Computational Fluid Dynamics MCQ

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• When the residuals are scaled, the vanishing value is ___________
  ক

  less than 10

  খ

  less than 10

  গ

  more than 10-5

  ঘ

  less than 10-5
• Which of these is the denominator while finding the root mean square residual?
  ক

  Sum of the absolute residuals

  খ

  Sum of the actual residuals

  গ

  Number of elements

  ঘ

  Sum of the scaled residuals
• Which of these values is used to find the normalized residual?
  ক

  The minimum of all the residuals

  খ

  The maximum of all the residuals

  গ

  The sum of all the residuals

  ঘ

  The product of all the residuals
• Which of these statements states the need for the normalization of the residual?
  ক

  Different variables result in different level of residuals

  খ

  Different variables result in the same level of residuals

  গ

  Different variables result in different residuals

  ঘ

  Different variables result in same residuals
• The maximum value of residual is used to __________
  ক

  decrease the importance of sign

  খ

  compare with the vanishing value

  গ

  include the sign of the residual

  ঘ

  increase the importance of sign
• The absolute residual is calculated __________
  ক

  to overcome high values of residuals

  খ

  to decelerate the convergence process

  গ

  to overcome the sign problems in the actual residual value

  ঘ

  to increase the rate of convergence
• Why is the residual form of the discretized equations used?
  ক

  It increases the rate of convergence

  খ

  It increases the stability

  গ

  It increases the accuracy

  ঘ

  Numerical errors are less
• When the field of the flow variable is exact, the residual will be __________
  ক

  negative

  খ

  positive

  গ

  zero

  ঘ

  one
• The standard form of the equations is solved for __________ and the residual form is solved for _________
  ক

  flow variables, residuals

  খ

  flow variables, corrections

  গ

  corrections, flow variables

  ঘ

  residuals, flow variables
• Which of these equations can be written in the residual form?
  ক

  The discretized equations

  খ

  The governing equations

  গ

  The PDEs

  ঘ

  The ODEs
• What is the relation between the E of the E-factor relaxation and the relaxation factor λ?
  ক

  E=\(\frac{1}{1-\lambda}\)

  খ

  E=\(\frac{\lambda}{1-\lambda}\)

  গ

  E=\(\frac{\lambda}{1+\lambda}\)

  ঘ

  E=\(\frac{1}{1+\lambda}\)
• The time-step advancement of the E-factor relaxation is dependent on ___________
  ক

  the convergence

  খ

  the stability

  গ

  the accuracy

  ঘ

  the cell volume
• Which of these statements about the Patankar’s under-relaxation is true?
  ক

  The value form the previous iteration is modified

  খ

  The diagonal coefficients are modified

  গ

  The whole equation is modified

  ঘ

  The neighbouring coefficient is modified
• Which of these relaxation techniques is used in the SIMPLE algorithm?
  ক

  Explicit over-relaxation

  খ

  Implicit over-relaxation

  গ

  Explicit under-relaxation

  ঘ

  Implicit under-relaxation
• What is the disadvantage of over-relaxation?
  ক

  Stability is decreased

  খ

  Divergence is increased

  গ

  Oscillations are increased

  ঘ

  Convergence is increased
• There is no relaxation when the relaxation factor is __________
  ক

  positive infinity

  খ

  negative infinity

  গ

  one

  ঘ

  zero
• When the relaxation factor is less than one, which of these will occur?
  ক

  Increase the speed of convergence

  খ

  Slow down the speed of convergence

  গ

  Decrease the stability

  ঘ

  Increase the divergence
• The explicit under-relaxation method means that __________
  ক

  the changes are made before each iteration

  খ

  the changes are made before the iteration process

  গ

  the changes are made after the iteration process

  ঘ

  the changes are made after each iteration
• The relaxation techniques slow down the __________
  ক

  whole iterative process

  খ

  effect of the sources

  গ

  effect of the neighbouring elements and the source terms

  ঘ

  effect of the neighbouring elements
• Relaxation techniques are used to ensure __________
  ক

  convergence

  খ

  stability

  গ

  accuracy

  ঘ

  boundedness
• The general form of the equation for the source term is ΦC+∑F~NB(C)aF ΦF =FluxVC. When the variable Φ is positive-definite, the FluxVC should be ______________
  ক

  ΦC+∑F~NB(C)aF ΦF =FluxVC. When the variable Φ is positive-definite, the FluxVC should be ______________ ] FluxVC must be greater than one

  খ

  aC-FluxCC

  গ

  aC-FluxCC

  ঘ

  aC-FluxCC
• The general form of the equation for the source term is ΦC+∑F~NB(C)aF ΦF =FluxVC. The constraint on the term FluxCC is imposed by ______________
  ক

  ΦC+∑F~NB(C)aF ΦF =FluxVC. The constraint on the term FluxCC is imposed by ______________ ] Scarborough criterion

  খ

  aC-FluxCC

  গ

  aC-FluxCC

  ঘ

  aC-FluxCC
• The general form of the equation for the source term is ΦC+∑F~NB(C)aF ΦF =FluxVC. What constraint does the term FluxCC have?
  ক

  ΦC+∑F~NB(C)aF ΦF =FluxVC. What constraint does the term FluxCC have? ] FluxCC must be greater than one

  খ

  aC-FluxCC

  গ

  aC-FluxCC

  ঘ

  aC-FluxCC
• For linearizing the source term, which of these methods is used?
  ক

  Weighted average

  খ

  Series expansion

  গ

  Normalization

  ঘ

  Central differencing
• When the source term varies highly, which of these properties is affected?
  ক

  Consistency

  খ

  Boundedness

  গ

  Stability

  ঘ

  Rate of convergence
• When the source term does not vary much, the source term is ___________
  ক

  implicitly calculated

  খ

  calculated from the previous iteration’s values

  গ

  solved simultaneously

  ঘ

  calculated form the current values
• The source term is ____________
  ক

  equal to the square of the source term

  খ

  equal to the source term

  গ

  a function of the flow variable

  ঘ

  a function of the product of flow variable and the sink term
• Which of these methods is recommended for the source term treatment in general?
  ক

  Treat sinks explicitly and sources implicitly

  খ

  Treat sinks implicitly and sources explicitly

  গ

  Treat the source term explicitly

  ঘ

  Treat the source term implicitly
• Which of these physical properties of the flow problems is affected by the source term?
  ক

  Order of accuracy

  খ

  Reduction of error

  গ

  Stability

  ঘ

  Accuracy
• Which of these transport phenomena do not involve any source term?
  ক

  Heat conduction

  খ

  Heat radiation

  গ

  Turbulence models

  ঘ

  Chemical reactions