Scramjet inlet flow computations by hybrid grid method

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Computations of internal viscous flowfields of scramjet models were conducted at inflow Mach number of 5.4. An unstructured hybrid grid method was used to compute complex geometries such as scramjet models with a short strut. The numerical method to solve the Navier-Stokes equations on the hybrid grid was developed using a finite volume cell vertex scheme and the LU-SGS implicit time integration algorithm. The computational results using one-equation turbulence models showed good agreement with the experimental data. The flow features and the changes of flowfields due to the short strut located in the upper passage were discussed. It was revealed that a thick subsonic region did not exist in the combustor near the top wall at Mach number 5.4. It was favorable features to avoid the engine unstart. With the strut, relatively low velocity regions became larger and the down wash flow toward the cowl behind the step became strong. The overconcentration of the fuel toward the top wall during the weak combustion was found in the experiment. From the computational results, the reason of this overconcentration was realized that the airflow near the injector was turned to the top wall due to the small influence by the combustion in the experiment. The computational time and the accuracy of the present method were the same level as the conventional structured grid methods. Thus the present method seemed to be engineeringly very useful for analysis and design of the high-speed propulsion engines.