BACKGROUND |
The ability to accurately predict both static and dynamic stability of sea and air vehicles using computational fluid dynamics (CFD) methods could revolutionize the vehicle design process for NATO air and sea vehicles. A validated capability would significantly reduce the number of ground tests required to verify a concept and, in general, could eliminate costly vehicle ‘repair’ campaigns required to fix performance anomalies that were not adequately predicted prior to full-scale vehicle development. As a result, significant reductions in acquisition cost, schedule, and risk could be realized. For both air and maritime vehicles, CFD has found its way into the design process especially for nominal cruise performance where flows are generally characterized by attached steady flows (aircraft) or flat sea state (ships). Unfortunately military vehicles routinely operate well outside of these steady boundary conditions. In fact, a significant portion of the vehicle preliminary design effort and cost is directed to those areas outside of the ‘steady, attached flow or steady sea state’ regime to ensure the vehicle operates as designed and can be qualified at the edges of the operating envelope. Both aircraft and maritime vehicles must be qualified at many transient states that contain unsteady, highly separated flows over the vehicle. State-of-the-art CFD methods are known not to be particularly robust in these regions, and their ability to predict onset and development of these problematic separated flow regimes is not well established. However, significant progress is being made with both steady and unsteady Reynolds Averaged Navier Stokes (RANS and URANS) computational methods as documented in the recent NATO AVT-123 Symposium on “Flow Induced Unsteady Loads and the Impact on Military Applications”. More recently, AVT-161 has formed and is beginning an ‘Assessment of Stability and Control Prediction Methods for NATO Air and Sea Vehicles’. Work already carried out for AVT-161 has confirmed that there are fundamental issues with current CFD approaches that make the reliable prediction of basic phenomena such as the onset and progression of separated flows especially for rounded/smooth surfaces very difficult, even at static conditions. As a result, this new task group is proposed in order to carry out an assessment of the state of the art for the prediction of smooth-surface separation onset and progression. As part of this work, a limited amount of uncertainty analysis will also be carried out.
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OBJECTIVES |
To conduct a new series of wind-tunnel experiments to gather a unique and comprehensive experimental aerodynamic data set for realistic configurations, including: surface flow topology; pressures; off-surface velocities; turbulence quantities etc. To use these data to assess, diagnose and improve the current state-of-the-art in CFD methods for predicting the onset and progression of flow separation, and associated unsteady phenomena.
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