Flow Management in a Double-Offset, Transitional Twin Air-Intake at Different Inflow Conditions

Abstract

Background: Transitional twin air-intake is a vital component of the air-induction system of single-engine combat aircraft. Combat aircraft do not always fly at steady, uniform flow conditions. But in some cases, it operates at different asymmetric flow conditions, which cause a change in aerodynamic performance of aircraft components like compressor and combustor. Objective: In order to improve the air quality at the outlet of air-intake- called Aerodynamic Inlet Plane (AIP) of this twin air-intake and to improve its aerodynamic performance for wide ranges of inflow conditions, slotted synthetic jets are used. Methods: Computational studies are carried out using Computational Fluid Dynamics (CFD) software for various types of skewed turbulent velocity profiles at inlet-2 with skewness number (ξ = 0, 0.3, 0.5, 0.7), while an average uniform velocity of 20m/s at inlet-1. Based on this analysis, worst case is selected and a pair of slotted synthetic jets is used just before the inflexion plane of the twin air-intake using transition SST turbulence model. Results: The flow behaviour of transitional twin air-intake becomes more complex with the increase in skewness number, thereby decreasing the aerodynamic performance of the air-intakes. With the use of slotted synthetic jets, an improvement in static pressure recovery and decrement in total pressure loss coefficient, distortion in coeffient swirl coefficient and secondary flow non-uniformity are observed which is a great sign of improved aerodynamic performance for the twin air-intakes. Conclusion: It is proved in this study that synthetic jet can be used effectively in twin air-intake to control the flow features leading to better flow uniformity and increased overall performance at the AIP without increasing the net-mass flow rate, thereby reducing the chance of stall/surge in the aeroengines. Hybrid flow control technique (synthetic jet coupled with vortex generator array) or newer flow control technique (plasma jet) are being explored for its possible use in engine air-intakes as revealed from recent patents filed/published in this area.