Development of an Experimental Data Base to Validate Compressor-Face Boundary Conditions Used in Unsteady Inlet Flow Computations
Dr. MiNos SajbenDr. Donald D. FreundDepartment of Aerospace Engineering and Engineering MechanicsUniversity of CincinnatiFinal Technical ReportResearch Grant Award fromNational Aeronautics and Space AdministrationNASA Lewis Research CenterPenod of Performance: January 1, 1997 to December 31, 1997May 15, 1998
Reflection of Large Amplitude Acoustic Pulses from an Axial Flow Compressor
The reliability of unsteady inlet flow computations may be seriously degraded by the lack of experimentally validated compressor-face (outflow) boundary conditions. It is common practice to require some flow variable to be constant (pressure, velocity or Mach number, etc.), but there is little if any documented evidence to support these assumptions. In addition, these assumptions do not have a basis in observation nor are they likely to actually occur during a rapid transient of a real inlet/engine system. The present paper presents measurements of acoustic reflection coefficients for an operating multistage compressor, a quantity appropriate for the characterization of the compressor face for computational purposes. The experiment used an impulse method, in which shortduration, large amplitude acoustic pulses (one msec, with a peak value of nearly 4% of the mean static pressure, respectively) were generated in an constantarea, annular inlet. The pulse and its reflection from the compressor-face were tracked by fast-response pressure transducers. Frequency-domain analysis of the data yields transfer functions that may be thought of as frequency-resolved reflection coefficients. It was demonstrated that transfer functions can be used for the accurate prediction of transients induced by arbitrary acoustic incident disturbances. None of the currently imposed compressor-face boundary conditions predict the data obtained in this study, indicating that current practices concerning outflow boundary conditions are in need of revision. Nomenclature
J85 Surge Transient Simulation
A one-dimensional model is presented for simulating surge disturbance propagations throughout an entire turbojet engine. The predicted results using this model are presented for the surge transient flow phenomena and the unsteady compressor operating-point excursion during surge in a J85 turbojet engine. The unknown stalled compressor stage characteristics are represented by parameters whose range was determined through a parametric study. The predicted stalled characteristics showed faster responses and larger pressure-ratio deterioration compared to low-speed compressors. Surge hammer overpressures were found to have a triangular shape in the time-space (engine axis) domain. The mass flow through the compressor was found to approach zero in 10-20 ms, thus affecting the peak hammer overpressures at the intake duct and the temperature rise in the compressor. Different stall methods were found to result in different compressor operating-point excursions.