Extending Fievisohn's triple-point model to nonzero inflow angle at the oblique shock — and what changes when you do.
An RDE's detonation wave isn't a single clean front — it's a small structure made up of an oblique shock, a slipline, a reactant fill layer, and the triple point where they all meet, all of it propagating around the annulus together. Getting chamber-level performance right eventually requires understanding that structure directly rather than treating the wave as a black box, which is what motivated this solver.
Fievisohn's triple-point model gives a method-of-characteristics description of this structure for the case where flow enters the oblique shock head-on — inflow angle θ₄ equal to zero. It's a strong foundation, but a real RDE doesn't guarantee that head-on condition; fill-layer geometry and upstream flow turning can leave the reactant layer meeting the oblique shock at an angle.
Once θ₄ is allowed to be nonzero, the oblique shock's deflection angle, the slipline orientation, and the triple-point trajectory all shift together — they're coupled through the same shock-jump relations, so you can't perturb one in isolation. Extending the model meant re-deriving the triple-point geometry and shock relations to carry θ₄ as a free parameter rather than assuming it away, and checking that the θ₄ = 0 case still recovers Fievisohn's original solution as a limit.
The solver uses the method of characteristics to march the flow field through each region of the structure — fill layer, post-shock flow, and the expansion around the triple point — propagating along characteristic lines rather than discretizing the full domain. That keeps the solver fast enough to sweep across θ₄ values and compare resulting wave structures directly.
The extended formulation is implemented and validated against the θ₄ = 0 limit; current work is sweeping nonzero inflow angles to characterize how triple-point trajectory and fill-layer geometry respond, with the goal of feeding that back into the chamber-level assumptions used in the RDE performance toolbox.