The flow around a sensor in a wind tunnel has been investigated experimentally and numerically. The design of the wind tunnel according to Eiffel allows a full-scale numerical simulation as a CFD model with the formation of the boundary layer developing from the inlet portal of the wind tunnel. Both designs are described. The test area has a cross-section of 0.25 m x 0.16 m, a length of 0.44 m and allows a velocity of up to 20 m/s. The sensor with a diameter of 8 mm and a flat cap is positioned symmetrically to the side walls and enters the wind tunnel from above. Unexpectedly, the velocity profile of the main flow in the wind tunnel shows a slightly lower value in the centre of the cross-section compared to the flow in the wall area. Further evidence for this phenomenon of a bulge-like increase in velocity before the drop in the boundary layer has been found both experimentally and numerically. An early study on the design of wind tunnel nozzles confirms the findings.