Importance of the Bleed System on the Overall Air Intake Performance

摘要

The objective of this paper is to investigate the sensitivity of the AI characteristic on the design of the bleed system based on wind tunnel tests and CFD calculations. The characteristic of an air intake (AI) can be regarded as one of the key parameters of the overall performance of a ram jet (RJ) propulsion sub-system (PSS). Apart from providing the oxidizer mass and limiting the maximum pressure within the ram combustor (R.C), which has direct impact on the achievable thrust, a well designed AI also gives the opportunity to reduce the drag of the system significantly. An AI characteristic is highly dependent on the flight conditions, the free stream Mach number M_0, the angle of attack α, the side slip angle β and the ambient pressure p_0 and temperature T_0 denned by the flight altitude. Due to the fact that modern missile systems do not allow an optimization to one specific operational point, one of the most critical challenges during the design of an AI is to find a good compromise for the overall performance of the PSS. On the one hand the PSS should deliver enough thrust to accelerate at low altitudes and low Mach numbers, on the other hand the stability margin (SM) of the AI should enable the system to operate at high altitudes. Besides the design of the compression ramps which define the Mach numbers at which the shocks will enter the air duct, the bleed system (BS) has a main impact on the characteristic of the AI performance.