Passive Flow Control over Airfoil at Transonic Speeds Using Porous Medium

What is it about?

Flow control for overall drag reduction over an airfoil is a popular research topic. 'Passive' control methods, unlike their 'active' counterparts, do not require external supply of energy for operation. We are exploring the viability of use of a layer of porous medium over an airfoil at the region where a shock is likely to occur at transonic speeds. The mechanism which promotes total pressure recovery is the weakening of the shock into a 'lambda' structure due to re-circulation of flow within the porous layer.

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Why is it important?

The re-circulation phenomena leading to passive flow control has traditionally been incorporated using a perforated plate over cavity system. Though this was inherently compatible with the structure of the wing plenum chamber, many studies have concluded that this configuration did not deliver the required results. On the other hand, while the prospect of having a layer of porous medium over a region of airfoil might seem unfavorable at first from a structural perspective, our studies have shown that even very thin porous layers are capable of delivering significant total pressure recovery, indicating that their use might be feasible.

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