Supersonic flow measurement and computation of a lobed-mixer for trapped vortex combustors

This paper described an experimental and computational effort aimed at understanding diffuser exit profiles, for a lobed duct design that will potentially be used for higher Mach combustion evaluations in the Trapped Vortex Combustor (TVC). Experimental hardware was described, using CAD solid models to show the major flow features present in this diffuser/combustor system. Initial CFD simulations were compared with experimental data, showing good agreement with total pressure measurements, but unacceptable agreement with static pressure measurements, all taken with a Pitot-static tube. Even taking axial and radial variations in positioning of either the probe or the CFD sampling plane, checking the pressure transducer calibrations, and verification of the CFD boundary conditions, poor agreement remained. The CFD modeling methodology was modified to take into account the presence of the Pitot-static probe, and the simulations were re-run. Flow field contours of static pressure and Mach number, in the vicinity of the probe, verified that the probe caused large, local disturbances. The graphics also showed that large axial, radial and tangential velocity and pressure gradients near the static pressure ports were acting on the probe, and were reflected in the experimental data points. With the probe included in the CFD model, six new simulations were run, with the probe traversed through the model as in the experiment. These results were very encouraging, in that the established good agreement between measured and predicted values for total pressure were repeated under the new methodology, and that static pressure profiles were now in good agreement.