M.Sc Thesis

M.Sc StudentFurman Yevgeni
SubjectProgress in the Development of a low-Speed Oscillatory-
Flow Wind Tunnel
DepartmentDepartment of Mechanical Engineering
Supervisor PROF. David Greenblatt
Full Thesis textFull thesis text - English Version


Unsteady flow is a characteristic phenomenon of various systems, including wind turbines. The simultaneous variation of both free-stream velocity and angle-of-attack results in a complex chain of events which can have an adverse influence on the system, including detrimental effects on structure. Very few experimental facilities are able to simulate the required conditions for studying these phenomena, most of which are modified steady-flow wind tunnels which have difficulties operating at the aforementioned conditions.

For this purpose, an unsteady wind tunnel was developed. The wind-speed was varied using a set of counter-rotating louver vanes, operated by a servo-motor, which effectively change the cross-section of the tunnel’s exit in a dynamic manner, thus forcing an arbitrary velocity profile inside the test section.

A theoretical model based on integrating and then linearizing the mechanical energy equation across the length of the tunnel was developed in order to predict the tunnel's time-dependent response to variation of the exit cross-section area. In addition to this, another model was developed in an effort to predict the tunnel's acoustics by assuming it acts similarly to a Helmholtz resonator.

The model was verified through a series of quasi-steady and dynamic experiments which consisted of varying the exit cross-section area in various frequencies and measuring the time-dependent velocity inside the test section. A welcomed result was the similarity of the magnitude ratio as a function of non-dimensional pitching frequency of the vanes. The measured results have a good correlation with the theory, validating the model.