Numerical and experimental investigations on multiple air jets in counterflow for generating aircraft gas turbine engine inlet flow distortion patterns

  • M. Sivapragasam

    Student thesis: Doctoral ThesisDoctor of Philosophy


    The performance of an aircraft gas turbine engine is adversely affected by the non-uniform or distorted flow in the inlet duct. Inlet flow distortion lowers the surge margin of the engine's compression system with surge occurring at much lower pressure ratios at all engine speeds. The compressor and/or engine are subjected to ground tests in the presence of inlet distortion to evaluate its performance. The simplest method of simulating inlet distortion during these tests is by installing a distortion screen ahead of the engine on the test bed. The uniform inlet flow to the compressor becomes nonuniform with total pressure loss after passing through the distortion screen. Though the distortion screens offer a number of significant advantages, they have some disadvantages. The air jet distortion system can alleviate many of the operational disadvantages encountered with the conventional distortion screens. The system consists of a number of air jets arranged in a circumferential array in a plane and issuing opposite to the primary air flow entering the engine. The jets interact with the primary stream and cause a local total pressure loss due to momentum exchange. The individual mass flow rates from the jets can be varied to obtain a required total pressure pattern ahead of the compressor at the Aerodynamic Interface Plane (AIP). A systematic study of the flow field of confined, turbulent, incompressible, axisymmetric jet issuing into counterflow is covered in this research programme. The jet penetration length and the jet width are reduced compared to unconfined counterflow and a linear relationship between the velocity ratio and the jet length ceases to be valid. The flow field of a circular compressible turbulent jet and then a system of four jets arranged circumferentially and issuing into a confined counterflow was studied experimentally and numerically. For the four jet system the mass flow rates in the four jets were equal in the first part of the study and in the second part they were unequal. The loss in total pressure due to the jet(s) interacting with the counterflow was quantified by a total pressure loss parameter λp0. The total pressure loss increased with increasing mass flow ratio. The total pressure loss distribution was evaluated at several locations behind the jet injector(s). The total pressure non-uniformity quantified by Distortion Index (DI) was found to be highest at a location just downstream of the jet injector and at far downstream locations low values of DI were observed. From the understanding gained with a single jet and four jets in counterflow a methodology was developed to generate a given total pressure distortion pattern at the AIP. The methodology employs computations to obtain the total pressure distortion at the AIP with quasi-one-dimensional inviscid analysis used as a starting point to estimate the mass flow rate in the jets. The inviscid analysis also provides a direction to the iterative procedure to vary the mass flow rate in the jets at the end of each computational step. The methodology is demonstrated to generate a given total pressure distortion pattern using four jets and is further extended to a larger number of jets, twelve and later twenty jets. The total pressure distortion patterns typical of use in aircraft gas turbine engine testing are generated accurately with a smaller number of jets than reported in the literature.
    Date of Award2014
    Original languageEnglish
    Awarding Institution
    • Coventry University
    • M S Ramaiah University of Applied Sciences
    SupervisorMohan D. Eshpande (Supervisor), Srinivasan Ramamurthy (Supervisor) & Peter White (Supervisor)

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