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Yingzheng Liu - One of the best experts on this subject based on the ideXlab platform.
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wall pressure fluctuations of separated and reattaching flow over blunt plate with chord to thickness ratio c d 9 0
Experimental Thermal and Fluid Science, 2012Co-Authors: Qing Shan Zhang, Yingzheng LiuAbstract:Abstract The separated and reattaching turbulent flow over a finite blunt plate with the chord-to-thickness ratio c/d = 9.0 was experimentally studied; the Reynolds number based on the plate’s thickness (d) was Re d = 1.58 × 10 4 . Wall-pressure fluctuations on the plate surface were taken into extensive consideration, which are closely related to unsteady flow behaviors buried in the separated and reattaching flow and the unsteady wake. Toward this end, synchronized measurements of wall-pressure fluctuations and velocity fluctuations were performed by using a microphone array and a split-fiber film probe, respectively. Characteristics of the separated and reattaching flow were discussed in terms of time-averaged streamwise velocity and its fluctuation intensity, reverse-flow intermittency, wall-pressure fluctuation coefficient, cross-correlation and coherence of wall pressure and velocity. The results showed that the peaked wall-pressure fluctuation coefficient (x/d = 4.25) appears 1d behind the time-mean Reattachment point (x/d = 3.25), which is due to the intensified impingement fluid induced by the growing large-scale vortical structures in the Reattachment Zone. Two characteristic frequencies fd/U0 = 0.118 and 0.162 were determined, which correspond to the shedding large-scale vortical structures and the unsteady wake, respectively. Cross-correlation of the wall-pressure field demonstrated rapid decay of the large-scale vortical structures beyond the Reattachment Zone (x/d > 4.75), which might be due to strong interference with the unsteady wake at higher frequency fd/U0 = 0.162. The wall-pressure auto-spectra showed that wall-pressure fluctuations near the trailing edge are overwhelmingly dominated by the unsteady wake at fd/U0 = 0.162. Coherence of the wall-pressure field and the streamwise velocity at x/d ⩾ 7.75 elucidated that unsteady behaviors of the redeveloping boundary layer at both frequencies fd/U0 = 0.118 and 0.162 play important role in wall-pressure fluctuations in large upstream area of the surface.
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unsteady separated and reattaching turbulent flow over a two dimensional square rib
Journal of Fluids and Structures, 2008Co-Authors: Yingzheng Liu, Hyung Jin SungAbstract:Abstract The spatio-temporal characteristics of the separated and reattaching turbulent flow over a two-dimensional square rib were studied experimentally. Synchronized measurements of wall-pressure fluctuations and velocity fluctuations were made using a microphone array and a split-fiber film, respectively. Profiles of time-averaged streamwise velocity and wall-pressure fluctuations showed that the shear layer separated from the leading edge of the rib sweeps past the rib and directly reattaches on the bottom wall (x/H=9.75) downstream of the rib. A thin region of reverse flow was formed above the rib. The shedding large-scale vortical structures (fH/U0=0.03) and the flapping separation bubble (fH/U0=0.0075) could be discerned in the wall-pressure spectra. A multi-resolution analysis based on the maximum overlap discrete wavelet transform (MODWT) was performed to extract the intermittent events associated with the shedding large-scale vortical structures and the flapping separation bubble. The convective dynamics of the large-scale vortical structures were analyzed in terms of the autocorrelation of the continuous wavelet-transformed wall pressure, cross-correlation of the wall-pressure fluctuations, and the cross-correlation between the wall pressure at the time-averaged Reattachment point and the streamwise velocity field. The convection speeds of the large-scale vortical structures before and after the Reattachment point were Uc=0.35U0 and 0.45U0, respectively. The flapping motion of the separation bubble was analyzed in terms of the conditionally averaged reverse-flow intermittency near the wall region. The instantaneous Reattachment point in response to the flapping motion was obtained; these findings established that the Reattachment Zone was a 1.2H-long region centered at x/H=9.75. The reverse-flow intermittency in one period of the flapping motion demonstrated that the thin reverse flow above the rib is influenced by the flapping motion of the separation bubble behind the rib.
V. I. Zapryagaev - One of the best experts on this subject based on the ideXlab platform.
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Dynamic layer formation in the Reattachment Zone for a supersonic laminar separated flow
Proceedings of the Institution of Mechanical Engineers Part G: Journal of Aerospace Engineering, 2019Co-Authors: V. I. Zapryagaev, I. N. Kavun, L. P. TrubitsynaAbstract:In this work, results of an experimental study of the flow structure in the region of Reattachment of a supersonic laminar separated flow are reported. The separated flow is generated by a model sh...
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flow effects in the Reattachment region of supersonic laminar separated flow
International Journal of Heat and Mass Transfer, 2019Co-Authors: I. N. Kavun, Igor I Lipatov, V. I. ZapryagaevAbstract:Abstract The structure of a laminar separation flow around a compression corner at a free-stream Mach number M∞ = 6 is considered. The existence of a new element in the Reattachment area—a high total-pressure layer—is shown. This layer is located downstream from the Reattachment line above the boundary layer, and its total pressure is higher than that in either the boundary layer beneath it or the supersonic flow above it. Its appearance is due to the difference in the total pressure losses of the streamlines passing through a compression-wave fan and a shock wave in the Reattachment Zone. The vortex structure in the area of attachment is considered and the formation of streamwise vortices is shown. The origin of these vortices is similar to that of Taylor–Goertler vortices in subsonic flow. The pressure-pulsation distribution in the Reattachment Zone is also analyzed. It is shown that the spectrum of wall-pressure pulsations in the separation Zone has two local maxima, the first caused by longitudinal fluctuations in the separation region and the second by pulsations of the vortices.
Gopalan Jagadeesh - One of the best experts on this subject based on the ideXlab platform.
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Shock tunnel measurements of surface pressures in shock induced separated flow field using MEMS sensor array
Measurement Science and Technology, 2015Co-Authors: Ram Sriram, S. N. Ram, Gopalkrishna M. Hegde, M. M. Nayak, Gopalan JagadeeshAbstract:Characterized not just by high Mach numbers, but also high flow total enthalpies-often accompanied by dissociation and ionization of flowing gas itself-the experimental simulation of hypersonic flows requires impulse facilities like shock tunnels. However, shock tunnel simulation imposes challenges and restrictions on the flow diagnostics, not just because of the possible extreme flow conditions, but also the short run times-typically around 1 ms. The development, calibration and application of fast response MEMS sensors for surface pressure measurements in IISc hypersonic shock tunnel HST-2, with a typical test time of 600 mu s, for the complex flow field of strong (impinging) shock boundary layer interaction with separation close to the leading edge, is delineated in this paper. For Mach numbers 5.96 (total enthalpy 1.3 MJ kg(-1)) and 8.67 (total enthalpy 1.6 MJ kg(-1)), surface pressures ranging from around 200 Pa to 50 000 Pa, in various regions of the flow field, are measured using the MEMS sensors. The measurements are found to compare well with the measurements using commercial sensors. It was possible to resolve important regions of the flow field involving significant spatial gradients of pressure, with a resolution of 5 data points within 12 mm in each MEMS array, which cannot be achieved with the other commercial sensors. In particular, MEMS sensors enabled the measurement of separation pressure (at Mach 8.67) near the leading edge and the sharply varying pressure in the Reattachment Zone.
L. P. Trubitsyna - One of the best experts on this subject based on the ideXlab platform.
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Dynamic layer formation in the Reattachment Zone for a supersonic laminar separated flow
Proceedings of the Institution of Mechanical Engineers Part G: Journal of Aerospace Engineering, 2019Co-Authors: V. I. Zapryagaev, I. N. Kavun, L. P. TrubitsynaAbstract:In this work, results of an experimental study of the flow structure in the region of Reattachment of a supersonic laminar separated flow are reported. The separated flow is generated by a model sh...
I. N. Kavun - One of the best experts on this subject based on the ideXlab platform.
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Dynamic layer formation in the Reattachment Zone for a supersonic laminar separated flow
Proceedings of the Institution of Mechanical Engineers Part G: Journal of Aerospace Engineering, 2019Co-Authors: V. I. Zapryagaev, I. N. Kavun, L. P. TrubitsynaAbstract:In this work, results of an experimental study of the flow structure in the region of Reattachment of a supersonic laminar separated flow are reported. The separated flow is generated by a model sh...
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flow effects in the Reattachment region of supersonic laminar separated flow
International Journal of Heat and Mass Transfer, 2019Co-Authors: I. N. Kavun, Igor I Lipatov, V. I. ZapryagaevAbstract:Abstract The structure of a laminar separation flow around a compression corner at a free-stream Mach number M∞ = 6 is considered. The existence of a new element in the Reattachment area—a high total-pressure layer—is shown. This layer is located downstream from the Reattachment line above the boundary layer, and its total pressure is higher than that in either the boundary layer beneath it or the supersonic flow above it. Its appearance is due to the difference in the total pressure losses of the streamlines passing through a compression-wave fan and a shock wave in the Reattachment Zone. The vortex structure in the area of attachment is considered and the formation of streamwise vortices is shown. The origin of these vortices is similar to that of Taylor–Goertler vortices in subsonic flow. The pressure-pulsation distribution in the Reattachment Zone is also analyzed. It is shown that the spectrum of wall-pressure pulsations in the separation Zone has two local maxima, the first caused by longitudinal fluctuations in the separation region and the second by pulsations of the vortices.
