LES Turbulence Model Research Articles

Heat transfer characteristics of a turbulent swirl jet issuing from a circular nozzle

Experimental and numerical studies on the flow field and cooling performance of a swirling jet, impinging on a flat surface is presented. A new nozzle that resembles the swirl injector of a liquid propellant rocket engine is used. This study considers different parameters including swirl number(S), Reynolds number(Re), normalised orifice to target spacing (Z/D) and confinement. The performance of various RANS and LES turbulence models is assessed using the data obtained from present experimental studies and that reported in literature. RNG k-ϵ turbulent model is successful in predicting heat transfer in non swirling flow. In the case of swirling flow, LES WALEM(Wall Adapting Local Eddy viscosity Model) predicts the heat transfer better than the other models. The performance of Swirling Impinging Jets(SIJ) and Cylindrical Impinging Jets (CIJ) is compared. At higher Z/D, introduction of swirl results in reduction in heat transfer and this is because of the increased spreading of the jet and reduction in velocity of the jet impinging on the target. Better performance is achieved at lower Z/D when a cylindrical jet is introduced with a small amount of swirl. For Z/D = 2 and S = 0.2, the peak Nu increases by 10 % and average Nu in the stagnation region increases by 6 % in comparison to CIJ. The position of the peak Nu moves away from the axis of the jet and there is better uniformity in Nu in the stagnation region. For Z/D = 2 swirling flow creates secondary peak(which usually occurs at high Re)even at low Re. At very low Z/D, top wall confinement causes increase in both peak heat transfer and average heat transfer in the stagnation region.

A mathematical‐boundary‐recognition domain‐decomposition Lattice Boltzmann method combined with large eddy simulation applied to airfoil aeroacoustics simulation

AbstractBeing a direct computational aeroacoustics method, Lattice Boltzmann method (LBM) has great potential and broad application perspective in the field of numerical simulation of aerodynamic noise due to its low dispersion and low dissipation. A series of numerical algorithms and the related improvements based on the standard LBM method are proposed and developed in this paper to adapt to the airfoil noise calculation with complex grid at middle‐high Reynolds number. First, a new mathematical‐boundary‐recognition algorithm based on Green's formula is proposed to deal with complex curved geometric models, which is validated by three‐element airfoil 30P30N benchmark. Then, in order to reduce grid redundancy and improve computing efficiency, the grid refinement technique of domain decomposition model (DDM) is adopted and also improved, which is verified by calculating the flow and sound fields around 2D and 3D cylinders at Reynolds number equal to 90,000. Finally, three different LES turbulence models are combined with the standard MRT‐LBM method, where different finite difference schemes are used to solve Reynolds stress tensor which is different from the traditional one. Through the direct acoustic numerical simulation of NACA0012 airfoil at Reynolds number equal to 200,000, the effects of Smagorinsky models and Wall‐adapting local eddy‐viscosity (WALE) model on aerodynamic noise prediction are compared and analyzed. Overall, the proposed methodology is shown to be appropriate for predicting the aerodynamic noise at low Mach number and can successfully simulate the generation and propagation of far field acoustics.

A study on the flow behavior inside fluidic oscillation tools for friction-reduction in extended reach well

The drilling distance of extended-reach wells is limited by mechanical friction between the drill string and the borehole wall. The fluidic oscillator axial vibratory tools (AVTs) can effectively reduce friction and increase the weight on bit, thereby extending the reach of horizontal wells. However, few studies have delved into the evolutionary mechanism of the internal flow field of fluidic oscillator AVTs. In this paper, two types of fluidic oscillators with different flow path are presented. One is the reverse-feedback oscillator, and the other is sweeping-chamber oscillator. Through computational fluid dynamics method, the internal flow field of these two fluidic oscillator AVTs were analyzed, and the frequency and pressure drop were verified by experiments. The results show that the LES turbulence model provides more accurate simulations, showing an error range of less than 9%. The pressure drop and vibration frequency of the two tools are linearly related to the flow rate. The pressure drop of the reverse feedback oscillation tool is in the range of 0.1–1 MPa, and the vibration frequency is between 13 and 50 Hz. The sweeping-chamber oscillator can reduce vibration frequency to below 15 Hz. The results also show that it is crucial to consider the lag in pressure signals when designing and analyzing fluid oscillator systems, as it can affect the timing and behavior of the system. This research provides profound insights for understanding and optimizing fluidic oscillator systems.

Validation of Smagorinsky LES turbulence model in FluidX3D LBM: In-place vs central difference

Lattice Boltzmann method (LBM) has been rapidly developing as a CFD approach throughout the last three decades. The rise of new computational architectures like GPU in the last decade pawed the way to emergence of high-performance CFD software based on this method. The most outstanding of such is FluidX3D, utilizing locality of algorithm operations in connection with massive parallelism of GPU. High performance and memory efficiency of this software make it a promising idea to apply FluidX3D to challenging CFD problems, like turbulence simulation. In this work an effort is put into validation of Smagorinsky LES turbulence model implemented in this software. In addition, direct central difference implementation of this model is added to verify existing approach. The validation is done on the turbulent plane channel flow at Reτ = 180. Reasonable agreement between two LES model results was obtained. The convergence of LES profiles to DNS profiles with sufficient resolution proves correctness of implemented model.

Fluid-structure interaction analysis of wind turbine aerodynamic loads and aeroelastic responses considering blade and tower flexibility

With the increasing size of wind turbines, the aeroelastic phenomenon plays an essential role in the safety of wind turbines. A fluid-structure interaction (FSI) analysis for wind turbine by integrating the LES turbulent model and a structural dynamic model is carried out to investigate the aerodynamic loads and aeroelastic responses considering different inflow conditions, and blade and tower flexibility. For the first time, the time series and statistical features of aerodynamic loads, the exceedance probability, the equivalent fatigue loads, and the time series and statistical features of aeroelastic responses of wind turbine are calculated by the two-way FSI model. Furthermore, effects of inflow wind conditions and the blade and tower flexibility are investigated. It is noted that the turbulent winds result in increased fluctuations of aerodynamic loads and the equivalent fatigue load. The flap-wise motions of blades are more critical to load magnitude than the edgewise motions, and the inclusion of tower motion mitigates this aerodynamic load due to the coupling effects. Finally, it is also observed that the tower motion has a noticeable impact on the flap-wise displacement at the blade tip, and the flap-wise motions of blades significantly affect the fore-aft displacement at the tower top.

Computational Analysis of Shrouded Ejector Effect on Starting Vortex and Combustion Efficiency in Pulse Detonation Combustor with Different Fuels

ABSTRACT This research paper deals with the starting vortex of detonation combustion wave flow field in pulse detonation combustor (PDC). In order to achieve the potential pressure gain from PDC the shrouded ejectors are placed at exit section of detonation tube. Therefore, influence of shrouded ejector position plays a great role on leading vortex and reduction of NOx formation. Furthermore, n-butane (C4H10) and hydrogen (H2) fuel are used for stoichiometric (= 1) fuel-air mixture condition to simulate the thermal and prompt NOx formation at pulse time of 0.022s to 0.030s. The LES turbulence model is used to simulate the unsteady flow field in CFD based fluent platform. The one step irreversible chemical kinetics model analyzed the details of exothermic chemical reaction mechanism inside the combustor. The non-dimensional value of /d = 1.5 geometry position of shrouded ejector is better for leading vortex. So far, pickup detonation wave speed of 2306 ms−1 is obtained at shortest pulse time of 0.028s and this magnitude is higher than C-J velocity. The minimum pollutant number of 0.0000341 is obtained from hydrogen-air detonation, this magnitude is lesser compared to n-butane (C4H10)-air combustion. Furthermore, the maximum combustion efficiency of 85% is obtained from hydrogen-air mixture in detonation combustion process, which is comparatively higher than deflagration combustion process.

Coherent Structures Analysis of Methanol and Hydrogen Flames Using the Scale-Adaptive Simulation Model

Computational fluid dynamics techniques were applied to reproduce the characteristics of the liquid methanol burner described in a previous paper by Guevara et al. In this work, the unstable Reynolds-averaged Navier–Stokes (U-RANS) approach known as the Scale-Adaptive Simulation (SAS) model was employed, together with the steady nonadiabatic flamelets combustion model, to characterize and compare methanol and hydrogen flames. These flames were compared to determine whether this model can reproduce the coherent dynamic structures previously obtained using the LES model in other investigations. The LES turbulence model still entails a very high computational cost for many research centers. Conversely, the SAS model allows for local activation and amplification, promoting the transitions of momentum equations from the stationary to the transient mode and leading to a dramatic reduction in computational time. It was found that the global temperature contour of the hydrogen flame was higher than that of methanol. The air velocity profile peaks in the methanol flame were higher than those in hydrogen due to the coherent structures formed in the near field of atomization. Both flames presented coherent structures in the form of PVC; however, in the case of hydrogen, a ring-type vortex surrounding the flame was also developed. The axial, tangential, and radial velocity profiles of the coherent structures along the axial axis of the combustion chamber were analyzed at a criterion of Q = 0.003. The investigation revealed that the radial and tangential components had similar behaviors, while the axial velocity components differed. Finally, it was found that, using the SAS model, the coherent dynamic structures of the methanol flame were different from those obtained in previous works using the LES model.

Numerical Investigation of Cavitating Jet Flow Field with Different Turbulence Models

In numerous industries such as drilling, peening, cleaning, etc., a cavitating jet is adopted. However, it is challenging to simulate the cavitating flow field numerically with accuracy. The flow field of the organ pipe cavitation nozzle is simulated in this research using the RNG k−ε, DES, and LES turbulence models. The LES model can more accurately predict the periodic shedding of a cavitating cloud, which is basically consistent with the jet morphology captured with a high−speed camera. The flow pattern, cavitating cloud evolution and shedding period of a cavitating jet are analyzed. The findings demonstrate that the LES model produces a cavitating effect inside the nozzle that is superior to those produced by the RNG k−ε and DES models. The vortex rings in the diffusion section are simulated using the LES model, which accelerates cavitation. The cavitating clouds of the organ pipe nozzle show periodic evolutions, with stages of generation, development, shedding and collapse. The periodic shedding of the cavitating clouds exhibits a similar pattern in the vorticities simulated using the LES model, and the vorticities display the small-scale structures where the cavitating bubbles collapse. This study can provide a reference for the simulation of a cavitating jet and the analysis of the cavitating mechanism.

Optimization of the Performance of a Cross-flow Gas Mixer for a Partial Oxidation Reactor Through Numerical Modelling

Efficient mixing of gases has many different applications in science and engineering. Gas mixers are often used in chemical reactors that use pre-mixed gases in their reaction process. In this work, we vary the geometry of a mixer in order to maximize the uniformity of the mixed gases. The mixing happens in several pipes that have small cross-flow inlets on the sides that stimulate turbulent mixing. The mixer geometry is varied by changing the configuration of the small cross-flow inlets on the pipes, and the mixing quality is quantified by the distribution of gases at certain distances from the cross-flow inlets. The flow was modelled by using open-source finite volume code. We show that standard RANS k-ϵ steady state numeric models greatly overestimate the mixing rate between different gasses, as it ignores transient changes in the flow. Transient simulations using a LES turbulence model show that the gas concentrations in the mixing pipe exhibit a pulsating behavior. The amount and the configuration of the cross-flow inlets play a significant role in how the gases mix and how the concentrations vary over time. The resulting mixer geometry will be used as a part of a partial oxidation reactor design in the future.

Three-dimensional numerical simulation of the interaction between high-pressure sub-cooled water jet impacting high-temperature liquid lead-bismuth metal

The rupture accident of the steam generator heat transfer tube of the lead-bismuth cooled fast reactor causes a high-pressure sub-cooled water jet impacting high-temperature liquid lead-bismuth, and the interaction mechanism between water and liquid lead-bismuth needs to be studied clearly. In this paper, based on the volume of fluid method, the LES turbulence model and the Lee phase transition model, a three-dimensional numerical model is developed to study the multiphase flow and heat transfer mechanism of water and lead-bismuth interaction. The effects of sub-cooled water temperature, inlet pressure, and nozzle diameter on the distribution of phase state, pressure, temperature, and generated steam volume are studied in detail. The results indicate that the water jet can be divided into the jet water zone, the water-steam mixed zone, and the multiphase flow zone, respectively. Among them, the appearance of water-steam mixed zone depends on the internal boiling of the jet, and this zone tends to appear under the condition of low inlet pressure, small nozzle diameter and high sub-cooled water temperature. For multiphase flow zone, the temperature increases with sub-cooled water temperature, decreases with nozzle diameter and is almost not influenced by inlet pressure; The pressure increases with sub-cooled water temperature, inlet pressure and nozzle diameter. When nozzle diameter is large enough, however, it no longer has any effect on the temperature and pressure distribution within the jet. The volume of steam generated by water boiling is positively correlated with all three factors. Overall, the steam migrates upward through the outer side of the jet, absorbing heat and expanding during the migration process, and forming a high-temperature area at the top of the jet.

On the influence of Bow region vortices on SFS2 bistable airwake

The flow field of a full-scale simplified frigate model SFS2 is simulated numerically in ANSYS Fluent® 19.0 environment using embedded LES turbulence model. The emphasis of this manuscript is to provide insight into the influence of bow region coherent vortical structures on the characteristics of the bistable airwake impacting the hovering region of flight deck. The constructive interaction of bow leading edge vortex on starboard side with the respective lobe of horseshoe vortex, generated at foot of forward face of superstructure, is found to be responsible for so called “locking” of otherwise uniform incoming flow towards starboard side. Hence, the asymmetry or bias of the bistable airwake towards starboard side can also be explained. Spectral analyses of the velocity measurements recorded in the bow region and the superstructure airwake supplements and validates the influence of bow vortical system on the airwake, as dominant frequencies associated with these vortices are also observed in airwake spectrum. Moreover, the drag force of the SFS2 as well as the airwake dynamics are found to be influenced by the turbulent flow structures shed from the both the port and starboard sides of superstructure.

Turbulent heat transfer in pipes with increased roughness through shavings of helical ribs

Large-eddy simulations of mircrostructured pipes are carried out in this study. The pipes are helically ribbed with several starts from which shavings are cut out along the rib. A Reynolds number of 16,000 and a Prandtl number of 9 are applied. Cyclic boundary conditions are used to simulate an infinitely long pipe and a LES turbulence model is applied. The results show that both the number of starts and the distance of the shavings along the rib, have an impact on turbulence and heat transfer. An optimum was found for the number of starts regarding heat transfer. The heat transfer area increases for a higher number of starts, but the flow-related heat transfer decreases. Thus, an optimal arrangement of starts was identified for this pipe configuration. The variation of the arrangement showed that the pressure loss can be reduced by an inline configuration, whereby the heat transfer is only slightly decreased. It can be shown that the simulations can contribute to optimising complex structures in the future and thus accelerate the development process of new geometries. It can be shown that the development of new heat exchanger pipes is also possible with complex structures, this can be demonstrated here for the first time for structures that can actually be fabricated.

: A high-order discontinuous Galerkin solver for flow simulations and multi-physics applications

We present the latest developments of our High-Order Spectral Element Solver (▪), an open source high-order discontinuous Galerkin framework, capable of solving a variety of flow applications, including compressible flows (with or without shocks), incompressible flows, various RANS and LES turbulence models, particle dynamics, multiphase flows, and aeroacoustics. We provide an overview of the high-order spatial discretisation (including energy/entropy stable schemes) and anisotropic p-adaptation capabilities. The solver is parallelised using MPI and OpenMP showing good scalability for up to 1000 processors. Temporal discretisations include explicit, implicit, multigrid, and dual time-stepping schemes with efficient preconditioners. Additionally, we facilitate meshing and simulating complex geometries through a mesh-free immersed boundary technique. We detail the available documentation and the test cases included in the GitHub repository. Program summaryProgram Title:▪CPC Library link to program files:https://doi.org/10.17632/738py2shk4.1Developer's repository link:https://github.com/loganoz/horses3d.Licensing provisions: MITProgramming language: Fortran 2008External routines/libraries: METIS, MPI, HDF5, MKL, PETSc (all are optional).Nature of problem:▪ is a high-order discontinuous Galerkin framework, capable of solving a variety of flow applications, including compressible flows (with or without shocks), incompressible flows, various RANS and LES turbulence models, particle dynamics, multiphase flows, and aeroacoustics.Solution method: high-order discontinuous Galerkin Spectral Element (DGSEM) and explicit/implicit time-steppers.Additional comments including restrictions and unusual features:▪ is a multiphysics environment where the compressible Navier-Stokes equations, the incompressible Navier–Stokes equations, the Cahn–Hilliard equation and entropy–stable variants are solved. Arbitrary high–order, p–anisotropic discretisations are used, including static and dynamic p–adaptation methods (feature-based and truncation error-based). Explicit and implicit time-steppers for steady and time-marching solutions are available, including efficient multigrid and preconditioners. Numerical and analytical Jacobian computations with a colouring algorithm have been implemented. Multiphase flows are solved using a diffuse interface model: Navier–Stokes/Cahn–Hilliard. Turbulent models implemented include RANS: Spalart-Allmaras and LES: Smagorinsky, Wale, Vreman; including wall models. Immersed boundary methods can be used, to avoid creating body fitted meshes. Acoustic propagation can be computed using Ffowcs-Williams and Hawkings models. ▪ supports curvilinear, hexahedral, conforming meshes in GMSH, HDF5 and SpecMesh/HOHQMesh format. A hybrid CPU-based parallelisation strategy (shared and distributed memory) with OpenMP and MPI is followed.

Global attractor for the three-dimensional Bardina tropical climate model

We prove the existence of global solutions and of a global attractor for a regularized viscous 3D tropical climate model. The regularization is carried out by means of the Helmholtz filter, in the spirit of what is done for some families of LES-turbulence models, thus obtaining (as α-model) the 3D Bardina tropical climate model for which we consider the associated dynamics.

Numerical investigation of AdBlue film formation and NH3 conversion in generic SCR system using Eulerian stochastic fields method

In this paper, the Eulerian stochastic fields (ESF) method in a LES framework is applied to a generic selective catalytic reduction (SCR) configuration in order to retrieve seamlessly the effect of turbulence–chemistry interaction on the NH3-conversion and AdBlue film formation. The ESF method is based on the transport equation of a joint scalar filtered density function. The injection of AdBlue and relevant spray dynamics are modeled by the Lagrange-particle description where a computational parcel represents a cluster of real AdBlue droplets. Owing to the low injection pressure, weak atomization of AdBlue leads to intense droplet wall-impingement and film formation on the SCR duct wall and/or on the mixer elements, if present. A 2-D thin film approach is adopted to model the film formation and dynamics in combination with multi-regimes droplet–wall interaction model. After verification tasks against the reference data for simple gas phase reactive cases, the verified ESF method is coupled with a one-equation based LES turbulence model together with the Lagrange particle-tracking which is combined with the 2-D thin film approach to simulate the AdBlue injection and the film formation in the generic SCR configuration. At first, the assessment of the adopted LES mesh is carried out in terms of the so-called LES quality of index to determine the optimal mesh resolution. Next, to ensure the convergence with respect to the number of required ESF and mesh resolution, SCR simulations are performed by using various (2, 4, 6, 8, 12 and 16) stochastic fields and also with refined mesh. Thereby, the sensitivity of the predictive capability of the numerical tool is evaluated for the production of NH3 and HNCO with and without ESFs. This clearly indicates the importance of an accurate description of the turbulence–chemistry interaction to retrieve reliably the conversion of NH3. Finally, the film dynamics especially the evolution of the film thickness described with six required ESF and without ESF is compared with experimental data from the generic SCR configurations. To further demonstrate the potential of suggested numerical approach, a detailed numerical analysis is provided in terms of spray-impingement dynamics, scalar uniformity index, droplet life time and characteristics of the droplets prone to form solid deposits in the monolith channel.

Influence of Stern Rudder Type on Flow Noise of Underwater Vehicles

The stern rudder of an underwater vehicle has a significant impact on the wake field and the flow noise. Hence, it is important to optimize the design of the stern rudder for reducing the radiated noise. In this work, a numerical model is set up to predict the flow noise of the underwater vehicle, based on the LES turbulence model and FW-H acoustic analogy method. After the verification study, the numerical prediction of the flow noise is compared with the experimental measurements to verify the accuracy of the numerical model. Then, the influence of sails on the flow noise is explored. It is observed that the existence of the sail significantly increases the noise at the low frequency. Furthermore, to examine the influence of the stern rudder type, the sound pressure levels of underwater vehicles with three full appendages having cross-type rudders, X-type rudders, and T-type rudders, are compared. The strong interaction between the sail’s wake and the stern rudder is evident. The underwater vehicle with T-type rudders exhibits the lowest sound pressure. In addition, the influence of the stern rudder type on the directivity of sound pressure levels is also presented.

Evaluation of RANS-DEM and LES-DEM Methods in OpenFOAM for Simulation of Particle-Laden Turbulent Flows

CFD-DEM modelling of particle-laden turbulent flow is challenging in terms of the required and obtained CFD resolution, heavy DEM computations, and the limitations of the method. Here, we assess the efficiency of a particle-tracking solver in OpenFOAM with RANS-DEM and LES-DEM approaches under the unresolved CFD-DEM framework. Furthermore, we investigate aspects of the unresolved CFD-DEM method with regard to the coupling regime, particle boundary condition and turbulence modelling. Applying one-way and two-way coupling to our RANS-DEM simulations demonstrates that it is sufficient to include one-way coupling when the particle concentration is small (O ~ 10−5). Moreover, our study suggests an approach to estimate the particle boundary condition for cases when data is unavailable. In contrast to what has been previously reported for the adopted case, our RANS-DEM results demonstrate that simple dispersion models considerably underpredict particle dispersion and previously observed reasonable particle dispersion were due to an error in the numerical setup rather than the used dispersion model claiming to include turbulence effects on particle trajectories. LES-DEM may restrict extreme mesh refinement, and, under such scenarios, dynamic LES turbulence models seem to overcome the poor performance of static LES turbulence models. Sub-grade scale effects cannot be neglected when using coarse mesh resolution in LES-DEM and must be recovered with efficient modelling approaches to predict accurate particle dispersion.

Influence of standard $$k-\varepsilon$$, SST $$\kappa -\omega$$ and LES turbulence models on the numerical assessment of a suspension bridge deck aerodynamic behavior

Influence of standard $$k-\varepsilon$$, SST $$\kappa -\omega$$ and LES turbulence models on the numerical assessment of a suspension bridge deck aerodynamic behavior

Influence of Sill on the Hydraulic Regime in Sluice Gates: An Experimental and Numerical Analysis

This study investigates experimentally and numerically the effects of sills with different geometric specifications at various positions on the hydraulic characteristics of flow through sluice gates. The simulation results showed that the RNG turbulence model’s statistical indicators yield high accuracy compared to the k-ε, k-ω, and LES turbulence models. The discharge coefficient (Cd) has an inverse relationship with gate opening. Regarding sill state, the discharge coefficient is higher than no-sill state. In the case of non-suppressed sills, the Cd decreases compared to the smaller openings as the opening of the gate changes. The results showed that the Cd with a sill in the tangent position upstream of the gate is higher than the downstream tangent and below situations. Increasing the sill length leads to an increase in flow shear stress and consequently a decrease in Cd. The Cd of gates with different sill thicknesses is always higher than the no-sill state, but due to the constant ratio of the fluid depth above the sill to the gate opening, the Cd increases to a certain extent and then decreases with increasing sill thickness.

A comprehensive investigation of RANS and LES turbulence models for diesel spray modeling via experimental diesel schlieren imaging

Spray simulation is the basis of many engine simulations and directly impacts the quality of other simulations. Various models have been proposed to simulate spraying and the breakup and evaporation of fuel particles. The Kelvin–Helmholtz/Rayleigh–Taylor (KH-RT) model is one of the most common of these models. In this study, while analyzing the sensitivity of the KH-RT model constants on spray simulation, the effect of the LES and RANS turbulence model on spray penetration length and shape of the diesel spray contour is investigated. This study shows that both LES and RANS turbulence models along with the KH-RT model predict the spray penetration length with appropriate accuracy. While the RANS model, due to its averaging nature, does not accurately simulate the shape of the spray contour, which has very soft edges. Finally, the best method for simulating diesel spray and the proposed constants of the KH-RT model is presented.