Abstract:
An ejector system and method of operation for combining high and low pressure fluid flow streams is disclosed. A nozzle chamber communicates with a high pressure fluid flow stream and a suction chamber communicates with a low pressure fluid flow stream. The outlet of the nozzle chamber exit into the suction chamber and include multiple nozzles such that the high pressure flow stream exits the nozzle chamber in multiple flow streams having multiple surface areas for interlayer drag between the flows. The low pressure fluid flow stream is entrained by the high pressure fluid flow streams exiting the multiple nozzles to define an intermediate pressure flow stream.

Description:
BACKGROUND OF THE INVENTION 
     The subject matter disclosed herein relates to a system for improving the cooling performance of a turbine engine by utilizing an ejector system that increases compressor air entrainment efficiency. The axial location, or stage, at which compressed air is diverted from a compressor for cooling a multi-stage turbine in a turbine engine is determined by the pressure required to drive the specific systems to be serviced by that air. Diverting compressed air from the earliest possible stage of a compressor will increase overall turbine efficiency by reducing the amount of compressor work invested in the diverted air, as well as reducing the temperature of the diverted and, thus, the delivered compressed air. Therefore, it is desirable to achieve the system supply pressure from the earliest and lowest pressure stage of the compressor. 
     Known systems divert compressed air from plural ports in a multi-stage compressor to provide cooling and/or sealing air to an associated multi-stage turbine. These systems utilize a low pressure extraction flow path for conducting compressed air from a lower pressure, lower temperature stage of the compressor to the turbine and a high pressure extraction flow path for conducting compressed air from a higher pressure, higher temperature stage of the compressor to the turbine. A crossover flow path may be used to interconnect the low pressure extraction flow path, and the high pressure extraction flow path. Such a crossover allows selective control of the compressed air delivered to the multi-stage turbine such that a desired pressure and an economic mixture of air are diverted from the compressor. 
     The low and high pressure air is combined through the use of an ejector system which utilizes the momentum of motive flow of the high pressure air through a nozzle to create a suction flow of low pressure air surrounding the nozzle. Interlayer shear operates between the high and low pressure air flow streams within the ejector system resulting in entrainment (suction flow) of the low pressure air with the high pressure flow stream. It is therefore desirable to increase the entrainment of low pressure air flow within the high pressure air flow, to improve the efficiency of the ejector system. 
     BRIEF DESCRIPTION OF THE INVENTION 
     In one embodiment of the invention an ejector system for combining a high pressure fluid flow stream with a low pressure fluid flow stream is described. A nozzle chamber in communication with a high pressure fluid flow stream has an inlet and an outlet. A suction chamber in communication with a low pressure fluid flow stream includes an inlet, an outlet and is configured to receive the outlet of the nozzle chamber. The outlet of the nozzle chamber includes multiple nozzles such that the high pressure flow stream exits the nozzle chamber to define multiple flow streams having multiple surface areas for interlayer drag between the multiple high pressure flow streams and the low pressure flow stream in the suction chamber. As such, the low pressure fluid flow stream is entrained by the high pressure fluid flow streams. 
     In another embodiment of the invention, a method of combining a high pressure fluid flow stream with a low pressure fluid flow stream from a multistage compressor includes diverting low pressure compressor air through a low pressure extraction circuit and diverting high pressure compressor air through a high pressure extraction circuit. The low pressure compressor air is delivered to an inlet of a suction chamber in an ejector assembly. The high pressure compressor air is delivered to an inlet of a nozzle chamber having an outlet disposed within the suction chamber and proximate to an outlet thereof. The high pressure compressor air is ejected through multiple outlet nozzles to define multiple, high pressure flow streams having multiple surface areas for interlayer drag between the multiple high pressure flow streams to thereby entrain the low pressure compressed air in the suction chamber in an intermediate pressure, compressed air flow stream. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention, in accordance with preferred and exemplary embodiments, together with further advantages thereof, is more particularly described in the following detailed description taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is a partially schematic, axial sectional view of a gas turbine engine in accordance with an exemplary embodiment of the present invention; 
         FIG. 2  is an axial sectional view of a portion of an ejector assembly of  FIG. 1 ; 
         FIG. 3  is an enlarged perspective view of a multi-nozzle ejector nozzle of the ejector assembly of  FIG. 2 ; and 
         FIG. 4  is a graph of the weighted entrainment ratio which illustrates the performance of the multi-nozzle ejector nozzle of  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to  FIGS. 1 and 2 , there is shown an extraction system  10  for diverting compressed air from plural ports of a multi-stage compressor  12  to provide cooling and sealing air to an associated multi-stage turbine  14 . A first casing port  16  is associated with a low pressure stage of the compressor  12  for extracting relatively low pressure, compressed air  18  therefrom. A low pressure, first extraction circuit  20  extends from the first casing port  16  to a first target port  22  of the multi-stage turbine  14  for cooling and/or sealing. A second casing port  24  is provided downstream from the first casing port  16 , and is associated with a higher pressure stage of the compressor for the extraction of relatively high pressure, compressed air  26  therefrom. A high pressure, second extraction circuit  28  is provided for flow of the higher pressure compressed air from the second casing port  24  to a second target port  30  of the turbine. In gas turbine engines of the type described, cooling air which is extracted from multiple ports  16 ,  24  of a multistage compressor  12  will typically have a pressure differential of at least 16 psi in order to achieve a desirable level of cooling in the multi-stage turbine. A cross-over circuit  32  is further provided for selective flow, between the lower pressure, first extraction circuit  20  and the higher pressure, second extraction circuit  28 , for selective air flow therebetween. In an exemplary embodiment an ejector system  34  is disposed in the cross-over circuit  32 . The ejector system includes a nozzle chamber  35 , which receives the high pressure compressed air  26  from second extraction circuit  28  through a motive inlet  36 . The nozzle chamber is disposed within a suction chamber  42  having a suction inlet  38 , which receives lower pressure compressed air  18  from first extraction circuit  20 . High pressure compressed air  26  exits the nozzle chamber  35  and enters the suction chamber  42 , through nozzle outlet  40 ,  FIG. 3 . Lower pressure compressed air entering suction chamber  42  through suction inlet  38  flows into the suction chamber adjacent to nozzle outlet  40 . 
     Nozzle outlet  40  comprises an inlet end  44  and an outlet end  46 . The outlet end  46  of nozzle  40  includes multiple high pressure feed air nozzles  48  through which the high pressure compressed air exits the nozzle chamber  35  and enters suction chamber  42 . Each of the high pressure feed air nozzles  48  have an outlet end  50 , where the outlet end  50  includes a series of undulations or teeth  51 . The teeth  51  may include a generally pointed configuration that is oriented with respect to a central axis A-A of the nozzle outlet  40 . Specifically, the teeth  51  may have an apex or point  53  that extends towards the central axis A-A. In particular, the teeth  51  are oriented generally axisymmetrical with respect to the central axis A-A. The injection of high pressure compressed air  26  into suction chamber  42  utilizes the momentum of the motive flow of the air to establish a suction flow in the suction chamber  42 . The use of multiple nozzles  48  increases the surface area for interlayer drag between the high pressure compressed air  26  exiting the nozzle chamber  35  and the lower pressure compressed air  18  in the suction chamber  42 , over the surface area defined by a single nozzle ejector. As such, lower pressure compressed air flow entrainment is improved over single nozzle ejectors. In a non-limiting embodiment, the number of multiple high pressure feed air nozzles  48  disposed at the outlet end  46  of the nozzle  40  is preferably an odd number such as the three nozzles shown in  FIG. 3 . Specifically, in the embodiment as shown in  FIG. 3 , the three high pressure feed air nozzles  48  are arranged around the central axis A-A. That is, there is no high pressure feed air nozzle  48  located at the central axis A-A of the nozzle outlet. The use of an odd number of nozzles defines a non-symmetrical nozzle configuration which has been found to have a preferential effect in lowering the flow induced vibration and acoustical effect arising therefrom. Such acoustics are more likely to occur in symmetrical situations such as in even numbered nozzle configurations. 
     Compressed air exiting suction chamber  42  includes a mixture of higher pressure compressed air  26  and lower pressure compressed air  18  which is effectively entrained by the higher pressure compressed air exiting the nozzles  48  of the multi-nozzle  40 . A high and low pressure compressed air mixture  52  results in an intermediate compressed air pressure and temperature exiting the suction chamber  42 . The intermediate compressed air  52  enters mixing tube  54  and passes through the diffuser  56  before delivery to the second target port  30  of turbine  14  through discharge outlet  58 . 
     The increased surface area for interlayer drag between the high and low pressure compressed air  26 ,  18  flowing through the suction chamber  42  results in the entrainment ratio (the quantity of low pressure air taken up by the motive force of the high pressure air) being increased and, over a broader range of operational conditions. With an improvement in the entrainment of lower pressure air, the efficiency of the turbine system can be increased. 
     Computational Fluid Dynamics (CFD) models have been created to evaluate ejector performance with different nozzle structures. As shown in  FIG. 4 , one example of an application of the multi-nozzle ejector system of the present invention results in an improved entrainment ratio over single nozzle ejectors in the same application. With the overall efficiency defined as the integral of weighted entrainment ratio over the ambient temperature range, a five percent gain in overall efficiency is shown with the multi-nozzle design illustrated in  FIG. 4 . This example is intended to show the performance improvement of the multi-nozzle ejector system over single nozzle systems and the actual percentage gain in overall efficiency is expected to vary based upon the specific application. While the multi-nozzle ejector system of the present invention has been described primarily as it may be applicable to an extraction system  10  for diverting compressed air from a multistage compressor  12  to a multi-stage turbine  14 , it is contemplated that the multi-nozzle ejector system has many applications where multiple fluid streams, not limited to air, at differential pressures, likely as low as 2 psi, are combined in an efficient manner. 
     This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.