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5、Revised 2013-09 Superseding AIR4989 Design Considerations for Enclosed Turboshaft Engine Test Cells RATIONALEThis revision is being issued to include suggestions to achieve improved aerodynamic performance and behavior. FOREWORDThe purpose of this SAE Aerospace Information Report (AIR) is to assist
6、those involved in designing new or significantly modified turboshaft engine test cells by documenting considerations compiled from a broad spectrum of industry and government technical specialists in this field. The intent is to provide a general discussion of the major design factors that impact th
7、e capability of the test cell when used to perform accurate repeatable performance tests of an engine and will add to the understanding of the significance of the aerodynamics of the engine test environment and the load absorption devices employed. Turboshaft engines operating in a ground-level test
8、 cell can encounter a number of problems which are directly attributable to the characteristics of the test cell environment. Some of the more important factors which must be considered in the development of test cell designs leading to desired engine operational stability, aerodynamic, acoustic per
9、formance and mechanical integrity are described. Test cell performance goals which typically might be used to define “excellent” cell performance are included. When these call performance goals are achieved, stable and repeatable engine operation can be assured. Since there is no need for an aerodyn
10、amic thrust correction, it is often a misconception that, turboshaft engine correlation only concerns the metrology associated with measurement (including torque/power). This is not true and if the engine inlet and exit pressure/temperature profiles are not optimum for the installation, or comparabl
11、e with the reference datum test facility, there is the possibility of either the engine performance or power turbine re-matching to produce a different orinconsistent performance, with correction factors being applied for unknown reasons. This aspect needs to be considered during the design process.
12、SAE INTERNATIONAL AIR4989A Page 2 of 18 TABLE OF CONTENTS 1. SCOPE 3 1.1 Purpose . 3 2. REFERENCES 3 2.1 Applicable Documents 3 2.2 Symbols and Abbreviations 4 2.2.1 Parameters 4 2.2.2 Abbreviations 4 2.2.3 Subscripts . 4 3. TECHNICAL BACKGROUND. 5 4. TEST CELL SYSTEM DESIGN CONSIDERATIONS . 5 4.1 I
13、nlet Plenum 6 4.2 Test Chamber . 10 4.3 Augmentor/Diffuser . 10 4.4 Load Absorption Devices 11 4.4.1 Air Dynamometers (See Figure 1) 11 4.4.2 Water Brakes (See Figure 2) 11 4.4.3 Electrical Load Banks (See Figure 3) . 11 4.4.4 Eddy Current Dynamometers . 12 4.5 Exhaust Stack . 12 4.6 Air Dynamometer
14、 Exhaust System . 13 5. FACTORS FOR EVALUATING TEST CELL PERFORMANCE . 13 5.1 Front Cell Velocity Distortion . 13 5.2 Front Cell Temperature Distortion 13 5.3 Front Cell Airflow . 14 5.4 Bellmouth Total Pressure Distortion . 14 5.5 Bellmouth/Engine Inlet Temperature Distortion 15 5.6 Cell Bypass Rat
15、io 15 5.7 Cell Depression . 15 6. GENERAL TEST CELL REQUIREMENTS AND GOALS 16 7. CONCLUSIONS 17 8. NOTES 17 APPENDIX A AIRFLOW EQUATIONS . 18FIGURE 1 AIR DYNAMOMETER EQUIPPED TEST CELL . 7 FIGURE 2 WATER BRAKE EQUIPPED TEST CELL 8 FIGURE 3 ELECTRIC DYNAMOMETER EQUIPPED TEST CELL . 9 SAE INTERNATIONA
16、L AIR4989A Page 3 of 18 1. SCOPE This SAE Aerospace Information Report (AIR) developed by a broad cross section of personnel from the aviation industry and government agencies is offered to provide state-of-the-art information for the use of individuals and organizations designing new or upgraded tu
17、rboshaft engine test facilities. 1.1 Purpose a. To provide guidelines for the design of state-of-the-art ground-level enclosed test facilities for turboshaft engine testing.b. To address the major test cell engine load absorption device physical, aerodynamic and acoustic characteristics which can in
18、fluence operation, performance, accuracy and stability of an engine under test. c. To consider acoustic and environmental effects and methods to control them. 2. REFERENCES 2.1 Applicable Documents The following publications form a part of this document to the extent specified herein. The latest iss
19、ue of SAE publications shall apply. The applicable issue of other publications shall be the issue in effect on the date of the purchase order. In the event of conflict between the text of this document and references cited herein, the text of this document takes precedence. Nothing in this document,
20、 however, supersedes applicable laws and regulations unless a specific exemption has been obtained. 2.1.1 Ashwood, P.F., et al.: “Operation and Performance Measurements on Engines in Sea Level Test Facilities”, AGARD Lecture Series Number 132(AGARD-LS-132), Advisory Group for Aerospace Research and
21、Development, North Atlantic Treaty Organization, Neuilly Sur Seine, France, 1984. 2.1.2 NAVAL AIR WARFARE CENTER AIRCRAFT DIVISION, PATUXENT RIVER, MARYLAND, Support Systems Department, Technical Report SY50-91-005, March 1991, “TECHEVAL of A/F37T-16(V)1 Test Facility”, MCAS Tustin, California. 2.1.
22、3 Karamanlis, A.I., Freuler, R.J., Lee, J.D., Hoelmer, W., and Bellomy, D.C.: “A Universal Turboshaft Engine Test Cell - Design Considerations and Model Test Results”, AIAA Paper Number 85-0382, Paper presented to the AIAA 23rdAerospace Sciences Meeting, Reno, Nevada, January 1985. 2.1.4 Joint Repor
23、t to Congress on the Environmental Protection Agency-Department of Transportation Study of Nitrogen Oxide Emissions and Their Control from Uninstalled Aircraft Engines on Enclosed Test Cells, dated September 1994. 2.1.5 Support Equipment Evaluation/Verification Technical Report 48L-95-027, 19 Oct. 1
24、995, Techeval of Multi-Cabability Turboshaft/Prop Engine Test Facility Complex, A/F37T-16(V) 1, 2 and A/F37T-19(V) 2, 3. 2.1.6 NAVAL AIR WARFARE CENTER AIRCRAFT DIVISION, PATUXENT RIVER, MARYLAND, Support Systems Department Technical Report, Letter Report KS90037SY, October, 1990, “Development Tests
25、 of A/F37T-16(V)3 Test Facility”, MCB Camp Pendelton, California. 2.1.7 NAVAL AIR WARFARE CENTER AIRCRAFT DIVISION, PATUXENT RIVER, MARYLAND, Support Systems Department Technical Report, Letter Report 13600 SY53J/662, January 1993, “Technical Evaluation of A/F37T-16 1,2,3 Engine Test Facilities”, MC
26、AS Futenma, Okinawa. SAE INTERNATIONAL AIR4989A Page 4 of 18 2.2 Symbols and Abbreviations The following parameters, abbreviations and subscript notations are used in this document. 2.2.1 Parameters A cross-sectional area Cdflow coefficient g gravitational constant M Mach number P pressure R gas con
27、stant T temperature V velocity W airflow rate cell bypass ratio ratio of specific heats (= Cp/Cv, where Cp is the specific heat of air at constant pressure, and Cv is the specific heat of air at a constant volume) 2.2.2 Abbreviations AIAA American Institute of Aeronautics and Astronautics AGARD Advi
28、sory Group for Aerospace Research and Development BM bellmouth ENG engine FC front cell FOD foreign object damage ft/s feet per second L/D length-to-diameter ratio m/s meters per second OEM original equipment manufacturer rpm revolutions per minute SHP Shaft Horse Power TOR Torque 2.2.3 Subscripts a
29、mb ambient condition avg average Dist distortion flow flow function max maximum min minimum s static t total SAE INTERNATIONAL AIR4989A Page 5 of 18 3. TECHNICAL BACKGROUND A ground-level turboshaft engine test cell may be defined as an enclosed structure with an engine and load absorption device mo
30、unting mechanism which is intended to provide conditions for stable, repeatable and accurate engine performance testing. Turboshaft engines operating in a test cell can encounter a number of problems which are directly attributable to the characteristics of the test cell environment. These problems
31、can be as minor as unsteady engine speed and SHP variations that lead directly to increased uncertainty about other engine performance measurements since many engine performance parameters are referenced either to engine inlet conditions at the compressor or to the engine rpm, Reference 2.1.1. In th
32、ese cases, the engine performance is unstable and not repeatable and often can cause an unnecessary test rejection and subsequent costly rebuild. In the worst situations, more severe problems such as excessive turbine inlet temperatures and stalls may occur which can result in serious engine damage
33、and catastrophic failure.The above problems are generally caused by pressure or temperature distortions arising from aerodynamic characteristics peculiar to the flow field of the test cell. More specifically, the problems are related to the design of the loadabsorption device, cell inlet and exhaust
34、 systems and the cell bypass ratio, which is the ratio of the airflow bypassing the engine to that which directly enters the engine inlet or bellmouth. Cell bypass air is generated by the ejector pumping action of the engine exhaust velocity in the augmenter tube. In some cases this ejector is very
35、weak as the power turbine extracts most of the work from the hot gas. In some test cells inlet, exhaust or cell extractor fans may be needed to increase the bypass flow and evacuate heat build-up. This can sometimes be described as “forced entrainment”. When one test cell is used for several types o
36、f engines differing in configuration/orientation, engine SHP level, bellmouth inlet flow requirements, and exhaust temperatures, the probability of distorted flows is increased. And although poor cell inlet designs can obviously contribute to distortions in the flow, it is often the case that insuff
37、icient cell bypass flow is primarilyresponsible for distorted flow and the recirculation of exhaust gas to the engine intake which should be avoided. Often, one of the most common aerodynamic problems is an unacceptable inlet temperature profile as a result of hot gas recirculation.A modern ground-l
38、evel turboshaft engine test cell must be able to accommodate a wide range or mix of engine types with differing SHP levels. Such a facility must also provide an aerodynamic environment of good quality for the operation of the engine, have small errors due to test cell interference effects and instru
39、mentation inaccuracies, and include acoustic treatment to minimize environmental disturbances. The facility may also have to include features for compliance with local air pollution standards recognizing the limitations of existing gaseous emission control technology especially related to Nitrogen O
40、xide (NOx), discussed further in 4.5. 4. TEST CELL SYSTEM DESIGN CONSIDERATIONS General design concepts or features for an engine test cell to accommodate turboshaft engines are shown in Figures 1, 2, and 3. It should be noted that the configurations in the figures are not necessarily optimum ones,
41、but rather are intended only to illustrate the major features of such engine test cells. The major structural elements or sections of the cell are the inlet plenum, the test chamber, the engine augmentor/diffuser or exhaust collector, an exhaust stack and in the example air dynamometer equipped cell
42、 an associated exhaust system for the dynamometer. Each must be tailored for its specific function and at the same time be compatible with the other elements to achieve proper aerodynamic and acoustic performance of the entire test cell system. Each will be described in terms of its purpose and func
43、tional considerations. The design of turboshaft engine test cell inlet and exhaust systems is obviously of basic significance. However, a third basic element that affects the facility design is the load absorption device that enables the turboshaft engine to develop its rated power during sea level
44、testing. While the airflow through a test cell is a direct function of the inlet and exhaust system designs, the flow field is significantly affected by the load absorption device type, configuration and mounting position.SAE INTERNATIONAL AIR4989A Page 6 of 18 The turboshaft test cell bypass ratio
45、is critical to aspirating the heat buildup in the test chamber that results from heat radiating from the engine, load absorption device and associated exhaust ducting for each. Because the exhaust energy from a turboshaft engine is low the ejector pumping action of the exhaust system is sometimes no
46、t adequate to evacuate the test chamber. The best method of achieving acceptable bypass ratio is with the use of extractor fans that can be fitted in the intake, exhaust systems or cell (including roof), depending on the configuration or nature of the problem, such as cell ventilation or hot gas re-
47、circulation/re-ingestion by the engine. One favored method is to place extractor fans symmetrically about engine center line in the test cell rear wall such that ambient air flow can be encouraged through the test cell in a preferred axial flow path to create a higher bypass flow as an artificial “f
48、orced entrainment” that is capable ofexpelling unwanted hot air or gas (see Figure 3). When doing this, every effort should be made to avoid any adverse effects on radial engine intakes, air dynamometers or engines with left or right hand off-set exhaust nozzles, e.g., T58 they have not been useable
49、 at remote test sites because of the lack of adequate water or electrical services needed for stable load application. The U.S. Army and Navy field experience with these types of devices was not successful in past years but some closed loop designs, are in use and effective. Air dynamometers were developed and are successfully employed by the Army and Navy for both open air and enclosed test systems after overcoming some difficulty with th
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