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For high-lift models like airfoils for wind turbines, aircraft or turbomachinery applications wind tunnel measurements in open test sections are often unsuitable for determining precise lift and drag coefficients as streamwise gradients and the imposed ambient pressure boundary condition at the shear layer of the free jet can lead to a deviation of the local base pressure. Therefore, based on the existing closed circuit wind tunnel Göttingen-Type with circular cross-section at the Jade University of Applied Sciences, the authors present an approach for an economically and aerodynamically optimized closure of the wind tunnel test section. For ease of installing models and measurement instrumentation as well as optical accessibility the cross-section of the test section was chosen to be square shaped. With the objective to keep the numbers of new components to be manufactured manageable the transition of the cross-sectional shape from round to square has been embedded into the designed nozzle geometry. For the investigation on its effect on the homogeneity of the flow quantities, numerical simulations of a simplified wind tunnel model were conducted. In total, three different setups have been considered, including a setup with fully circular and mostly square shaped cross-sections for comparison. The evaluation was carried out based on the percentage velocity variation on a fixed number of evaluation planes within the test section. The results show that the financially most reasonable setup also positively affects the flow homogeneity in the closed test section. With the outlined design approach an overall higher flow homogeneity can be achieved compared to a setup with a fully square cross-section. Further as a lower energy demand for operation can be expected due to lower pressure losses of circular shaped flow guiding components a corresponding setup is economical beneficial .