Numerical and experimental investigations on the reduction of wind tunnel wall interference by means of adaptive slots

The flow in many wind tunnel experiments is affected by the presence of tes t section walls. The resulting interference can be minimised by correcting the measured model pressures, or by influencing the model flow directly wit h the use of ventilated or adaptive test section walls. The objective behin d the latter technique is to guide the flow in the test section to achieve low interference (i.e. free flow) condition at the model. The most successf ul technique of flexible, adaptive walls is still restricted to small resea rch wind tunnels due to its mechanical complexity. However, a very promisin g alternative is the use of adaptive slots in the test section walls. This concept combines the method of passive slotted walls, as they are already i mplemented in many large wind tunnels, and flexible walls. Additionally, th is technique presents the opportunity of full 3D adaptations because the sl ots can be situated in all four test section walls. This paper presents preliminary experimental results and the latest numeric al calculations on the effectiveness of adaptive slots. The experiments wer e conducted under high subsonic flow conditions in the new slotted test sec tion of the transonic wind tunnel at TU Berlin's Aeronautical Institute (IL R). The numerical results presented are focussed on the 2D slot adaptation of a 2D-model (CAST7 aerofoil) and the 3D slot adaptation of a body of revoluti on (3D-ETB). In addition, basic studies were made of the flows associated w ith a single slot on one wall and a bump on the other. The numerical and the first experimental investigations have shown the pote ntial of adaptive slots to reduce wall interferences effectively. The adapt ation accuracy of the investigated slot configurations deviated not more th an 3% from the reference case (2D-wall adaptation).