Compressible Dynamic Stall Control Using Microjets

• Other Authors: Beahn, James Jay (authoraut)
• Format: Others
• Language: English; English
• Published: Florida State University
• Subjects: Mechanical engineering
• Online Access: http://purl.flvc.org/fsu/fd/FSU_migr_etd-1167

Control of Dynamic Stall using microjet perturbation at the upper, leading edge was studied experimentally in a subsonic wind tunnel facility. A NACA 0015 airfoil was fabricated with a field of microjets (200- or 400-micrometers in diameter) to study the effectiveness of control. It was tested in subsonic flow velocities of Mach 0.3 and 0.4 while being dynamically pitched sinusoidal between 0- and 20-degrees at reduced frequencies of 0.05 and 0.10. The Point Diffraction Interferometry (PDI) technique was utilized to qualitatively visualize the general flowfield and quantitatively to determine the leading edge surface pressure distribution. In addition, a high speed pressure transducer was placed at the 7.5-percent chord location on the upper surface. The airfoil exhibits typical characteristics of dynamic stall until the microjets were activated including boundary layer separation, formation and shedding of a dynamic stall vortex, and a loss in leading-edge suction pressure. However, with microjet control activated the flow over the airfoil appears to remain attached at angles of attack well beyond the static and dynamic stall angles. All data showed no evidence of dynamic stall occurring using this control method up to the maximum angle of attack of 20-degrees. The PDI data shows a slight loss in peak pressure with control, as compared to the uncontrolled case, at low angles of attack. However, the controlled case does not exhibit the large loss in leading-edge suction pressure and does not have a strong hysteresis variation during the cycle, indicating the suppression of dynamic stall. This control method also alleviates shock induced separation in the Mach 0.4 case by preventing shocks from forming at the airfoil's leading edge area. Control was also tested with 200-micrometer diameter microjets with similar results but was slightly less effective even with a higher mass flow rate, making the smaller microjet option less desirable. === A Thesis Submitted to the Department of Mechanical Engineering in Partial Fulfillment of the Requirements for the Degree of Master of Science. === Fall Semester, 2003. === November 3, 2003. === Compressible Dynamic Stall, Microjets, Stall Control, Dynamic Stall, Rotorcraft, Helicopter === Includes bibliographical references. === Chiang Shih, Professor Directing Thesis; Farrukh S. Alvi, Committee Member; Emmanuel Collins, Committee Member.