Problems in the validation of CFD codes through comparison with experiment
Abstract
Accurate predictions of the effects of shock wave turbulent boundary layer interactions are of particular importance in the design of hypersonic vehicles. Such flows can generate intense heat transfer rates and pressure levels, complex largescale unsteady separated flows, and largeamplitude fluctuating loads. With increased reliance on computation, it is critical that the predictions are accurate. Thus, it is imperative that such codes be validated and calibrated and deficiencies be identified and rectified. Comparison of the predictions of computational fluid dynamics (CFD) codes with experimental data is the key element of the validation process. However, drawing meaningful conclusions about the strengths and weaknesses of solution methodologies or of turbulence models from these comparisons is not a trivial task. As recently stated by Jameson, 'Simply comparing experimental data with numerical results provides no way to distinguish the source of the discrepancies, whether they are due to faulty numerical approximation or programming, or to deviations between the math model and true physics.' The conclusions drawn may be quite misleading if it is not clearly understood what the computations represent and what the experimental data represent. This paper discusses why it is important to know how experimental mean flowfield and surface data being used for comparison with CFD are generated. If the flowfields exhibit local or global largescale unsteadiness, then such mean measurements, which form the bulk of the existing data base, may mask the underlying flow physics and be inappropriate for comparison with computation.
 Publication:

In AGARD
 Pub Date:
 April 1993
 Bibcode:
 1993temh.agar.....D
 Keywords:

 Computational Fluid Dynamics;
 Flow Measurement;
 Hypersonic Flow;
 Hypersonic Vehicles;
 Shock Waves;
 Turbulence Models;
 Turbulent Boundary Layer;
 Flow Distribution;
 Mathematical Models;
 Separated Flow;
 Wave Interaction;
 Fluid Mechanics and Heat Transfer