# Cylinder Wake calculation

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 January 28, 2007, 10:00 Cylinder Wake calculation #1 Adam Chapman Guest   Posts: n/a Hello, I am working on a dissertation project which aims to reduce the vibration of wind turbine structures by pitching the rotor blades, changing the thrust force. At the moment I am trying to make a model of the flow field downwind of the cylindrical tower from which I can determine the local angle of attack on the rotor blades. I was not expecting the flow behind a 2-D cylinder to be as complex as it appears to be from my searches for academic papers on the topic. As a guide, the reynold's number's I am interested in are the order of 10^5. The academic papers I have found say that 3D instabilities occur at around Re=200, and don't say if any other effects come into play at higher Re's. I understand that this flow is dynamic, although I have a book on wind turbines that says the time-averaged tower wake is sufficient for this application. I thought about taking the drag coefficient at a particular reynold's number and reversing the wake traverse technique to find the local velocities, assuming the wake has a "1-cos^2" profile, but this is impossible without knowing either the wake width or the peak velocity defecit. All the material I have found on the flow behind a cylinder uses the Navier stokes equations, which I understand, but then the papers tend to skip the process used to calculate the data before they show those pretty chloropleth pictures of vorticity. I would like to be able to cretae these vorticity diagrams myself in matlab, because the blade pitch control loop can then be integrated with simulink. If anybody knows of a report or website explaining how to calculate the wake profile downsream of a cylinder, or even the name of a particular method which I may ot of heard of before, I really would be in your debt. If there is a method for finding the time averaged wake directly then that would be even better. Thanks for any help which can be offered, Regards, Adam