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Estimating Engine Airflow in Gas-Turbine Powered Aircraft with Clean and Distorted Inlet Flows
| Content Provider | Semantic Scholar |
|---|---|
| Author | Williams, John G. Steenken, William G. Yuhas, Andrew J. |
| Copyright Year | 1996 |
| Abstract | The F404-GE-400 powered F/A18A High Alpha Research Vehicle (HARV) was used to examine the impact of inlet-generated total-pressure distortion on estimating levels of engine airflow. Five airflow estimation methods were studied. The Reference Method was a fan corrected airflow to fan corrected speed calibration from an uninstalled engine test. In-flight airflow estimation methods utilized the average, or individual, inlet duct staticto total-pressure ratios, and the average fan-discharge staticpressure to average inlet total-pressure ratio. Correlations were established at low distortion conditions for each method relative to the Reference Method. A range of distorted inlet flow conditions were obtained from -10 ° to +60 ° angle of attack and -7 ° to + l l o angle of sideslip. The individual inlet duct pressure ratio correlation resulted in a 2.3 percent airflow spread for all distorted flow levels with a bias error of-0.7 percent. The fan discharge pressure ratio correlation gave results with a 0.6 percent airflow spread with essentially no systematic error. Inlet-generated total-pressure distortion and turbulence had no significant impact on the F404-GE-400 engine airflow pumping. Therefore, a speed-flow relationship may provide the best airflow estimate for a specific engine under all flight conditions. 1.0INTRODUCTION Total engine airflowis a parameter used in a number of ways when addressing turbofan-engine-powered aircraft issues. For example, inlet distortion is often correlated with total-engine airflow (in the absence of inlet bleed, environmental control system bleed, or bypass flows) corrected to the aerodynamic interface plane (ALP), and AlP total engine airflow (physical or uncorrected) is an important part of the net thrust calculation. Our intent, as the title suggests, is to provide a means for estimating engine airflows under a variety of flight conditions with accuracies suitable to the needs at hand. In static test cells, total-engine clean (undistorted) airflow can be obtained in a straightforward manner using calibrated bellmouths or venturis. While straightforward, the history associated with measuring total-engine airflow abounds with experiences marred by lack of attention to the issues required for accuracy and repeatability. In flight, these problems of accuracy and repeatability are made more difficult due to the presence of inlet flow distortion, instrumentation and data-acquisition-system space limitations, and changing thermal and pressure environments. A unique opportunity was presented by the highly instrumented NASA High Alpha Research Vehicle (HARV) for addressing the difficult issue of providing reliable estimates of in-flight-determined totalengine airflow. The HARV, an F/A-18A aircraft powered by two F404-GE-400 afterburning turbofan engines was specifically instrumented to accomplish propulsion-system-oriented research as part of its total mission and was flown at the NASA Dryden Flight Research Center. The propulsion mission was designed, in order of descending priority, to obtain distorted-flow AIP measurements during: 1) Stabilized high angle-of-attack/high angle-of-sideslip aerodynamic attitude conditions for comparison with computational fluid dynamic calculations, 2) Controlled maneuver transients to determine if differences exist between stabilized and transiently determined distortion measurements, and 3) Departed flight maneuvers. Correlation of the flight-obtained measurements required knowledge of the AlP corrected inlet flow. This need was the inspiration for investigating a number of methods for estimating engine-corrected airflow in flight. Significant attention was given to the instrumentation and data acquisition/data reduction systems to assure they possessed state-of-the-art capabilities. Thus, the HARV aircraft allowed comparison of three different methods of correlating and estimating airflow with one method having three variants. Briefly, these are: 1) Engine corrected airflow correlated with fan corrected speed known as the flow-speed method (also referred to as the Reference Method). 2) Engine corrected airflow correlated with forms of the AlP static-pressure to total-pressure ratio. This method has three variants: A) the average wall-static pressure ratioed to the average total pressure, B) the rake-average static pressure ratioed to the individual total pressures, and C) the estimated local static pressures ratioed to the individual total pressures. These methods are given the shorthand notation of Methods 1, 2, and 3, respectively. 3) Engine corrected airflow correlated with fan-discharge static pressure ratioed to AIP total pressure (Method 4). Crucial tothesuccess oftheseffortswastheground-test-cell flowcalibration oftheengine andthe establishment offlowcorrelations foreachmethod inflightatminimuminlet-flow-distortion conditions. Thesecorrelations thencouldbeexamined against theReference Method(corrected flowcorrected speed) calibration at the fixed aerodynamic attitude conditions to determine if inlet distortion produced systematic deviations in the Methods l, 2, 3, and 4 correlations, and which ones were least impacted by the effects of distortion. The following sections of this report provide a description of the HARV aircraft, the instrumentation, each airflow estimation method, the method of calibration, the establishment of correlation functions, and the manner in which each correlation behaved in the presence of distortion and estimates of the systematic and random errors associated with each method. The report concludes with recommendations for the most optimum method for correlating and estimating engine airflow in the presence of high levels of inlet distortion. 2.0 TEST HARDWARE, DATA ACQUISITION, AND DATA REDUCTION SYSTEMS DESCRIPTIONS The HARV aircraft, specifically configured to accomplish high angle-of-attack research, was highly instrumented and possessed state-of-the-art data acquisition and data reduction systems as described below. Further, the ground-test-cell calibration of the flight test engine and the results obtained are described. 2.1 HARV Aircraft Description The HARV is a single-seat F/A-18A aircraft (preproduction aircraft Number 6) powered by two afterburning turbofan F404-GE-400 engines. The high angle-of-attack capability is obtained by thrust vectoring, in this case, by removing the divergent nozzle flaps from the convergent-divergent exhaust nozzle and deflecting the nozzle exit flow by inserting three externally mounted paddles into each exhaust stream in a controlled and coordinated manner to produce the desired thrust vectoring (Reference 1). This thrust-vectoring capability allowed achieving a wide range of stabilized angles of attack and sideslip at the desired Mach numbers of 0.3 and 0.4. The wide range of inlet conditions, in terms of inlet distortion to which the inlet was subjected, provided the database necessary for conducting the desired airflow correlation/estimation study. The F/A-18 A aircraft inlets are two-dimensional, external compression inlets with 5-degree compression ramps mounted on the sides of the aircraft fuselage under the aft portion of the LEX (Leading Edge Extension of the wing) approximately 25 feet aft of the aircraft nose. Additional details of the inlet are described in Reference 2. The propulsion research was completed on the right-hand inlet aft looking forward (ALF). The HARV aircraft and F/A-18 inlet system are shown in Figure 1. 2.2 F404-GE-400 Engine Description The two F404-GE-400 engines that were installed on the HARV aircraft, during which the data discussed in this report were obtained, are Engine Serial Numbers (ESN) 310-083 installed on the left-hand side of the aircraft and 310-051 installed on the right-hand side of the aircraft. Both engines were equipped with an original engine control which placed the IRP flat at 87 degrees PLA. ESN 310-051 had the standard complement of engine readout parameters as shown in Part A of Table 1. Additionally, flight test instrumentation was installed to provide additional readouts of bill-of-material parameters or additional parameters that were of interest to propulsion research. These parameters are listed in Part B of Table 1. 2.3 Ground Test Phase The purpose of the ground test phase was to establish the test cell calibration of engine inlet corrected airflow with engine corrected speed for ESN 310-051 with bellmouth inlet (low distortion) conditions. Also, the use of fan-discharge-static-pressure/fan-inlet-total-pressure (cell ambient) ratio was investigated to determine if a better flow correlation could be established which took advantage of the fact that inlet distortion is attenuated as it passes through a compression component. With the total-pressure distortion attenuated, is was expected that the variation in static pressure would also be decreased. Thus, a few measurements averaged should give a reasonably valid estimate of the static pressure at the fan discharge. Figure1.HighAlphaResearch Vehicle(HARV)andF/A-18InletSystem. |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19970027377.pdf |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
