Inlet Influence on the Pressure and Temperature Distortion Entering the Compressor of an Air Vehicle

One of the possible origins of High Cycle Fatigue in a compressor blade is the rotating stall under the influence of (rotating) inlet pressure or temperature distortion leading to a varying angle of attack on the compressor blades. This paper will be oriented towards the propagation of total pressure and total temperature nonuniformities in axial flow fans and compressors and their subsequent effect on downstream and upstream stages. An analytical technique will be used to correlate the inlet distortion patterns to the reduction of the stall/surge margin. A first part of this paper is dealing with the role of the inlet on the total pressure and temperature distortion at the fan or compressor face. A second part is concentrated on distortion propagation through the compressor. Given a total pressure or total temperature distortion entering a compressor, the methodology developed in this paper allows to predict the downstream total pressure and pressure ratio and therefore to give insight into the potential danger of a given inlet distortion pattern. 1.0 INTRODUCTION An important contributor to the HCF-problems in compressor blades is the response to aerodynamics forcing generated by upstream stators, Inlet Guide Vanes (IGV’s) and distorted inlet flow conditions. This is particularly bad in non-typical axial-flow compressors like in new applications as a lift-fan duct with a high turning angle before entering the fan, an effect becoming even worse with increasing flight speed. Under such adverse operating conditions, IGV’s are probably not able to clean up the high inlet distorted field and could even induce higher responses in the downstream blades. Pressure distortion due to the inlet can be of very different origins, ranging from reasons due to a high angle of attack, side wind, position of the inlet compared with the main rotor and the turboshaft exhaust in a helicopter or shock-boundary layer interaction in a supersonic external compression inlet as on the MIG29 (Fig. 1). It is even quite possible that the inlet itself introduces a pressure swirl distortion due to its geometry or its change of geometry as in the case of the JSF intake (Fig. 2). This concern can thus become of particular importance for such a special inlet as in the case of STOL and lift-fan. Hendrick, P. (2005) Inlet Influence on the Pressure and Temperature Distortion Entering the Compressor of an Air Vehicle. In Evaluation, Control and Prevention of High Cycle Fatigue in Gas Turbine Engines for Land, Sea and Air Vehicles (pp. 8-1 – 8-8). Meeting Proceedings RTO-MP-AVT-121, Paper 8. Neuilly-sur-Seine, France: RTO. Available from: http://www.rto.nato.int/abstracts.asp. Report Documentation Page Form Approved OMB No. 0704-0188 Public reporting burden for the collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to a penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number. 1. REPORT DATE 01 OCT 2005 2. REPORT TYPE N/A 3. DATES COVERED 4. TITLE AND SUBTITLE Inlet Influence on the Pressure and Temperature Distortion Entering the Compressor of an Air Vehicle 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) 5d. PROJECT NUMBER 5e. TASK NUMBER 5f. WORK UNIT NUMBER 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) Université Libre de Bruxelles, ULB Avenue F.D. Roosevelt, 5