# Aerodynamics Questions and Answers – Lifting Flow over Cylinder

This set of Aerodynamics Questions and Answers for Experienced people focuses on “Lifting Flow over Cylinder”.

**1. What is the reduction of drag by installing the small cylinder?**

**a) 48%**

b) 55%

c) 30%

d) 75%

**Explanation**: By putting a considerably smaller cylinder in the upstream direction of flow, a cylinder’s drag is reduced by 48 percent. The shear layer created by the smaller cylinder alters the pressure distribution surrounding the layer cylinder, resulting in a significant shift in drag.

**2. What are the quantitative flow visualization techniques?**

**a) Smoke flow visualization**

b) Surface framing

c) Shadow projecting

d) Shadow graphic technique

**Explanation**: To locate the transition and separation of a boundary layer, visualisation techniques such as smoke flow visualisation, surface oil film method, and particle image velocimetry were used.

**3. What types of visualization is used to delay the separation of the flow?**

a) PVT

b) Surface oil film technique

**c) Smoke flow visualization**

d) Shadow projecting

**Explanation:** Bakic and Peric employed smoke flow visualisation to illustrate the delayed separation of the flow over a smooth sphere. When the boundary layer travels far enough against an unfavourable pressure gradient, flow separation occurs.

**4. How drag is formed on the cylinder?**

**a) Due to viscous effect**

b) Due to friction

c) Due to boundary layer

d) Due to surface layer

**Explanation:** Drag is caused by a viscous effect that creates a frictional shear stress at the body surface, causing the flow to separate from the back of the body’s surface. A stagnation point is produced near the cylinder’s leading edge. Where the oncoming flow comes to a halt. The pressure here is comparable to the pressure of stagnation. A thin boundary layer is produced adjacent to the cylinder surface. The drag on the cylinder is caused by this.

**5. What is the lift on the cylinder?**

a) One

**b) Zero**

c) Negative

d) Greater than zero

**Explanation:** Because the pressure distribution in the top half of the cylinder is equal to that in the bottom half, the lift must be zero. The air flow on the cylinder is deflected upwards by the same amount that it is deflected downwards at the cylinder’s rear. As a result, the up wash balances out the downwash in terms of reaction forces. The free stream hasn’t been deflected at all in the end, but lift still persists.

**6. What is the position of stagnation point, when a cylinder is placed in the wind tunnel?**

**a) Lower part**

b) Upper part

c) Middle part

d) No stagnation point

**Explanation: **Similar to the theoretical flow, the stagnation point goes to the lower half of the cylinder. The stagnation point lifts off the surface when the spin is sufficiently high. The position of the stagnation point is a strong function of circulation; when circulation is nil, the stagnation point is zero.

**7. How the finite lift is measured in the cylinder?**

a) Moving up and down

b) Moving up

c) Moving left and right

**d) Spinning cylinder**

**Explanation:** In the wind tunnel, a finite lift is measured for the rotating cylinder. The friction between the fluid and the cylinder’s surface causes the fluid to be dragged along the surface in the same direction as the rotation.

**8. What is the flow of velocity at the top of the cylinder?**

**a) Higher**

b) Lower

c) Constant

d) Does not varies

**Explanation**: This increased velocity contribution causes a higher-than-usual velocity at the top of the cylinder and a lower-than-usual velocity at the bottom, resulting in a higher-than-usual velocity at the top and a lower-than-usual velocity at the bottom. Bernoulli’s equation assumes that these velocities are just outside the viscous boundary layer on the surface.

**9. Is flow over a circular cylinder can produce a finite lift?**

**a) True**

b) False

**Explanation**: A net upward force is created by the pressure imbalance, which is a finite lift. As a result of Bernoulli’s equation, flow over a circular cylinder can provide a finite lift since the pressure reduces as the velocity increases, and the pressure on the top of the cylinder is lower than on the bottom. A net upward force, or a finite lift, will result from this pressure imbalance.

**10. Why the circular cylinder will create more drag?**

**a) The pressure difference between upstream and downstream direction of flow**

b) The pressure difference between relative wind and downstream direction of flow

c) The pressure difference between upstream and direction of flow

d) The pressure difference between downstream of flow

**Explanation:** Because of the pressure difference between upstream and downstream of the flow, a circular cylinder produces a lot of drag. The periodic separation of flow along the cylinder’s surface causes the pressure differential. The drag in the cylinder will rise as a result of this.

**11. How the cylinder will vibrate in the wind tunnel test?**

a) Due to high pressure

b) Due to low pressure

c) Due to relative pressure

**d) Due to fluctuations in the flow**

**Explanation:** The periodic separation of flow along the cylinder’s surface causes the pressure differential. Periodic separation causes flow variations and cylinder vibrations in the wind tunnel.

**12. What is passive flow control method used to reduce the drag co-efficient over a cylinder?**

a) Surface framing

b) Flow visualization

**c) Roughened surfaces**

d) Wiring surfaces

**Explanation:**Various active and passive flow control methods have been used and proven effectively to lessen the amount of drag on a cylinder. Dimpled surfaces, trip wires, and roughened surfaces are examples of these methods.

The lift (force) produced by a thin slice is the lift (force) per unit span of that slice. Every slice of a uniform (straight, not tapered, swept, or twisted) wing produces the same amount of lift, hence the lift per unit span is simply the total lift divided by the wing span, as Riccati points out. The Magnus effect occurs when a cylinder rotates, resulting in an unbalanced wake flow and a net lift force. L. No. 7 A revolving cylinder provides lift when the velocity is higher at the bottom than at the top, and the pressure is higher at the bottom than at the top. The lifting force is said to be directed perpendicular to the cylinder velocity.