Three-dimensional swimming motility of microorganism in the near-wall region

2016 ◽  
Vol 57 (2) ◽  
Author(s):  
Sang Joon Lee ◽  
Taesik Go ◽  
Hyeokjun Byeon
Keyword(s):  
Three Dimensional ◽  
Wall Region ◽  
Swimming Motility ◽  
Near Wall

scholarly journals Simulation of Boiling Flow Experiments Close to CHF with the Neptune_CFD Code

2008 ◽  
Vol 2008 ◽  
pp. 1-8 ◽  
Author(s):  
Boštjan Končar ◽  
Borut Mavko
Keyword(s):  
Volume Fraction ◽  
Flow Boiling ◽  
Three Dimensional ◽  
Heated Wall ◽  
Wall Region ◽  
Two Phase ◽  
Subcooled Flow Boiling ◽  
Boiling Flow ◽  
Flow Experiments ◽  
Near Wall

A three-dimensional two-fluid code Neptune_CFD has been validated against the Arizona State University (ASU) and DEBORA boiling flow experiments. Two-phase flow processes in the subcooled flow boiling regime have been studied on ASU experiments. Within this scope a new wall function has been implemented in the Neptune_CFD code aiming to improve the prediction of flow parameters in the near-wall region. The capability of the code to predict the boiling flow regime close to critical heat flux (CHF) conditions has been verified on selected DEBORA experiments. To predict the onset of CHF regime, a simplified model based on the near-wall values of gas volume fraction was used. The results have shown that the code is able to predict the wall temperature increase and the sharp void fraction peak near the heated wall, which are characteristic phenomena for CHF conditions.

Experimental study on dominant vortex structures in near-wall region of turbulent boundary layer based on tomographic particle image velocimetry

2019 ◽  
Vol 874 ◽  
pp. 426-454 ◽  
Author(s):  
Chengyue Wang ◽  
Qi Gao ◽  
Jinjun Wang ◽  
Biao Wang ◽  
Chong Pan
Keyword(s):  
Particle Image Velocimetry ◽  
Particle Image ◽  
Three Dimensional ◽  
Vortex Structures ◽  
Wall Region ◽  
Tomographic Particle Image Velocimetry ◽  
Image Velocimetry ◽  
Inclination Angles ◽  
The Difference ◽  
Near Wall

Vortex structures are very popular research objects in turbulent boundary layers (TBLs) because of their prime importance in turbulence modelling. This work performs a tomographic particle image velocimetry measurement on the near-wall region ($y<0.1\unicode[STIX]{x1D6FF}$) of TBLs at three Reynolds numbers $Re_{\unicode[STIX]{x1D70F}}=1238$, 2286 and 3081. The main attention is paid to the wall-normal evolution of the vortex geometries and topologies. The vortex is identified with swirl strength ($\unicode[STIX]{x1D706}_{ci}$), and its orientation is recognized by using the real eigenvector of the velocity gradient tensor. The vortex inclination angles in the streamwise–wall-normal plane and in the streamwise–spanwise plane as functions of wall-normal positions are investigated, which provide useful information to speculate on the three-dimensional shape of the vortex tubes in a TBL. The difference between the orientations of vorticity and swirl is discussed and their inherent relationship is revealed based on the governing equation of vorticity. Linear stochastic estimation (LSE) is further deployed to directly extract three-dimensional vortex models. The LSE velocity fields for ejection events happening at different wall-normal positions shed light on the evolution of the topologies for the vortices dominating ejection events. LSE based on a centred prograde spanwise vortex provides a typical packet model, which indicates that the population density of the packets in a TBL is large enough to leave footprints in conditionally averaged flow fields. This work should help to settle the severe debate on the existence of packet structures and also lays some foundation for the TBL model theory.

Three-Dimensional Measurement of Near-Wall Velocity in Millimeter Channel by a Single View Imaging

2015 ◽  
Author(s):  
Yoshiyasu Ichikawa ◽  
Kojiro Nishiwake ◽  
Hiromu Wakayama ◽  
Yuki Kameya ◽  
Makoto Yamamoto ◽  
...  
Keyword(s):  
Velocity Field ◽  
Velocity Distribution ◽  
Three Dimensional ◽  
Wall Region ◽  
Measured Velocity ◽  
Wall Velocity ◽  
Wall Area ◽  
Micro Piv ◽  
Wall Flow ◽  
Near Wall

It is well known that there is a strong correlation between heat transfer and near-wall flow. It is important to obtain the detailed near-wall flow field, but it has a lot of difficulties to measure near-wall region by traditional approaches for example hot wire anemometry and particle image velocimetry (PIV). The purpose of this study is to determine the three-dimensional velocity field at near-wall area in micron resolution by the astigmatism particle tracking velocimetry (APTV). In this study, an estimation of depth location of tracer particles by applying a specialized imaging optics controlling the astigmatism [1] was employed. We have developed a measurement system to get the particle location within 15 μm from wall using a long-working-distance microscope with astigmatic optics. As a proof-of-concept, near-wall velocity field in a millimeter-ordered parallel plate channel was measured with low Reynolds numbers (Re = 1 ∼ 5) Poiseuille flow to confirm the validity of it. As a result, we can obtain the near-wall velocity within 15 μm from the wall precisely. From the velocity distribution, the standard deviation of the velocity at each location was calculated and the dispersion of velocity was evaluated. As a result, it was confirmed that the measurement was carried out more accurately in high-speed area. Comparison of the measured velocity distribution with a theoretical calculation and micro-PIV results were also done. From these velocity distributions, the wall shear stress on the wall was determined.

scholarly journals Numerical Calculation of Three-Dimensional Turbulent Flow in a Turbine-Stator Passage

1996 ◽  
Author(s):  
B. Song ◽  
R. S. Amano
Keyword(s):  
Kinetic Energy ◽  
Turbulent Flow ◽  
Numerical Study ◽  
Interpolation Method ◽  
Three Dimensional ◽  
Turbulence Kinetic Energy ◽  
Wall Region ◽  
Staggered Grids ◽  
Turbine Stator ◽  
Near Wall

A numerical study on three-dimensional turbulent flow in a turbine-stator passage is presented in this paper. The standard κ–ε model with the one equation, near-wall model (SKE) and the Launder-Sharma model (L-S) are used for turbulence computations. The computational results obtained using these models were compared in order to investigate the turbulence effect in the near-wall region. The governing equations in a generalized curvilinear coordinate system are discretized by using the SIMPLEC method with non-staggered grids. The oscillation of pressure and velocity due to non-staggered grids is eliminated by using the interpolation method suggested by Rhie and Chow (1983). The predicted midspan pressure coefficients using SKE and L-S models are compared with experimental data. It was shown that the present results obtained by using both models are satisfactory. Computations were then extended to cover the entire blade-to-blade flow passage, and the three-dimensional effects on pressure and turbulence kinetic energy were evaluated. It was observed that two turbulence models predict similar results for the pressure and velocity but these predict different results in the turbulence kinetic energy.

Resistance Reduction in Pulsating Turbulent Pipe Flows

2003 ◽  
Author(s):  
Marcello Manna ◽  
Andrea Vacca
Keyword(s):  
Large Scale ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Turbulent Pipe Flow ◽  
Navier Stokes ◽  
Recent Experimental Data ◽  
Wall Region ◽  
Navier Stokes Equations ◽  
Oscillating Motion ◽  
Near Wall

The paper describes the effects of a forced harmonic oscillations of fixed frequency and amplitudes in the range Λ = Um/Ub = 1 ÷ 11 on the characteristics of a turbulent pipe flow with a bulk Reynolds number of 5900. The resulting Stokes layer δ is a fraction of the pipe radius (χ = R/δ = 53) so that the vorticity associated to the oscillating motion is generated in a small near wall region. The analysis is carried out processing a set of statistically independent samples obtained from wall resolved Large Eddy Simulations; time and space averaged global quantities, extracted for the sake of comparison with recent experimental data, confirm the presence of a non negligible drag reduction phenomenon. Phase averaged profiles of the Reynolds stress tensor components provide valuable material for the comprehension of the effects of the time varying mean shear upon the near wall turbulent flow structures. The large scale of motion are directly computed through numerical integration of the space filtered three dimensional Navier-Stokes equations with a spectrally accurate code; the subgrid scale terms are parametrized with a dynamic procedure.

Resistance Reduction in Pulsating Turbulent Pipe Flows

2005 ◽  
Vol 127 (2) ◽  
pp. 410-417 ◽  
Author(s):  
Marcello Manna ◽  
Andrea Vacca
Keyword(s):  
Stokes Equations ◽  
Three Dimensional ◽  
Turbulent Pipe Flow ◽  
Navier Stokes ◽  
Recent Experimental Data ◽  
Wall Region ◽  
Navier Stokes Equations ◽  
Resistance Reduction ◽  
Oscillating Motion ◽  
Near Wall

The paper describes the effects of forced harmonic oscillations of fixed frequency and amplitudes in the range Λ=Um/Ub=1-11 on the characteristics of a turbulent pipe flow with a bulk Reynolds number of 5900. The resulting Stokes layer δ is a fraction of the pipe radius χ=R/δ=53 so that the vorticity associated to the oscillating motion is generated in a small near wall region. The analysis is carried out processing a set of statistically independent samples obtained from wall-resolved large eddy simulations (LES); time and space averaged global quantities, extracted for the sake of comparison with recent experimental data, confirm the presence of a non-negligible drag reduction phenomenon. Phase averaged profiles of the Reynolds stress tensor components provide valuable material for the comprehension of the effects of the time varying mean shear upon the near wall turbulent flow structures. The large scales of motion are directly computed through numerical integration of the space filtered three-dimensional Navier-Stokes equations with a spectrally accurate code; the subgrid scale terms are parametrized with a dynamic procedure.

Direct numerical simulations of Rayleigh–Bénard convection in water with non-Oberbeck–Boussinesq effects

2019 ◽  
Vol 881 ◽  
pp. 1073-1096 ◽  
Author(s):  
Andreas D. Demou ◽  
Dimokratis G. E. Grigoriadis
Keyword(s):  
Numerical Simulations ◽  
Two Dimensions ◽  
Direct Numerical Simulations ◽  
Wall Region ◽  
Number Range ◽  
Bénard Convection ◽  
Benard Convection ◽  
Rayleigh Benard Convection ◽  
Rayleigh Benard ◽  
Near Wall

Rayleigh–Bénard convection in water is studied by means of direct numerical simulations, taking into account the variation of properties. The simulations considered a three-dimensional (3-D) cavity with a square cross-section and its two-dimensional (2-D) equivalent, covering a Rayleigh number range of $10^{6}\leqslant Ra\leqslant 10^{9}$ and using temperature differences up to 60 K. The main objectives of this study are (i) to investigate and report differences obtained by 2-D and 3-D simulations and (ii) to provide a first appreciation of the non-Oberbeck–Boussinesq (NOB) effects on the near-wall time-averaged and root-mean-squared (r.m.s.) temperature fields. The Nusselt number and the thermal boundary layer thickness exhibit the most pronounced differences when calculated in two dimensions and three dimensions, even though the $Ra$ scaling exponents are similar. These differences are closely related to the modification of the large-scale circulation pattern and become less pronounced when the NOB values are normalised with the respective Oberbeck–Boussinesq (OB) values. It is also demonstrated that NOB effects modify the near-wall temperature statistics, promoting the breaking of the top–bottom symmetry which characterises the OB approximation. The most prominent NOB effect in the near-wall region is the modification of the maximum r.m.s. values of temperature, which are found to increase at the top and decrease at the bottom of the cavity.

The Effects of Adverse Pressure Gradients on Momentum and Thermal Structures in Transitional Boundary Layers: Part 2—Fluctuation Quantities

1996 ◽  
Vol 118 (4) ◽  
pp. 728-736 ◽  
Author(s):  
S. P. Mislevy ◽  
T. Wang
Keyword(s):  
Boundary Layer ◽  
Shear Stress ◽  
Transition Region ◽  
Boundary Layers ◽  
Reynolds Shear Stress ◽  
Turbulent Shear ◽  
Wall Region ◽  
Pressure Gradients ◽  
Baseline Case ◽  
Near Wall

The effects of adverse pressure gradients on the thermal and momentum characteristics of a heated transitional boundary layer were investigated with free-stream turbulence ranging from 0.3 to 0.6 percent. Boundary layer measurements were conducted for two constant-K cases, K1 = −0.51 × 10−6 and K2 = −1.05 × 10−6. The fluctuation quantities, u′, ν′, t′, the Reynolds shear stress (uν), and the Reynolds heat fluxes (νt and ut) were measured. In general, u′/U∞, ν′/U∞, and νt have higher values across the boundary layer for the adverse pressure-gradient cases than they do for the baseline case (K = 0). The development of ν′ for the adverse pressure gradients was more actively involved than that of the baseline. In the early transition region, the Reynolds shear stress distribution for the K2 case showed a near-wall region of high-turbulent shear generated at Y+ = 7. At stations farther downstream, this near-wall shear reduced in magnitude, while a second region of high-turbulent shear developed at Y+ = 70. For the baseline case, however, the maximum turbulent shear in the transition region was generated at Y+ = 70, and no near-wall high-shear region was seen. Stronger adverse pressure gradients appear to produce more uniform and higher t′ in the near-wall region (Y+ < 20) in both transitional and turbulent boundary layers. The instantaneous velocity signals did not show any clear turbulent/nonturbulent demarcations in the transition region. Increasingly stronger adverse pressure gradients seemed to produce large non turbulent unsteadiness (or instability waves) at a similar magnitude as the turbulent fluctuations such that the production of turbulent spots was obscured. The turbulent spots could not be identified visually or through conventional conditional-sampling schemes. In addition, the streamwise evolution of eddy viscosity, turbulent thermal diffusivity, and Prt, are also presented.

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