WKU Gas Dynamics

Ansys Fluent Workbench

Simulating a converging-diverging rocket nozzle under isentropic flow conditions, analyzing different scenarios like design condition, shock at exit, subsonic and incompressible exit pressures.

Launch Fluent Flow Analysis

Mesh Generation

Geometry Setup in DesignModeler

Mach number contour shows isentropic flow through a converging-diverging nozzle under design conditions, where the exit pressure matches the nozzle's design exit pressure (75 kPa). The flow is smooth and symmetric, accelerating from subsonic (blue) at the inlet, reaching Mach 1 at the throat (light cyan), and then expanding to supersonic flow at the exit (red to orange), reaching Mach numbers above 3. This is a classic shock-free, isentropic expansion showing proper nozzle operation at matched back pressure.

This Mach number contour represents off-design conditions where the back pressure is higher than the nozzle design pressure. While the flow accelerates and becomes supersonic just after the throat (up to ~Mach 1.7), a normal shock wave forms shortly downstream in the diverging section. This causes a sudden drop in Mach number and an increase in pressure and temperature. The irregular patterns and blue zones after the shock indicate subsonic, disturbed flow and flow separation, a typical result of over-expanded nozzle flow (i.e., nozzle exit pressure is too low for the ambient pressure).

Diamond Wedge External Flow

0° tilt: The flow is symmetric about the centerline, with oblique shock waves and expansion fans forming symmetrically at the wedge corners. The flow accelerates downstream, reaching Mach numbers above 3.7 

Tilted 5°

5° tilt: Tilting the wedge breaks the symmetry, producing stronger oblique shocks on the lower surface and weaker shocks or expansion on the upper side. This causes asymmetric flow patterns and a slightly different shock structure, with peak Mach numbers reaching over 4.2 due to localized expansion.