Throat length effect on the flow patterns in off-design conical nozzles

In the present work, a flow field study was performed for off-design conical nozzles with non-circular cylindrical throat sections such as those found in experimental sounding rocket motor applications. The flow field was simulated with the RANS model in ANSYS-Fluent R16.2 code for 2D domains. The governing equations used are conservation of mass, momentum, energy, and state. Sutherland's equation for viscosity as a function of temperature and the Spalart-Allmaras turbulence model was used to simulate overexpanded flow turbulence. The results showed pressure and Mach number fluctuations as the throat length increased. In the throat section, it is concluded that for the length range of 5 to 15% of the throat diameter, the flow accelerates without the presence of internal shock.