scholarly journals Relative velocity distribution of inertial particles in turbulence: A numerical study

2015 ◽  
Vol 92 (4) ◽  
Author(s):  
Vincent E. Perrin ◽  
Harm J. J. Jonker
Keyword(s):  
Velocity Distribution ◽  
Relative Velocity ◽  
Numerical Study ◽  
Inertial Particles

Vortex synchronization in the cylinder wake due to harmonic and non-harmonic perturbations

2016 ◽  
Vol 804 ◽  
pp. 248-277 ◽  
Author(s):  
Efstathios Konstantinidis ◽  
Demetri Bouris
Keyword(s):  
Relative Velocity ◽  
Numerical Study ◽  
Vortex Formation ◽  
Phase Portraits ◽  
Cylinder Wake ◽  
Frequency Space ◽  
Flow Past A Cylinder ◽  
Harmonic Perturbation ◽  
Perturbation Frequency ◽  
Vortex Patterns

This paper reports a numerical study of two-dimensional periodically perturbed flow past a cylinder. Both harmonic and non-harmonic perturbation waveforms of the inflow velocity are considered for a maximum instantaneous Reynolds number of 180. Phase portraits of the lift force are employed to identify the dynamical state of the cylinder wake and determine the range of kinematical parameters for which primary synchronization occurs, that is the regime where vortex formation is phase-locked to the subharmonic of the perturbation frequency. The effect of different perturbation waveforms on the synchronization range and on patterns of vortex formation is examined in detail over the normalized amplitude–frequency space. It is shown that systematic shifts of the synchronization range, towards either higher or lower frequencies, can be attained by imposing different perturbation waveforms. As a consequence, in certain regions of the parameter space it is possible to obtain multiple periodic and/or quasi-periodic wake states for waveforms of exactly the same amplitude and frequency. For the range of parameters where synchronization occurs, different vortex patterns are attained in the wake involving the shedding of solitary and binary vortices, or mixtures thereof, which can be controlled by the perturbation waveform. The phenomenology of these patterns, which result from modification of the basic Kármán mode in the unperturbed wake, is discussed and explained in terms of the generation of circulation that is induced by perturbations in the relative velocity. Vortex patterns from cylinders oscillating either in line with or transverse to a free stream are recast in the framework of the relative velocity.

Non-Gaussianity in turbulent relative dispersion

2019 ◽  
Vol 867 ◽  
pp. 877-905
Author(s):  
B. J. Devenish ◽  
D. J. Thomson
Keyword(s):  
Stochastic Model ◽  
Velocity Distribution ◽  
Relative Velocity ◽  
Isotropic Turbulence ◽  
Dispersion Model ◽  
Original Model ◽  
Direct Numerical Simulations ◽  
Relative Dispersion ◽  
Lagrangian Stochastic Model ◽  
Homogeneous Isotropic Turbulence

We present an extension of Thomson’s (J. Fluid Mech., vol. 210, 1990, pp. 113–153) two-particle Lagrangian stochastic model that is constructed to be consistent with the $4/5$ law of turbulence. The rate of separation in the new model is reduced relative to the original model with zero skewness in the Eulerian longitudinal relative velocity distribution and is close to recent measurements from direct numerical simulations of homogeneous isotropic turbulence. The rate of separation in the equivalent backwards dispersion model is approximately a factor of 2.9 larger than the forwards dispersion model, a result that is consistent with previous work.

Effects of Trailing Edge Position of Splitter Blade on the Pressure Pulsation in a Low Specific Centrifugal Pump

2019 ◽  
Author(s):  
Jinfeng Zhang
Keyword(s):  
Velocity Distribution ◽  
Turbulence Intensity ◽  
Pressure Fluctuation ◽  
Relative Velocity ◽  
Pressure Pulsation ◽  
Suction Side ◽  
Maximum Pressure ◽  
Trailing Edge ◽  
Flow Rates ◽  
Pulsation Amplitude

Abstract A combination of experimental and numerical simulation was carried out to analyze influence of trailing edge position of splitter blade on the pressure fluctuation in low specific pumps with and without splitter blades under different flow rates. Performance experiments and PIV tests were performed to verify the results of numerical calculation. Several monitor points were placed in the calculation model pump to collect the pressure fluctuation signals, which were processed by Fast Fourier Transform to obtain the frequency results for further analysis. Besides, turbulence intensity and relative velocity distribution were also analyzed in regions of impeller and volute. The results showed that compared with prototype without splitter blade and the splitter blade schemes, when the trailing edge of splitter blade deviates to the suction side of main blade, the maximum pressure pulsation amplitudes are the lowest at different monitoring points of model pump. And the variation of pressure pulsation amplitude in this scheme is relatively stable with the change of flow rates compared with other schemes. Furthermore, the splitter blade scheme with an appropriate trailing edge position has the lowest average turbulence intensity and optimal relative velocity distribution in main flow passage component. Therefore, this paper proposes a reference scheme of the trailing edge position of the splitter blade to effectively decrease predominate pressure pulsation amplitude.

Investigation of sub-Kolmogorov inertial particle pair dynamics in turbulence using novel satellite particle simulations

2013 ◽  
Vol 720 ◽  
pp. 192-211 ◽  
Author(s):  
Baidurja Ray ◽  
Lance R. Collins
Keyword(s):  
Structure Function ◽  
Power Law ◽  
Particle Motion ◽  
Relative Velocity ◽  
Velocity Structure ◽  
Inertial Particles ◽  
Particle Clustering ◽  
Particle Pair ◽  
Velocity Statistics ◽  
Particle Simulations

AbstractClustering (or preferential concentration) of weakly inertial particles suspended in a homogeneous isotropic turbulent flow is driven primarily by the smallest eddies at the so-called Kolmogorov scale. In particle-laden large-eddy simulations (LES), these small scales are not resolved by the grid and hence their effect on both the resolved flow scales and the particle motion have to be modelled. In order to predict clustering in a particle-laden LES, it is crucial that the subgrid model for the particles captures the mechanism by which the subgrid scales affect the particle motion (Ray & Collins, J. Fluid Mech., vol. 680, 2011, pp. 488–510). In this paper, we describe novel satellite particle simulations (SPS), in which we study the clustering and relative velocity statistics of inertial particles at separation distances well below the Kolmogorov length scale. SPS is designed to isolate pairwise interactions of particles, and is therefore well suited for developing two-particle models. We show that the power-law dependence of the radial distribution function (RDF), a statistical measure of clustering, is predicted by the SPS in excellent agreement with direct numerical simulations (DNS) for Stokes numbers up to 3, implying that no explicit information from the inertial range is required to accurately describe particle clustering. This result further explains our successful prediction of the RDF power using the drift-diffusion model of Chun et al. (J. Fluid Mech., vol. 536, 2005, pp. 219–251) for $\mathit{St}\leq 0. 4$. We also consider the second-order longitudinal relative velocity structure function for the particles; we show that the SPS is able to capture its power-law exponent for $\mathit{St}\leq 0. 5$ and attribute the disagreement at larger $\mathit{St}$ to the effect of the larger scales of motion not captured by the SPS. Further, the SPS is able to capture the ‘caustic activation’ of the structure function at zero separation and predict the critical $\mathit{St}$ and rate of activation in agreement with the DNS (Salazar & Collins, J. Fluid. Mech., vol. 696, 2012, pp. 45–66). We show comparisons between filtered DNS and equivalently filtered SPS, and the findings are similar to the unfiltered case. Overall, SPS is an efficient and accurate computational tool for investigating particle pair dynamics at small separations, as well as an interesting platform for developing LES subgrid models designed to accurately reproduce particle clustering.

Numerical investigation of the effects of splitter blade deflection on the pressure pulsation in a low specific speed centrifugal pump

2019 ◽  
Vol 234 (4) ◽  
pp. 420-432 ◽  
Author(s):  
Jinfeng Zhang ◽  
Guidong Li ◽  
Jieyun Mao ◽  
Shouqi Yuan ◽  
Yefei Qu ◽  
...  
Keyword(s):  
Velocity Distribution ◽  
Turbulence Intensity ◽  
Pressure Fluctuation ◽  
Relative Velocity ◽  
Pressure Pulsation ◽  
Maximum Pressure ◽  
Flow Rates ◽  
Pulsation Amplitude ◽  
Low Specific Speed ◽  
Specific Speed

A combination of experimental and numerical simulation was carried out to analyze the influences of the splitter blade deflection on the performance and pressure fluctuation in low specific speed pumps with and without splitter blades under different flow rates. Performance experiments and particle image velocimetry (PIV) tests were performed to verify the results of the numerical calculation. Several monitoring points were placed in the calculation model pump to collect the pressure fluctuation signals, which were processed by Fast Fourier Transform to obtain the frequency results for further analysis. In addition, turbulence intensity and relative velocity distribution were also analyzed in the regions of the impeller and volute. The results showed that compared with a prototype without a splitter blade and the splitter blade schemes, the maximum pressure pulsation amplitudes are the lowest at different monitoring points of the model pump when the splitter blade deflects to the suction side of the main blade. The variation of pressure pulsation amplitude in this scheme is relatively stable with the change of flow rates compared with other schemes. Furthermore, the impeller scheme with an appropriate deflection of the splitter blade has the lowest turbulence intensity and optimal relative velocity distribution in the main flow passage. Therefore, this paper proposes a reference scheme of the impeller with the splitter blade to effectively decrease the predominate pressure pulsation amplitude.

Experimental and numerical study of particle velocity distribution in the vertical pipe after a 90° elbow

2017 ◽  
Vol 314 ◽  
pp. 500-509 ◽  
Author(s):  
Yong Lu ◽  
Zhenbo Tong ◽  
Donald H. Glass ◽  
William J. Easson ◽  
Mao Ye
Keyword(s):  
Velocity Distribution ◽  
Particle Velocity ◽  
Numerical Study ◽  
Vertical Pipe

Preferential concentration and relative velocity statistics of inertial particles in Navier–Stokes turbulence with and without filtering

2011 ◽  
Vol 680 ◽  
pp. 488-510 ◽  
Author(s):  
BAIDURJA RAY ◽  
LANCE R. COLLINS
Keyword(s):  
Velocity Field ◽  
Time Scale ◽  
Relative Velocity ◽  
Stokes Number ◽  
Separation Distance ◽  
Inertial Particles ◽  
Subgrid Scale ◽  
Preferential Concentration ◽  
P 75 ◽  
Particle Statistics

The radial distribution function (RDF, a statistical measure of preferential concentration), and the relative velocity measured along the line-of-centres of two particles are the key statistical inputs to the collision kernel for finite-inertia particles suspended in a turbulent flow Sundaram & Collins (J. Fluid Mech., vol. 335, 1997, p. 75). In this paper, we investigate the behaviour of these two-particle statistics using direct numerical simulation (DNS) of homogeneous isotropic turbulence. While it is known that the RDF for particles of any Stokes number (St) decreases with separation distance Sundaram & Collins (J. Fluid Mech., vol. 335, 1997, p. 75), Reade & Collins (Phys. Fluids, vol. 12, 2000, p. 2530), Salazar et al. (J. Fluid Mech., vol. 600, 2008, p. 245), we observe that the peak in the RDF versus St curve shifts to higher St as we increase the separation distance. Here, St is defined as the ratio of the particle's viscous relaxation time to the Kolmogorov time-scale of the flow. Furthermore, as found in a previous study Wang, Wexler, & Zhou (J. Fluid Mech., vol. 415, 2000, p. 117), the variance of the radial relative velocity (wr) is found to increase monotonically with increasing separation distance and increasing Stokes number; however, we show for the first time that the parameteric variation of the skewness of wr with St and r/η is qualitatively similar to that of the RDF, and points to a connection between the two. We then apply low-pass filters (using three different filter scales) on the DNS velocity field in wavenumber space in order to produce ‘perfect’ large-eddy simulation (LES) velocity fields without any errors associated with subgrid-scale modelling. We present visual evidence of the effect of sharp-spectral filtering on the flow structure and the particle field. We calculate the particle statistics in the filtered velocity field and find that the RDF decreases with filtering at low St and increases with filtering at high St, similar to Fede & Simonin (Phys. Fluids, vol. 18, 2006, p. 045103). We also find that the variation of the RDF with St shifts towards higher St with filtering at all separation distances. The variance of wr is found to decrease with filtering for all St and separation distances, but the skewness of wr shows a non-monotonic response to filtering that is qualitatively similar to the RDF. We consider the variation of the RDF and moments of wr with filter scale and find that they are approximately linear in the inertial range. We demonstrate that a simple model consisting of a redefinition of the St based on the time-scale of the filtered velocity field cannot recover the unfiltered statistics. Our findings provide insight on the effect of subgrid-scale eddies on the RDF and wr, and establish the requirements of a LES model for inertial particles that can correctly predict clustering and collisional behaviour.

Sign in / Sign up

Export Citation Format

Share Document