Have you ever thought the tiny little ridges on the top of any automobile, would actually help to increase the traction and prevent the stall in case of aircraft?
Those tiny ridges are called VORTEX GENERATORS that are responsible for increased traction, lift, and stall prevention.
Now, we are pretty sure that they have some role to play in aerodynamics. But, here comes the real question HOW?
HOW VORTEX GENERATORS WORK?
Generally, when flow passes through an object (be it airfoil, be it a car-top etc…) the flow might be attached flow or separated flow.
The attached flow plays an effective role in aerodynamics and is responsible for all the pros we have discussed earlier. Coanda effect explains the attached flow. However, the attached flow is not always possible to achieve because of adverse pressure gradients.To keep the flow attached as much as possible, vortex generators are used.
CAUSE OF FLOW SEPARATION
Adverse pressure gradients are the prime cause for a flow to be separated. To know more about adverse pressure gradients, we have to dive in through the concept of BOUNDARY LAYER.
When a fluid flows through an object, the flow nearer to the surface has low velocity compared to the flow away from the surface. The curve joining all the unequal velocities gives the Boundry Layer of the velocity gradient. The flow that is far away from the surface has the maximum velocity called free stream velocity.
When flow passes through the curved surface, it experiences an opposing force as it is flowing from low pressure to high pressure (generally, anything flows from high to low pressure). The flow which is away from the surface of the object has enough momentum to overcome the opposing force. But, the flow which is near to the surface couldn’t overcome the opposing force due to the less momentum it has and causes the flow separation.
ENERGIZING THE FLOW
Vortex generators are used to increase the velocity or energize the flow nearer to the surface which helps to keep the flow attached. Vortex generators energize the flow nearer to the surface by mixing the high-pressure air (flow near the surface) and low-pressure air (free stream flow which is away from the surface) in the boundary layer. So, the flow nearer to the surface gets momentum which is enough to overcome the adverse pressure gradient and the flow stays attached.
In this way, the vortex generators keep the flow attached and increase the downward force in case of cars and delays the flow separation time to prevent the stall in case of aircraft.
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