Pressure distributions on circular cylinders at critical Reynolds numbers

Batham, J. P.

doi:10.1017/s0022112073001114

Cited by 149 publications

(54 citation statements)

References 10 publications

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“…The sensitivity of the drag crisis 11 to geometrical defects is then evidenced since the scenario of reattachments is now quite different. Drastic changes after a rotation of the cylinder was also reported by Batham 28 . The interesting feature in our case is the appearance of a simultaneous reattachment on both sides of the cylinder (two bubbles transition) around Re = 3.6 × 10 5 as observed in Fig.…”

Section: B Geometry and Pressure Measurementssupporting

confidence: 66%

Statistics and dynamics of the boundary layer reattachments during the drag crisis transitions of a circular cylinder

et al. 2015

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Section: B Geometry and Pressure Measurementssupporting

confidence: 66%

Statistics and dynamics of the boundary layer reattachments during the drag crisis transitions of a circular cylinder

et al. 2015

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“…2a. The calculation agrees well with the measurements of Batham [37]. Figure 2b shows the vorticity magnitude distribution on the cylinder, in which the maximum vorticity magnitude occurs at around 60…”

Section: Validation Of the Methodssupporting

confidence: 85%

On aerodynamic noises radiated by the pantograph system of high-speed trains

Zhang

2013

Acta Mech Sin

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Pantograph system of high-speed trains become significant source of aerodynamic noise when travelling speed exceeds 300 km/h. In this paper, a hybrid method of non-linear acoustic solver (NLAS) and Ffowcs WilliamsHawkings (FW-H) acoustic analogy is used to predict the aerodynamic noise of pantograph system in this speed range. When the simulation method is validated by a benchmark problem of flows around a cylinder of finite span, we calculate the near flow field and far acoustic field surrounding the pantograph system. And then, the frequency spectra and acoustic attenuation with distance are analyzed, showing that the pantograph system noise is a typical broadband one with most acoustic power restricted in the medium-high frequency range from 200 Hz to 5 kHz. The aerodynamic noise of pantograph systems radiates outwards in the form of spherical waves in the far field. Analysis of the overall sound pressure level (OASPL) at different speeds exhibits that the acoustic power grows approximately as the 4th power of train speed. The comparison of noise reduction effects for four types of pantograph covers demonstrates that only case 1 can lessen the total noise by about 3 dB as baffles on both sides can shield sound wave in the spanwise direction. The covers produce additional aerodynamic noise themselves in the other three cases and lead to the rise of OASPLs.

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“…In the attached flow region, the pressure fluctuation nearly vanishes. The peak value occurs around the mean separation location, which is related to the fluctuating displacement of instantaneous separation (Batham 1973;Shvets 1983). The pressure fluctuation obviously exists in the base region of the cylinder.…”

Section: Pressure and Friction On The Surfacementioning

confidence: 99%

Large-eddy simulation of the compressible flow past a wavy cylinder

Chen

2010

J. Fluid Mech.

116

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Numerical investigation of the compressible flow past a wavy cylinder was carried out using large-eddy simulation for a free-stream Mach number M∞ = 0.75 and a Reynolds number based on the mean diameter Re = 2 × 105. The flow past a corresponding circular cylinder was also calculated for comparison and validation against experimental data. Various fundamental mechanisms dictating the intricate flow phenomena, including drag reduction and fluctuating force suppression, shock and shocklet elimination, and three-dimensional separation and separated shear-layer instability, have been studied systematically. Because of the passive control of the flow over a wavy cylinder, the mean drag coefficient of the wavy cylinder is less than that of the circular cylinder with a drag reduction up to 26%, and the fluctuating force coefficients are significantly suppressed to be nearly zero. The vortical structures near the base region of the wavy cylinder are much less vigorous than those of the circular cylinder. The three-dimensional shear-layer shed from the wavy cylinder is more stable than that from the circular cylinder. The vortex roll up of the shear layer from the wavy cylinder is delayed to a further downstream location, leading to a higher-base-pressure distribution. The spanwise pressure gradient and the baroclinic effect play an important role in generating an oblique vortical perturbation at the separated shear layer, which may moderate the increase of the fluctuations at the shear layer and reduce the growth rate of the shear layer. The analysis of the convective Mach number indicates that the instability processes in the shear-layer evolution are derived from oblique modes and bi-dimensional instability modes and their competition. The two-layer structures of the shear layer are captured using the instantaneous Lamb vector divergence, and the underlying dynamical processes associated with the drag reduction are clarified. Moreover, some phenomena relevant to the compressible effect, such as shock waves, shocklets and shock/turbulence interaction, are analysed. It is found that the shocks and shocklets which exist in the circular cylinder flow are eliminated for the wavy cylinder flow and the wavy surface provides an effective way of shock control. As the shock/turbulence interaction is avoided, a significant drop of the turbulent fluctuations around the wavy cylinder occurs. The results obtained in this study provide physical insight into the understanding of the mechanisms relevant to the passive control of the compressible flow past a wavy surface.

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Pressure distributions on circular cylinders at critical Reynolds numbers

Cited by 149 publications

References 10 publications

Statistics and dynamics of the boundary layer reattachments during the drag crisis transitions of a circular cylinder

Statistics and dynamics of the boundary layer reattachments during the drag crisis transitions of a circular cylinder

On aerodynamic noises radiated by the pantograph system of high-speed trains

Large-eddy simulation of the compressible flow past a wavy cylinder

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