Jawaharlal Nehru Technological University Hyderabad
Jawaharlal Nehru Technological University Hyderabad B.Tech IV GROUND VEHICLE AERODYNAMICS Previous Question Paper (July - 2021 - R16)
Answer any Five Questions. All Questions Carry Equal Marks.
Main
Differentiate between external and internal flow problems by taking real life examples.
Answer
External flow refers to the flow of a fluid over a solid body that is completely immersed in the fluid, where the boundary layer development and wake formation are critical. In contrast, internal flow refers to the flow of a fluid confined by solid boundaries, such as pipes, ducts, or channels, where the flow is constrained and the entire cross-section is typically filled with the fluid.
A primary example of external flow is the airflow over the exterior body of an automobile or an aircraft wing, where the aerodynamic drag and lift are the primary concerns. An example of internal flow is the flow of air through an automotive radiator or the intake manifold of an engine, where the pressure drop and heat transfer efficiency are the primary design considerations.
Describe the motion of a vehicle resisted by Aerodynamic drag, rolling resistance and climbing resistance.
Answer
The motion of a vehicle is governed by the balance between the tractive force provided by the engine and the total resistive forces acting against it. The total resistance force Ftotal is the sum of aerodynamic drag, rolling resistance, and climbing resistance.
1. Aerodynamic Drag (FD): This is the resistance experienced by the vehicle as it moves through the air. It is calculated as:
where ρ is air density, V is vehicle velocity, CD is the drag coefficient, and A is the frontal area.
2. Rolling Resistance (FR): This arises from the deformation of the tires and the road surface at the contact patch. It is expressed as:
where Crr is the coefficient of rolling resistance, m is vehicle mass, g is gravitational acceleration, and θ is the road inclination angle.
3. Climbing Resistance (FG): This is the component of the vehicle's weight acting against the direction of motion when traveling on an incline:
For a vehicle to maintain a constant velocity, the engine must provide a tractive force equal to the sum of these three resistances. If the tractive force exceeds this sum, the vehicle accelerates; if it is less, the vehicle decelerates.
Explain different practical objectives of aerodynamics. Describe side force and yaw moment in car aerodynamics.
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A passenger car has a frontal area of 20 ft2 and a drag coefficient of 0.42. It is travelling along at 55 mph. Calculate the aerodynamic drag and the associated horse power requirements, if it is driving into a 25 mph headwind and with a 25 mph tailwind.
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Illustrate the aerodynamic effects on modification of hatch back, fast back and square back.
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Under what condition of yawing moment, a vehicle becomes aerodynamically unstable? Explain.
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Describe the lateral stability problems and explain the methods to avoid such problems.
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What is the significance of following simple add-ons for a racing car aerodynamics:
Spoilers
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Strakes and wickers
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Explain different transducers used in a wind tunnel for measurement of pressure.
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What is the purpose of a wind tunnel? Name various parts of a wind tunnel.
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What are the limitations of prototype test for the measurement of aerodynamic parameters?
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