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4、ndardAIR1191 RE V. AIssued 1971-11Reaffirmed 1989-05Revised 1999-03Superseding AIR1191P erformance of L ow P ressure R atio E jectorsfor E ngine N acelle C oolingFOREWORDChanges in this revision are format/editorial only.1. SCOPE:1.1 Method:A general method for the preliminary design of a single, st
5、raight-sided, low subsonic ejector is presented. The method is based on the information presented in References 1, 2, 3, and 4, and utilizes analytical and empirical data for the sizing of the ejector mixing duct diameter and flow length. The low subsonic restriction applies because compressibility
6、effects were not included in the development of the basic design equations. The equations are restricted to applications where Mach numbers within the ejector primary or secondary flow paths are equal to or less than 0.3.1.2 Procedure:A recommended step-by-step procedure is shown.1.3 Equations:The e
7、quations used in the procedure, as well as their derivations, are given.1.4 Sample Calculation:A sample calculation is presented to illustrate the use of the basic method.SAE AIR1191 Revision A- 2 -1.5 Purpose:In typical helicopter gas turbine engine installations, the engine is enclosed within a na
8、celle. Within the nacelle, heat is rejected from the engine skin and from other sources such as the engine oil cooler, generator, and airframe accessories. Therefore, it becomes necessary to provide a flow of ventilating air through the nacelle to maintain the ambient temperature surrounding the eng
9、ine at an acceptable level.One possible means of providing this ventilating air is to utilize the kinetic energy of the engine exhaust gas in an ejector to induce an airflow through the enclosure. This device is also commonly called an eductor, an aspirator, or a jet pump.A straightforward method of
10、 defining the ejector geometry to provide the required cooling flow for a given application is needed.2. REFERENCES:1. Hussman, A. W., Professor of Engineering Research, Pennsylvania State College, “Ventilation Eductors in Gas Turbine Exhaust Stacks,” Contract Nobs-56173, Index No. NS622-078, May, 1
11、953.2. Hussman, A. W., Professor of Engineering Research, Pennsylvania State College, “Eductor Design Manual for Straight-Walled Ventilation Eductors in Gas Turbine Exhaust Stacks,” Contract Nobs-56173, Index No. NS622-078, May, 1953.3. Stephenson, D. W., AiResearch Mfg. Co. of Arizona, “A General M
12、ethod for the Preliminary Design of Single, Straight Sided, Subsonic Gas Turbine Eductors,” AiResearch Report GT-6880, Nov. 21, 1962.4. London, A. L., and Pucci, Paul F., Stanford University, “Exhaust Stack Ejectors for Marine Gas Turbine Installations,” Technical Report No. 26, July, 1955.5. Keenan
13、, J. H., and Kaye, J., “Gas Tables, Thermodynamic Properties of Air, Products of Combustion, and Component Gases,” John Wiley and Sons, Inc., New York, October, 1957.6. McAdams, W. H., “Heat Transmission,” McGraw-Hill Book Company, Inc., New York, 1942.3. METHOD:3.1 Description:An ejector is a devic
14、e that utilizes the kinetic energy of a relatively high velocity gas stream to induce the flow of another, lower velocity, stream into a common duct by depressing the static pressure at the point where the high velocity stream enters the mixing duct.3.1.1 Figures 1 and 2 illustrate schematically the
15、 two most generally used types of gas turbine-ejector systems. Figure 1 represents an installation where the compartment and gas turbine engine have separate inlets. This is the most common type of installation encountered. Figure 2 represents an installation where the gas turbine engine receives it
16、s airflow from the compartment. Refer to TableI for nomenclature.SAE AIR1191 Revision A- 3 -FIGURE 1. Flow Schematic and Station Identification for Gas Turbine-EjectorInstallation Where Engine and Nacelle have Separate InletsFIGURE 2. Flow Schematic and Station Identification for Gas Turbine-Ejector
17、Installation Where Engine Air is Taken from the NacelleSAE AIR1191 Revision A- 4 -TABLE I. NomenclatureA Cross-sectional area or equivalent orifice area sq ftC Flow coefficient DimensionlessD Diameter ft or inchesE Ventilation characteristic Dimensionlessf Fanning friction factor Dimensionlessg Grav
18、itational constant (32.174) ft/s 2h Enthalpy Btu/lbL Mixing zone length ft or inchesM Mixing constant DimensionlessP Absolute pressure lb/in. 2 P Differential pressure in H 2 OQ Volume flow ft 3 /sR Gas constant (53.32 for air) ft/RRe Reynolds number DimensionlessT Absolute temperature RV Velocity f
19、t/sW Weight flow lb/s Density lb/ft 3 Efficiency Dimensionless Viscosity lb/ft-sSubscripts1 Refers to entrance to compartment or engine inlet duct2 Refers to engine inlet3 Refers to compressor discharge4 Refers to engine discharge5 Refers to engine discharge6 Refers to exit of engine discharge tail
20、pipe (ejector primary nozzle)7 Refers to compartment inlet8 Refers to compartment flow path9 Refers to ejector secondary nozzle10 Refers to exit of ejector mixing section11 Refers to exit of diffuser sectionam Refers to ambientc Refers to compartmentd Refers to diffusere Refers to enginef Refers to
21、fanm Refers to mixing zonevp Refers to velocity pressureSAE AIR1191 Revision A- 5 -3.1.2 The main components of the ejector are as follows:a. The ejector primary nozzle, which is also the exit of the engine-mounted tail pipe. This is represented schematically by Station 6. The relatively high veloci
22、ty exhaust gas enters the ejector at this point.b. The ejector mixing duct, extending from Station 6 to Station 10. In the mixing duct, the kinetic energy of the exhaust gas is partly transferred to the ventilating airflow.c. The ejector secondary nozzle, which is the annular area between the engine
23、 tail pipe or primary nozzle and the ejector mixing duct at the point where the ventilating airflow enters the ejector. The secondary nozzle is represented by Station 9.3.1.3 Another component sometimes present in an ejector system is an exhaust diffuser. This device is shown schematically in Figure
24、s 1 and 2 as extending from Station 10 to Station 11. Use of this device will reduce the static pressure at Station 10.3.2 Flow Path Assumptions:3.2.1 With the separately ducted configuration illustrated in Figure 1, the engine air flow is assumed to enter the engine inlet duct at Station 1 at a spe
25、cified pressure and a specified temperature. The nacelle internal ventilating air is assumed to enter at a specified temperature and a specified pressure through a separate entrance at Station 7, from which it flows through the nacelle with a resultant rise in temperature due to heat transfer from t
26、he engine and its accessories and a drop in pressure due to flow losses and velocity increases. The engine exhaust leaves the turbine tailpipe (ejector primary nozzle) with a velocity V 6 , at a temperature T 6 , and with a static pressure P 6 . The ventilating-air flow enters the ejector at Station
27、 9 at a temperature equal to T 9 , at a velocity, V 9 , and at a pressure, P 9 , which is assumed to be equal to P 6 . In the mixing zone of the ejector, the kinetic energy of the exhaust gas is partly transferred to the ventilating-air flow, so that the exhaust gas velocity decreases and the ventil
28、ating-air velocity increases. The mixed stream leaves the ejector at Station 10 or Station 11, as applicable. In most cases, because of the usual physical limitations on mixing zone length, the two streams are not completely mixed. This deviation from perfect mixed conditions is taken into considera
29、tion in the basic equations by the use of an empirical mixing constant M. The mixed stream is discharged at a mean temperature T 10 , at a mean velocity V 10 , and at a pressure P 10 or P 11 , as applicable, which is usually equal to ambient pressure.3.2.2 With the configuration shown in Figure 2, t
30、he engine and ventilating air enter the nacelle through a common inlet at Station 1. Part of this air enters the engine and the balance flows through the nacelle around the engine and into the ejector. Other assumptions are the same as above for the separate inlet configuration.SAE AIR1191 Revision
31、A- 6 -3.3 Ejector Performance Requirements:The quantity of nacelle cooling-airflow required for a given engine installation will depend on the amount of heat to be removed in each engine zone and on the maximum allowable temperature of each zone. This may be seen by examining the following equation
32、for the transfer of heat to the ventilating airflow.where q = total heat transferred in a given zone, Btu per hourW c = nacelle ventilating airflow, lbs per minT b = applicable zone ventilating air discharge temperature, FT a = applicable zone ventilating air inlet temperature, FC p = mean specific
33、heat of ventilating air, Btu per (lb-F)3.3.1 Once the following are known, it is a simple matter to solve the above equation for the required nacelle cooling airflow:The total heat to be removed in each zone, q.The inlet temperature of each zone (the discharge temperature of a given zone will be the
34、 inlet temperature of the next zone).The maximum allowable nacelle cooling-air temperature of each zone (this is usually specified in the engine installation manual).3.3.2 Typical sources of heat release to the nacelle cooling airflow in a gas turbine installation include the following:Heat transfer
35、 from the engine external skin, including the accessory gearbox, the tail pipe, and the external skin of the engine oil cooler.Heat rejection to the generator cooling air.Heat rejection to the oil-cooler airflow.Heat rejection from engine-driven airframe accessories.3.3.3 The values of heat rejectio
36、n from engine external surfaces and to the engine lubricating oil are normally supplied by the engine manufacturer. Both of these types of heat rejection vary as a function of engine load and ambient temperature surrounding the engine. The heat rejection from engine external surfaces also typically
37、varies as a function of the cooling air velocity around the engine. Heat rejection to generator cooling air or to oil cooler airflow need to be included in the nacelle cooling load only if these airflows are discharged into the nacelle.qWcCp Tb Ta()60=SAE AIR1191 Revision A- 7 -3.4 Recommended Desig
38、n Procedure:3.4.1 General Guidelines: The following general guidelines are recommended in the design of gas turbine exhaust ejectors:(a) The mixing duct should be made adequately long to assure good mixing of the two flow streams. If space permits, a flow length equal to several mixing duct diameter
39、s is recommended. The design procedure described herein, however, enables one to design a shorter ejector if the resulting cooling airflow is adequate for the installation.(b) The ejector should be designed, if possible, with use of a primary nozzle area equal to the engine exhaust area upon which t
40、he engine estimated performance is based. If, after investigating various combinations of mixing-duct diameter and length, the nacelle cooling airflow obtained with this tail-pipe configuration is still inadequate, the cooling airflow can be increased by use of a diffuser at the end of the mixing du
41、ct to reduce the back pressure or by decreasing the tail-pipe discharge flow area to increase the velocity of the primary flow. It should be recognized that reducing the tail-pipe discharge area will result in a loss in available engine performance.(c) If turning of the exhaust gas is necessary, thi
42、s turning should be made as gradually as possible. Abrupt turns and bends in the exhaust duct should be avoided.(d) The effect of mixing-duct pressure losses (caused by friction and turning of the exhaust gas in the mixing duct) on ejector performance may be treated in the calculation procedure by u
43、se of an equivalent frictional loss coefficient, 4fL/D 10 .(e) The ejector primary and secondary nozzles should be as concentric as possible and the center lines of the secondary nozzle and the mixing-duct inlet section should be as parallel as possible in order to promote uniform distribution of th
44、e airflow through the secondary nozzle.(f) The design procedure presented herein is for the primary nozzle throat located as shown in Figure 3(a). However, location (c) or (d) where the primary nozzle throat is located approximately one diameter outside the mixing duct throat gives better performanc
45、e and location (b) gives poorer performance.SAE AIR1191 Revision A- 8 -FIGURE 3. Alternate Throat Locations3.4.2 Design Procedure: The design method consists of the solution of the basic equations given in Table II with the use of known and estimated data. The derivation of the equations of Table II
46、 is given in Section 5.The following inputs are required to solve the basic equations:1. Engine and nacelle inlet temperatures, T 1 and T 72. Engine and nacelle inlet pressures, P 1 and P 73. Engine discharge temperature, T 64. Engine air flow rate, W e5. Engine tail-pipe or ejector primary nozzle d
47、ischarge area, A 66. Required compartment cooling-air flow rate, W c7. Compartment cooling-air temperature rise, T 9 -T 7 or T 9 -T 11 as applicable8. Compartment inlet “pressure drop”, P 79. Compartment flow path pressure drop, P 810. Ejector discharge pressure, P 1111. Mixing duct discharge diffus
48、er area ratio and efficiency, if applicableSAE AIR1191 Revision A- 9 -TABLE II. Basic EquationsSAE AIR1191 Revision A- 10 -TABLE II. Basic Equations (Continued)SAE AIR1191 Revision A- 11 -TABLE II. Basic Equations (Continued)3.4.2 (Continued):Items 1, 2, 3, and 10 are usually given operating conditi
49、ons for the gas turbine engine. Item 4 may be read from basic gas turbine performance curves as a function of items 1, 2, and 3. Item 5 is known or specified. Items 6 and 7 are interrelated, since the heat transferred to the ventilating air is equal to these two quantities times the mean specific heat of the ventilating air. If the heat release to the compartment and the maximum allowable compartment temperature are known, the required W c can be calculated from these quantities. Items 8 and 9 can be estimated from the geometry of the compartment
