Numerical investigation of oblique detonation waves for a shcramjet combustor

Research in hypersonic airbreathing propulsion strives to provide an efficient, cost-effective alternative to rocket propulsion for space transportation systems. The supersonic combustion ramjet (scramjet) is one of the most common hypersonic airbreathing propulsion concepts, but its massive combustor could have detrimental effects on its efficiency. The shock-induced combustion ramjet (shcramjet) overcomes this drawback by using standing oblique detonation waves (coupled shock-combustion fronts) as a means of nearly instantaneous heat addition. A numerical investigation of standing oblique detonation waves for their use in shcramjet propulsion is the main purpose of this investigation. The laminar, two-dimensional Navier-Stokes equations coupled with non-equilibrium hydrogen/air combustion models based on chemical kinetics are used to represent the physical system. The combustion models are incorporated into an in-house computational fluid dynamics solver based on a shock-capturing scheme by Yee scheme and an approximate factorization algorithm with a dual-time stepping technique to regain time-accuracy. The solver is validated with experimental data found in the literature. A time accurate simulation of the formation of a standing oblique detonation wave (ODW) near the Chapman Jouguet (minimum entropy) condition yields a non-oscillatory, stable structure. The stability of the ODW to inhomogeneities in the oncoming fuel/air mixture is assessed through other time-accurate simulations by artificially introducing small disturbances consisting of pure air just upstream of the ODW structure. The ODW is shown to be resilient to these disturbances: an upstream displacement is observed followed by the return of the ODW to its original position. Steady-state simulations are carried out to determine the effect of laminar boundary layers on ODW structures and properties above and below the Chapman-Jouguet point. A comparison with analogous inviscid simulations shows that the effect is minimal and that the shorter induction distance in laminar flow does not entail a significantly earlier onset of the ODW. A novel shcramjet combustor design that makes use of oblique detonation waves stabilized over wedge-shaped flame-holders and configured such that detonation wave-wall interactions are avoided, is presented and analyzed through steady-state simulations. The design is shown to be a viable one for shcramjet propulsion by means of thrust potential calculations.