Engine Test Cell Aeroacoustics and Recommendations

Ground testing of turbojet engines in test cells necessarily involves very high acoustic amplitudes, often enough and severe enough that testing is interrupted and facility hardware and test articles are damaged. The acoustic response of test cells containing energetic jets is poorly understood and generally unpredictable. Nevertheless, there is a clear need to be able to predict deleterious acoustic events in advance of facility entry. A predictive capability would permit evaluating possible fixes in advance of the entry to preclude interruption of testing and damage to hardware, both of which are costly and disruptive of weapons systems program schedules. To establish the needed predictive capability, the Arnold Engineering Development Center AEDC is implementing a computational aeroacoustics CAA capability. This report by C. K. Tam is one of several steps toward that goal. Here, Tam consolidates what is presently known about the aeroacoustics of jets and flowing ducts. The material presented includes analytical and semi-empirical models of various acoustic situations as well as test data. Also included is a proposal to ameliorate a particularly damaging acoustic event referred to as super resonance. A future report will present CAA technology appropriate for numerical solution of the flow equations as applied to jet cells.