Assessment of the organization of a turbulent separated and reattaching flow by measuring wall pressure fluctuations

Liu, Ying Zheng; Kang, Wanmo; Sung, Hyung Jin

doi:10.1007/s00348-005-0929-0

Cited by 49 publications

(28 citation statements)

References 18 publications

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“…As the fluid flows downstream of the reattachment point, the slow reduction of the streamwise velocity fluctuation intensity is due to the persistence of the large-scale vortical structures in the redeveloping turbulent boundary layer [16]. As shown in Fig.…”

Section: Time-averaged Statisticsmentioning

confidence: 98%

“…Going from the first mode to the third one, the dominant frequency is slightly increased while the magnitude at the low-frequency range is considerably reduced; this might be due to modulation of the high-frequency contents on the low-frequency behaviors. The dominance of the low-frequency spectrum for the first three modes reflects the strongly nonlinear coupling of flow structures buried in the separated and reattaching flow [16], which introduces the difficulty of distinctly extracting the large-scale behaviors by using a single POD mode. Until the sixth POD mode, the spectrum magnitude in the overall low-frequency range is 10 dB lower than that of the first POD mode, indicating that the linear combination of the first five POD modes is capable of representing the large-scale behaviors of the separated and reattaching turbulent flow over the surface-mounted square cylinder.…”

Section: Proper Orthogonal Decomposition Analysismentioning

confidence: 99%

“…As the vortices begin to emanate over the leading edge of the square cylinder, the zone of negative vorticity grows rapidly in size and expands to a maximum state at 2.5D behind the cylinder, which coincides with the core of the large separation bubble. This is attributed to the amalgamation of spanwise vortices and emergence of the large-scale vortical structures [16]. At the lower side of the negative vorticity zone, further expansion of the zone is significantly suppressed due to the influence of the bottom wall, while at the upper side the zone grows until the reattachment zone.…”

Section: Time-averaged Statisticsmentioning

confidence: 99%

“…3(b), the vertical extent of the large negative shear stress grows rapidly and expands to the maximum state 2 D behind the cylinder. Until the station / x D = 6.5, the magnitude begins to be gradually reduced due to the slowly decaying large-scale vortical structures [16]. Inspecting the central part of the separation bubble (2< /…”

Section: Time-averaged Statisticsmentioning

confidence: 99%

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TR-PIV measurement of separated and reattaching turbulent flow over a surface-mounted square cylinder

2010

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The separated and reattaching turbulent flow over a surface-mounted two-dimensional square cylinder was experimentally studied by using time-resolved particle image velocimetry (TR-PIV). A total of 61,440 instantaneous image frames were acquired at a framing rate of 125 Hz, yielding a reliable result of the statistical quantities. The time-averaged features of the separated and reattaching flow were analyzed in terms of distributions of the velocity vectors, vorticity, the streamwise velocity fluctuation intensity and shear stress. The association between the large-scale vortical structures and spatial variation of these time-averaged quantities were thoroughly discussed. The unsteady features of the flow were revealed from distributions of the reverse-flow intermittency, space-time contour plot of the fluctuating streamwise velocity, and cross-correlation of the streamwise velocity. Subsequently, a comprehensive understanding of the contribution of the flow structures into the fluctuating flow field was gained by using a snapshot proper orthogonal decomposition (POD) analysis. The results showed that the linear combination of the first five POD modes, which capture 57% of the fluctuation energy, was capable of representing the large-scale behaviors of the separated and reattaching turbulent flow in the senses of spectrum, instantaneous feature and spatial variation of the velocity fluctuation intensity.

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Section: Time-averaged Statisticsmentioning

confidence: 98%

Section: Proper Orthogonal Decomposition Analysismentioning

confidence: 99%

Section: Time-averaged Statisticsmentioning

confidence: 99%

Section: Time-averaged Statisticsmentioning

confidence: 99%

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TR-PIV measurement of separated and reattaching turbulent flow over a surface-mounted square cylinder

2010

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“…In both horn-ice and backward-facing step flowfields, the high values of RMS C p just upstream of mean reattachment are concomitant with the shedding of these large-scale vortical structures from the shear layer. 45,46 At and downstream of reattachment, the shear layer approaches the wall and reattaches, resulting in decreasing values of RMS C p with increasing chordwise distance.…”

Section: Horn-ice Flowfieldmentioning

confidence: 99%

Experimental Study of Full-Scale Iced Airfoil Aerodynamic Performance Using Sub-Scale Simulations

Busch

Bragg

2009

1st AIAA Atmospheric and Space Environments Conference

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Determining the aerodynamic effects of ice accretion on aircraft surfaces is an important step in aircraft design and certification. The goal of this work was to develop a complete sub-scale wind tunnel simulation methodology based on knowledge of the detailed iced-airfoil flowfield that allows the accurate measurement of aerodynamic penalties associated with the accretion of ice on an airfoil and to validate this methodology using full-scale iced-airfoil performance data obtained at near-flight Reynolds numbers. In earlier work, several classifications of ice shape were developed based on key aerodynamic features in the iced-airfoil flowfield: ice roughness, streamwise ice, horn ice, and tall and short spanwise-ridge ice. Castings of each of these classifications were acquired on a full-scale NACA 23012 airfoil model and the aerodynamic performance of each was measured at a Reynolds number of 12.0 x 10 6 and a Mach number = 0.20. In the current study, sub-scale simple-geometry and 2-D smooth simulations of each of these castings were constructed based on knowledge of iced-airfoil flowfields. The effects of each simulation on the aerodynamic performance of an 18-inch chord NACA 23012 airfoil model was measured in the University of Illinois 3 x 4 ft. wind tunnel at a Reynolds number of 1.8 x 10 6 and a Mach number of 0.18 and compared with that measured for the corresponding full-scale casting at high Reynolds number. Geometrically-scaled simulations of the horn-ice and tall spanwise-ridge ice castings modeled C l,max to within 2% and C d,min to within 15%. Good qualitative agreement in the C p distributions suggests that important geometric features such as horn and ridge height, surface location, and angle with respect to the airfoil chordline were appropriately modeled. Geometrically-scaled simulations of the ice roughness, streamwise ice, and short-ridge ice tended to have conservative C l,max and C d . The aerodynamic performance of simulations of these types of accretion was found to be sensitive to roughness height and concentration. Scaled roughness heights smaller than those ii found on the casting were necessary to improve simulation accuracy, resulting in C l,max and C d,min within 3% and 5% of the casting, respectively.iii

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Multi-resolution Analysis of the Large-scale Coherent Structure in a Turbulent Separation Bubble Affected by Unsteady Wake

Chun¹,

Liu²,

Sung³

Springer Proceedings in Physics

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Assessment of the organization of a turbulent separated and reattaching flow by measuring wall pressure fluctuations

Cited by 49 publications

References 18 publications

TR-PIV measurement of separated and reattaching turbulent flow over a surface-mounted square cylinder

TR-PIV measurement of separated and reattaching turbulent flow over a surface-mounted square cylinder

Experimental Study of Full-Scale Iced Airfoil Aerodynamic Performance Using Sub-Scale Simulations

Multi-resolution Analysis of the Large-scale Coherent Structure in a Turbulent Separation Bubble Affected by Unsteady Wake

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