Ignition criteria and the effect of boundary layers on wedge-stabilized oblique detonation waves

TL;DR

This study investigates how boundary layers influence ignition and stability of oblique detonation waves over wedges using high-fidelity simulations, establishing an ignition criterion to predict ODW formation under various conditions.

Contribution

It introduces an ignition criterion for predicting oblique detonation wave formation considering boundary layer effects in supersonic reactive flows.

Findings

Boundary layer ignition can lead to ODW formation at certain temperatures.

ODW formation depends on shock wave augmentation by the boundary layer.

A receding ODW oscillatory mode was observed at specific conditions.

Abstract

Simulations of a supersonic, premixed, reacting flow over a wedge were performed to investigate the effect of a boundary layer on the wedge surface on ignition and stability of oblique detonation waves (ODWs). Two computational domains were used: one containing a wedge of a single angle with a straight after-body, and the other containing a double-angle wedge geometry. Both domains were channels with a supersonic inflow of stoichiometric hydrogen-air and a nonreflecting outflow, and the wedge was modeled using an immersed boundary method. The compressible reactive Navier-Stokes equations were solved using a high-order numerical algorithm on an adapting grid. Inviscid and viscous wedge surfaces were modeled using slip and no-slip adiabatic boundary conditions, respectively. Inviscid wedge surface cases are presented for a range of inflow conditions and compared to previous work outlining several different ODW structures. An ignition criterion is established as an accurate method of predicting the formation of an ODW for a given inflow temperature, Mach number, wedge angle, and length of the inviscid wedge surface. A viscous wedge surface is then considered for a Mach 5 inflow at temperatures of 600 K, 700 K, and 800 K. The 600 K flow ignites in the boundary layer, but does not detonate, while the 700 K and 800 K flows ignite and form ODWs. It was determined that ODW formation depends on the degree of augmentation of the leading oblique shock wave by the burning boundary layer and that ODW formation is therefore predictable based on the ignition criterion. The 700 K flow produces a unique oscillatory mode of a receding ODW followed by a redetonation event occurring near the leading edge. A mechanism for this cycle, which repeats indefinitely, is proposed.