# Aerodynamics Questions and Answers – Infinitesimal Fluid Element

This set of Aerodynamics Multiple Choice Questions & Answers (MCQs) focuses on “Infinitesimal Fluid Element”.

**1. Interia force falls under which flow similarity?**

a) Geometric Similarity

b) Kinematic Similarity

**c) Dynamic Similarity**

d) Dimensionless number

**Explanation:** The model and prototype must be geometrically and kinematically similar for dynamic similarity, as well as the total amount of forces acting at a place on the model and prototype must be identical. Because the inertia force satisfies the requirement, it is classified as dynamically comparable.

**2. Which of the following can attribute the flow of jet of oil in an unbroken stream?**

a) Capillarity

**b) Surface tension**

c) Temperature

d) Density

**Explanation:** Because the molecules at the surface and the free layer of an oil jet differ, the oil resists external force. The oil molecules’ cohesive structure aids in increasing the oil’s surface area.

**3. Which of the following is an example of Newtonian fluid?**

**a) Water**

b) Plastic

c) Colloids

d) Gel

**Explanation: **Newtonian fluids are those that obey Newton’s viscosity law. It states that the amount of deformation is directly proportional to the applied shear stress.

τ = μdv/dy

Where, μ—–viscosity of the fluid

τ—-shear stress

dv/dy -velocity gradient.

**4. In which of the following does the shock wave form?**

a) subsonic flow

b) transonic flow

**c) supersonic flow**

d) incompressible flow

**Explanation:** Supersonic flows are defined by the presence of shock waves, which cause the flow characteristics and streamlines to alter abruptly.

**5. Reynold’s number is the ratio of ____________**

**a) Inertia force to viscous force**

b) Viscous force to inertia force

c) Inertia force to gravity force

d) Pressure force to inertia force

**Explanation:** Reynold’s number is given by Re = VL ρ / μ, which signifies the inertia to viscous force occurring in a flow. ρ / μ is called as kinematic viscosity of the fluid. Larger Reynold’s number, greater will be the inertial effects.

**6. Centre of pressure is defined as the point on the body where the resultant forces acts.**

**a) True**

b) False

**Explanation:** Various sections of an aeroplane are subjected to pressure force. When these forces are reduced to a single component, they act at a single place, which is the pressure centre. It is also the focal point of all hydrostatic forces (fluid-induced forces).

**7. The aircraft fly in the atmosphere due to which of the following principle?**

a) Archimedes principle

**b) Bernoulli’s principle**

c) Gravitational force

d) Newton’s law of viscosity

**Explanation:** The sum of all forms of energy (potential energy, kinetic energy, and internal energy) remains constant, according to Bernoulli’s principle. The body is only affected by its own weight and pressure forces.

**8. What is a suitable flow model for a fluid?**

a) Finite control volume approach

b) Infinitesimal fluid element approach

c) Molecular approach

**d) All the three models can be used based on the need**

**Explanation:** The finite control volume takes into account a finite volume that is either fixed in space or moving through a fluid. The infinitesimal little element takes into account a finite element that can be fixed or move with the flow. The molecular method is a microscopic method that can be used to study atoms and molecules.

**9. In the equation, ∇.V=1/ v*D (v)/Dt, the term ∇.V is _________**

a) change in velocity

**b) divergence of velocity**

c) volume

d) velocity as a function of time

**Explanation:** Divergence of velocity is the rate at which the volume of a moving fluid element changes over time per unit volume, where v is small and because of this small volume, Throughout the volume, V is the same. For the physical interpretation of velocity divergence, a moving control volume is used.

**10. Length, Scale and Volume fall under which of the following flow similarity?**

**a) Geometric Similarity**

b) Kinematic Similarity

c) Dynamic Similarity

d) Dimensionless number

**Explanation:** When the model and prototype have the same dimensional ratio in each direction, they are said to be geometrically similar. Scale ratios are the name for these ratios. For example, the length scale ratio Lr = Lm/Lp, where m and p denote model and prototype, respectively.

Infinitesimal Fluid Element – Aerodynamics Questions and Answers Explanation: The finite control volume takes into account a finite volume that is either fixed in space or moving through a fluid. The infinitesimal little element takes into account a finite element that can be fixed or move with the flow. When the model and prototype have the same dimensional ratio in each direction, they are said to be geometrically similar. Scale ratios are the name for these ratios. For example, the length scale ratio Lr = Lm/Lp, where m and p denote model and prototype, respectively.