Investigation of time-frequency analysis and transitional boundary layer over a pitching airfoil

Document Type : Research Note

Authors

1 Department of Aerospace Engineering, Sharif University of Technology, Tehran, Iran

2 Department of Mechanical Engineering, Faculty of Engineering, Ferdowsi University of Mashhad, Mashhad, Iran

Abstract

Transitional boundary layer over a pitching airfoil at low Reynolds number (Re = 2.7×10^5) is experimentally investigated through the space-frequency and time-frequency analyses of hot-film signals. Boundary layer events are visualized based on the space-frequency and time-frequency plots. The precursor phenomena for turbulent as well as fully separated flows are presented based on the time-frequency analysis. A new technique based on the time-frequency analysis of hot-film signals is presented to measure the transition onset as well as the relaminarization locations. This technique is based on the analysis of high-frequency disturbances of the measured data. Special attention is focused on the spatial/temporal progression of the transition onset and the relaminarization points, compared to the static values, for different oscillation frequencies and amplitudes. Investigations are
performed prior to, within and beyond the static stall angle of attack conditions. The results obtained by the new technique will be discussed and compared with the observations from the previous investigators.

Keywords

References

References

1-     Richter, K. and Schülein, E. “Boundary-layer transition measurements on hovering helicopter rotors by infrared thermography”. Experiments in Fluids 55(7), 1755 (2014).
2-     Bellhouse, B. J.  and Schultz, D. L.  “Determination of mean and dynamic skin friction, separation and transition in low-speed flow with a thin-film heated element.”  Journal of Fluid Mechanics 24(2), 379-400 (1966).
3-     Stack, J., Mangalam, S. and Berry, S. “A unique measurement technique to study laminar-separation bubble characteristics on an airfoil.” In 19th AIAA Fluid Dynamics, Plasma Dynamics, and Lasers Conference, AIAA 87-1271 (1987).
4-     Nakayama, A., Stack, J., Lin, J. and Valarezo, W. “Surface hot-film method for the measurement of transition, separation and reattachment points.” In 23rd Fluid Dynamics, Plasmadynamics, and Lasers Conference, 2918 (1993).
5-     Hodson, H. P., Huntsman, I. and Steele, A. B.  “An investigation of boundary layer development in a multistage LP turbine.”  Journal of Turbomachinery 116(3), 375-383 (1994).
6-     Chandrasekhara, M. S. and Wilder, M. C.  “Heat-flux gauge studies of compressible dynamic stall.”  AIAA Journal 41(5), 757-762 (2003).
7-     Braune, M. and Koch, S. “Application of hot-film anemometry to resolve the unsteady boundary layer transition of a laminar airfoil experiencing limit cycle oscillations.” 15th International Conference on Fluid Control, Measurements and Visualization, 27-30 May, Naples, Italy (2019).
8-     Lee, T. and Basu, S. “Measurement of unsteady boundary layer developed on an oscillating airfoil using multiple hot-film sensors.”  Experiments in Fluids 25(2), 108-117 (1998).
9-     Lee, T. and Gerontakos, P. “Investigation of flow over an oscillating airfoil.”  Journal of Fluid Mechanics 512, 313-341 (2004).
10- Rudmin, D., Benaissa, A. and Poirel, D. “Detection of laminar flow separation and transition on a NACA-0012 airfoil using surface hot-films.”  Journal of Fluids Engineering 135(10), 101104 (2013).
11- Poels, A., Rudmin, D., Benaissa, A. and D. Poirel, “Localization of flow separation and transition over a pitching NACA0012 airfoil at transitional Reynolds numbers using hotfilms.”  Journal of Fluids Engineering 137(12), 124501 (2015).
12- Richter, K., Koch, S., Gardner, A. D., Mai, H., Klein, A. and Rohardt, C. H. “Experimental investigation of unsteady transition on a pitching rotor blade airfoil.” Journal of the American Helicopter Society 59(1), 012001 (2014).
13- Gardner, A. D., Eder, C., Wolf, C. C.  and Rafel, M. “Analysis of differential infrared thermography for boundary layer transition detection.”  Experiments in Fluids 58(9), 122 (2017).
14- Gardner, A. D., Wolf, C. C. and Raffel, M. “Review of measurement techniques for unsteady helicopter rotor flows.”  Progress in Aerospace Sciences 111, 100566 (2019).
15- Soltani, M. R.  and Bakhshalipour, A. “Effect of amplitude and mean angle-of-attack on the boundary layer of an oscillating airfoil.”  The Aeronautical Journal 112(1138), 705-713 (2008).
16- Soltani, M. R., Seddighi, M. and Marzabadi, F. R.  “Comparison of pitching and plunging effects on the surface pressure variation of a wind turbine blade section.” Wind Energy 12(3), 213-239 (2009).
17- Soltani, M. R.  and Marzabadi, F. R.  “Experimental investigation of transition on a plunging airfoil.”  Scientia Iranica, Transaction B, Mechanical Engineering 17(6), 468-479 (2010).
18- Marzabadi, F. R.  and Soltani, M. R. “Experimental study of the boundary layer over an airfoil in plunging motion.”  Acta Mechanica Sinica 28(2), 372-384 (2012).
19- Soltani, M. R., Marzabadi, F. R.  and Mohammadi, Z. “Experimental study of the plunging motion with unsteady wind tunnel wall interference effects.”  Experimental Techniques 36(5), 30-45 (2012).
20- Popov, A. V.,  Botez, R. M. and Labib, M. “Transition point detection from the surface pressure distribution for controller design.” AIAA Journal 45(1), 23–28 (2008).
21- Trapier, S., Deck, S., Duveau, P. and Sagaut, P. “Time-frequency analysis and detection of supersonic inlet buzz.”  AIAA Journal 45(9), 2273-2284 (2007).
22- Soltani, M. R., Daliri, A., Younsi, J. S.  and Farahani, M. “Effects of bleed position on the stability of a supersonic inlet.”  Journal of Propulsion and Power 32(5), 1153-1166 (2016).
Scientia Iranica
Volume 28, Issue 2
Transactions on Mechanical Engineering (B)
March and April 2021
Pages 860-876

Files

Share

How to cite

Statistics