Engineering Questions with Answers - Multiple Choice Questions
MCQs on Types of Flow in Channels
The flow characteristics of a channel does not change with time at any point. What type of flow is it?
a) Steady flow
b) Uniform flow
c) Laminar flow
d) Turbulent flow
Explanation: The flow characteristics unchanged with time is a steady flow, characteristics unchanged with space is a uniform flow. Laminar and turbulent flows are classified with reference to Reynolds number.
The Reynolds number for a flow in a channel is 1000. What type of flow is it?
Explanation: Reynolds number – 500 to 600 – Laminar flow
Reynolds number – 500 to 2000 – Transition
Reynolds number – > 2000 – Turbulent flow.
The ratio of inertia force and gravitational force is called as ______
a) Reynolds number
b) Stokes number
c) Froude’s number
d) Euler’s number
Explanation: Froude’s number is the ratio of inertia forces and gravitational forces. Froude’s number is used to classify the flow into critical, sub critical and super critical.
The Froude’s number for a flow in a channel section is 1. What type of flow is it?
a) Sub Critical
c) Super critical
Explanation: Froude’s number = 1 – Critical flow
Froude’s number < 1 – Sub Critical flow Froude’s number > – Super Critical flow.
What is the Froude’s number for a channel having mean velocity 4.34 m/s and mean hydraulic depth of 3m?
Explanation: Froude’s number (Fr) = V/ (gD2)
= 4.34/ (9.81) (32)
Calculate the mean hydraulic radius for a channel having 20m2 cross sectional area and 50m of wetted perimeter.
Explanation: Hydraulic Radius(R) = A/P
Calculate the mean hydraulic depth of a channel having top width of 7m and cross sectional area of 35m2.
Explanation: Hydraulic depth (D) = A/T
Estimate the section factor for a channel section having cross sectional area of 40m2 and hydraulic depth of 6m.
Explanation: Section factor (Z) = A√D
Calculate the Froude’s number for a channel having discharge of 261.03m3/s, cross sectional area of 42m2 and the top width being 6m.
Explanation: Fr= V⁄√gD
V = Q/A
V = 261.03/42 = 6.215 m/s
D = A/T = 42/6 = 7m
Fr = 0.75 (Subcritical).
Calculate the aspect ratio having channel width of 6m and depth of 8m.
Explanation: Aspect ratio = Depth / width
= 8/6 = 1.33m.
Estimate the type of flow in a channel having cross sectional area of 50m2 and top of the channel is 5m. The mean velocity of flow is 0.1m/s and the absolute viscosity of water is 0.625 N-s/m2.
Explanation: Reynolds number (Re)=1000VD/µ
Re = 1000(0.1) (D)/ 0.625
D = A/T = 50/5 = 10 m
Re = 1000(0.1) (10)/ 0.625
Transition flow (500 – 2000).