ANALYSIS OF SUPERSONIC FLOW OVER A DOUBLE WEDGe
When a supersonic flow encounters a sharp body, the result is a striking interplay of oblique shocks and expansion fans — phenomena that are both theoretically elegant and practically critical in the design of high-speed vehicles and inlets. This project simulates two-dimensional supersonic flow over a double-wedge airfoil at Mach 2 using ANSYS Fluent, examining how the shock structure, pressure distribution, and aerodynamic coefficients vary with angle of attack.
The double wedge geometry has a half-angle of 20° and a chord length of 100 mm. The computational domain extends 12.5 chord lengths upstream and 20 chord lengths downstream, with far-field and outlet pressure boundary conditions applied. The domain was meshed in ICEM CFD using a structured blocking strategy tailored to accurately resolve the oblique shockwaves and expansion fans around the wedge. A density-based steady-state solver was employed in ANSYS Fluent with the Spalart–Allmaras turbulence model, ideal gas law for density, and Sutherland's law for viscosity. Both flow and turbulent viscosity discretization used second-order upwind schemes.
Two cases were studied: flow at zero angle of attack and flow at a 10° angle of attack. For each case, contours of static pressure, density, and Mach number were extracted and analyzed. Lift and drag coefficients were monitored for convergence, and pressure coefficient distributions along the airfoil surface were compared against theoretical predictions from shock-expansion theory.
At zero angle of attack, the symmetric shock structure produces zero lift and a drag coefficient of approximately 0.0078, consistent with wave drag expected from oblique shock theory. At 10° angle of attack, the flow asymmetry generates measurable lift (Cl ≈ 0.046) and a slightly elevated drag (Cd ≈ 0.0085), with an aerodynamic efficiency of approximately 5.4. In both cases, CFD results agree closely with analytical values derived from isentropic relations, with small discrepancies attributable to turbulence-model approximations and the idealized assumptions underlying shock-expansion theory.