Computational investigation of axi-symmetric plume induced flow separation

Abstract

The flow over a rocket may result in plume induced flow separation (PIFS) depending on flight conditions and nozzle-to-ambient pressure ratios. In the current study, the flow structure over a generic rocket model has been investigated to determine the conditions that would results in PIFS over the rocket body. The rocket used in the current study has a tangent-ogive nose with a length of 25.4 cm (nose length/diameter ∼ 4.0), followed by a 57.2-cm long cylindrical rocket body (overall length/diameter ∼ 13.0). A 45° conical nozzle with an exit Mach number of 2.7 (nozzle expansion ratio, ε ∼1.786) was used to simulate the plume. The total temperature and the total pressure in the combustion chamber were kept as 3589 K (6000 °F), and 5.86 MPa ab (850 psia). The flow conditions investigated including flight Mach numbers from 0.7 to 2.0, at five different altitudes; 0, 3.05, 6.10, 9.14 and 12.2 km (0, 10,000, 20,000, 30,000 and 40,000 feet). Based on the validation study using various eddy-viscosity turbulence models, the k-ε RNG turbulence model was selected for the parametric study. PIFS is not observed at Mach numbers less than 1.0 up to altitudes including 9.1 km (30,000 ft), and occurs only between Mach 1.0 and 2.0. The Mach number range where PIFS is observed increases with increasing altitude. However at 12.2 km (40,000 ft) PIFS is observed at every Mach number considered, including subsonic range.