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Showing papers on "Reynolds number published in 2012"


Book
01 Jan 2012
TL;DR: The FDLIB software library as mentioned in this paper provides a comprehensive overview of numerical methods for hydrodynamic stability analysis of a flow and the equation of motion and vorticity transport of flow.
Abstract: Preface Note to the Instructor Note to the Reader 1 Kinematic structure of a flow 2 Kinematic analysis of a flow 3 Stresses, the equation of motion, and vorticity transport 4 Hydrostatics 5 Exact solutions 6 Flow at low Reynolds numbers 7 Irrotational flow 8 Boundary-layer analysis 9 Hydrodynamic stability 10 Boundary-integral methods for potential flow 11 Vortex motion 12 Finite-difference methods for convection-diffusion 13 Finite-difference methods for incompressible Newtonian flow A Mathematical supplement B Primer of numerical methods C FDLIB software library D User Guide of directory 08 stab of FDLIB on hydrodynamic stab References Index

625 citations


Journal ArticleDOI
TL;DR: In this paper, the authors modified the resolution requirements for large eddy simulation (LES) using accurate formulae for high Reynolds number boundary layer flow and showed that the number of grid points required for wall-modeled LES is proportional to ReLx, where Lx is the flat-plate length in the streamwise direction.
Abstract: Resolution requirements for large eddy simulation (LES), estimated by Chapman [AIAA J. 17, 1293 (1979)], are modified using accurate formulae for high Reynolds number boundary layer flow. The new estimates indicate that the number of grid points (N) required for wall-modeled LES is proportional to ReLx, but a wall-resolving LES requires NReLx13/7, where Lx is the flat-plate length in the streamwise direction. On the other hand, direct numerical simulation, resolving the Kolmogorov length scale, requires NReLx37/14.

583 citations


Journal ArticleDOI
TL;DR: The algorithm is based upon Fick's law of diffusion and shifts particles in a manner that prevents highly anisotropic distributions and the onset of numerical instability, and is validated against analytical solutions for an internal flow at higher Reynolds numbers than previously.

513 citations


Journal ArticleDOI
TL;DR: Turbulence measurements over an unprecedented range of Reynolds numbers are reported using a unique combination of a high-pressure air facility and a new nanoscale anemometry probe, revealing previously unknown universal scaling behavior for the turbulent velocity fluctuations.
Abstract: Both the inherent intractability and complex beauty of turbulence reside in its large range of physical and temporal scales. This range of scales is captured by the Reynolds number, which in nature and in many engineering applications can be as large as 10(5)-10(6). Here, we report turbulence measurements over an unprecedented range of Reynolds numbers using a unique combination of a high-pressure air facility and a new nanoscale anemometry probe. The results reveal previously unknown universal scaling behavior for the turbulent velocity fluctuations, which is remarkably similar to the well-known scaling behavior of the mean velocity distribution.

307 citations


Journal ArticleDOI
TL;DR: Schlatter et al. as mentioned in this paper assessed available direct numerical simulation (DNS) data from turbulent boundary layer flows and found that the simulation results showed surprisingly l l l o r...
Abstract: A recent assessment of available direct numerical simulation (DNS) data from turbulent boundary layer flows (Schlatter & Orlu, J. Fluid Mech., vol. 659, 2010, pp. 116-126) showed surprisingly l ...

238 citations


Journal ArticleDOI
TL;DR: In this paper, a collaborative experimental effort employing the minimally perturbed atmospheric surface-layer flow over the salt playa of western Utah has enabled us to map coherence in turbulent boundary layers at very high Reynolds numbers.
Abstract: A collaborative experimental effort employing the minimally perturbed atmospheric surface-layer flow over the salt playa of western Utah has enabled us to map coherence in turbulent boundary layers at very high Reynolds numbers, \({Re_{\tau}\sim\mathcal{O}(10^6)}\) . It is found that the large-scale coherence noted in the logarithmic region of laboratory-scale boundary layers are also present in the very high Reynolds number atmospheric surface layer (ASL). In the ASL these features tend to scale on outer variables (approaching the kilometre scale in the streamwise direction for the present study). The mean statistics and two-point correlation map show that the surface layer under neutrally buoyant conditions behaves similarly to the canonical boundary layer. Linear stochastic estimation of the three-dimensional correlation map indicates that the low momentum fluid in the streamwise direction is accompanied by counter-rotating roll modes across the span of the flow. Instantaneous flow fields confirm the inferences made from the linear stochastic estimations. It is further shown that vortical structures aligned in the streamwise direction are present in the surface layer, and bear attributes that resemble the hairpin vortex features found in laboratory flows. Ramp-like high shear zones that contribute significantly to the Reynolds shear-stress are also present in the ASL in a form nearly identical to that found in laboratory flows. Overall, the present findings serve to draw useful connections between the vast number of observations made in the laboratory and in the atmosphere.

236 citations


Journal ArticleDOI
TL;DR: In this article, a new consolidated database of 7115 frictional pressure gradient data points for both adiabatic and condensing mini/micro-channel flows is amassed from 36 sources.

224 citations


Journal ArticleDOI
TL;DR: In this paper, the authors analyzed the thermal-hydraulic behavior of three types of enhancement technique based on artificial roughness: corrugated tubes, dimpled tubes and wire coils.

207 citations


Journal ArticleDOI
TL;DR: An improved three-dimensional 19-velocity lattice Boltzmann model for immisicible binary fluids with variable viscosity and density ratios and numerically investigates a single bubble rising under buoyancy force in viscous fluids for a wide range of Eötvös and Morton numbers.
Abstract: We present an improved three-dimensional 19-velocity lattice Boltzmann model for immisicible binary fluids with variable viscosity and density ratios. This model uses a perturbation step to generate the interfacial tension and a recoloring step to promote phase segregation and maintain surfaces. A generalized perturbation operator is derived using the concept of a continuum surface force together with the constraints of mass and momentum conservation. A theoretical expression for the interfacial tension is determined directly without any additional analysis and assumptions. The recoloring algorithm proposed by Latva-Kokko and Rothman is applied for phase segregation, which minimizes the spurious velocities and removes lattice pinning. This model is first validated against the Laplace law for a stationary bubble. It is found that the interfacial tension is predicted well for density ratios up to 1000. The model is then used to simulate droplet deformation and breakup in simple shear flow. We compute droplet deformation at small capillary numbers in the Stokes regime and find excellent agreement with the theoretical Taylor relation for the segregation parameter β=0.7. In the limit of creeping flow, droplet breakup occurs at a critical capillary number 0.35

206 citations


Journal ArticleDOI
TL;DR: In this article, the Nusselt number and the drag coefficient for cuboid, spherical and ellipsoidal particles in steady-state regimes corresponding to Reynolds numbers (Re ) from 10 up to 250 were investigated.

196 citations


Journal ArticleDOI
TL;DR: In this paper, the influence of the buckets overlap ratio of a Savonius wind rotor on the averaged moment and power coefficients, over complete cycles of operation, is discussed, based on the commercial software Star-CCM+.

Journal ArticleDOI
TL;DR: In this paper, the effects of varying frequency and plunge amplitude for the same effective angle-of-attack time history are considered, and it is shown that for constant effective angle of attack, flow evolution is independent of Strouhal number, and as the reduced frequency is increased the leading edge vortex separates later in phase during the downstroke.
Abstract: Experimental studies of the flow topology, leading-edge vortex dynamics and unsteady force produced by pitching and plunging flat-plate aerofoils in forward flight at Reynolds numbers in the range 5000–20 000 are described. We consider the effects of varying frequency and plunge amplitude for the same effective angle-of-attack time history. The effective angle-of-attack history is a sinusoidal oscillation in the range to with mean of and amplitude of . The reduced frequency is varied in the range 0.314–1.0 and the Strouhal number range is 0.10–0.48. Results show that for constant effective angle of attack, the flow evolution is independent of Strouhal number, and as the reduced frequency is increased the leading-edge vortex (LEV) separates later in phase during the downstroke. The LEV trajectory, circulation and area are reported. It is shown that the effective angle of attack and reduced frequency determine the flow evolution, and the Strouhal number is the main parameter determining the aerodynamic force acting on the aerofoil. At low Strouhal numbers, the lift coefficient is proportional to the effective angle of attack, indicating the validity of the quasi-steady approximation. Large values of force coefficients () are measured at high Strouhal number. The measurement results are compared with linear potential flow theory and found to be in reasonable agreement. During the downstroke, when the LEV is present, better agreement is found when the wake effect is ignored for both the lift and drag coefficients.

Journal ArticleDOI
TL;DR: In this paper, the effects of twist ratios (y/D, 2.5, 3, 3.5 and 4) and clearance ratios (c/D = 0.0178 and 0.0357) were discussed in the range of Reynolds number from 5132 to 24,989.

Journal ArticleDOI
TL;DR: In this paper, the authors presented a simulation of multi-longitudinal vortices in a tube induced by triple and quadruple twisted tapes insertion, and the results verified the theory of the core flow heat transfer enhancement.

Journal ArticleDOI
TL;DR: In this article, a set of petascale direct numerical simulations (DNS) modelling lean hydrogen combustion with detailed chemistry in a temporally evolving slot-jet configuration is presented as a database for the development and validation of models for premixed turbulent combustion.

Journal ArticleDOI
TL;DR: In this paper, the effect of nanoparticle volume fraction on the convection heat transfer characteristics and pressure drop of TiO2 (30nm) water nanofluids with nanoparticles volume fraction between 0.002 and 0.02, and Reynolds number between 8000 and 51,000.

Journal ArticleDOI
TL;DR: In this article, the authors investigated numerically the unsteady separated turbulent flows around an oscillating airfoil pitching in a sinusoidal pattern that induces deep dynamic stalls in the regime of relatively low Reynolds number.

Journal ArticleDOI
TL;DR: In this paper, the effects of initial turbulence on flow development and noise generation were investigated by large-eddy simulations to investigate the effect of initial turbolifting on flow and noise.
Abstract: Five isothermal round jets at Mach number and Reynolds number originating from a pipe nozzle are computed by large-eddy simulations to investigate the effects of initial turbulence on flow development and noise generation. In the pipe, the boundary layers are untripped in the first case and tripped numerically in the four others in order to obtain, at the exit, mean velocity profiles similar to a Blasius laminar profile of momentum thickness equal to 1.8 % of the jet radius, yielding Reynolds number , and peak turbulence levels around 0, 3 %, 6 %, 9 % or 12 % of the jet velocity . As the initial turbulence intensity increases, the shear layers develop more slowly with much lower root-mean-square (r.m.s.) fluctuating velocities, and the jet potential cores are longer. Velocity disturbances downstream of the nozzle exit also exhibit different structural characteristics. For low , they are dominated by the first azimuthal modes , 1 and 2, and show significant skewness and intermittency. The growth of linear instability waves and a first stage of vortex pairings occur in the shear layers for . For higher , three-dimensional features and high azimuthal modes prevail, in particular close to the nozzle exit where the wavenumbers naturally found in turbulent wall-bounded flows clearly appear. Concerning the sound fields, strong broadband components mainly associated with mode are noticed around the pairing frequency for the untripped jet. With rising , however, they become weaker, and the noise levels decrease asymptotically down to those measured for jets at , which are likely to be initially turbulent and to emit negligible vortex-pairing noise. These results correspond well to experimental observations, made separately for either mixing layers, jet flow or sound fields.


Journal ArticleDOI
TL;DR: In this paper, the flow over a circular cylinder at Reynolds number 3900 and Mach number 0.2 was predicted numerically using the technique of large-eddy simulation using an O-type curvilinear grid of size of 300 × 300 × 64.
Abstract: The flow over a circular cylinder at Reynolds number 3900 and Mach number 0.2 was predicted numerically using the technique of large-eddy simulation. The computations were carried out with an O-type curvilinear grid of size of 300 × 300 × 64. The numerical simulations were performed using a second-order finite-volume method with central-difference schemes for the approximation of convective terms. A conventional Smagorinsky and a dynamic k-equation eddy viscosity sub-grid scale models were applied. The integration time interval for data sampling was extended up to 150 vortex shedding periods for the purpose of obtaining a fully converged mean flow field. The present numerical results were found to be in good agreement with existing experimental data and previously obtained large-eddy simulation results. This gives an indication on the adequacy and accuracy of the selected large-eddy simulation technique implemented in the OpenFOAM toolbox.

Journal ArticleDOI
TL;DR: In this paper, the authors use numerical simulations to address locomotion at zero Reynolds number in viscoelastic (Giesekus) fluids, where the swimmers are assumed to be spherical, to self-propel using tangential surface deformation, and the computations are implemented using a finite element method.
Abstract: We use numerical simulations to address locomotion at zero Reynolds number in viscoelastic (Giesekus) fluids. The swimmers are assumed to be spherical, to self-propel using tangential surface deformation, and the computations are implemented using a finite element method. The emphasis of the study is on the change of the swimming kinematics, energetics, and flow disturbance from Newtonian to viscoelastic, and on the distinction between pusher and puller swimmers. In all cases, the viscoelastic swimming speed is below the Newtonian one, with a minimum obtained for intermediate values of the Weissenberg number, We. An analysis of the flow field places the origin of this swimming degradation in non-Newtonian elongational stresses. The power required for swimming is also systematically below the Newtonian power, and always a decreasing function of We. A detail energetic balance of the swimming problem points at the polymeric part of the stress as the primary We-decreasing energetic contribution, while the contributions of the work done by the swimmer from the solvent remain essentially We-independent. In addition, we observe negative values of the polymeric power density in some flow regions, indicating positive elastic work by the polymers on the fluid. The hydrodynamic efficiency, defined as the ratio of the useful to total rate of work, is always above the Newtonian case, with a maximum relative value obtained at intermediate Weissenberg numbers. Finally, the presence of polymeric stresses leads to an increase of the rate of decay of the flow velocity in the fluid, and a decrease of the magnitude of the stresslet governing the magnitude of the effective bulk stress in the fluid.

Journal ArticleDOI
TL;DR: In this paper, a 2D Smoothed Particle Hydrodynamics (SPH) model is used to simulate a broad range of open-channel flows, and an appropriate algorithm is developed to enforce different upstream and downstream flow conditions and simulate uniform, nonuniform and unsteady flows.
Abstract: The present work deals with the development and application of a 2D Smoothed Particle Hydrodynamics (SPH) model to simulate a broad range of open-channel flows. Although in the last decades the SPH modelling has been widely used to simulate free-surface flows, few applications have been performed for free-surface channels. For this reason, an appropriate algorithm is developed to enforce different upstream and downstream flow conditions and simulate uniform, non-uniform and unsteady flows. First, the proposed algorithm is validated for a viscous laminar flow in open channel characterized by Reynolds numbers of order O ( 10 2 ) . The second test case deals with a hydraulic jump for which different upstream and downstream conditions are needed. Varying the Froude number, several types of jumps are investigated with specific focus on the velocity field, pressure forces, water depths and location of the jump. Comparisons between numerical results, theory and experimental data are provided. Finally, the interaction between a flash flood generated by an unsteady inflow condition and a bridge is shown as an example of an engineering application.

Journal ArticleDOI
TL;DR: In this paper, the effect of geometrical parameters of multi v-shaped ribs with gap on heat transfer and fluid flow characteristics of rectangular duct with heated plate having rib roughness on its underside have been reported.

Journal ArticleDOI
TL;DR: In this paper, the authors used data from well-resolved direct numerical simulations at Taylor-scale Reynolds numbers from 140 to 1000 to study the statistics of energy dissipation rate and enstrophy density (i.e., the square of local vorticity).
Abstract: We use data from well-resolved direct numerical simulations at Taylor-scale Reynolds numbers from 140 to 1000 to study the statistics of energy dissipation rate and enstrophy density (i.e. the square of local vorticity). Despite substantial variability in each of these variables, their extreme events not only scale in a similar manner but also progressively tend to occur spatially together as the Reynolds number increases. Though they possess non-Gaussian tails of enormous amplitudes, ratios of some characteristic properties can be closely linked to those of isotropic Gaussian random fields. We present results also on statistics of the pressure Laplacian and conditional mean pressure given both dissipation and enstrophy. At low Reynolds number intense negative pressure fluctuations are preferentially associated with rotation-dominated regions but at high Reynolds number both high dissipation and high enstrophy have similar effects.

Journal ArticleDOI
TL;DR: In this article, a new approach to model order reduction of the Navier-Stokes equations at high Reynolds number is proposed, which does not rely on empirical turbulence modeling or modification of the NST equations.
Abstract: A new approach to model order reduction of the Navier-Stokes equations at high Reynolds number is proposed. Unlike traditional approaches, this method does not rely on empirical turbulence modeling or modification of the Navier-Stokes equations. It provides spatial basis functions different from the usual proper orthogonal decomposition basis function in that, in addition to optimally representing the training data set, the new basis functions also provide stable and accurate reduced-order models. The proposed approach is illustrated with two test cases: two-dimensional flow inside a square lid-driven cavity and a two-dimensional mixing layer.

Journal ArticleDOI
TL;DR: In this article, an experimental study has been conducted on a transitional water jet at a Reynolds number of Re = 5,000, where the jet exhibits a primary axisymmetric instability followed by a pairing of the vortex rings.
Abstract: An experimental study has been conducted on a transitional water jet at a Reynolds number of Re = 5,000. Flow fields have been obtained by means of time-resolved tomographic particle image velocimetry capturing all relevant spatial and temporal scales. The measured threedimensional flow fields have then been postprocessed by the dynamic mode decomposition which identifies coherent structures that contribute significantly to the dynamics of the jet. Both temporal and spatial analyses have been performed. Where the jet exhibits a primary axisymmetric instability followed by a pairing of the vortex rings, dominant dynamic modes have been extracted together with their amplitude distribution. These modes represent a basis for the low-dimensional description of the dominant flow features.

Journal ArticleDOI
TL;DR: In this paper, the authors studied flow and heat transfer in periodic wavy channels with rectangular cross sections using direct numerical simulation, for increasing Reynolds numbers spanning from the steady laminar to transitional flow regimes.

Journal ArticleDOI
TL;DR: In this article, the peristaltic transport of nanofluid in a channel with complaint walls has been investigated by utilizing long wavelength and low Reynolds number assumptions, and the coupled nonlinear boundary value problem has been solved numerically by using shooting technique through software Mathematica.

Journal ArticleDOI
TL;DR: In this paper, a low Reynolds number airfoil was designed for applications in small horizontal axis wind turbines to achieve better startup and low wind speed performances, and the results from particle image velocimetry (PIV) together with smoke flow visualization were used to study the flow around the air foil.

Journal ArticleDOI
TL;DR: In this article, the effects of particle-laden turbulent flow in a horizontal channel were investigated for different settling coefficients and volume fractions (0.79 % −7.08 %) for the channel Reynolds number being 5000.
Abstract: A fictitious domain method is used to perform fully resolved numerical simulations of particle-laden turbulent flow in a horizontal channel. The effects of large particles of diameter 0.05 and 0.1 times the channel height on the turbulence statistics and structures are investigated for different settling coefficients and volume fractions (0.79 %–7.08 %) for the channel Reynolds number being 5000. The results indicate the following. (a) When the particle sedimentation effect is negligible (i.e. neutrally buoyant), the presence of particles decreases the maximum r.m.s. of streamwise velocity fluctuation near the wall by weakening the intensity of the large-scale streamwise vortices, while increasing the r.m.s. of the streamwise fluctuating velocity in the region very close to the wall and in the centre region. On the other hand, the particles increase the r.m.s. of transverse and spanwise fluctuating velocities in the near-wall region by inducing the small-scale vortices. (b) When the particle settling effect is so substantial that most particles settle onto the bottom wall and form a particle sediment layer (SL), the SL plays the role of a rough wall and parts of the vortex structures shedding from the SL ascend into the core region and substantially increase the turbulence intensity there. (c) When the particle settling effect is moderate, the effects of particles on the turbulence are a combination of the former two situations, and the Shields number is a good parameter for measuring the particle settling effects (i.e. the particle concentration distribution in the transverse direction). The average velocities of the particle are smaller in the lower half-channel and larger in the upper half-channel compared to the local fluid velocities in the presence of gravity effects. The effects of the smaller particles on the turbulence are found to be stronger at the same particle volume fractions.