handwriting should be clear please I almost cant read it ev

handwriting should be clear please . I almost can\'t read it everytime someone post their answer

As shown in Figure 1, the flow fields of cricket balls in a uniform flow were visualized by using oil smoke techniques. From the flow visualization results shown in Figure 1(a), one can see the flow over the lower of ball separates earlier than the flow over upper surface. Please give the brief reasoning for this phenomenon and the physics behind this. Based on the knowledge you learn in aerodynamics, which direction (upward or downward) do you expect the cricket ball will move normal its flight path? Give the brief reasoning for your answer. From the flow visualization results shown in Fig. 1(b1) & Fig. 1(b2), one can see the flow over the surface of cricket balls of Fig. 1 (b2), separates earlier than the flow of Fig. 1(b1). Based on the knowledge you learn in aerodynamics, which drag is larger (Fig. 1(b1) or Fig 1(b2))? Give the brief reasoning for your answer.

Solution

solution:

answer a)

1)when ball is throw in uniform flow and if circulation is provided to ball in reverse direction at that time such condition arises when upper layer separation occure later than lower layer,it is because

when ball is throw in uniform flow at that time at initial touch time flow velicty is such that (du/dy)>0 and hence flow is stick to ball and as this flow proceed in upper and lower layer then

for upper layer velocity of fluid particle goes down due to friction but at the same time due to circulation or rotation of ball in reverse or clockwise direction,it will add some kinetic energy to fluid particle and its velocity get increased and hence separation point occure later on in flow.

while for lower layer fluid particle fluid velocity is decrease by friction as well circulation of ball and hence its net kinetic energy and corresonding velocity comes down and as (du/dy)<0 fluid will separate erlier for lower layer than upper layer.

2)due to magnus effect when ball is rotating at that time it experienced some lift force in direction normal to flow and as ball rotating clockwise it will acted upon by lift force in upward direction and as result balls trajectory shifted upward. and hence ball will moves upward,this is the reason why cricketers throws ball by providing some spin in reverse direction to maintain its height as it is goes down with increasing distance because of gravity forces.

answer to b)

1)as for b2 wake region is larger than b1 and hence it will cause more pressure difference between upstream and downstream side of ball and hence for given case of ball pressure drag is more for b2 than b1 as wake region is large for b2 than b1.but for each case skin friction drag is still greater than pressure drag.