A 6m cube in an atmospheric boundary layer flow. Part 2. Computational solutions

Computation solutions for the flow around a cube, which were generated as part of thernComputational Wind Engineering 2000 Conference Competition, are compared with full-scale measurements.rnThe three solutions shown all use the RANS approach to predict mean flow fields. The major differencesrnappear to be related to the use of the standard k- e, the MMK k- e and the RNG k- e turbulence models.rnThe inlet conditions chosen by the three modellers illustrate one of the dilemmas faced in computationalrnwind engineering. While all modeller matched the inlet velocity profile to the full-scale profile, only onernof the modellers chose to match the full-scale turbulence data. This approach led to a boundary layer thatrnwas not in equilibrium. The approach taken by the other modeller was to specify lower inlet turbulentrnkinetic energy level, which are more consistent with the turbulence models chosen and lead to a homogeneousrnboundary layer. For the 0 o case, wind normal to one face of the cube, it is shown that the RNG solutionrnis closest to the full-scale data. This result appears to be associated with the RNG solution showing therncorrect flow separation and reattachment on the roof. The other solutions show either excessive separationrn(MMK) or no separation at all (K-E). For the 45 o case the three solutions are fairly similar. None of themrncorrectly predicting the high suctions along the windward edges of the roof. In general the velocityrncomponents are more accurately predicted than the pressures. However in all cases the turbulence levelsrnare poorly matched, with all of the solutions failing to match the high turbulence levels measured aroundrnthe edges of separated flows. Although all of the computational solutions have deficiencies, the variabilityrnof results is shown to be similar to that which has been obtained with a similar comparative wind tunnelrnstudy. This suggests that the computational solutions are only slightly less reliable than the wind tunnel.