Numerical analysis of passive techniques for optimizing the performance of scramjet combustor

In this research paper numerical analysis of scramjet combustor has been carried out with different passive techniques to improve the mixing efficiency of supersonic airstream and hydrogen fuel. The actual mixing rate of air and hydrogen is very less because of the less resident time of supersonic air in the combustion chamber. The mixing of hydrogen fuel with supersonic airstream is greatly affected by the development of shock waves, streamline vortices and shear layer of mixing in the flow filed of the combustor. The experimental DLR scramjet model has been considered as a reference and standard model to compare and validate the numerical results. In this research article three different passive techniques are considered and defined as a uniform zigzag surface, small parabola shape cavities and bumps at lower wall of the combustion chamber. The computational scramjet domains are modeled as modified versions of DLR scramjet by the implementation of passive techniques. Two dimensional numerical analyses are carried out by solving Favre-averaged Navier-Stokes governing equations and SST k-omega turbulence model along with finite rate/eddy dissipation combustion chemistry turbulence model is also considered for accurate analysis of streamline vortices, shear layer development and shock waves. From the numerical results of various passive techniques it is found that the development or creation of gradient fluxes of flow property are increased. By incorporating these types of surfaces at combustor bottom wall it is identified that the growth rate of mixing layer has been increased along the flow field of combustor. Hence the more amount of hydrogen fuel being carried out by streamline vortices and velocity gradients or shock waves and this phenomenon improve the mixing efficiency of scramjet combustor and also it leads to increase in combustion efficiency. From the numerical analysis results and discussion it is to be concluded that highest mixing and combustion efficiency is identified with a uniform zigzag (wavy wall) surface combustor wall design. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.