Total pressure distortion levels at the aerodynamic interface plane of a military aircraft

Abstract

Military aircrafts are often subjected to severe flight maneuvers with high Angles-of -Attack (AOA) and Angles of Sideslip (AOSS). These flight attitudes induce non-uniform in flow conditions to their gas turbine engines which may include distortion of inlet total pressure and total temperature at the Aerodynamic Interface Plane (AIP). Operation of the downstream compression system with distorted inflow typically results in reduced aerodynamic performance, reduced stall margin, and increased blade stress levels. In the present study the steady state total pressure distortion induced to the Aerodynamic Interface Plane due to the aircraft’s flight attitude have been estimated in terms of distortion descriptors. The distorted conditions at the interface between the intake and the engine have been predicted by using Computational Fluid Dynamics (CFD), where 33 different aircraft flight attitudes have been tested. Based on the obtained results the effect of Angle-of-Attack (AOA) and Angle of Side Slip (AOSS) on the distortion descriptors have been studied. The results showed that the distortion effect becomes more pronounced whenever this specific airframe configuration is exposed to incoming flow with an AOSS. Among the tested cases, the greatest total pressure defect at the AIP in terms of difference from the average value and of circumferential extent was calculated for the flight attitudes of 0·35M flight with 0° AOA and 8° AOSS and 0·35M fight with 16° AOA and 16° AOSS.

Numerical simulation of the airflow over a military aircraft with active intake

“…The process described herein is a part of a wider study (11), (21) the main objective of which is to estimate how the installed gas turbine engine's performance is affected by the aircraft's flight attitude. The airflow reaching the engine's face was predicted for each one of the examined flight attitudes and a total pressure profile at this plane was obtained.…”

Stability assessment of an airflow distorted military engine’s FAN

“…In the context of the current study, each one of the 27 CFD tested flight attitudes induced a total pressure distortion into the engine's face (AIP). This pressure distortion was quantified through the calculation of distortion descriptors in the way that has been described in detail in Triantafyllou et al 21 These distortion parameters can be correlated to the loss in surge pressure ratio (ÁPRS) in the way suggested by SAE AIR 1419. 12 ÁPRS is the loss in surge pressure ratio due to inlet distortion, normalised by the undistorted surge pressure ratio.…”

“…where C t is the radial offset term for the tip. Based on the distortion descriptor results obtained in Triantafyllou et al, 21 the loss in surge pressure ratio (ÁPRS) for the examined flight attitudes is presented in Table 6. It is clarified that the flight attitudes with negative values of ÁPRS result in an increase in surge pressure ratio (relative to the uninstalled FAN) because in accordance with equation 3, in these cases the absolute value of the radial distortion component was greater than that of the circumferential distortion and since the radial distortion was negative in these cases the outcome of equation 3was also negative.…”

“…This pressure distortion was quantified through the calculation of distortion descriptors in the way that has been described in detail in Triantafyllou et al. 21…”

Experimental investigation of flow characteristics and performance parameters of a podded aft engine air intake

“…Of course, in this case, the air intake is integrated into the body. In another study, the effect of AoA and SSA has been numerically investigated for a military aircraft equipped with an S-type inlet [7]. The authors have shown that the flight attitudes induce non-uniformities on both the temperature and the total pressure distribution at AIP.…”