Wake Distribution

Hey,
I was studying about wake distribution and I would like to know how to get nominal wake distribution for axial and tangential velocities from the DTMB model (Ref. PNA)

 

The secret lies in the word "nominal"....see here

http://en.wikipedia.org/wiki/Real_versus_nominal_value

Basicly it requires engineering judgment.

 

Thank you for your reply,
So you mean to tell that I follow the theory and end up with Nominal numbers?

 

Which theory? Defining the wake or defining the propeller?

In order to design a wake adapted propeller you must form some idea of the wake to design for. Because the instantaneous wake is ever changing due to the environment, ship response, and even the propeller action, you must use some "nominal" wake to enter the blade design process with in order to maximize thrust and minimize vibration over the rotation cycle. Even a wake measured with a rake is subject to variation and recursive CFD opens the whole "self licking ice cream cone' issue. So, armed with the wake data you have, you have to determine a "nominal" wake that you feels best fits the design goals of the ship and propulsion plant. There are no hard and fast rules because different hull forms will require different treatment. FWIW, for a typical displacement ship, I would use a radial distribution of the annular mean wake offset by 1-2 RMS sigma to the conservative (either torque, SHP, or blade loading) side.