TESTING 3-DIMENSIONAL BLUFF-BODY MODELS IN A LOW-SPEED 2-DIMENSIONAL ADAPTIVE WALL TEST SECTION

Thin, sharp-edged disk models were evaluated in a low-speed two-dimens ional adaptive flexible wall test section to determine the optimum ada ptive wall testing environment for three-dimensional bluff-body models , by providing model testing recommendations for nominal solid blockag e ratio and model span ratio. Drag coefficient measurements obtained u nder straight wall and adapted wall conditions showed that for a two-d imensional adaptive wall test section, the model span ratio imposes a more severe restriction upon model size than does the nominal solid bl ockage ratio. Minimum wall interference conditions were achieved with adapted walls for nominal solid blockage ratios less than 3 percent an d model span ratios less than 21 percent, independent of the nominal t est section aspect ratio, based on favorable comparison with previousl y-published experimental data. Data obtained under straight wall condi tions confirmed that wall interference effects can only be neglected i n conventional, straight-walled test sections for solid blockage ratio s less than 0.5 percent and model span ratios less than 10 percent. Th e post-test boundary correction method of Maskell was successfully use d to adjust the straight wall test section drag coefficient measuremen ts of the larger models for wall interference effects, bur no direct m easurements of wall interference are used with this method. The result s support the careful use of a two-dimensional wall adjustment strateg y for three-dimensional nonlifting flows.