Control of Tollmien-Schlichting Waves Using Piezoelectrically Driven Oscillating Surface

Abstract

The feasibility of using dynamic surface modification (via discrete Piezoelectrically Driven Oscillating Surface, PDOS, actuators) to delay transition from laminar to turbulent flow on a flat plate was explored experimentally using Particle Image Velocimetry. Two circular PDOS actuators were used to excite and control the T-S waves on a flat plate. The actuators were placed at the mid-span of a flat plate at two streamwise locations downstream from the leading edge, where the free-stream velocity was U = 16 m/s. The upstream actuator was used to excite and phase-lock the T-S wave at an excitation frequency of 250 Hz (corresponding to the most amplified wave from stability analysis), and the downstream PDOS was used to mitigate the T-S wave by driving it at an anti-phase with the appropriate amplitude. Timeand phase-averaged flow fields were acquired at two downstream interrogation domains. The data from the first domain (located in between the two PDOS actuators) explored the effect of the excitation amplitude on the magnitude of the excited T-S wave. At the second window, located downstream of both PDOS actuators, activation of both actuators resulted in a significant reduction or augmentation of the T-S wave, depending on the phase shift between the two actuators. 1 Graduate Student, Mechanical, Aerospace, and Nuclear Engineering, 110 8 th Street, Troy, NY. 2 Postdoctoral Research Fellow, Mechanical, Aerospace, and Nuclear Engineering, 110 8 th Street, Troy, NY. 3 Professor and James L. Decker ’45 Endowed Chair of Aerospace Engineering; and Director, Center for Flow Physics and Control, 110 8 th Street, Troy, NY. AIAA Associate Fellow. Corresponding author, email: amitam@rpi.edu Nomenclature b = Flat plate’s width (m) c = Flat plate’s length (m) F = Non-dimensional frequency f = Dimensional frequency (Hz) Reδ* = Reynolds number based on displacement thickness U = Free-stream velocity (m/s) = Time-averaged velocity (m/s) = Phase-averaged velocity (m/s) = T-S wave’s phase velocity (m/s) p/U = Coherent streamwise velocity fluctuations p/U = Coherent wall-normal velocity fluctuations x = Streamwise direction (m) y = Cross-stream direction (m) yPDOS = peak displacement of the PDOS actuator (m) δ * = Displacement thickness ω = Local non-dimensional frequency (used in the stability analysis) PDOS = Piezoelectrically Driven Oscillating Surface PIV = Particle Image Velocimetry T-S = Tollmien-Schlichting