Pressure recovery in test facility diffusers : an engineering analysis including the effects of afterburning heat release, aerodynamic blockage, and duct expansion

As engineers design new aircraft engine test facilities to accommodate new technologies such as hydrogen burning variable-cycle engines, they will need methods to easily evaluate diffuser duct performance. In this thesis, a simple control-volume analysis of engine test facility diffuser performance has been embodied in a computer program to predict basic flow conditions such as diffuser exit Mach number, temperature, and pressure, subject to such effects as heat release from afterburning, aerodynamic blockage from flameholding bars, and sudden-expansion of the flow. It was found that straight diffuser ducts result in serious limitations on the Mach number and mass flow rate of the facility bypass air flow, especially when the diffuser flow is partially blocked. The sudden-expansion duct, on the other hand, exhibited superior performance with better static pressure recovery at most conditions and lower exit Mach numbers. Its performance was not seriously degraded by either aerodynamic blockage or heat release in the diffuser.