Wind tunnel testing belongs to the most significant aspects of the technical development process. In order to improve the test environment conditions and open the possibility of closed loop operation, a flow capturing device is developed for a highspeed wind tunnel previously exhausting to ambient. The highspeed wind tunnel is used in conjunction with annular sector cascade test rigs to evaluate the performance of intermediate turbine ducts. In the presented paper, a modular design approach for the flow capturing device is presented; particular attention is reserved to optimal integration within the pre-existing test environment and to an efficient sealing strategy. Computational results provide the basis for the correct sizing of the device; the aerodynamic effects induced by the flow capturing device down-stream of an annular sector cascade rig are shown to bear no influence on the quality of the test data. The presented results of several tests conducted under a wide range of conditions confirm the viability of the developed flow capturing device. The improvements to the pre-existing experimental setup achieved with the addition of the flow capturing device are furthermore presented in this paper, focusing on the obtained reduction in sound pressure and temperature level within the test facilities.