Explore topic-wise MCQs in Computational Fluid Dynamics Questions and Answers.

This section includes 9 Mcqs, each offering curated multiple-choice questions to sharpen your Computational Fluid Dynamics Questions and Answers knowledge and support exam preparation. Choose a topic below to get started.

1.

Consider the continuity equation \(\frac{\partial\rho}{\partial t}+\nabla.(\rho \vec{V})=0\). For a steady flow this equation becomes ___________

A. \(\nabla.(\rho \vec{V})=0\)
B. \(\nabla.(\vec{V})=0\)
C. \(div(\vec{V})=0\)
D. \(curl(\vec{V})=0\)
Answer» B. \(\nabla.(\vec{V})=0\)
Discussion
2.

Consider the continuity equation \(\frac{\partial\rho}{\partial t}+\nabla.(\rho \vec{V})=0\). For an incompressible flow, this equation becomes ___________

A. \(\nabla.(\rho \vec{V})=0\)
B. \(\frac{\partial(\rho\vec{V})}{\partial t}=0\)
C. \(div(\vec{V})=0\)
D. \(div(\rho\vec{V})=0\)
Answer» D. \(div(\rho\vec{V})=0\)
Discussion
3.

Consider an infinitesimally small fluid element with density ρ (of dimensions dx, dy and dz with mass δ m and volume δ V) moving along with the flow with a velocity \(\vec{V}=u\vec{i}+v \vec{j}+w\vec{k}\). The continuity equation is \(\frac{D\rho}{Dt}+\rho \nabla.\vec{V}=0\). Where does this second term come from?

A. Integral
B. The rate of change of element’s volume
C. Elemental change in mass
D. Local derivative
Answer» C. Elemental change in mass
Discussion
4.

Consider an infinitesimally small fluid element with density ρ (of dimensions dx, dy and dz with mass δ m and volume δ V) moving along with the flow with a velocity \(\vec{V}=u\vec{i}+v\vec{j}+w\vec{k}\). What is the time rate of change of mass of this element?

A. \(\frac{D(\rho \delta V)}{Dt}\)
B. \(\frac{\partial(\rho \delta m)}{\partial t}\)
C. \(\frac{\partial(\rho \delta V)}{\partial t}\)
D. \(\frac{D(\rho \delta m)}{Dt}\)
Answer» B. \(\frac{\partial(\rho \delta m)}{\partial t}\)
Discussion
5.

Consider an infinitesimally small fluid element with density ρ (of dimensions dx, dy and dz) fixed in space and fluid is moving across this element with a velocity \(\vec{V}=u\vec{i}+v\vec{j}+w\vec{k}\). What is the final reduced form of net mass flow across the fluid element?

A. \(\frac{\partial\rho}{\partial t}\)
B. \(\rho\vec{V} dx \,dy \,dz\)
C. \(\nabla.(\rho\vec{V})\)
D. \(\nabla.(\rho\vec{V})\)dx dy dz
Answer» E.
Discussion
6.

According to the conservation law, “Net mass flow across the fluid element is equal to the rate of change of mass inside the element”. But, stating the final equation, “Net mass flow across the fluid element + the rate of change of mass inside the element = 0”. Why is the operation not subtraction?

A. Irrespective of the law, the sum is always zero
B. The two terms are always opposite in sign
C. Change in sign is not considered
D. Rate of change may be increase or decrease
Answer» C. Change in sign is not considered
Discussion
7.

Consider an infinitesimally small fluid element with density ρ (of dimensions dx, dy and dz) fixed in space and fluid is moving across this element with a velocity \(\vec{V} = u\vec{i} + v\vec{j} + w\vec{k}\). The rate of change in mass of the fluid element is given by ____________

A. \(\frac{\partial(\rho u)}{\partial x} + \frac{\partial(\rho v)}{\partial y} + \frac{\partial(\rho w)}{\partial z}\)
B. \(\frac{\partial \rho}{\partial t}\)
C. \(\frac{\partial\rho}{\partial t}(dx \,dy \,dz) \)
D. \([\frac{\partial(\rho u)}{\partial x} + \frac{\partial(\rho v)}{\partial y} + \frac{\partial(\rho w)}{\partial z}]dx \,dy \,dz\)
Answer» D. \([\frac{\partial(\rho u)}{\partial x} + \frac{\partial(\rho v)}{\partial y} + \frac{\partial(\rho w)}{\partial z}]dx \,dy \,dz\)
Discussion
8.

Consider an infinitesimally small fluid element with density ρ (of dimensions dx, dy and dz) fixed in space and fluid is moving across this element with a velocity \(\vec{V}=u\vec{i}+v\vec{j}+w\vec{k}\). The net mass flow across the fluid element is given by ______

A. \([\frac{\partial(\rho u)}{\partial x} + \frac{\partial(\rho v)}{\partial y} + \frac{\partial(\rho w)}{\partial z}]dx \,dy \,dz\)
B. \([\frac{\partial(\rho u)}{\partial x} + \frac{\partial(\rho v)}{\partial y} + \frac{\partial(\rho w)}{\partial z}]\)
C. [ρ]dx dy dz
D. \([\frac{\partial(\rho)}{\partial x} + \frac{\partial(\rho)}{\partial y} + \frac{\partial(\rho)}{\partial z}]dx \,dy \,dz\)
Answer» B. \([\frac{\partial(\rho u)}{\partial x} + \frac{\partial(\rho v)}{\partial y} + \frac{\partial(\rho w)}{\partial z}]\)
Discussion
9.

Which of the equations suit this model?

A. \(\frac{\partial}{\partial t}\iiint_V\rho dV + \iint_s \rho \vec{V}.\vec{dS} = 0\)
B. \(\frac{D}{Dt}\iiint_V\rho dV = 0\)
C. \(\frac{\partial\rho}{\partial t}+\nabla.(\rho \vec{V})=0\)
D. \(\frac{D\rho}{Dt}+\rho \nabla.\vec{V}=0\)
Answer» D. \(\frac{D\rho}{Dt}+\rho \nabla.\vec{V}=0\)
Discussion