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The correct choice is (d) Validity

The best I can explain: Validity of a mathematical MODEL is the relevancy of the model with the problem taken. If the mathematical model does not comply with the problem being solved, the entire PREDICTION may GO WRONG.

The correct choice is (a) CFD analysis

The explanation: This is an OPTIMIZATION case. CFD can be used to do trial and ERROR analysis on the BEST fitting WING.

The CORRECT OPTION is (C) Flow visualization

The explanation is: Post-processing is the FINAL step in CFD after pre-processing and solving. This involves various methods of visualizing the flow as well as GETTING quantitative information.

The correct ANSWER is (d) FLOW over airfoils

Best explanation: An airfoil is a two-dimensional profile of a wing. Flow over this two-dimensional profile will not need any three-dimensional ANALYSIS.

Right ANSWER is (c) Flow visualization

The best explanation: A flow can be categorized into laminar or turbulent by seeing it. So, the flow of air should be made visible by some flow visualization techniques. In the CASE of CFD, it can be EASILY seen from the resulting plot of flow PROPERTIES.

Right ANSWER is (b) Experimental set-up will have imperfections

To elaborate: Some research purposes will NEED non-practical processes to be analysed. SETTING up experimental analysis for such CASES involves a lot of STEPS and that may not yield proper results as the set-up cannot be perfect.

Correct choice is (d) Expensive

The best explanation: For DIFFICULT problems with complex geometry, strong non-linearity, ETC., if the OBJECTIVE is very limited, then use of CFD will become COSTLIER than experimenting. For such cases, experimental results are suitable.

The correct option is (d) To generate an optimal grid which is a COMPROMISE between desired accuracy and solution cost

The explanation: Accuracy of a CFD solution directly depends on the NUMBER of grids. On the other hand, if there are more grids, the cost of computation will INCREASE. To OVERCOME this, a grid which is a compromise between both of these should be GENERATED. So, a lot of time is spent on grid generation.

Correct option is (a) Change of flow equations from elliptic to hyperbolic

The explanation is: STRAIGHT to the nose of the vehicle, the shock is normal. This results in a subsonic region and elliptic flow equations. But, downstream the shock is oblique which creates a supersonic region resulting in the elliptic EQUATION. This was the PROBLEM in modelling supersonic blunt nose. In LATER years this was overcome by a better model.

The CORRECT option is (c) IMPROVE casting techniques

The explanation: The mould cannot be changed according to fluid flow. It should have the shape of the product needed. Choosing the metal DEPENDS upon the APPLICATION and structural concern. The temperature change may affect the quality of the product. By knowing the flow pattern, casting techniques can be improved.

Correct option is (C) Lift analysis

To explain I would say: Hydrodynamic analysis on the propeller of a naval vehicle is done. As a vehicle will be MOVING through the AIR, wind LOADS should also be analysed. The stability of a vehicle when it changes its position (manoeuvring) is also analysed. But, the lift FORCE need not be analysed.

Right answer is (C) Flexibility

For explanation: Analytical methods of solving a problem is not applicable for many of the cases. Only a tiny PART of the range of practical problems can be solved using analytical methods. Numerical methods can be USED to solve a very wide range of practical problems.

The correct CHOICE is (a) Faster than

For explanation I WOULD say: Computational investigation can be carried out at a higher speed when compared to experiments especially when the MODELS are SIMPLE and suitable for computation.

The CORRECT option is (C) CODE creator

Explanation: In order to provide their users with EASY access to its solver, CFD packages have sophisticated input and output interfaces. The three MAIN elements of CFD packages are pre-processor, solver and post-processor.

The CORRECT choice is (d) The type of computers and algorithms that existed

The explanation is: The computers and algorithms that existed that time was not SUITABLE for three-dimensional analyses. STORAGE and speed CAPACITIES of computers were not ENOUGH.

Right answer is (c) INCREASING load capacity

The BEST explanation: For increasing the load capacity, the strength of the VEHICLE should be more. Therefore, a structural analysis WOULD be ideal for that purpose. There will not be a need for fluid FLOW analysis.

The correct option is (C) STRUCTURAL

The explanation: A structural engineer is the one who analyses the loads to be CARRIED and decides the MATERIALS for various aircraft parts. So, the loads ACTING on the parts must be known to him.

Correct choice is (b) Domain

The best I can explain: The region of interest for solving a PARTICULAR fluid FLOW PROBLEM is called domain. The first step in pre-processing is to DEFINE the geometry of this domain.

The correct choice is (c) Interpret

Explanation: CFD does not just PROVIDE a QUANTITATIVE comparison with the wind tunnel results. It provides a means to interpret the EXPERIMENTAL CONDITIONS. For example, to determine whether the flow is LAMINAR or turbulent in a quantitative experiment carried out in a wind tunnel.

The correct answer is (a) Non-uniform

The EXPLANATION is: A uniform GRID has all the cells with the same dimensions. The flow properties may not vary UNIFORMLY in the domain. Therefore, a non-uniform grid with more cells in the areas with large variations is an OPTIMAL WAY of grid generation.

The correct CHOICE is (a) Increased, reduced

The BEST explanation: Thermal efficiency should be increased to get the best out of the input ENERGY. CONSIDERING the environmental effects, the EMISSION of pollutants should be less.

The correct answer is (d) 3-D Navier-Stokes equation for incompressible flow with a turbulence MODEL

Explanation: Incompressible flow is CHOSEN as the flow of water will MOSTLY be incompressible unless the flow velocity is very high. Turbulence model is chosen as the flow PROPERTIES will GET abrupt change due to high Reynolds number.

Right choice is (a) Transient

The best explanation: The PISTON inside an internal COMBUSTION Otto-engine MOVES up and down continuously which makes the flow UNSTEADY. A flow of fluid can be called steady if its properties do not vary with time.

Correct choice is (b) PRESSURE

Easiest explanation: LIFT force can be obtained by the difference in pressure between the top and BOTTOM surfaces of a body. Similarly, the pressure drag of a body can be obtained by finding the pressure difference between the front and BACK halves of a body. Both of these quantities DEPEND upon the pressure distribution.

Right choice is (b) Drag

For EXPLANATION: The drag FORCE is the one which pushes a BODY backward during its motion. Therefore, to increase the efficiency of a vehicle, there should be LESS drag.

Right choice is (d) Pre-processing

The EXPLANATION is: BOUNDARY conditions at the cells which are in touch with the DOMAIN boundaries must be specified before STARTING to solve a PROBLEM in CFD. So, it comes under pre-processing.

Correct choice is (b) ITERATIVE

Explanation: The PHYSICAL PHENOMENA makes the ALGEBRAIC equations complex and non-linear. Hence, an iterative method is used in CFD PACKAGES to solve these equations.

The correct choice is (B) Discrete points of SPACE and time

For explanation: CFD discretizes the equations and ALSO the domain and solves the discretized equations for only the points in the discretized domain using numerical METHODS.

The CORRECT choice is (a) AERODYNAMIC

To explain: An aerodynamic ENGINEER needs the pressure distribution, vortex formation and other aerodynamic details to make an aircraft aerodynamically efficient.

Correct answer is (b) ANALOGOUS to

The explanation: CFD RESULTS completely depend on the problem and solution models we opt to simulate the flow. So, if the CHOSEN models are correct, the CFD results will be analogous to experimental results. In fact, by comparing the results with wind tunnel results, CFD models are changed.

Correct CHOICE is (b) Reynolds Number

The explanation is: Reynolds number of the flow would be the major CHANGE as the density and viscosity of water will be higher than that of air. Therefore, while modelling a hydrodynamic flow, CARE should be taken.

The correct CHOICE is (d) Nodes

The explanation: Nodes are the intersection of cells in a domain. These are the points where the flow PROPERTIES are defined after solving the problem. The flow is not analysed in CONTINUOUS points of the domain.

Correct answer is (d) NUMERICAL

For EXPLANATION I WOULD say: CFD uses numerical experimentation to obtain the flow PROPERTIES at discrete points. Computer programs are used to carry out these experiments.

The correct answer is (d) Cost-effective and fast

For EXPLANATION: For design optimization, multiple TESTS should be DONE on different cases and MANY trials should be done. CFD is faster and cost-effective than experiments in this CASE.

Right choice is (a) UNWIELDY

The explanation: A CFD tool just means a COMPUTER program that makes it very easy to carry or transfer. Moreover, the source program can EVEN be remotely ACCESSED. This makes it a READILY transportable tool. A wind tunnel is a tool which is unwieldy.

Correct choice is (c) Simultaneously modelling high Mach numbers and high temperatures

To explain: Continuous CHANGE in Mach numbers can be done in wind TUNNELS. Transonic and hypersonic wind tunnels also exist. If we try to model high speeds at high temperatures, the wind tends to reduce the temperature as we have wind FLOWING over the STATIONARY model in a wind tunnel.

Right answer is (B) HiMAT

For explanation: HiMAT (Highly Manoeuvrable AIRCRAFT Technology) is a NASA EXPERIMENTAL aircraft designed to test concepts of high MANOEUVRABILITY. Wind tunnel tests showed that there will unacceptable drag. Wings of this aircraft is redesigned using CFD to overcome this problem.

The correct option is (b) Facilities do not exist in all fight regimes

Explanation: Ground TEST facilities can be used to model three-dimensional flows also and even they PRODUCE accurate results in a LESS run-time. But they cannot be used to test all flight regimes as they want artificial set-up for EVERY SINGLE property of the flow.

Right ANSWER is (d) 17^th century

Best explanation: Experimental fluid dynamics was started in France and ENGLAND in the 17^th century when the relation between FORCE and velocity is FOUND from experiments.

Correct answer is (C) Numerical

Easy explanation: As the experimental analysis of fluid flow problems are very expensive, CFD uses theoretical method to analyse them. Among the two theoretical METHODS stated above (ANALYTICAL and Numerical), the analytical method uses approximations which makes the theory UNRELIABLE. So, CFD uses the numerical method.

Right OPTION is (c) European

The explanation: Theoretical fluid dynamics was DEVELOPED in European COUNTRIES in the 18^th and 19^th CENTURIES FIRST theoretical derivation of drag equation is found.

D ∝ ρ SV^2

Right ANSWER is (d) CFD will replace the approaches of pure theory and pure experiments

The explanation: The future of fluid DYNAMICS will rest upon a PROPER BALANCE of pure experiment, pure theory and computational fluid dynamics, each complementing one another in their limitations.

Right OPTION is (a) High-speed DIGITAL COMPUTERS

Easiest explanation: Invention of high-speed digital computers ALLOWED modelling and simulating fluid flows with high accuracy as the level of computing involved in the numerical methods is very high. Without this, it would have been very difficult to solve the numerical algorithms.

Right answer is (a) Theoretical and experimental

The explanation is: PURE theoretical and pure experimental approaches were the two approaches PRIOR to the advent of CFD. To overcome the DISADVANTAGES in both of these approaches, COMPUTATIONAL FLUID Dynamics was invented.