Welcome to the page where I present the Masters' thesis project I carried out at the Department of Mechanics at KTH, Stockholm. My instructor was Dr. Barbro Muhammad-Klingmann.

The project was an experimental study of turbulent boundary layers affected by a strong adverse pressure gradient. Several different pressure gradients were examined and mean flow separation was encountered in several cases. One of the purposes of the study was to see if quality PIV measurements were possible in this kind of flow, so most of the cases were examined with PIV as well as a large number of static pressure taps, Preston tubes and (where possible) hot-wire probes. Comparisons with old methods for the prediction of the position of the separation line for given pressure gradients were also made.

It was found that the old separation criteria grossly underpredicted the ability of a turbulent boundary layer to withstand a strong adverse pressure gradient like those found in the experiment. Further it was found that PIV is well-suited for the study of separated turbulent boundary layers. Unlike laminar separation, there is sufficient smoke in the separated region to enable PIV measurements there. There are several problems though - the resolution of PIV tends to be lower than for hot-wire measurements, so good results close to the plate are hard to acquire. Smoke released into the boundary layer tends to remain there, even though there is a relatively high turbulence level (ca 2%) in the free-stream. This means that other methods (Prandtl tube) etc must be used to accurtedly measure the free-stream velocity. The inablilty of PIV to measure the flow velocity close to the wall accurately may be an explaination for the unusually high value of the shape factor H=ca 3.5 at reattachment (where the back-flow at the plate was measured to 50%) that was found in this study.

You may want to read the html abstract of the report first.

The complete report is supplied as an Adobe Acrobat document (1.0MB) here. (v3.99f7)

There is also a pure text version of the report, but you will miss the figures and formulae (and possibly the line-breaks too)!

Should you desire to own a hardcopy of the latest available version of the report, all you have to do is to contact me and your request will be handled swiftly.

During spring 1999, a more advanced study, where the spearation of the flow from a wind-energy airfoil at high angles of attack and a Re based on chord length of about 1 000 000, was carried out as a cooperation between my employer at the time, the Aeronautical Research Institure of Sweden (FFA) and the Department of Mechanics at KTH. The report from this PIV study can be requested from the Wind energy department at the Aeronautical Research Institute of Sweden.

The experiments on separation of a turbulent boundary layer on a flat plate have been continued, and greatly improved, by Kristian Angele, who is persuing his PhD at The Department of Mechanics at the Royal Institute of Technology.