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SAE AIR1191 Revision A, March 1, 1999
Performance of Low Pressure Ratio Ejectors for Engine Nacelle Cooling
Description / Abstract:
1. SCOPE:
1.1 Method:
A general method for the preliminary design of a single, straight-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 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 equations 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.
1.5 Purpose:
In typical helicopter gas turbine engine installations, the engine is enclosed within a nacelle. 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 engine 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 defining the ejector geometry to provide the required cooling flow for a given application is needed.
1. SCOPE:
1.1 Method:
A general method for the preliminary design of a single, straight-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 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 equations 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.
1.5 Purpose:
In typical helicopter gas turbine engine installations, the engine is enclosed within a nacelle. 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 engine 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 defining the ejector geometry to provide the required cooling flow for a given application is needed.
SAE AIR1191 Revision A, March 1, 1999
Performance of Low Pressure Ratio Ejectors for Engine Nacelle Cooling