During the Semester you carried out an experiment with a wat

During the Semester you carried out an experiment with a water jet impacting on two different surfaces, a flat plate and a hemispherical cup. You were able to determine the impact force three different ways. Explain, with one sentence for each, the three different values for impact force and how they were obtained. Comment on how you would expect the three forces to compare with each other. Comment on how results from the hemispherical cup and the flat plate are expected to compare. Provide an example of when knowledge of the impact force of a water jet might be applied.

Solution

a. Impact force on flate is given by F = AVin*Vin where

= density

A = area of jet

Vin = inlet velocity of jet

and Vout= outlet velocity = 0

For hemispherical cup, F = 2AVin*Vin as the outlet velocity Vout = -Vin

For an unsymmetrical surface or jet,the impact force would depend on the orientation angle of the surface. There will be two force components - one parallel to the jet and another normal to it.

b and c - The impact force for a hemispherical cup is 2 times that on a flat plate

d - Example when knowledge of the impact force of a water jet is applied - Pelton turbine.

Clearly, the impact force is greater for hemispherical surface than for flat plate.