Computational Analysis of Unstart in Variable-Geometry Inlet

Abstract

Computational fluid dynamics was used to study the flow through a scaled, mixed-compression, high-speed inlet with a rotating cowl at Mach 4.0 conditions. First, steady Reynolds-averaged Navier-Stokes computations were undertaken with a range of popular turbulence models including the Spalart-Allmaras model, the realizable k-ε model, the cubic k-ε model, and the Menter shear stress transport (SST) model to assess the impact on the inlet operating state. It was found that two models, the Spalart-Allmaras model and the Menter SST model, predicted the inlet to become unstarted at a cowl angle where the experimental data indicated the inlet remained started. Next, steady-state flow structures were studied at three discrete cowl positions, identifying highly three-dimensional flow features including regions of separated flow and spanwise gradients that became stronger as the cowl opened. Finally, the study culminated with the development of the new transient model, which allowed for time-accurate investigation into the unstart, restart, and hysteresis. The evolution of the separation bubbles was shown to be a major factor in the hysteresis, causing the inlet to restart at an angle different from where it unstarted. The utility of unsteady Reynolds-averaged Navier-Stokes computations to capture the complex time-dependent details of such flows was demonstrated.

Grid Adaptive Technique for Simulation of Scramjet Intake-Isolator at Hypersonic Speeds

“…Janarthanam et al, CFD results of three-dimensional flow in the dual mode scramjet intake-isolator are agreed with experimental results at Mach 4 using SST k-ω turbulence model [6]. Jonathan P. et al, has noticed two turbulence models SA and SST could predict the unstarting condition of intake with flow separation bubbles [7].…”

“…Similarly, Eqs. ( 4)- (7) gives static pressure, density, temperature and total pressure ratios across shocks. The same procedure is followed for all the shocks to know the flow properties at the inlet of isolator and tabulated in Table 1.…”

Scramjet Intake Aerodynamic Studies Using Sharp Interface Immersed Boundary Method

“…Extensive experimental and numerical investigations have been conducted on scramjet engines, with particular emphasis placed on their aerodynamic performance. Among the unfavourable phenomena that can significantly impact the aerothermodynamic efficiency of scramjets, the occurrence of 'unstart' has gathered significant attention [2][3][4][5][6][7][8] . Unstart refers to a series of events in which an increase in downstream backpressure causes flow constriction, leading to an upstream propagation of a wave that disrupts the established configuration of oblique shock waves within the isolator.…”

“…Significant research efforts have been dedicated to investigating the phenomenon of unstart, employing both experimental techniques conducted in wind tunnels [4][5][6][7][8] , as well as various numerical methodologies, including Computational Fluid Dynamics (CFD) [3][4][5][6][7][8][9][10] , and Reduced Order Models 11 . However, due to the unique and transient nature of the flow patterns observed during unstart in different inlet configurations, the process becomes highly intricate and demands further exploration.…”

Research on Computational Method of Supersonic Inlet/Isolator Internal Flow

“…Xu et al [7] and Li et al [8] used the commercial CFD solver ANSYS Fluent to study the shock train movements inside the supersonic inlet caused by the back pressure on the outlet boundary. Reardon et al [9] completed a 3D flow simulation of a two-dimensional supersonic inlet/isolator based on CFD++ (mainly studying the starting performance), which indicated the turbulence models can greatly affect the computational performance of the inlet and the subtle differences between 2D and 3D computations have also been compared. He et al [10] used ANSYS Fluent to simulate the effect of ejecting flow on the supersonic inlet/isolator performance of resisting the back pressure, and revealed the mechanism: the ejecting increases the mixing of momentum, mass and energy to narrow the subsonic band and suppress the adverse pressure gradient.…”