Experimental Investigation of Surface Pressure Fluctuations in a Laminar Separation Bubble Using Piezoelectric Sensor Array
L. Belli (TU Delft - Aerospace Engineering)
Theodorus Michelis – Mentor (TU Delft - Aerodynamics)
L.L.M. Veldhuis – Graduation committee member (TU Delft - Flight Performance and Propulsion)
A. Sciacchitano – Graduation committee member (TU Delft - Aerodynamics)
More Info
expand_more
Other than for strictly personal use, it is not permitted to download, forward or distribute the text or part of it, without the consent of the author(s) and/or copyright holder(s), unless the work is under an open content license such as Creative Commons.
Abstract
Laminar separation bubbles (LSBs) play a crucial role in determining the aerodynamic performance of airfoils operating at low Reynolds numbers, conditions commonly encountered by unmanned aerial vehicles (UAVs), wind turbines, and small aircraft. Their inherently unsteady nature significantly influences lift, drag, and noise generation. This thesis investigates the dynamic behavior of LSBs that forms on the suction side of a NACA 0015 airfoil through surface pressure measurements obtained using piezoelectric sensors (”piezofoils”) integrated into a wing model tested in the Boundary Layer Wind Tunnel of the Technische Universität Berlin. The device are tested at chord-based Reynolds numbers of 144,000, 197,000 and
262,000 and at angles of attack comprised between 1 and 5 degrees, in 1 degree increments. Two different piezofoil designs are used, ”in-line”, spanning most of the airfoil chord and ”staggered”, shorter but with an improved spatial resolution. Complementary measurements are performed using surface hot wire anemometry, oil flow visualization, and surface pressure taps to provide a comprehensive characterization of both mean and fluctuating flow features.
The primary objective of the study is to relate the surface pressure fluctuations within the LSB to its dynamic phenomena, specifically, shear-layer flapping and vortex shedding, and to identify the optimal sensor placement for their detection. The existence and the characteristics of the laminar separation bubbles at the range of Reynolds number and angles of attack considered is confirmed through surface pressure measurements using pressure transducers and oil flow visualization. Analysis of the spectra and of the standard deviation in the separation and reattachment regions demonstrates that the piezofoil sensor successfully detects and accurately resolves vortex shedding, but is unable to capture the low-frequency flapping motion. The cross correlation analysis provided further insight into the vortex shedding process, enabling the estimation of the convective velocity and streamwise wavelength of the vortical structures. Heating of the piezofoil and appropriate signal filtering are found to be effective in enhancing the signal-to-noise ratio and mitigating electromagnetic interference effects.