High Fluid Velocity:
As the fluid velocity increases, the boundary layer over the object becomes thinner. This is because the high-velocity fluid exerts a stronger shear stress on the boundary layer, causing it to be stretched and thinned out. The thinning of the boundary layer leads to a reduction in the pressure drag component of the total drag force. As a result, the overall drag coefficient (Cd) decreases with increasing fluid velocity.
Low Temperature:
When the temperature of the fluid decreases, its viscosity increases. Viscosity represents the fluid's resistance to flow. As the viscosity increases, the fluid becomes thicker and more resistant to movement. This increased resistance to flow results in higher friction drag on the object. Consequently, the overall drag coefficient (Cd) increases with decreasing fluid temperature.
In summary, high fluid velocity tends to decrease the drag coefficient (Cd), while low temperature tends to increase Cd. These effects are primarily due to changes in the boundary layer behavior and friction drag.
