Experiment No 02

To investigate the relationship between Specific Energy (E) and Depth of Flow (y) in a rectangular channel.

Dated: 11-03-2015

Objectives:

There are following purposes of this experiment.

To study the variation in specific energy as a function of depth of flow for a given discharge in a lab flume.

To validate the theories of E ~ y diagram.

Apparatus:

S-6 Tilting laboratory flume with manometer, slope adjusting scale and flow arrangement.

Point gauge (to measure depth of water)

Related Theory:

Flume:

It is an open channel generally supported on or above the ground.

S6 (glass sided) tilting flume apparatus:

A glass sided tilting flume apparatus is fabricated with stainless steel with monomeric flow arrangement and slope adjusting scale which use in laboratory to perform the various experiments. It is a function of the shape of the pipe, channel, or river in which the water is flowing. A working cross-section of 300mm wide by 450 mm deep with working lengths of 5m, 7.5, 10m and 15m.

(Figur

Point Gauge:

It is used to measure the depth of flowing flow in tilting flume at different points of section.

(Figure: Point Gauge)

Specific Energy:

It is the total energy per unit weight measured relative to the channel bed.E = y+ (V2)/2gy2

Assumptions:

Following assumptions are being done.

Normal flow conditions exist in channel. ( Steady uniform flow )

Velocity correction factor ( α = 1 )

Bed Slope is very small. ( Practically S < 1: 10

Critical Depth:

It is the depth of flow in the channel at which specific energy is minimum.

Froude No:

It is the ratio of inertial forces to gravitational forces.

Critical Flow:

It is the flow corresponding to critical depth. (Fr = 1)

Sub-Critical Flow:

It is the flow with larger depths & less flow velocities. (Fr < 1)

Super-Critical Flow:

It is the flow with lesser depths & larger flow velocities. (Fr > 1)

Emin (Minimum Specific Energy):

It is the specific energy at critical depth under critical velocity condition in the channel

Critical Velocity:

Velocity of flow at critical depth is called Critical Velocity.

Alternate Depths:

For any value of Specific energy other than at the critical point for a constant discharge, there are two water depths, one is greater than the critical depth and the other is less than the critical depth. These two depths for a given specific energy are termed as specific depths.

yc theoretical and Emin theoretical:

yc theoretical and Emin theoretical is find out by following formulas.

Procedure:

Start the pump to maintain constant discharge in the open channel. Allow the flow in the flume to be stabilized. For one particular value of slope find out the water depths at three different locations

and calculate the average depth of flow. Calculate the specific energy using relationship.

Repeat this procedure for different values of slope. Draw the specific energy curve. Find out the critical depth and Emin. Find out yc theoretical and Emin theoretical.

Precautions:

Tip of the hook gauge should just touch the water. Take piezometric readings when flow is ready. Take more than three readings.

Performance:

A picture was taken during performing the experiment.

Observations and Calculations:

Flume width = B= 11’’ = 0.2794 m

Value of k to find the Q = 1.2

Sr. #

Channel bed

slope(S)

Rise of water in pizometric

tubes and their

difference (m)

Average Depth of flow

Y= (Y1+Y2+Y3)/3(m)

Area of flowA=

(B*Y)(m2)

Flow rateQ=

kA√(2g∆h)(m3/sec)

Flow rate per unit width

q= Q/B(m2/sec)

Specific EnergyE= Y+

(q2/2gy2)(m)

h1 h2 ∆h Y1 Y2 Y3 Y

1

2

3

4

5

6

7

0.04 0.045 0.05 0.055 0.06 0.065 0.07 0.0750

0.01

0.02

0.03

0.04

0.05

0.06

0.07

Graph b/w Specific Energy & Depth

Specific Energy (E)

Dep

th (Y

)

Comments: