hypersonic-piston-theorylisted

# Lighthill Piston Theory Surface Pressure (aerodynamics/high-speed/hypersonic-piston-theory) Use when the task is the surface pressure on a small-perturbation hypersonic surface by Lighthill piston theory (the Lighthill 1953 piston analogy in the Ashley-Zartarian hypersonic small-perturbation class): a surface element moving into the gas compresses it like a piston pushing down a tube, so the local pressure ratio follows the closed form p/p_inf = (1 + ((gamma - 1)/2) * (v/a_inf))^(2 gamma/(gamma - 1)) from the local piston velocity ratio v/a_inf, positive for a compression (shock-side) motion and negative for an expansion, with the law collapsing to p/p_inf = 0 at the expansion cutoff v/a_inf = -2/(gamma - 1). This leaf evaluates that law, its linearized limit p/p_inf = 1 + gamma * v/a_inf, the piston velocity ratio of a steady surface inclined theta to the freestream (v/a_inf = M * sin(theta)), the per-side surface-pressure coefficient Cp = 2/(gamma M^2) * (p/p_inf - 1) with the linearized hypersonic limit Cp = 2 * sin(theta)/M, and the extension to an unsteady surface whose normal wall motion adds to the geometric piston velocity for the instantaneous pressure at any phase of its motion. Pure Python, stdlib only, deterministic. It is the unsteady complement to the steady blunt-body impact theory of aerodynamics/high-speed/hypersonic-flow: the same hypersonic surface-pressure physics built from the local piston velocity rather than from steady impact integrals. ## Domain