Experimental and numerical inestigation of an s-duct diffuser designed for a micro turbojet engine powered aircraft

Aslan, Samet
S-duct diffusers are often used for aircraft propulsion systems that convey the intake air to the engine compressor. In this thesis, flow structure at separated entrance conditions in an S-duct diffuser that designed for a micro turbojet engine powered aircraft is investigated using experimental and numerical methods. Flow characteristics such as flow separation, secondary flows, and swirl are investigated to find out the source of distortions and pressure loss at aerodynamics interface plane. Experiments are performed at three different mass flow rates at TEI test facility. Measurements of total pressures and static pressures are obtained at the aerodynamic interface plane (AIP). Also, wall static pressures through the duct are measured. Results show that stream wise flow separation is occurred within the duct. Total pressure loss is seen as a result of the flow structure. Total pressure loss is seen to increase with increasing mass flow rate. Furthermore, circumferential distortion is also examined. Flow structure in a short S-duct diffuser at representative cruise conditions is numerically investigated for validation of simulations. Computations are compared with the experimental data obtained from literature. The results are found to compare well with experiment. Spalart-Almaras turbulence model gives the most suitable results considering mass flow rate, Mach number and pressure recovery values together. The experiment that performed at TEI is simulated and results are compared with the experimental data. RANS equations are solved with Ansys Fluent 14 commercial CFD code. Various turbulence models are used and their efficiencies are compared. Furthermore, effect of the inlet boundary profile is surveyed. Lip separation is seen at the entrance of the S-duct. Also, streamwise flow separation regions were caught through the bends of the diffuser. It is found that lip separation strengthen the effect of the wall separations inside the duct and increases the AIP distortion drastically. Numerical analyses approach the experimental wall pressure values considerably well. Reynolds Stress Model gives the closest results to the ones experimentally obtained. However, RANS solutions overpredict the pressure loss and pressure gradient across the AIP. Afterwards, transient analyses are performed for the same case using URANS and SAS approaches. While results of URANS computations are almost identical with RANS results, SAS analyses provide impressive improvement especially for predicting distortion.
Citation Formats
S. Aslan, “Experimental and numerical inestigation of an s-duct diffuser designed for a micro turbojet engine powered aircraft,” M.S. - Master of Science, Middle East Technical University, 2016.