School of Mechanical Engineering: Bar Mizrahi

01 בינואר 2020, 14:00 - 15:00 
בניין וולפסון 206 
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School of Mechanical Engineering: Bar Mizrahi

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SCHOOL OF MECHANICAL ENGINEERING SEMINAR
Wednesday, January 1, 2020 at 14:00
Wolfson Building of Mechanical Engineering, Room 206

Development, Characterization and Implementation of Oscillatory Suction Actuator for Boundary Layer Control
Bar Mizrahi
M.Sc. student of Prof. Avraham ‘Avi’ Seifert

An experimental study of a new innovative fluidic device aimed at creating oscillatory suction and oscillatory blowing (OSOB) with no moving parts was conducted, to be used as an actuator for active flow control applications.
Following the previous generation highly successful SaOB (Steady Suction and Oscillatory Blowing) actuator, a new device was developed, with the aim to create both oscillatory suction (compared to steady suction in the SaOB) and oscillatory blowing. The use of unsteady suction has been shown both experimentally (by Morgulis) and theoretically (by Seifert) to be more efficient than its steady counterpart. The new actuator concept is based on the principle of pulsing a pair of ejectors by a single fluidic oscillator.
The study was conducted in three steps. The first step included benchtop characterization of the new actuator in still-air, with the focus on the oscillatory quality of the suction (also termed ‘switching quality’), and a wide range of suction velocities and frequencies. The second step included an investigation of the actuation – transitional boundary layer interaction over a flat-plate with zero-pressure-gradient, in a small-scale, low–speed wind tunnel. In this stage, four configurations were tested, including base flow (unexcited), steady suction, oscillatory suction, and oscillatory suction combined with oscillatory blowing. Two types of hot-wire surveys were conducted– surface mapping at a constant height above the plate and vertical velocity scan for boundary layer characterization. The third step included a comparison between steady to unsteady suction, both combined with oscillatory-blowing (SaOB and OSOB actuators), on a special-designed airfoil performance, which was tested in the Knapp-Meadow wind tunnel, with both a load-cell and pressure-taps.
The benchtop results show the actuator is capable of creating mean suction velocities of more than 30m/s, with fluctuations to mean ratio of up to 0.7, and wide-range, controllable frequency response. The actuation – boundary layer interaction results show a clear impact of the oscillatory suction on the flow field, expressed in dominant frequency maps and phase-lag maps. Integral parameters of the boundary layer present a shape-factor in the range 2≤H≤1.6 for the base flow, which points on a transitional boundary layer. Both the displacement and the momentum thickness decreased by applying steady and unsteady suction, with certain advantages to unsteady suction, especially at low suction magnitudes. The results of the comparison between the two actuators on the airfoil performance show an increase in the actuation efficiency of the oscillatory suction in comparison to steady suction, resulting from a lower energy consumption that leads to the same desired airfoil performance.

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