Most Asked CFD Technical Interview Questions with Answers

The field of fluid mechanics, known as Computational Fluid Dynamics, or CFD combines data structures and numerical analysis to solve and study fluid flow problems. CFD engineers can start their careers in the automotive, chemical, electronics, or aerospace industries.

CFD engineers utilise their expertise to develop new components for machinery. They create and test prototypes and perform analysis to optimise the efficiency of the existing or new parts and components. The average salary of a CFD engineer in India is ₹5,60,421 yearly. 

Here we have listed a few basic CFD interview questions for aspiring candidates.

Most Frequently Asked CFD Interview Questions Asked by Top Recruiters Across India 

 

• Describe the steps you use to run a CFD simulation. 

Sample answer: 

I will begin by compiling all the data I require for the project I'm working on. This contains the client's or stakeholders' requirements, existing data or research, and the simulation's objectives.

Using the preferred CFD simulation tool will construct a mesh.

Finally, I will report the simulation results to respective stakeholders or clients.

The fundamental procedure for carrying out a CFD analysis is described here: 

• Discussion of the flow Issue
• Creating the boundary and initial conditions after modelling the geometry and flow domain
• Producing the grid
• Creating a simulation strategy.
• Setting up the files and input parameters
• After the simulation, obtaining the results.
• Making comparisons between the results and evaluating the performance of the component. 

• Make a distinction between a uniform and non-uniform flow? 

Sample answer: 

If the flow characteristics remain constant with distance along the flow path, the fluid flow is considered to be uniform. Also, if the flow characteristics change and vary at various places along the flow channel, the fluid flow is not uniform. For achieving a uniform flow the cross-section of the flow path must be kept constant.

The flow of a fixed discharge through a pipe that tapers is called non-uniform flow. An excellent illustration of such flow is water flowing through a river with a constant discharge because the river's width typically changes with distance yet the rate of water flow remains constant. 

• What is laminar flow? 

Sample answer: 

When a fluid flows in minuscule parallel layers without interruption, it is said to be laminar. Laminar flows consist of parallel-moving fluid layers with no currents, eddies, or swirls that are typical of the flow itself. Because non-crossing streamlines characterise it, this form of flow is also known as streamline flow. 

• What is Newton’s Law of Viscosity?  

Sample answer:

According to Newton's law of viscosity, the shear stress for a flowing fluid is inversely proportional to the shear strain rate. Viscosity is a physical characteristic that describes the flow resistance of simple fluids. 

With a given temperature and pressure, the ratio of shear stress to shear rate is constant and is known as the viscosity or coefficient of viscosity. Newtonian fluids obeys Newton's law of viscosity. 

• What is Reynolds number? 

Sample answer: The ratio of inertial and viscous forces is expressed by the dimensionless quantity known as the Reynolds number (Re). Although Osborne Reynolds discovered it as the measure to detect the transition between laminar and turbulent flows, George Gabriel Stokes first introduced the idea in 1851.

The Reynolds number is theoretically defined as

Re = ρud/μ = ud/v where:

ρ is the fluid's density.

u is the fluid's macroscopic speed.

D is the diameter.

v is the fluid's dynamic viscosity. 

• What is numerical viscosity?

Sample answer:

Numerical viscosity results from either re-zoning processes employed in Lagrangian formulations or discrete approximations to the momentum advection factors in Eulerian equations. The use of a homogenising assumption in the underlying elements or control volumes of the approximation scheme is the cause of the impact. 

• Explain the different turbulence models.

Sample answer:

Turbulence models are mathematical models used to simulate the effects of turbulent flow in a fluid. They are used to predict the behaviour of a fluid in a variety of situations, such as in aerodynamics, hydrodynamics, and combustion. 

Turbulence models can be divided into two main categories: 

• Reynolds-averaged Navier-Stokes (RANS) models: For fluid flow, these are time-averaged equations of motion. The equations are based on Osborne Reynolds' theory of decomposition, which states that a variable at a given instant may be divided into its time-averaged and fluctuating components.
• Large Eddy Simulation (LES) models: It is a numerical method for integrating spatially filtered equations of motion that model time-evolving three-dimensional turbulence with a high Reynolds number. 

• What are the differences in flow between a rocket nozzle and an ablation jet?

Sample answer:

The main difference between a rocket nozzle and an ablation jet is the way in which they generate thrust. A rocket nozzle uses the combustion of fuel to generate thrust, while an ablation jet uses the ablation of material from the nozzle walls to generate thrust. Additionally, a rocket nozzle is typically designed to be more efficient than an ablation jet, as it is able to generate significant thrust with less fuel. Finally, a rocket nozzle is meant to be more durable than an ablation jet, as it is able to withstand higher temperatures and pressures. 

• Explain the concept of the slip ratio

Sample answer:

The ratio of the gas phase's velocity to the liquid phase's velocity is known as the slip ratio (or velocity ratio) in a gas-liquid flow.

The slip ratio in the homogeneous model of two-phase flow is, by definition, taken to be 1 (no slip). However, experimental findings show that, depending on the flow pattern, the velocities of the gas and liquid phases might differ dramatically (e.g. plug flow, annular flow, bubble flow, stratified flow, slug flow, churn flow). Separated flow models are those that take the existence of the slip into consideration. 

• What is the behaviour of subsonic flow?

Sample answer:

Subsonic flow is a type of fluid flow in which the speed of the fluid is less than the speed of sound. This type of flow is characterised by a gradual decrease in pressure and velocity as the fluid moves downstream. The flow is typically laminar and is characterised by low turbulence.

Conclusion 

Job interviews are like the preliminary rounds for you to start your career. The above-mentioned questions will give a basic overview of the possible questions that you can expect in a technical interview round for the role of a CFD engineer. 

For a detailed interview preparation strategy, enrol in Skill-Lync’s PG Program in Computational Fluid Dynamics. It is a mentor-led course that will teach you key technical skills and help you prepare for interviews.

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