Question

6.It is proposed to study the entry of an aircraft launched torpedo into seawater. The full-size prototype torpedo is 2.44 m in length and enters at 100 m/s into seawater which has a kinematic viscosity, ν = 1.17 x 10-6 m2/s (see the table in the front cover of your textbook). A model test is proposed where the length of the model torpedo is 0.537 m in length. The desire is to predict the force on the prototype torpedo upon entry into the water, using the measured force in the model study.

a.Assuming F = f(ρ, μ, V, L, g) determine the relevant dimensionless parameters for this flow phenomenon. Use ρ, V and L as the repeating variables in your analysis. V is the entry velocity, L is the length of the torpedo and g is the acceleration of gravity.

b.Assuming the dimensionless parameter containing the viscosity is not important at these conditions determine the necessary launch velocity in the model study and the force on the prototype if the measured model force is 9 N. (Assume g is the same for both the model and prototype. Also assume seawater is used in the model study.)

c.Now, assume the dimensionless parameter containing the viscosity is important. Can the fluid used in the model study be the same as the prototype fluid (seawater)? Explain. If not, can you find a fluid for the model study such that full similitude is achieved between the model and prototype? What fluid?

Answer 1