scholarly journals CFD Simulation of the Discharge Flow from Standard Rushton Impeller

2014 ◽  
Vol 2014 ◽  
pp. 1-7 ◽  
Author(s):  
Bohuš Kysela ◽  
Jiří Konfršt ◽  
Ivan Fořt ◽  
Zdeněk Chára
Keyword(s):  
Large Eddy Simulation ◽  
Cfd Simulation ◽  
Laser Doppler Anemometry ◽  
Rushton Turbine ◽  
Sliding Mesh ◽  
Eddy Simulation ◽  
Large Eddy ◽  
The Mean ◽  
Rushton Impeller ◽  
Good Agreement

The radial discharge jet from the standard Rushton turbine was investigated by the CFD calculations and compared with results from the Laser Doppler Anemometry (LDA) measurements. The Large Eddy Simulation (LES) approach was employed with Sliding Mesh (SM) model of the impeller motion. The obtained velocity profiles of the mean ensemble-averaged velocity and r.m.s. values of the fluctuating velocity were compared in several distances from the impeller blades. The calculated values of mean ensemble-averaged velocities are rather in good agreement with the measured ones as well as the derived power number from calculations. However, the values of fluctuating velocities are obviously lower from LES calculations than from LDA measurements.

Large Eddy Simulation of Round Impinging Jets With Large Stand-Off Distance

2014 ◽  
Author(s):  
Mehrdad Shademan ◽  
Vesselina Roussinova ◽  
Ron Barron ◽  
Ram Balachandar
Keyword(s):  
Large Eddy Simulation ◽  
Flow Characteristics ◽  
Impinging Jet ◽  
Impinging Jets ◽  
Vortical Structures ◽  
Nozzle Height ◽  
Eddy Simulation ◽  
Large Eddy ◽  
The Mean ◽  
Good Agreement

Large Eddy Simulation (LES) has been carried out to study the flow of a turbulent impinging jet with large nozzle height-to-diameter ratio. The dynamic Smagorinsky model was used to simulate the subgrid-scale stresses. The jet exit Reynolds number is 28,000. The study presents a detailed evaluation of the flow characteristics of an impinging jet with nozzle height of 20 diameters above the plate. Results of the mean normalized centerline velocity and wall shear stress show good agreement with previous experiments. Analysis of the flow field shows that vortical structures generated due to the Kelvin-Helmholtz instabilities in the shear flow close to the nozzle undergo break down or merging when moving towards the plate. Unlike impinging jets with small stand-off distance where the ring-like vortices keep their interconnected shape upon reaching the plate, no sign of interconnection was observed on the plate for this large stand-off distance. A large deflection of the jet axis was observed for this type of impinging jet when compared to the cases with small nozzle height-to-diameter ratios.

scholarly journals Predicting Unsteady Loads in Marine Propulsor Crashback Using Large Eddy Simulation

2012 ◽  
Vol 2012 ◽  
pp. 1-12 ◽  
Author(s):  
Hyunchul Jang ◽  
Aman Verma ◽  
Krishnan Mahesh
Keyword(s):  
Large Eddy Simulation ◽  
Reverse Flow ◽  
Reverse Direction ◽  
Unsteady Forces ◽  
Eddy Simulation ◽  
Large Eddy ◽  
The Mean ◽  
Submarine Hull ◽  
Marine Propulsor ◽  
Good Agreement

Propulsor crashback is an off-design operating condition where a propulsor rotates in the reverse direction to yield negative thrust. Crashback is characterized by the interaction of the free stream with the reverse flow generated by propulsor rotation. This causes a highly unsteady vortex ring which leads to flow separation and unsteady forces and moments on the blades. Large eddy simulation (LES) is performed for marine propulsors in crashback for various configurations and advance ratios and validated against experiments. The predictive capability of LES as a tool for propulsor crashback is demonstrated on an open propulsor, open propulsor with a submarine hull, and ducted propulsor with and without stator blades. LES is in good agreement with experiments for the mean and RMS levels, and spectra of the unsteady loads on the propulsors.

scholarly journals Hydrodynamics of gliding penguin flipper suggests the adjustment of sweepback with swimming speeds

2021 ◽  
Author(s):  
Masateru Maeda ◽  
Natsuki Harada ◽  
Hiroto Tanaka
Keyword(s):  
Large Eddy Simulation ◽  
Cfd Simulation ◽  
Lift Coefficient ◽  
Angle Of Attack ◽  
Force Balance ◽  
Hydrodynamic Performance ◽  
Vertical Force ◽  
Sweep Angle ◽  
Eddy Simulation ◽  
Large Eddy

Hydrodynamic performance of a gliding penguin flipper (wing) considering the backward sweep was estimated with computational fluid dynamics (CFD) simulation. A flipper of a gentoo penguin (Pygoscelis papua) was 3D scanned, smoothed, and a numerical fluid mesh was generated. For accurate yet resource-saving computation, an embedded large-eddy simulation (ELES) methods was employed, where the flow near the flipper was solved with large-eddy simulation (LES) and flow far away from the flipper was solved with Reynolds-averaged Navier-Stokes (RANS). The relative flow speed was fixed at 2 m s-1, close to the typical foraging speed for the penguin species. The sweep angle was set to be 0°, 30°, and 60°, while the angle of attack was varied between -40° and 40°, both are within the realistic ranges in the wing kinematics measurement of penguins in an aquarium. It was revealed that a higher sweep angle reduces the lift slope, but the lift coefficient is unchanged at a high angle of attack. Drag coefficient was reduced across the angles of attack with increasing the sweep angles. The drag polars suggest the sweep angle may be adjusted with the change in swimming speed and anhedral (negative dihedral) angle to minimise drag while maintaining the vertical force balance to counteract the positive buoyancy. This will effectively expand the swimming envelope of the gliding penguin, similar to a flying counterpart such as swift.

Study of wave effect on vorticity in Langmuir turbulence using wave-phase-resolved large-eddy simulation

2019 ◽  
Vol 875 ◽  
pp. 173-224 ◽  
Author(s):  
Anqing Xuan ◽  
Bing-Qing Deng ◽  
Lian Shen
Keyword(s):  
Large Eddy Simulation ◽  
Correlation Effect ◽  
Wave Turbulence ◽  
Langmuir Turbulence ◽  
Streamwise Vorticity ◽  
Wave Phase ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Vorticity Dynamics ◽  
The Mean

The effects of a water surface wave on the vorticity in the turbulence underneath are studied for Langmuir turbulence using wave-phase-resolved large-eddy simulation. The simulations are performed on a dynamically evolving wave-surface-fitted grid such that the phase-resolved wave motions and their effects on the turbulence are explicitly captured. This study focuses on the vorticity structures and dynamics in Langmuir turbulence driven by a steady and co-aligned progressive wave and surface shear stress. For the first time, the detailed vorticity dynamics of the wave–turbulence interaction in Langmuir turbulence in a wave-phase-resolved frame is revealed. The wave-phase-resolved simulation provides detailed descriptions of many characteristic features of Langmuir turbulence, such as elongated quasi-streamwise vortices. The simulation also reveals the variation of the strength and the inclination angles of the vortices with the wave phase. The variation is found to be caused by the periodic stretching and tilting of the wave orbital straining motions. The cumulative effect of the wave on the wave-phase-averaged vorticity is analysed using the Lagrangian average. It is discovered that, in addition to the tilting effect induced by the Lagrangian mean shear gradient of the wave, the phase correlation between the vorticity fluctuations and the wave orbital straining is also important to the cumulative vorticity evolution. Both the fluctuation correlation effect and the mean tilting effect are found to amplify the streamwise vorticity. On the other hand, for the vertical vorticity, the fluctuation correlation effect cancels the mean tilting effect, and the net change of the vertical vorticity by the wave straining is negligible. As a result, the wave straining enhances only the streamwise vorticity and cumulatively tilts vertical vortices towards the streamwise direction. The above processes are further quantified analytically. The role of the fluctuation correlation effect in the wave-phase-averaged vorticity dynamics provides a deeper understanding of the physical processes underlying the wave–turbulence interaction in Langmuir turbulence.

LARGE EDDY SIMULATION OF THE PHENOMENOLOGY OF THE FLOW THROUGH A LINEAR BLADE CASCADE – THE MEAN FIELD

2017 ◽  
Vol 20 (1) ◽  
pp. 1-20
Author(s):  
Karima Heguehoug ép. Benkara-Mostefa ◽  
Zoubir Nemouchi ◽  
Lahouari Adjlout
Keyword(s):  
Large Eddy Simulation ◽  
Mean Field ◽  
Eddy Simulation ◽  
Blade Cascade ◽  
Large Eddy ◽  
Flow Through ◽  
The Mean

Wind-Driven Natural Ventilation in an Areaway-Attached Basement with a Single-Sided Opening for Residential Purposes

2011 ◽  
Vol 383-390 ◽  
pp. 5344-5349
Author(s):  
Zhen Bu
Keyword(s):  
Natural Ventilation ◽  
Ventilation Rate ◽  
Navier Stokes ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Effective Ventilation ◽  
The Mean ◽  
Ventilation Rates ◽  
Les Model ◽  
Good Agreement

This paper discusses the sustainability of the areaway-attached basement concept with the attentions focused on wind-driven single-sided natural ventilation. First, numerical simulations were performed on an areaway-attached basement with a single-sided opening. Two CFD approaches: Reynolds averaged Navier-Stokes (RANS) and large-eddy simulation (LES) were used and compared with the previous experimental results of effective ventilation rate. A good agreement between the measurement and LES model was found and RANS model tends to underestimate the ventilation rates. Furthermore, Based on LES with the inflow turbulent fluctuations, the mean airflow patterns within and around the areaway-attached basement was investigated for different wind incidence angles to examine the influences of wind direction on ventilation performances.

Comparison of Partially Averaged Navier–Stokes and Large-Eddy Simulations of the Flow Around a Cuboid Influenced by Crosswind

2012 ◽  
Vol 134 (10) ◽  
Author(s):  
Siniša Krajnović ◽  
Per Ringqvist ◽  
Branislav Basara
Keyword(s):  
Experimental Data ◽  
Large Eddy Simulation ◽  
Large Eddy Simulations ◽  
Navier Stokes ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Better Than ◽  
Good Agreement ◽  
Near Wall

The paper presents a partially averaged Navier–Stokes (PANS) simulation of the flow around a cuboid influenced by crosswind. The results of the PANS prediction are validated against experimental data and results of a large-eddy simulation (LES) made using the same numerical conditions as PANS. The PANS shows good agreement with the experimental data. The prediction of PANS was found to be better than that of the LES in flow regions where simulations suffered from poor near-wall resolution.

Effect of Impeller Speed Perturbation in a Rushton Impeller Stirred Tank

2012 ◽  
Vol 134 (6) ◽  
Author(s):  
Somnath Roy ◽  
Sumanta Acharya
Keyword(s):  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Rotational Speed ◽  
Stirred Tank ◽  
Azimuthal Direction ◽  
Mean Flow ◽  
Eddy Simulation ◽  
Large Eddy ◽  
The Mean ◽  
Rushton Impeller

Flow inside an unbaffled Rushton-impeller stirred tank reactor (STR) is perturbed using a time dependent impeller rotational speed. Large eddy simulation (LES) revealed that the perturbation increased the width of impeller jet compared to the constant rotational speed cases. The turbulent fluctuations were also observed to be enhanced in the perturbed flow and showed higher values of production and convection of turbulent kinetic energy. Changes in the mean flow-field during the perturbation cycle are investigated. The trailing edge vortices were observed to propagate farther both in the radial and azimuthal direction in the perturbed case. Production of turbulent kinetic energy is observed to be related to the breakup of the impeller jet in the perturbed case. Dissipation of turbulent kinetic energy is augmented due to the perturbation ensuring a better mixing at the molecular scale.

Rapid and Slow Decomposition in Large Eddy Simulation of Scalar Turbulence

2010 ◽  
Author(s):  
L. Fang ◽  
L. Shao ◽  
J. P. Bertoglio ◽  
L. P. Lu ◽  
Z. S. Zhang
Keyword(s):  
Large Eddy Simulation ◽  
A Priori ◽  
Scalar Dissipation ◽  
Scalar Flux ◽  
Mean Flow ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Slow Part ◽  
The Mean ◽  
Subgrid Stress

In large eddy simulation of turbulent flow, because of the spatial filter, inhomogeneity and anisotropy affect the subgrid stress via the mean flow gradient. A method of evaluating the mean effects is to split the subgrid stress tensor into “rapid” and “slow” parts. This decomposition was introduced by Shao et al. (1999) and applied to A Priori tests of existing subgrid models in the case of a turbulent mixing layer. In the present work, the decomposition is extended to the case of a passive scalar in inhomogeneous turbulence. The contributions of rapid and slow subgrid scalar flux, both in the equations of scalar variance and scalar flux, are analyzed. A Priori numerical tests are performed in a turbulent Couette flow with a mean scalar gradient. Results are then used to evaluate the performances of different popular subgrid scalar models. It is shown that existing models can not well simulate the slow part and need to be improved. In order to improve the modeling, an extension of the model proposed by Cui et al. (2004) is introduced for the slow part, whereas the Scale-Similarity model is used reproduce the rapid part. Combining both models, A Priori tests lead to a better performance. However, the remaining problem is that none eddy-diffusion model can correctly represent the strong scalar dissipation near the wall. This problem will be addressed in future work.

scholarly journals Large Eddy Simulation of Microbubble Drag Reduction in Fully Developed Turbulent Boundary Layers

2020 ◽  
Vol 8 (7) ◽  
pp. 524
Author(s):  
Tongsheng Wang ◽  
Tiezhi Sun ◽  
Cong Wang ◽  
Chang Xu ◽  
Yingjie Wei
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Large Eddy Simulation ◽  
Drag Reduction ◽  
High Speed ◽  
Streamwise Velocity ◽  
Burst Frequency ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Good Agreement

Microbubble drag reduction has good application prospects. It operates by injecting a large number of bubbles with tiny diameters into a turbulent boundary layer. However, its mechanism is not yet fully understood. In this paper, the mechanisms of microbubble drag reduction in a fully developed turbulent boundary layer over a flat-plate is investigated using a two-way coupled Euler-Lagrange approach based on large eddy simulation. The results show good agreement with theoretical values in the velocity distribution and the distribution of fluctuation intensities. As the results show, the presence of bubbles reduces the frequency of bursts associated with the sweep events from 637.8 Hz to 611.2 Hz, indicating that the sweep events, namely the impacting of high-speed fluids on the wall surface, are suppressed and the streamwise velocity near the wall is decreased, hence reducing the velocity gradient at the wall and consequently lessening the skin friction. The suppression on burst frequency also, with the fluid fluctuation reduced in degree, decreases the intensity of vortices near the wall, leading to reduced production of turbulent kinetic energy.

Sign in / Sign up

Export Citation Format

Share Document