Patent Application
20140208758
Gas turbines, which (for example) are used in terrestrial power generation and jet aircraft propulsion, include turbine blades that are design-constrained according to a maximum “lift” or rotational force that may be applied by any one blade under a given set of conditions. One limiting factor is a tendency for streamwise pressure variation along a low pressure side of the turbine blade to cause a near-surface velocity reversal with concomitant loss of stream adhesion to the turbine blade. The phenomenon of loss of adhesion may typically be referred to as flow separation. Flow separation may be regarded as a form of aerodynamic stall. The tendency to undergo flow separation may be most pronounced near trailing edges of the turbine blades.
According to a related application, gas turbine blades may be configured to operate at higher than previously attainable combustion gas (free stream) temperatures through the use of Coulombic repulsion of charged particles in the combustion gas, combined with film-cooling. This may result in higher thermodynamic efficiency of the gas turbine. However, a higher free stream temperature may result in higher lift per turbine blade at relatively lower free stream velocity. This greater lift at lower velocity may increase streamwise pressure variations along the low pressure side of the turbine blade, and hence (absent redesign of turbine blade aerodynamics) may be associated with an increased propensity for flow separation.
Moreover, the Coulombic repulsion itself may tend to urge the free stream away from surfaces of the turbine blade, and further add to flow separation, especially on the low pressure side of the turbine blade.
Additionally, the power output range (dynamic range) of a gas turbine may be related to an allowable range of combustion gas volume delivered to the turbine at a given rotational rate of the rotor, which (for a given cross-sectional area) can be related to a range of mass flows at which a given turbine blade/stator aerodynamic design will work most efficiently. Just as an airplane wing will stall at low velocities, corresponding to a high angle of attack, and operate less efficiently at velocities that differ significantly from a designated cruise velocity, turbine blades may suffer similar flow separation at extremes of dynamic range.
Moreover, flow separation effects may force gas turbines to use a relatively large number of stages to extract all power. More stages negatively affect capital cost, weight, and size of the gas turbine (particularly the length of the rotor shaft).
What is needed is a gas turbine that can operate with a higher combustion gas temperature without requiring turbine blade redesign, can exhibit larger dynamic range, have a lower capital cost, have a lower weight, and/or have a reduced size compared to previous gas turbines.
According to an embodiment, a gas turbine may include a combustor configured to output a combustion gas stream, the combustion gas stream being controlled or driven to at least intermittently or periodically include charged particles having a first sign. For example the first sign may be positive during at least an instant. The gas turbine also includes at least one turbine configured to receive the combustion gas stream (carrying the charged particles at least intermittently or periodically). The turbine includes at least one turbine stage having turbine blades. Each turbine blade includes a repelling surface configured to be at least intermittently or periodically held or driven to a repelling voltage having a polarity the same as the charged particles having the first sign. At least some turbine blades also include an adhesion surface configured to be at least intermittently or periodically held, driven, or in equilibrium to an adhesion voltage or charge having lower magnitude than or opposite polarity from the repelling voltage. This may cause a reduced net force of repulsion, the reduction of which may improve boundary layer and free stream adhesion.
An air channel may be configured to deliver film-cooling air adjacent to the repelling surface of the turbine blade.
According to another embodiment, a method of operating a gas turbine includes providing a combustion gas stream at least intermittently or periodically carrying charged particles having a first sign; converting thermodynamic energy to rotational energy with turbine blades; at least intermittently or periodically applying Coulombic repulsion to the charged particles from a repelling portion of each turbine blade by applying a repelling voltage to the repelling portion; and at least intermittently or periodically applying reduced Coulombic repulsion from or increased Coulombic attraction to an adhesion portion of each turbine blade by at least one of shielding the Coulombic repulsion caused by the repelling voltage or by applying an adhesion voltage to attract the charged particles to the adhesion portion of the turbine blade.
The method may include providing film-cooling air adjacent to at least the repelling portion of the turbine blade.
According to an embodiment, a turbine blade includes a repelling surface configured to be at least intermittently or periodically held or driven to a repelling voltage and an adhesion surface configured to be at least intermittently or periodically held, driven, or in equilibrium to an adhesion voltage or charge having lower magnitude than or opposite polarity from the repelling voltage. The turbine blade may include a gas channel configured to deliver film-cooling gas adjacent to at least the repelling surface. The adhesion surface may include an electrical insulator disposed adjacent to the repelling surface and an electrical conductor or semiconductor disposed adjacent to the electrical insulator.
In the following detailed description, reference is made to the accompanying drawings, which form a part hereof. In the drawings, similar symbols typically identify similar components, unless context dictates otherwise. The illustrative embodiments described in the detailed description, drawings, and claims are not meant to be limiting. Other embodiments may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented here.
Fuel is introduced to the combustor 114 through one or more nozzles 120. The combustor 114 includes a wall 122 that must be kept cool. Typically, the wall 122 may be cooled by introducing cool air through vents (not shown). The combustor wall 122 may also be cooled according to methods described herein.
Turbine blade cooling air from the compressor may be admitted, such as through an air passage 124 formed by the shaft 118. The turbine blade cooling air provides cooling to the shaft 118 by forced convection, and travels into the turbine blades. Cooling of the turbine blades is described in greater detail in conjunction with
During combustion, a flame produces charged intermediate species or transition states. These charged species include free electrons, fuel and fuel fragments, oxygen radicals, etc. Conservation of charge dictates that positive and negative charges nominally balance such that the total charge is approximately neutral. The electrode(s) 126 may attract charge of opposite sign. For example, the electrode(s) 126 may be held or modulated to a positive voltage, and may responsively attract electrons from the flame. Similarly, the electrode(s) 126 may be held or modulated to a negative voltage, which responsively removes positively charges species from the flame. The electrode(s) 126 may be modulated across a positive and negative voltage range, may be modulated in voltage above and below a DC bias voltage, and/or may be held at a substantially constant DC bias voltage. According to embodiments, the electrode(s) 126 may be modulated between relative ground and a positive voltage of a few hundred volts at a time-varying frequency of a few kilohertz up to a few hundred kilohertz. Higher or lower voltages may be used and/or higher or lower frequency may be used.
The effect of at least intermittently or periodically removing charged particles of one sign or polarity from the flame results in a charge imbalance that may be used to apply Coulombic forces on the combustion gas. The applied Coulombic forces may directly affect the movement of charged particles, and the charged particles, in turn, may transfer momentum to uncharged particles. As used herein, a “particle” may include an aerosol such as unburned fuel, a gas molecule, an ion, and/or an electron, for example. As will be described below, the applied Coulombic forces may be used to repel hot gas from temperature-sensitive surfaces, such as turbine blades, turbine inlet guide vanes, turbine stators, the turbine shaft, and/or the combustor wall.
The electrode(s) 126 may be voltage isolated from other portions of the gas turbine 101 by suitable clearances (e.g., “air gaps”) or electrical insulators 128. A voltage source 134 may provide the voltage to the electrode(s) 126. The voltage source 134 may also apply a voltage to the combustor wall 122 and to the turbine 116 blades and optionally turbine shaft 118 via a voltage conduction circuit 130. The voltage conduction circuit 130 may include one or more electrical insulators 128. Optionally, the voltage source 134 may provide different voltages to the electrode(s) 126, combustor wall 122, and/or turbine 116 blades. The voltage source 134 may include a DC voltage source and/or a modulated voltage source.
Optionally, the number density of ions may be increased or the ions may be produced by a mechanism other than the electrode(s) 126 acting on the combustion reaction to produce a majority species. Increasing the number density of ions may be used to increase the Coulombic forces acting on the hot gas. Operating by a mechanism other than the electrode(s) 126 acting on the combustion reaction to produce a majority species may be used according to designer preferences.
According to an embodiment, an electrode (optionally, electrode(s) 126 or a different electrode, not shown) may be operated at sufficient voltage to generate a corona discharge upstream of the turbine blades. In another embodiment, an additive such as one or more alkali salt(s) may be included in the fuel. In another embodiment, an additive such as one or more alkali salt(s) may be injected into the combustor 114.
Approaches for producing or increasing an ion number density are described by Lawton and Weinberg in Electrical Aspects of Combustion, incorporated herein by reference.
It is possible that alternative theories could be constructed to explain the conversion of Coulombic repulsion to electrostatic or electrodynamic acceleration of the bulk region of the fluid.
A body, such as a turbine blade 202, may be driven to or held at a voltage, VT, such as a positive voltage. A film-cooling layer 204 may include substantially only neutral particles 206. Neutral particles 206 may be regarded as not interacting with the positive voltage VT of the body 202 (ignoring dipole interactions). Accordingly, the film-cooling layer 204 may be substantially unaffected by Coulombic forces.
A bulk region 207, separated from the body 202 by the film-cooling layer 204, may include neutral particles 206 and charged particles 208. For purposes of description, charged particles 208 may be regarded as positively charged. The positively charged particles 208, 208a may be Coulombically (electrostatically) repelled by the same sign voltage VT of the body 202 and may be responsively accelerated along a path 209. The path 209 may be visualized as the positive particle 208 “falling” through a voltage gradient caused by the voltage VT of the body 202. The path 209 (e.g., the mean free path 209) typically has a probable distance inversely proportional to density. The path 209 eventually intersects another particle 206, whereupon a collision 210 between the charged particle 208 and a second particle 206 causes momentum transfer from the charged particle 208 to the second particle 206. For an average elastic collision (or a particular elastic collision of favorable orientation), momentum of the charged particle 208 may be halved, and the momentum of the second particle 206 may be increased by the same amount.
For systems where charged particles 208 are present in low concentration (which corresponds to most or all embodiments described herein), most collisions 210 involving a charged particle 208 may be binary interactions between the charged particle 208 and a neutral particle 206. After the collision 210, momentum transferred to the neutral particle 206 causes it to travel a distance near a mean free path until it undergoes a collision 212 with another particle after a time approximating a mean time between collisions. For systems where charged particles 208 are present in low concentration, most collisions 212 involving momentum transfer from a neutral particle 206 may be binary interactions between the first neutral particle 206 and a second neutral particle 206′. For an average elastic collision, half the momentum of the first neutral particle 206 may be transferred to the second neutral particle 206′. The first neutral particle 206 and the second neutral particle 206′ may then travel along respective paths until each collides with other respective neutral particles in collisions 212 and momentum is again transferred. The series of neutral particle collisions 212 thus distribute momentum originally received from the charged particle 208 across a large number of neutral particles 206 according to an exponential 2N progression in a parallel process.
Meanwhile, the charged particle 208 is again accelerated responsive to Coulombic interaction with the voltage VT of the body 202, and accelerates along a path to another collision 210, whereupon the process is repeated as described above.
According to an illustrative embodiment, charged particles 208 may be present in the free stream (also referred to as a combustion gas stream) 207 at a concentration on the order of one to one-hundred parts per billion (ppb). According to the geometric momentum distribution described above, momentum may be transferred from one charged particle 208 to a majority of all particles 206, 208 in the free stream 207 in about 24 to 30 generations of collisions 210, 212 (230>1×109, 223>8×106). The amount of transferred momentum at each collision is a function of the voltage VT of the body 202, the magnitude of charge carried by the charged particle 208, the density of the free stream 207 (and hence the mean free path length), and the distance from the surface of the body 202 to the charged particle 208 at the point of each collision 210.
Because Coulombic forces substantially do not act on particles in the film-cooling layer 204, the film-cooling layer 204 undergoes substantially no repulsion. Moreover, the Coulombic repulsion acting on the charge-carrying free stream 207 may be viewed as producing a partial vacuum in regions between the surface of the charged body 202 and the free stream 207. The film-cooling layer 204 may thus also be viewed as being held in contact with the surface of the body 202 by the partial vacuum produced by evacuation of charged particles 208.
Referring to
An optional counter-ion injection lead 138 may optionally provide charge of opposite sign to the charge imbalance in the gas stream, and thus allow the combustion reaction to proceed to completion. Optionally, the counter-ion injection lead 138 may be configured to inject the counter-ions after the first stage turbine blades, between later turbine stages, or at the outlet end of the turbine 116. The counter-ion injection lead may produce exhaust gas that is less reactive than a charged gas stream, thereby reducing environmental effects of the system described herein. The counter-ion injection lead may further be used to balance charges delivered by the voltage source 134, and thereby reduce power consumption and/or charge bleed to isolated system components.
A gas channel 306 may be configured to deliver film-cooling gas 204 adjacent to at least the repelling surface 304. For example, the gas channel 306 may be a first gas channel configured to deliver film-cooling gas through slots or holes 308 proximate a flow forward edge 310 of the repelling surface 304. Nominally, the film-cooling gas 204 and the combustion gas stream 207 may travel along streamlines 312 parallel to the surface 304 of the turbine blade 302. Because streaming is parallel to the surface 304, the film-cooling gas 204 and the combustion gas 207 may tend to not mix. Moreover, the repulsion of the charged particles 208 by the repelling voltage VT of the repelling surface 304 may tend to prevent mixing of the combustion gas 207 with the film-cooling gas 204.
A location 314 along the surface 304 may be characterized by a first pressure P1, as shown in
Referring to
The system illustrated by
v∂v/∂s=(−1/ρ)∂p/∂s+u∂2v/∂y2
where s is the streamwise axis,
y is the normal axis,
v is velocity along the streamwise axis,
ρ is density,
p is pressure, and
u is a second derivative constant.
For a case where non-streamwise velocity gradients and gradient curvatures are small compared to streamwise gradients, the equation reduces to:
v∂v/∂s=(−1/ρ)∂p/∂s.
In other words, the change in streamwise velocity is nonlinear and negative with the increase in pressure along the stream path. For otherwise conventional turbine blade designs (e.g. absent “steps”), pressure may vary monotonically and increasing with distance along the turbine blade 302 beyond the minimum pressure point.
When ∂p/∂s>0,
velocity v decreases as s increases.
There may be conditions under which v is less than or equal to 0, a result of which is illustratively shown in
For cases where P2 is sufficiently greater than P1, the streamline 312 may lift off the surface 304 of the turbine blade 302 as indicated by a stall streamline 320. In fact, the streamline 320 may represent the outer edge of a region characterized by the spanwise vortex shedding. Such behavior may be referred to as an aerodynamic stall.
Referring again to
Referring again to
The adhesion surface 324 creates the velocity profile 328 and the streamline 326 by reducing or reversing the repulsion exerted by the repelling surface 304 across at least a portion of the turbine blade 302. The adhesion surface 324 is configured to be at least intermittently or periodically held, driven, or in equilibrium to produce an adhesion voltage VA or charge having lower magnitude than or opposite polarity from the repelling voltage VT.
As described above, the repelling surface 304 may be configured to repel the combustion gas stream 207 by Coulombic repulsion. The gas channel 308 may thus deliver the film-cooling gas 204 to a volume adjacent to the repelling surface 304 between the repelling surface 304 and the combustion gas stream 207. The Coulombic repulsion of the combustion gas stream 207 by the repelling surface 304 may help to maintain the relative positions of the repelling surface 304, the film-cooling gas 204, and the combustion gas 207, and thereby reduce turbine blade 302 heating and deterioration or failure.
According to embodiments, the adhesion surface 324 may act to shield the combustion gas 207 from the repelling action of the repelling surface 304 at locations prone to stall 318.
According to embodiments, the adhesion surface 324 may be configured as an electrical shield to shield the combustion gas stream 207 from the repelling voltage VT applied to the repelling surface 304 of the turbine blade 302. The adhesion surface 324 may provide extended flow adhesion and reduce or substantially eliminate flow separation, as shown by the alternative, non-separated stream 326 and the “squished” velocity profile 328.
An electric field environment different than the electric field environment caused by VT may be formed by the adhesion surface 324. For example, a conductor or semiconductor of the adhesion surface 324 (optionally as image charge balanced against charges deposited on an overlying insulator) may be driven or otherwise carry an equilibrium or pseudo-equilibrium voltage or charge deposited by the ionized combustion gas 207. For example, the charge or voltage VA carried by the adhesion surface may be normally in equilibrium with the time-averaged charge(s) carried by the combustion gas. According to one view, this may be visualized as a Faraday cage shielding the electric field environment corresponding to adhesion flow 326. A charge 208b shielded from the repulsion voltage VT and/or responsive to an adhesion voltage VA may “feel” less Coulombic acceleration away from the surface 304 than the acceleration felt by charges 208a operatively coupled to the repulsion voltage VT.
According to an embodiment, the adhesion surface 324 may be configured to be in charge equilibrium or pseudo-equilibrium with the charged combustion gas stream 207 such that the adhesion surface 324 is charged to an adhesion voltage VA having an average value lower in magnitude than an average of the turbine blade 302 repelling voltage VT. For example, at least one of the sign of the charged particles 208 or the concentration of the charged particles 208 in the combustion gas 207 may be modulated responsive to modulation of voltage of the electrode(s) by the voltage source (
According to other embodiments, the adhesion surface 324 may be driven to or held at an adhesion voltage VA opposite in polarity from the repelling voltage VT of the repelling surface 304. Referring to
According to an embodiment, the adhesion voltage VA may be modulated in phase with a variation in passing charged particle 208 concentration and/or sign. The phase may optionally be selected responsive to mass flow rate, fuel burn rate, and/or flow velocity of the combustion gas 207. According to another embodiment, the adhesion voltage VA may follow a phase-delayed varying equilibrium with a concentration and/or sign of passing charged particles 208.
Various physical embodiments of the adhesion surface 324 are contemplated. According to embodiments, the adhesion surface 324 may be configured to apply at least reduced Coulombic repulsion on the combustion gas stream 207 compared to the repelling surface 304. As illustrated in
According to an embodiment, the adhesion surface 324 may be configured to apply Coulombic attraction to the combustion gas stream 207. For example, a gas turbine 101 (
The adhesion surface 324 may be shaped to occupy a void 406 defined by the repelling surface 304. The adhesion surface 324 may include an electrical insulator 408 adjacent to one or more voids 406 defined by the repelling surface 304. An electrical conductor or semiconductor 410, operable as an adhesion electrode, may be disposed adjacent to the electrical insulator 408. For example, the electrical conductor or semiconductor (adhesion electrode) 410 may be disposed in a recess or void 412 defined by the electrically insulating material 408. A second electrical insulator or semiconductor portion 408 may be disposed over the electrical conductor or semiconductor 410 forming the adhesion electrode. In such an arrangement, the adhesion electrode 410 may be referred to as “buried”. According to other embodiments, the adhesion electrode 410 may be exposed.
The adhesion surface 324 may comprise at least a flow rearward portion 330 of a low pressure side of the turbine blade 302. The repelling surface 304 may include substantially the remainder of the surface of the turbine blade 302. According to embodiments, the repelling surface 304 may include at least a flow forward portion of a low pressure side of the turbine blade 302 and at least a portion of a high pressure side of the turbine blade 302.
Referring to
Referring again to
According to embodiments, tantalum (Ta) may form at least a portion or alloy of the adhesion electrode 410. Tantalum may be advantageous due to its relatively high electrical opacity.
As described above, the adhesion surface 324 may include a spanwise variation in area with regions having relatively high area and regions having relatively low area. According to other embodiments, the adhesion surface 324 may be configured to support a spanwise variation in applied voltage or charge, or a spanwise variation in coupling efficiency to the combustion gas 207.
Various arrangements are contemplated.
Streamlines superimposed over the adhesion surface indicate relative combustion gas flow over the turbine blade surface. Streamwise vortices 404 may be set up by a difference between repulsion of the charged particles 208 from the repelling surface 304 and the adhesion electrode 410.
While various aspects and embodiments have been disclosed herein, other aspects and embodiments are contemplated. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.
The present application claims priority benefit from U.S. Provisional Patent Application No. 61/582,243, entitled “GAS TURBINE WITH EXTENDED TURBINE BLADE STREAM ADHESION”, filed Dec. 30, 2011, which, to the extent not inconsistent with the disclosure herein, is incorporated by reference. The present application is related to U.S. Non-Provisional patent application Ser. No. 13/172,652, entitled “GAS TURBINE WITH COULOMBIC THERMAL PROTECTION”, filed Dec. 12, 2012, which, to the extent not inconsistent with the disclosure herein, is incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61582243 | Dec 2011 | US |
