D2. Bluff vs. Streamlined Bodies

In analyzing flow problems, the similarity of flow around the object is crucial, as highlighted in the wind tunnel guidelines. Generally, a distinction is made between streamlined and bluff bodies, though the boundary between these categories is not always clear-cut. Streamlined bodies are characterized by the flow following the contours of their geometry. Shear forces play an essential role here, and the drag coefficients vary with the Reynolds number. Determining the separation point of the flow is complex and often variable. In contrast, bluff bodies have defined separation points at their edges. This results in outcomes that, above a certain Reynolds number (with fully developed turbulence), are less dependent on the Reynolds number. Consequently, findings from wind tunnel tests can be more readily transferred to full-scale scenarios. For bluff bodies, the drag coefficients primarily result from pressure differences. This distinction is fundamental for the accurate modeling and interpretation of flow phenomena in CFD simulation and wind tunnel testing.