity (u is radial, v is tangential, w is axial).
The rotor adds swirl to the flow, thus increasing the total energy carried in the flow by increasing the angular momentum (adding to the kinetic energy associated with the tangential or swirl velocity, ½rv2).
The stator removes swirl from the flow, but it is not a moving blade row and thus cannot add any net energy to the flow. In the invention, the electric multiaxial compressor concept, every stator row is a slower moving airfoil blade row, thus having the capacity to add net energy to the flow, as well as acting as a conversion device to the flow, adding some kinetic energy to the flow and raising the static pressure simultaneously of the flow. Typical velocity and pressure profiles through a multistage axial compressor look like those shown in
Note that the IGV also adds no energy to the flow. It is designed to add swirl in the direction of rotor motion to lower the Mach number of the flow relative to the rotor blades, and thus improve the aerodynamic performance of the rotor.
Velocity Triangles for an Axial Compressor Stage
Velocity triangles are typically used to relate the flow properties and blade design parameters in the relative frame (rotating with the moving blades), to the properties in the stationary or absolute frame. We begin by “unwrapping” the compressor. That is, we take a cutting plane at a particular radius and unwrap it azimuthally to arrive at the diagrams shown in
In drawing these velocity diagrams it is important to note that the flow typically leaves the trailing edges of the blades at approximately the trailing edge angle in the coordinate frame attached to the blade (Le. relative frame for the rotor, absolute frame for the stator). We will now write the Euler Turbomachinary Equation in terms of stage rotor design parameters: w, the rotational speed, and bb and bc′ the leaving angles of the blades.
C
p(−)=ω(rcvc−rbvb)
From geometry,
v
b
=w
b tan bb and vc=wc tan bc=wTcwc tan β′c
so
C
p(−)=ω(ωrc2−rcwc tan β′c−rbwb tan βb)
or
So we see that the total or stagnation temperature rise across the stage increases with the tip Mach number squared, and for fixed positive blade angles, decreases with increasing mass flow. This behavior is represented schematically.
Velocity Traiangles for an Axial Flow Mechanical Compressor Stage and an Axial Flow Electrical Compressor Stage
We can apply the same analysis techniques to a turbine. Again, the stator does no work. It adds swirl to the flow, converting internal energy into kinetic energy. The turbine rotor then extracts work from the flow by removing the kinetic energy associated with the swirl velocity.
The appropriate velocity triangles are shown in
The propulsive efficiency of a simple turbojet can be improved by extracting a portion of the energy from an engine's gas generator to drive a ducted propeller, called a fan. The ducted propeller pushes a portion of the overall air through the turbine, but by-passes the turbine, exhausting to the rear at ambient air conditions. The fart increases the propellant mass flow rate with an accompanying decrease in the required propellant exit velocity for a given thrust. Since the rate of production of “wasted” kinetic energy in the exit propellant gases varies as the first power with mass flow rate and as the square of the exit velocity, the net effect of increasing mass flow rate and decreasing the exit velocity is to reduce the wasted kinetic energy production and to improve the propulsive efficiency.
Subsequently modern turbine design has incorporated a marginalized design approach to incorporating turbofans into baseline turbojet turbomachinary to what is termed the “hot section” of the turbine. To achieve high Mach numbers for supersonic flight, with good propulsive efficiency via reduced kinetic energy losses, turbomachinary design has moved to supersonic low-bypass jet engine designs, whereby the bypass fan is reduced in size compared to a pure turbofan to maintain a relatively high mass air flow and exhaust velocity Mach number. The approach offers greater efficiency through moderation of typically high endothermic and entropic thermal reactions of pure turbojets by optimizing mass flow rates and exhaust velocities.
The use of a turbofan stage(s) enables the turbine to be refined to the cruise flight condition and low-speed flight conditions by utilizing more of the combustion gases efficiently and by reducing the wasted kinetic energy. Improvements can be observed in a ring motor turbofan where it is not constrained by the available rotating speeds in a multi-shaft turbine design as it is rim driven and enables the fan stage to optimize and maximize typically constrained design variables as follows: optimized design in turbomachinary is focused on Ideal” mass flow through the engine core and the fan. In current turbofan designs, or supersonic low-bypass turbine designs the temperature drop through the turbine is greater than the temperature rise through the compressor since the turbine drives the fan in addition to the compressor.
In the invention, there is no drive shaft driving the fan subsequently the temperature drop across the fan can be minimized as compared to across the compressor, as this is beneficial in maintaining temperature during compression and assists in the entropic and endothermic reactions in the atomization of fuel in the combustor, subsequently mass flow of the fan can be increased relative to the compressor, more air can be compressed, Delta M over Delta C at any given T. However, without a drive shaft there remains a load on the turbine, in the form of a future design iteration for an electric generation source in the form of a turbine ring generator, which causes an electric load on the turbine machine invention. With electric filter conditioning, direct AC to AC power transmittal and superconducting power transmission (bringing electric resistance to zero), and the inner compressor or fan rotating ring, with an in-situ advanced composite thermal management barrier (aerogel), allows for coil induction heat to be contained internally in the compressor (the inner rotating ring) where it is needed, but offers cool operating conditions externally against the airframe (outer fixed ring). Delta T across the compressor is conserved (reduces temperature drop, assists in maintaining heating of air due to compression and ultimately hotter combustion temperature for fuel atomization).
Mass flow can be increased since stage loading for each compressor stage can be increased in an electric compressor as previously discussed (mass flow increases load capacity). A ring motor electric bypass fan in the SonicBlue configuration of superconducting electromagnetics and magnetically levitated compressor offers zero electric resistance and zero drag. This further adds to the ability of the invention to mass load the turbo fan with inlet air beyond current design levels, thus increasing over all mass flow in the engine.
Quasi-One-Dimensional Compressible Flow in an Area Duct from a Turbofan
This implies that:
Then from conservation of mass equation:
The above equation relates the flow area, the mass flow, the Mach number and the stagnation conditions. For fan design and analysis it is frequently rewritten in a non-dimensional form by dividing through by the value at M=1 (where the area at M=1 is A*):
which takes a form something like that shown
A turbofan engine is presented with an electric turbofan upstream of a multiaxial electric compressor as previously described in this paper. Here the core flow and bypass flow are mixed together through an afterburner and nozzle. This is shown in Figure XXX, a general form of relationship between flow area and Mach number of a Turbofan (does not account for stagnation condition at the IGV of the compressor). The Ideal turbofan cycle with mechanical compressor and mixed stream with afterburner is shown in the T-s Diagram.
In the current art, modern fighter aircraft use this type of engine because it gives the high specific thrust with the afterburner on and lower thrust specific fuel consumption than a pure turbojet engine when the afterburner is off.
The analysis of this type of engine requires the definition of the total temperature and total pressure ratios across the mixer. The flow in the bypass duct from station 13 to 16 is considered to be reversible and adiabatic, The bypass stream enters the mixer at station 16 with the same total properties as the fan discharge. An energy balance of the mixer gives:
m6CpT16+m16CpTt16=m6aCpTt6A
Fluid dynamics requires equal static pressures at stations 6 and 16. Normal design of the mixer has the mach numbers of the two entering streams equal. In the case of an electric ringmotor turbofan, and electric multiaxial compressor, the Mach numbers of the two respective streams can be matched, thus reducing boundary layer drag at the mixer wall, unsteady enthalpic mixing currents mid-stream, and the two pressures of the entering streams can be made equal, thus converse to mechanically driven designs total pressure ratio of the mixer can be brought to unity creating an ideal low-bypass turbofan engine with fan and compressor driven electrically.
Compared to the core stream, the fan stream of the turbofan contains a fan rather than a compressor and does not have either a combustor or a turbine. In low-bypass supersonic mixer turbine designs the turbofan sits upstream of the compressor, its ambient temperature flow mixing downstream outside of the combustor and ahead of the afterburner. Current art in turbomachinary design of a mixed flow turbofan engine with afterburner as shown in Figure XXX using mechanical linkages (drive shaft) versus electrical load linkages as in the current invention prevent any management of gas mixing in the mixer area just described. Since velocity of bypass air and compressor air can be controlled electrically through RPM, the mixing process can be optimized. Further the management of the mixing process in this type of turbine proposed in the invention can have a positive effect on the combustion forming process adjacent to the mixer behind the turbine.
Turbofan Cycle Analysis: Mechanical vs. Electric
The power balance between the fan (Tf), compressor (Tc) and turbine (Tr) is developed through the relationship between the total temperature (Tt) ratios across these components in the following expression:
Tt=1−Tr/TA[Tc−1+@9(Tf−1)]
For the given values of Tr, TA, and Tc, there is one value of Tf for each value of @ (alpha) that satisfies all temperature ratios across these components. This can be further expressed in terms of bypass ratio, ©, such that
An expression of this equation can be derived in integral form (change in temperature and pressure over time, to total change in bypass air and thus fan pressure ratio) to demonstrate a variable fan pressure ratio and bypass ratio for an electric turbofan as compared to a mechanically driven turbofan as it relates to temperature, as bypass ratio is inversely proportional to temperature and velocity.
The invention described herein demonstrates that a multi-disc, turbofan assembly concept, because each fan disc is driven independently by an electric ring motor, the fan pressure ratio (hence the mass flow) and the bypass ratio can be varied and optimized against temperature across the main components, fan, compressor and turbine. An integral expression of an “electric variable ratio bypass fan” with “bypass flow” in a mixed flow after burning turbofan, as it relates to pressure and temperature, is described as:
In an electric bypass turbofan in an after burning mixed flow turbine, due to the variable speed fan (multi-ringmotor fan), for the integral formation
The multistage bypass fan has a plurality of stages, where each stage corresponds to an electrically driven fan rotors. In the preferred embodiment of the invention, each electrically driven fan motor is driven by one or more electric ring motors and is independently controllable. Ideally, each fan rotor may be rotated independently of any other fan rotor, although the fan rotors may be driven synchronously as well. The ring motor is disposed about the periphery of the corresponding fan rotor, with the result that the fan rotors are compressively loaded at all time. As discussed above the output air flow from the multistage bypass fan is at a higher velocity relative to the input air.
A diffuser portion is included between the multi-stage bypass fan and the multi-stage compressor, which discussed in more detail below. The diffuser has a smaller diameter than the bypass fan is designed to increase the air velocity, but lower its pressure. This allows the air flow to be managed for each stage.
The multistage compressor is coupled to the diffuser output and is sized and configured to receive only a portion of the output air flow from the diffuser. As in all bypass jet engines, a portion of the air flow from the bypass fan, bypasses the compressor and provides for a portion of the output power of the engine. The multi-stage compressor includes a plurality of compressor rotor and stator stages. Each stator and rotor combination forms one complete compressor stage. Each compressor rotor is driven by one or more electric ring motors disposed about the periphery of the rotor section. In this way, each compressor rotor section is able to be rotated independently of any other compressor rotor. Thus, each compressor rotor can be individually controlled, although it is a mode of operation to synchronously rotate some or all of the compressor rotors. In one embodiment, each compressor stator is driven at a higher rate of rotation than the compressor rotor in the preceding compression stage. Thus, the third output airflow will have a compression ratio of at least 12:1/In one embodiment where there are 8 compressor stages, the compression ratio can be in excess of 40:1. As with all bypass jet engines, a bypass path that is coupled to the output of the diffuser provides for a portion of the second output airflow around the periphery of the multistage compressor. Typically, the bypass fan is of a greater diameter than the compressor sections that follow it, and in some embodiments, each compressor stage has a smaller diameter than the preceding compressor stage. In general, the compressor includes a plurality of compressor stages where the size of the rotors in each stage is sized and dimensioned as a function of the compression ratio, mass air flow, thrust requirements, and desired flight envelope.
In one embodiment of the electric bypass fan and compressor a central hollow core is disposed upon a longitudinal axis of the bypass fan and compressor. This core, which is not load bearing as the bypass fan and compressor stages are loaded at the periphery due to be driven by individual ring motors, has a plurality of sections, some of which rotate independently of one another, and some of which are stationary. Each of the plurality of bypass fan rotors and each of the compressor rotors are coupled to the central core at rotating sections. Each of the compressor stators are stationary and affixed to the central core via non-rotating portions. The central core may includes a central passage located on the longitudinal axis that allows the flow through of 6.
Number | Date | Country | |
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60757369 | Jan 2006 | US |
Number | Date | Country | |
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Parent | 11828030 | Jul 2007 | US |
Child | 13419562 | US |
Number | Date | Country | |
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Parent | PCT/US2007/000307 | Jan 2007 | US |
Child | 11828030 | US |