Wall Pressure and Shear Stress Spectra from Direct Simulations of Channel Flow

Hu, Zhiwei; Morfey, C. L.; Sandham, Neil D.

doi:10.2514/1.17638

Cited by 201 publications

(183 citation statements)

References 38 publications

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“…In the p.d.f. of thickness of the blanketing layer in inner units (see figure 15), a near-wall peak is sustained at D + (Hu, Morfey & Sandham 2006). As the Reynolds number increases, the distribution of streamwise velocity fluctuations widens before it approaches (at the highest Reynolds number) an approximately constant shape.…”

Section: Discussionmentioning

confidence: 93%

Reynolds-number dependence of the near-wall flow over irregular rough surfaces

2016

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The Reynolds-number dependence of turbulent channel flow over two irregular rough surfaces, based on scans of a graphite and a grit-blasted surface, is studied by direct numerical simulation. The aim is to characterise the changes in the flow in the immediate vicinity of and within the rough surfaces, an area of the flow where it is difficult to obtain experimental measurements. The average roughness heights and spatial correlation of the roughness features of the two surfaces are similar, but the two surfaces have a significant difference in the skewness of their height distributions, with the graphite sample being positively skewed (peak-dominated) and the grit-blasted surface being negatively skewed (valley-dominated). For both cases, numerical simulations were conducted at seven different Reynolds numbers, ranging from Re τ = 90 to Re τ = 720. The positively skewed surface gives rise to higher friction factors than the negatively skewed surface in all cases. For the highest Reynolds numbers, the flow has values of the roughness function U + well in excess of 7 for both surfaces and the bulk flow profile has attained a constant shape across the full height of the channel except for the immediate vicinity of the roughness, which would indicate fully rough flow. However, the mean flow profile within and directly above the rough surface still shows considerable Reynolds-number dependence and the ratio of form to viscous drag continues to increase, which indicates that at least for some types of rough surfaces the flow retains aspects of the transitionally rough regime to values of U + or k + well in excess of the values conventionally assumed for the transitionally to fully rough threshold. This is also reflected in the changes that the near-wall flow undergoes as the Reynolds number increases: the viscous sublayer, within which the surface roughness is initially buried, breaks down and regions of reverse flow intensify. At the highest Reynolds numbers, a layer of near-wall flow is observed to follow the contours of the local surface. The distribution of thickness of this 'blanketing' layer has a mixed scaling, showing that viscous effects are still significant in the near-wall flow.

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Section: Discussionmentioning

confidence: 93%

Reynolds-number dependence of the near-wall flow over irregular rough surfaces

2016

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“…It is well known that wall-pressure fluctuations, in wall-units, [p w ] + rms , show a marked influence on Reynoldsnumber (Goody 2004;Hu et al 2006;Tsuji et al 2007), although alternative scalings exhibit a less pronounced dependence (Tsuji et al 2007, Fig. 14, p.21).…”

Section: Plane Channel Flow Configuration and Computational Methodsmentioning

confidence: 99%

“…Understanding the physics of turbulent fluctuations of pressure p is of major importance, not only because of their direct implication in noise (Hu et al 2002(Hu et al , 2006 and excitation of immersed solid surfaces (Corcos 1964), but also because they appear in correlations present in the transport equations for the Reynolds-stresses and the dissipation tensor (Pope 2000;Jovanović 2004). Traditionally the analysis of p is based on the Poisson equation for the fluctuating pressure (Chou 1945), which, at the incompressible flow limit (ρ const =ρ ; ∀t, x and µ const =μ ; ∀t, x), in a nonrotating frame-of-reference, reads…”

Section: Introductionmentioning

confidence: 99%

Wall effects on pressure fluctuations in turbulent channel flow

2013

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The purpose of the present paper is to study the influence of wall-echo on pressure fluctuations p , and on statistical correlations containing p , viz redistribution φ ij , pressure diffusion d (p) ij , and velocity/pressure-gradient Π ij . We extend the usual analysis of turbulent correlations containing pressure fluctuations in wall-bounded dns computations [Kim J.: J. Fluid Mech. 205 (1989) ) and surface (wall-echo; p (r;w) and p (s;w) ) terms. An algorithm, based on a Green's function approach, is developed to compute the above splittings for various correlations containing pressure fluctuations (redistribution, pressure diffusion, velocity/pressure-gradient), in fully developed turbulent plane channel flow. This exact analysis confirms previous results based on a method-of-images approximation [Manceau R., Wang M., Laurence D.: J. Fluid Mech. 438 (2001) 307-338] showing that, at the wall, p (V) and p (w) are usually of the same sign and approximately equal. The above results are then used to study the contribution of each mechanism on the pressure correlations in low Reynolds-number plane channel flow, and to discuss standard second-moment-closure modelling practices.

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“…(b) Pressure fluctuation intensities at the wall. Numerical channels: •, from table 2; •, (Hu, Morley & Sandham 2006). Numerical boundary layers:…”

Section: Basic Statisticsmentioning

confidence: 99%

Turbulent boundary layers and channels at moderate Reynolds numbers

et al. 2010

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The behaviour of the velocity and pressure fluctuations in the outer layers of wall-bounded turbulent flows is analysed by comparing a new simulation of the zero-pressure-gradient boundary layer with older simulations of channels. The 99 % boundary-layer thickness is used as a reasonable analogue of the channel half-width, but the two flows are found to be too different for the analogy to be complete. In agreement with previous results, it is found that the fluctuations of the transverse velocities and of the pressure are stronger in the boundary layer, and this is traced to the pressure fluctuations induced in the outer intermittent layer by the differences between the potential and rotational flow regions. The same effect is also shown to be responsible for the stronger wake component of the mean velocity profile in external flows, whose increased energy production is the ultimate reason for the stronger fluctuations. Contrary to some previous results by our group, and by others, the streamwise velocity fluctuations are also found to be higher in boundary layers, although the effect is weaker. Within the limitations of the non-parallel nature of the boundary layer, the wall-parallel scales of all the fluctuations are similar in both the flows, suggesting that the scale-selection mechanism resides just below the intermittent region, y/S =0.3-0.5. This is also the location of the largest differences in the intensities, although the limited Reynolds number of the boundary-layer simulation (Reg «2000) prevents firm conclusions on the scaling of this location. The statistics of the new boundary layer are available from http://torroja.dmt.upm.es/ftp/blayers/.

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Wall Pressure and Shear Stress Spectra from Direct Simulations of Channel Flow

Cited by 201 publications

References 38 publications

Reynolds-number dependence of the near-wall flow over irregular rough surfaces

Reynolds-number dependence of the near-wall flow over irregular rough surfaces

Wall effects on pressure fluctuations in turbulent channel flow

Turbulent boundary layers and channels at moderate Reynolds numbers

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