Abstract
This work presents an experimental study of the effect of an installed propeller slipstream on a wing boundary layer. The main objective was to analyse through wind tunnel experiments the effect of the propeller slipstream on the wing boundary layer characteristics such as: laminar flow extension and transition, laminar separation bubbles and reattachment and turbulent separation. Two propeller/wing configurations were studied: pusher and tractor. Experimental work was performed using two different models: a two-dimensional wing with a central cylindrical nacelle for the tractor configuration, and a simple two-dimensional wing with a downstream propeller for the pusher tests. The relative position between propeller and wing could be changed in the pusher model, and a total of 7 positions were analysed. For the tractor tests the relative propeller/wing was fixed, but three different propellers: two, three and four bladed were tested. Measurements included pressure distribution, hot wire anemometry and boundary layer characteristics by flow visualisation. The results showed that the pusher propeller inflow affects the wing characteristics by changing the lift, drag, and also delays the boundary layer transition and separation. These effects are highly dependent on the relative position of the wing/propeller. On the other hand, the tractor propeller slipstream induces transition and its effect is dependent on the number of blades.
Highlights
During the 1980s a large number of works [1,2,3,4] on UDF or propfans brought attention back to the use of advanced propellers in transport aviation
Concerning aircraft drag reduction we have to take into account the effect of the propeller slipstream, on the wing boundary layer characteristics
It was decided to use propellers with two, three and four blades in order to investigate the effect of the propeller wake and tip vortex frequency crossing the wing The second method concentrated on testing the effect of a high thrust pusher propeller driven by a hydraulic motor on a two-dimensional wing at a wide range of incidence and with the propeller positioned at several positions behind the wing
Summary
During the 1980s a large number of works [1,2,3,4] on UDF (unducted fans) or propfans brought attention back to the use of advanced propellers in transport aviation. Despite the fact that attention on propofans has decreased, there is still great interest in the use of propellers in general aviation and commuter [2, 4, 8] aircraft as well as in RPV and unmanned aircraft [5] For these classes of aeroplane the distance between the wing and the propeller can be close enough to induce quite large effects on the wing surfaces, especially when the propellers are operating at high thrust as in take-off and climb. The tractor propeller acts in a unsteady fashion, due to the propeller wake and tip vortex crossing the wing surfaces Such an effect can promote transition [12] or induce an alternation between laminar and turbulent states. Measurements included pressure distributions for the pusher case only, flow visualisation for both cases and hot wire measurements for the tractor case
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