Autonomous Systems and Connectivity

Transonic Cavity Flow

The next-generation of uninhabited air vehicles carry stores in internal bays for stealth. This has a drawback that once the bays are exposed they act as resonant cavities producing substantial noise and vibration. This complex flow problem is usually studied using idealised configurations of flows inside rectangular cavities exposed to a stream of high speed flow. Strong interactions arise from the shear layer formed across the cavity and the acoustic waves radiated from the downstream cavity wall. This feedback mechanism can be seen using numerical schlieren that highlights the complexity of the flow-field inside the cavity. The computations are demanding since these require long time-histories of the flow to be captured for the flow statistics to be extracted. Computations of the idealised cavity typically require CFD grids of about 5 million cells but this size increases with the Reynolds number and the complexity of the flow geometry.

The current project uses turbulence simulation methods including Detached-Eddy Simulation and Scale-Adaptive Simulation to resolve this very turbulent, energetic flow field. The cost of turbulence simulation is high due to having to resolve a range of flow scales from small to large and short-lived to long-lived.

The study of cavity flow in weapon bay has two main objectives. First, to understand how the trajectories are affected by the unsteadiness. A large variability of the trajectories is seen that can lead in rare case to a return of a store toward the bay. Second, the stuctures are subject to large unsteady loads leading in some case to structure resonance and fatigue problems.  HMB3 can perform multiphisic simulation coupling Computational Fluid Dynamics, aeroelasticity with a modal method and release trajectory with a Six Degrees of Freedom to assess the complex physics of weapon bay flow.

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