Jean Tensi

Collaborative studies on flow separation control

This paper presents the wind tunnel test results concerning the effects of deploying steady and synthetic jets on a NACA0015 airfoil and describes the design of a multi-orifice-single-chamber synthetic jet actuator. Three steady jets with different configurations were tested. The orifice diameter, orientation and spacing were the varying parameters. Synthetic jets were deployed through a single row of orifices that were orientated normal to the airfoil surface. A single row of each type was positioned at 30% of chord from the leading edge. These jets exhibited varying degree of control authority over the lift and drag coefficients. The timescales of attachment and separation were estimated for the test cases of angled steady and synthetic jets. In view of controlling the flow separation in a dynamic manner, a multi-orifice-single-chamber actuator with a typical response time smaller than that of the afore-mentioned time scales was designed, fabricated and tested in quiescent condition.

Control of Flow Separation and Its Associated Physics on a NACA0015 Using Synthetic Jet Actuators

Wind tunnel flow control experiments are conducted on two NACA0015 airfoil models, one of which having a chord length of 1.0m and the other having a chord of 0.35m, with the aim of exploring the separated flow physics and delaying flow separation. The larger model is tested in a low speed wind tunnel, measuring 1.25m by 1.25m at a Reynolds number of 0.4 and 0.27 million. This model is used to provide a quick proof of concept concerning the efficiency of various synthetic jet designs. Laser light visualization and Particle Image Velocimetry (PIV) studies are performed on this model. The synthetic jet actuators implemented (mechanically and acoustically generated) is realized through holes (2 and 3mm in diameter). The actuators are positioned at 20% or 70% of chord length from the leading edge for controlling separation at incidences between 12° and 15°. Flow separation delay and reattachment, depending on the frequency and momentum of the synthetic jet are observed qualitatively via laser sheet visualization in all cases. The efficiency of the actuator is quantified via the extent of separation observed with the PIV measurements. The technique of Proper Orthogonal Decomposition (POD) is applied to further reveal the large eddies in the separated shear layer and its interaction with the boundary layer. The smaller model is tested in a larger wind tunnel measuring 2.4m by 2.6m at a Reynolds number of 0.9 million. This is a more realistic flow condition with minimal wall and aspect ratio influence as compared to the larger model. The main experimental objective concerning this model is to quantify the baseline aerodynamic of the NACA0015 before implementation of synthetic jets. Laser light and surface oil visualizations are performed. Measurements concerning surface pressure and wake velocity characteristics are also made for this model. The lift of which is estimated via the integration of surface static pressure and the drag is estimated by wake survey technique using a pitot tube that is made to traverse in the wake. In addition, time resolved data are obtained in the wake of the airfoil by means of hotwires. Both hotwire measurement reveal typical Strouhal number of 0.34–0.4. These results are extrapolated to the large airfoil for interpretation of the flow physics during control. To sum up, the main results in the current study highlight the characteristics of the baseline airfoil and the ability of synthetic jet actuator techniques to obtain significant delay of the separation.Copyright