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In the region where flow separation has occurred (i.e. where the wake has been formed) this becomes a relatively low pressure region. However, the region of fluid in front of the object will be a higher pressure region with respect to this.
Given that the fluid wants to reach equilibrium it will want to move from the high pressure to low pressure region. This imparts a force onto our object. Utilizing the image below there would be a Pressure Drag Force moving from Left to Right while our object is travelling Right to Left (see image below). This Pressure Drag Force force exerted by the fluid onto our object is proportional to the pressure at each specific region, we can identify that the Frontal Pressure Force will be greater than the Rear Pressure Force. Adding these two opposing forces up (or really subtracting given that they are in opposite directions) we get the resultant Pressure Drag Force that will be in the same direction as the Frontal Pressure Force. If we use the image below,this force will be pointing Left to Right if our object were travelling Right to Left. Therefore this Pressure Drag Force opposes the direction of motion and will force us to utilize more energy from the battery pack to maintain the same speed and thus decrease our overall range / efficiency.
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Flow separation creates a pressure differential between the front and the rear of the object that is travelling through a fluid.
In the area in front of the object there exists a theoretical “stagnation point”, here the fluid is hitting the surface perfectly perpendicularly and as such has zero velocity. That being said this “stagnation point” is an infinitesimally small point and the molecule’s of fluid have a certain size, thus, the fluid particles will never exactly be at the stagnation point and so they will always have a non-zero velocity, albeit the
How can we Mitigate Flow Separation?
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The most intuitive method to mitigating flow separation is to change the geometry of the object such that it allows for the boundary layer to “continue to follow it” and thus prevent separation. A more technical definition would be to have the geometry of the object be shaped such that it does not force the path of air to deviate significantly from its default state (as if no object were there)cause a pressure differential between the front and the rear where the front has a higher pressure with respect to the rear.
This is the reason why many so called “aerodynamic” shapes are tear-drop shaped (see examples below)
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