Uncertainty Quantification and CFD Validation

A Benchmark Facility for CFD Validation Experiments

Computational Fluid Dynamics (CFD) provides the only practical means for the prediction of many marine and aerospace vehicle flows. 

Unfortunately, CFD models have not yet achieved a level of accuracy, particularly with respect to separated flows, corner flows and complex surfaces such as roughness, needed to provide relieable real-time estimation of vehicle and system performance. Improving models requires comparison with measurements, usually involving testing campaigns in wind tunnel facilities.

Successfully modeling complex flows in wind tunnels include many challenges such as how much of the facility circuit needs to be modelled, the fidelity with which as-built geometry needs to be known and included within the computation, the need to have measurements and understanding of the test section or contraction inflow at a level of detail consistent with the CFD model, the difficulty in modeling how reference quantities, such as free stream velocity, are determined in the experiment, the challenge of gridding and how much of the facility to grid, the appropriate choice of computational model, and how best to represent and document wind tunnel test models and their supports.   

Our goal is to make the Stability Wind Tunnel a benchmark facility for uncertainty quantification and CFD validation experiments. As such, efforts have been undertaken to fully document the boundary conditions and reference conditions in the facility, including:

• settling chamber dynamic pressure cross-section
• contraction and test-section wall pressures
• test-section wall boundary layer and corner flow development
• freestream turbulence intensity
• test-section flow uniformity and angularities

Of high importance is also the need for clearly defining the physical boundaries of the facility with detailed as-designed CADs and as-built geometries (obtained from high fidelity optical scans of the entire circuit as seen above).

Since the Stability Tunnel is involved in ongoing blind CFD validation challenges (see current list below), information regarding the boundary conditions above will not be published until 2024: