Patent Application
20090047134
Subject matter disclosed herein relates generally to a backswept inducer for turbomachinery.
Turbine performance depends on available energy content per unit of drive gas and the blade tangential velocity, U, wherein the available energy for the turbine pressure ratio may be expressed as an ideal velocity, C. The turbine velocity ratio or blade-jet-speed ratio, U/C, may be used to empirically characterize the available energy and blade tangential velocity with respect to turbine efficiency. The blade-jet-speed ratio may also be defined as the ratio of circumferential speed and the jet velocity corresponding to an ideal expansion from inlet total to exit total conditions.
Turbochargers often operate at conditions with low blade-jet-speed ratio values (e.g., U/C<0.7). Radially stacked turbine rotors typically have an optimum U/C value of 0.7 where they achieve their highest efficiency. This rotor characteristic reduces the efficiency of the turbines at low blade-jet-speed ratio conditions. Further, the inducer of a radially stacked turbine rotor has a blade (metal) angle of zero degrees at its leading edge, which leads to positive incidence (flow angle minus blade angle) in the inducer when the U/C value drops below 0.7. The positive incidence can cause flow separation in the rotor with reduction in turbine efficiency.
A need exists for blades that reduce positive incidence at low U/C values. Various exemplary methods, devices, systems, etc., disclosed herein aim to meet this need and/or other needs.
A more complete understanding of the various methods, devices, systems, etc., described herein, and equivalents thereof, may be had by reference to the following detailed description when taken in conjunction with the accompanying drawings wherein:
Various exemplary methods, devices, systems, etc., disclosed herein address issues related to turbine efficiency. For example, as described in more detail below, exemplary technology addresses reduction of positive incidence at low U/C values.
Turbochargers are frequently utilized to increase the output of an internal combustion engine. Referring to
The exemplary turbocharger 120 acts to extract energy from the exhaust and to provide energy to intake air, which may be combined with fuel to form combustion gas. As shown in
Adjustable vanes positioned at an inlet to a turbine typically operate to control flow of exhaust to the turbine. For example, GARRETT® VNT™ turbochargers adjust the exhaust flow at the inlet of a turbine in order to optimize turbine power with the required load. Movement of vanes towards a closed position typically increases the pressure differential across the turbine and directs exhaust flow more tangentially to the turbine, which, in turn, imparts more energy to the turbine and, consequently, increases compressor boost. Conversely, movement of vanes towards an open position typically decreases the pressure differential across the turbine and directs exhaust flow in more radially to the turbine, which, in turn, reduces energy to the turbine and, consequently, decreases compressor boost. Thus, at low engine speed and small exhaust gas flow, a VGT turbocharger may increase turbine power and boost pressure; whereas, at full engine speed/load and high gas flow, a VGT turbocharger may help avoid turbocharger overspeed and help maintain a suitable or a required boost pressure.
A variety of control schemes exist for controlling geometry, for example, an actuator tied to compressor pressure may control geometry and/or an engine management system may control geometry using a vacuum actuator. Overall, a VGT may allow for boost pressure regulation which may effectively optimize power output, fuel efficiency, emissions, response, wear, etc. Of course, an exemplary turbocharger may employ wastegate technology as an alternative or in addition to aforementioned variable geometry technologies. In yet other examples, a turbine does not include variable geometry technology.
As mentioned in the Background section, the inducer of a radially stacked turbine rotor has a blade (metal) angle of zero degrees near its leading edge, which leads to positive incidence (flow angle minus blade angle) in the inducer when the U/C value drops below 0.7. The positive incidence can cause flow separation in the rotor with reduction in turbine efficiency. According to various exemplary methods, devices, systems, etc., disclosed herein, a turbine wheel blade includes a backswept inducer with a positive blade angle near the leading edge (i.e., on an approach to the leading edge). Such an exemplary blade reduces positive incidence when a turbine operates at U/C values less than about 0.7.
Of course, turbines may need to operate at U/C values greater than about 0.7. Under such conditions, the backswept inducer increases the negative incidence; however, turbine wheels can typically tolerate large negative incidences. Thus, turbine efficiency under negative incidence will not be affected by a modest inducer backsweep. Where a turbine operates constantly at U/C values greater than about 0.7, a forward-swept inducer may be used to reduce the negative incidence. While the various figures do not illustrate a forward-swept inducer, such an inducer may be readily understood with respect to the description set forth herein.
In
tan(β)=r dΘ/dxm (1).
Given Eqn. 1, local blade angle may be described as being near an edge as a construction line described by the meridional coordinate essentially ends at the edge.
An exemplary blade optionally includes an inducer with a modest backsweep. For example, a modest backsweep may correspond to a local blade angle near the leading edge of a blade from about 10 degrees (10°) to about 25 degrees (25°). As already mentioned, blade angle near the leading edge of an exemplary blade may vary. For example, an exemplary blade may include a blade angle proximate to the backplate end of the leading edge that exceeds the blade angle proximate to the shroud end of the leading edge. Thus, the local blade angle may vary as one moves along (and near) the leading edge.
A backswept inducer may act to increase mechanical stress of the inducer under centrifugal load. To counteract such increases in mechanical stress, where appropriate, a turbine with backswept inducer blades may operate at a reduced speed compared to a turbine without such blades; a modest backsweep may be used (e.g., about 10° to about 25°); inducer tip width (leading edge width) may be reduced compared to a blade without a backswept inducer; backsweep angle may be small near the shroud end of the leading edge and increase toward the backplate end of the leading edge; and/or inducer blade thickness may be chosen in a manner to account for any increase in stress with respect to a blade that does not include a backswept inducer.
An exemplary method of reducing positive incidence of a turbine wheel blade at U/C values less than about 0.7 includes providing a blade with a backswept inducer where the backswept inducer includes one or more positive local blade angles near the leading edge.
As already mentioned, a forward-swept inducer may be used to reduce negative incidence for turbines that typically operate at U/C values in excess of about 0.7. The description herein allows for an understanding of such exemplary blades. For example, Eqn. 1 and the coordinate system of
Although some exemplary methods, devices, systems, etc., have been illustrated in the accompanying Drawings and described in the foregoing Detailed Description, it will be understood that the methods, devices, systems, etc., are not limited to the exemplary embodiments disclosed, but are capable of numerous rearrangements, modifications and substitutions without departing from the spirit set forth and defined by the following claims.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/GB04/05361 | 12/21/2004 | WO | 00 | 2/19/2008 |
