DNS study of decaying homogeneous isotropic turbulence with polymer additives

The complex three-dimensional turbulent flow field in a centrifugal water pump with three asymmetrical diffusers was numerically simulated. The characteristics of pressure and force fluctuations inside the model pump were investigated. Fast Fourier transformation was performed to obtain the spectra of pressure and force fluctuations. It indicates that the dominant frequency of pressure fluctuations is the blade passing frequency in all the sub-domains inside the pump and the first blade passing frequency energy (first order of blade passing frequency) is the most significant. The dominant frequency of pressure fluctuations at the location of diffuser outlet is featured by low frequency (less than 1 Hz), which may be due to the locally generated eddy structures. Besides, the dominant frequency force fluctuations on the impeller blades are also the blade passing frequency. The existence of the three asymmetrical diffusers has damping effect on the pressure fluctuation amplitude and energy amplitude of pressure fluctuations in the diffuser domain dramatically, which indicates that the diffusers can effectively control the hydraulically excited vibration in the pump. Besides, the prediction of the dominant frequency of pressure fluctuations inside the pump can help to utilize the pump effectively and to extend the pump life. The main findings of this work can provide prediction of the pump performance and information for further optimal design of centrifugal pumps as well.

Section: Analysis Of the Characteristics Of Pressure Fluctuations Onmentioning

confidence: 99%

Numerical simulation of dynamic flow characteristics in a centrifugal water pump with three-vaned diffuser

Shuai

Jiang

Wang

et al. 2015

“…Sureshkumar et al 9 first used DNS to simulate turbulent drag-reducing flow with the finitely extensible nonlinear elastic in the Peterlin approximation (FENE-P) model based on pseudospectral method. Following that, more and more DNS works have been carried out to resolve the detailed characteristics of turbulent drag-reducing flows and investigate the mechanism of DR. [10][11][12][13][14][15][16][17][18][19] Due to the constraint of computer hardware, the performed DNSs had to be limited to most flows with moderate Reynolds number. Regarding RANS method, several researchers paid attention to the proposition of RANS models for viscoelastic fluid flow and the inquiry on the overall characteristics of polymer solution flows.…”

Section: Introductionmentioning

confidence: 99%

Wavelet analysis of coherent structures and intermittency in forced homogeneous isotropic turbulence with polymer additives

Wang

Zheng

Cai

et al. 2017

Large eddy simulation was performed for forced homogeneous isotropic turbulence with/without polymer additives. Wavelet transform in one dimension and two dimensions were performed to investigate the multi-resolution features of coherent structures and intermittency in forced homogeneous isotropic turbulence based on large eddy simulation database. Using wavelet decomposition in one dimension and two dimension, it is found that polymer additives behave inhibitive effect on the intermittent pulse and the amount of coherent structures in forced homogeneous isotropic turbulence. The reconstructions of velocity waveform for coherent structures with strongest intermittence were surveyed at the scale a = 2 6 obtained by maximum energy criterion, showing that the quasi-periodicity and intermittence for coherent structures in polymer solutions are not as distinct as that in the Newtonian fluid. To detect intermittency, the flatness factor and local intermittency measure for velocity fluctuation signals were calculated by wavelet coefficients. The results for flatness factor in one-dimensional wavelet transform and LIM in both one-dimensional and twodimensional wavelet transform intuitively show that the local contribution to intermittency in polymer solutions flow is relatively smaller, leading to the suppression of intermittency in forced homogeneous isotropic turbulence with polymer additives. The robustness of wavelet transform method has been demonstrated in exploring the characteristics of turbulent structures and intermittency, which are of key importance in understanding the mechanism of turbulent drag reduction.

“…The presence of elasticity brings viscoelastic fluid special rheological characteristics which are different from those of Newtonian fluid, such as shear thinning in viscosity, nonzero normal stress difference, Weissenberg effect (rod-climbing), extrusion swell, tubeless siphon, elastic recoil [1], and turbulent drag reduction effect [2][3][4][5][6][7]. Among these characteristics, turbulent drag reduction is an exciting phenomenon and has great potential in energy saving for industrial application systems.…”

Section: Introductionmentioning

confidence: 99%

Modeling Asymmetric Flow of Viscoelastic Fluid in Symmetric Planar Sudden Expansion Geometry Based on User-Defined Function in FLUENT CFD Package

Zheng

Yang

2013

Through embedding an in-house subroutine into FLUENT code by utilizing the functionalization of user-defined function provided by the software, a new numerical simulation methodology on viscoelastic fluid flows has been established. In order to benchmark this methodology, numerical simulations under different viscoelastic fluid solution concentrations (with solvent viscosity ratio varied from 0.2 to 0.9), extensibility parameters (100 ≤ 2 ≤ 500), Reynolds numbers (0.1 ≤ Re ≤ 100), and Weissenberg numbers (0 ≤ Wi ≤ 20) are conducted on unsteady laminar flows through a symmetric planar sudden expansion with expansion ratio of 1 : 3 for viscoelastic fluid flows. The constitutive model used to describe the viscoelastic effect of viscoelastic fluid flow is FENE-P (finitely extensive nonlinear elastic-Peterlin) model. The numerical simulation results show that the influences of elasticity, inertia, and concentration on the flow bifurcation characteristics are more significant than those of extensibility. The present simulation results including the critical Reynolds number for which the flow becomes asymmetric, vortex size, bifurcation diagram, velocity distribution, streamline, and pressure loss show good agreements with some published results. That means the newly established method based on FLUENT software platform for simulating peculiar flow behaviors of viscoelastic fluid is credible and suitable for the study of viscoelastic fluid flows.