Numerical approach to theoretical aspects of wedge-induced oblique detonation wave in a hydrogen concentration gradient

Abstract

The present study conducts numerical simulations of oblique detonation wave (ODW) induced on a wedge in the concentration gradient of a hydrogen–air mixture. As a continuation of the author's previous work on the morphology of the initiating flame in a non-uniform mixture, the concentration gradient is provided only to the ODW front to address its theoretical characteristics: the propagation velocity and structures of post-shock reactive flow associated with the Chapman–Jouguet and Zeldovich–von-Neumann–Doering theories, respectively. Applying a Gaussian distribution of the hydrogen mole fraction to the ODW front induces a curved shape that is concave or convex in fuel-rich or fuel-lean compositions, respectively. The local wave angle on a curved ODW matches the one-dimensional theory in a uniform mixture, which proves its robustness in predicting the detonation velocity in a non-uniform mixture. Furthermore, tracing streamlines with different compositions reveals that the flow path and variations in temperature and pressure are almost coincident with those predicted by one-dimensional and uniform assumptions. The slight variation among the different conditions is attributed to the effects of two-dimensional convergence/divergence that are intensified at stronger gradients. The understanding achieved in the present study will also benefit the evaluation of propagating detonation in a non-uniform mixture layer formed in propulsion devices.