I have done an experiment to calculate the loss coefficient at contraction and expansion of an open channel flow. water levels were measured at upstream and downstream to the expansion and contraction for different known discharges.
Then a graph between velocity head loss and energy head loss was drawn. The gradient of the graph is greater than 45 degrees which gives the loss coefficient greater than 1. Can anyone please explain how can this be possible?
Thank you.
I do not think that is possible. I also think you have an incorrect calculation or formula problem or a problem during the experiment. It should be indicated, just for information, whether it is sudden (abrupt) or gradual contractions, sudden (abrupt) or gradual expansions. Singular head loss coefficient may be calculated from the reference handbook (Idelchik, 1969; 1986). It is a reference document for everything related to the calculation of head loss coefficients for most possible configurations.
In the case of channel contractions, the energy losses are smaller than for expansions. For an abrupt contraction, the singular head loss is about :
dH = KXV2^2/(2g) (Sudden sidewall contraction)
Where V2 is the downstream flow velocity and K = 0.23 - 0.35 for square-edged contractions in the rectangular channel and K = 0.1 - 0.2 for rounded-edged contractions.
The values of K can be greater than unity in the case of a pipeline arriving in a large tank (K varies between 1.06 and 1.1) or a sudden bend of more than 75 ° (K is 1.50 for an angle of 90 °).
I advise you to consult the reference that I indicated to you above.
Regards.
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