Scale Adaptive Simulation Turbulence Model Research Articles

Influence of Door Gap on Aeroacoustics and Structural Response of a Cavity

Numerical aeroacoustic analysis using the Shear Stress Transport–Scale Adaptive Simulation turbulence model was conducted on a weapon bay model based on the M219 geometry with doors incorporating radar cross-section reduction features. The effect of the introduction of a gap between the doors and the cavity edge on the aeroacoustic and structural response of the cavity was analyzed at Mach 0.85. The effect of introducing 3 deg of sideslip was also investigated. Both mean and unsteady flow analyses were conducted. The results showed a strong palliative effect of the door gap with and without sideslips. The overall analysis of the spectral signature on the forces and moments acting on the doors indicated the possibility of fluid–acoustic coupling, as all acoustic spectra showed a predominant tone located at the same frequency of the first structural mode.

Influence of cavitation on energy loss in a side channel pump at different flow rates

Side channel pumps are extremely prone to cavitation, and the internal exchange flow between the impeller and the side channel induces numerous vortical structures that causes significant energy loss. Therefore, it is important to investigate the cavitation characteristics and flow loss in side channel pumps under cavitating conditions. This paper investigates the cavitating flow in a side channel pump using the scale-adaptive simulation turbulence model coupled with the Zwart cavitation model. The development of cavitation in the side channel pump is divided into three stages according to the critical net positive suction head and turning net positive suction head. Stages I, II, and III correspond to the inception of cavitation, development of cavitation, and severe cavitation, respectively. The vortex energy is adopted to analyze the variations in vortices with respect to the available net positive suction head. Entropy production considering viscous dissipation, turbulent dissipation, and the wall effect is used to calculate the irreversible energy loss. However, the energy loss caused by the rotation of vortices cannot be calculated by this method, resulting in large discrepancies between the entropy production and the hydraulic loss calculated by the pressure drop method. The entropy production generated by turbulent dissipation (S2) is found to be dominant in the side channel pump and increases with decreasing flow rate. S2 exhibits different variation trends with respect to the available net positive suction head at different flow rates under severe cavitation. S2 also dominates in the impeller, but the entropy production terms exhibit slight discrepancies in the side channel. The distribution of local entropy production rate further reveals the complicated interaction mechanism between cavitation and entropy production.

Comparative evaluation of DES and SAS turbulence models for incompressible flow in a Venturi tube

Computational fluid dynamics employs the Large Eddy Simulation (LES) and Reynolds-averaged Navier-Stokes (RANS) models and combines both models to perform a hybrid RANS/LES simulation of the transient state flow field, within which there are the Detached Eddy Simulation (DES) and Scale-Adaptive Simulation (SAS) models. In the present work, the objective is to evaluate the DES and SAS turbulence models for flow (water) in a Venturi tube, for 2D computational domains. The domain was discretized for grids with quadrilateral cells, and the flow field was studied for four flow rates. The results of the pressure flow field simulations for the DES and SAS models were compared with experimental data reported in the literature, which fit the experiments. However, the DES k-ε model presented a negative pressure drop for a region of the flow adjacent to the wall, at the entrance of the throat section, the other models DES S-A, DES SST k-ω and SAS presented positive pressures. The discharge coefficients yielded values in the range of 0.94-0.951, which were lower than the experiments, for errors in the range of 1.57-2.76%.

Numerical study of flow behavior in a cavitation tunnel using RANS with Scale-Adaptive Simulation (SAS) turbulence model in an OpenFOAM framework

The present paper focuses on the study of flow through a cavitation Venturi tunnel. Motivated by the results obtained in the studies of “Simultaneous observation of cavitation structures and cavitation erosion” and “Combined numerical and experimental investigation of the cavitation erosion process” by Dular et al. A structured mesh based on previous studies has been generated using the free software GMSH. The numerical study was performed using the Navier-Stokes equations with RANS approximation. For that, the k − ω − SST SAS turbulence model and the implemented Zwart-Gerber-Belamri have been applied in OpenFOAM. The results show that the phenomena in a vapor volume fraction where the formation, growth, detachment and collapse of the cavitation cloud can be appreciated. These results agree with the aforementioned studies. Furthermore, the results show the peak pressure formation corresponding to the detachment and collapse of the cloud during the cavitation cycle, which is the main reason for erosion. It is concluded that the model satisfactorily predicts the phenomena behavior on a Δt = 9 × 10−6[s] being suitable to capture adverse pressure gradients.

Model evaluation and experimental validation of thermal jet drilling for geothermal energy

Thermal jet drilling is a technology, which has the potential to be suitable for the exploitation of geothermal energy in relatively deep formations with low costs. Several investigations on this drilling method have been carried out for the depths of less than 1 km or deeper than 2 km. To the best of our knowledge, there is almost no specific study on simulation for thermal jet drilling at the depths between 1 km and 2 km. This paper focuses on investigating applications of different reaction (i.e., laminar, non-premixed, eddy dissipation concept, eddy dissipation model and finite rate), turbulence (i.e., standard k-epsilon, realizable k-epsilon, renormalization group k-epsilon and scale-adaptive simulation) and radiation (i.e., P1, discrete ordinate, discrete transfer radiation model and surface-to-surface) models to downhole reaction of thermal jet drilling. The objective is to identify the pros and cons of each model and determine a set of models that are the most appropriate for the reaction. Experiments are also carried out and data are collected as the benchmark for comparison. Relative errors and iteration for convergence are analyzed for each simulation model. Results show that the modified simulation temperature by considering the environmental temperature becomes more accurate compared with the experimental data. The laminar model over-predicts the temperature and yields unreasonable results. Finite rate and eddy dissipation model are the candidates with highest accuracy and acceptable computational time within selected model settings and boundary conditions. In addition, compared with renormalization group, realizable and scale-adaptive simulation turbulence models, the standard k-epsilon model is the most appropriate model under the conditions selected for this investigation. The discrete ordinate model can be applicable for the simulation if the error tolerance is 10%. The P1 model is the most suitable radiation model. Results in this paper can provide implications for the reaction simulation of thermal jet drilling.

Reynolds-Averaged, Scale-Adaptive and Large-Eddy Simulations of Premixed Bluff-Body Combustion Using the Eddy Dissipation Concept

A lean premixed propane/air bluff-body stabilized flame (Volvo test rig) is calculated using the Scale-Adaptive Simulation turbulence model (SAS) and Large-Eddy simulations (LES) as well as the conventional Reynolds-averaged approach (RAS). RAS and SAS are closed by the standard k-𝜖 and the k-ω Shear Stress Transport (SST) turbulence models, respectively. The conventional Smagorinsky and the k-equation sub-grid scales models are used for the LES closure. Effects of the sub-grid scalar flux modeling using the classical gradient hypothesis and Clark’s tensor diffusivity closures both for the inert and reactive LES flows are discussed. The Eddy Dissipation Concept (EDC) is used for the turbulence-chemistry interaction. It assumes that molecular mixing and the subsequent combustion occur in the ’fine structures’ (smaller dissipative eddies, which are close to the Kolmogorov scales). Assuming the full turbulence energy cascade, the characteristic length and velocity scales of the ’fine structures’ are evaluated using different turbulence models (RAS, SAS and LES). The finite-rate chemical kinetics is taken into account by treating the ’fine structures’ as constant pressure and adiabatic homogeneous reactors, calculated as a system of ordinary-differential equations (ODEs) described by a Perfectly Stirred Reactor (PSR) concept. Several further enhancements to model the PSRs are proposed, including a new Livermore Solver (LSODA) for integrating stiff ODEs and a new correction to calculate the PSR time scales. All models have been implemented as a stand-alone application $\text {edcPisoFoam}$ based on the OpenFOAM technology. Additionally, several RAS calculations were performed using the Turbulence Flame Speed Closure model in Ansys Fluent to assess effects of the heat losses by modeling the conjugate heat transfer between the bluff-body and the reactive flow. Effects of the turbulence Schmidt number on RAS results are discussed as well. Numerical results are compared with available experimental data. Reasonable consistency between experimental data and numerical results provided by RAS, SAS and LES is observed. In general, there is satisfactory agreement between present LES-EDC simulations, numerical results by other authors and measurements without any major modification to the EDC closure constants, which gives a quite reasonable indication on the adequacy and accuracy of the method and its further application for turbulent premixed combustion simulations.

Application of the aeroacoustic analogy to a shrouded, subsonic, radial fan

A study was conducted to investigate the predictive capability of computational aeroacoustics with respect to a shrouded, subsonic, radial fan. A three dimensional unsteady fluid dynamics simulation was conducted to produce aerodynamic data used as the acoustic source for an aeroacoustics simulation. Two acoustic models were developed: one modeling the forces on the rotating fan blades as a set of rotating dipoles located at the center of mass of each fan blade and one modeling the forces on the stationary fan shroud as a field of distributed stationary dipoles. Predicted acoustic response was compared to experimental data measured at two operating speeds using three different outlet restrictions. The blade source model predicted overall far field sound power levels within 5dB averaged over the six different operating conditions while the shroud model predicted overall far field sound power levels within 7dB averaged over the same conditions. Doubling the density of the computational fluids mesh and using a scale adaptive simulation turbulence model increased broadband noise accuracy. However, computation time doubled and the accuracy of the overall sound power level prediction improved by only 1dB.

Scale adaptive simulation of bubble column flows

Numerical investigations using scale adaptive simulation (SAS) in 3D transient Euler–Euler framework for bubble columns have been carried out and all the simulation results are compared with available experimental data. The performance of SAS model was also compared with re-normalization group (RNG), large eddy simulation (LES) and k-ε models. Numerical results are in good agreement with experiments in predicting time averaged turbulent kinetic energy and axial velocity profiles. The superior flow predicting ability of SAS model is highlighted and it has shown that SAS turbulence model can capture large scale turbulence behavior and can be used efficiently for simulating flow field and turbulent quantities in case of bubble column flows.

The effect of arrangement of two circular cylinders on the maximum efficiency of Vortex-Induced Vibration power using a Scale-Adaptive Simulation model

The complex behaviour of an unsteady flow around two circular cylinders in tandem is of interest for many civil engineering applications across a wide range of aerospace, mechanical and marine applications. The present paper analyses Vortex-Induced Vibration (VIV) for the flow around two circular cylinders. It has been shown that the amount of kinetic energy which can be captured by VIV is a function of the arrangement of the two cylinders. The upstream cylinder is fixed while the downstream is mounted elastically with one degree of freedom normal to the mean flow direction. The efficiency of the VIV power obtained from downstream cylinder is compared for different arrangement of the cylinders. For this purpose, the longitudinal and lateral distances between the cylinders were varied and the Reynolds number was kept constant. Scale-Adaptive Simulation (SAS) and Shear Stress Transport (SST) CFD models are utilized to analyse the validity of the SAS turbulence model. The results indicate that both turbulence models predict the flow characteristics around the cylinders with reasonable precision; however, the predictions from SAS were more accurate compared to the SST. Based on this comparison, SAS model was chosen as a tool to analyse the VIV response of the downstream cylinder. The location of the downstream cylinder has been altered in the wake of upstream one in order to obtain the optimum efficiency of the VIV power. The results reveal that the arrangement of the cylinders can significantly change the efficiency. It is also observed that cylinders offset from one another show a higher efficiency compared to cylinders with their centres aligned.

A comparative study between combustion performances of turbine inter-guide-vane burner and trapped vortex combustor

To improve the performance of aero gas turbine engines, more and more interests have been shown on turbine inter-guide-vane burner based on the ultra-compact combustion concept. To make a universal turbine inter-guide-vane burner, a new concept is proposed using a trapped vortex cavity to replace the high swirling circumferential cavity combustor to address the need to scale the configuration for a larger turbine spool. Three models, including trapped vortex combustor, transition model, and turbine inter-guide-vane burner, are designed. Comparative analysis between combustion performances of three models by using numerical simulation method is carried out. The scale-adaptive simulation turbulence model is used in the simulation process, aiming to reduce the deviation between numerical simulation value and actual value. Finally, the turbine inter-guide-vane burner model is found to be the superior design proposal for turbine inter-guide-vane combustion technology, compared with the other two models.

Choice of a turbulence model for pump intakes

This article is focused on the choice of a suitable turbulence model for simulations of an industrial pump's intake, from the perspective of accuracy and, partially, also the CPU time. Twelve steady-state and transient simulations were made on a fine computational mesh, using turbulence models such as: the shear stress transport (SST), the scale-adaptive simulation (SAS), the Reynolds stress model, the explicit algebraic Reynolds-stress model, the detached eddy simulation and the large eddy simulation (LES). The curvature-correction (CC) option was assessed for the SST and SAS turbulence models. The results were compared with the LES and with published experimental results. Although all the models could predict the main floor vortex, there were still some substantial differences. It can be able to conclude that it is better to use either the SST-CC turbulence model, due to its low-computational resources and far better results than the SST model, or the SAS-CC turbulence model, since its predictions are quite similar to the LES results. In the final step, good agreement with experimental results was shown for a longer simulation with the SAS-CC turbulence model.

Numerical simulation of flow‐induced noise using LES/SAS and Lighthill's acoustic analogy

AbstractWe present a finite element (FE) formulation of Lighthill's acoustic analogy for the hybrid computation of noise generated by turbulent flows. In the present approach, the flow field is computed using large eddy simulation and scale adaptive simulation turbulence models. The acoustic propagation is obtained by solving the variational formulation of Lighthill's acoustic analogy with the FE method. In order to preserve the acoustic energy, we compute the inhomogeneous part of Lighthill's wave equation by applying the FE formulation on the fine flow grid. The resulting acoustic nodal loads are then conservatively interpolated to the coarser acoustic grid. Subsequently, the radiated acoustic field can be solved in both time and frequency domains. In the latter case, an enhanced perfectly matched layer technique is employed, allowing one to truncate the computational domain in the acoustic near field, without compromising the numerical solution. Our hybrid approach is validated by comparing the numerical results of the acoustic field induced by a corotating vortex pair with the corresponding analytical solution. To demonstrate the applicability of our scheme, we present full 3D numerical results for the computed acoustic field generated by the turbulent flow around square cylinder geometries. The sound pressure levels obtained compare well with measured values. Copyright © 2009 John Wiley & Sons, Ltd.

The Scale-Adaptive Simulation Method for Unsteady Turbulent Flow Predictions. Part 2: Application to Complex Flows

The paper summarises the validation activity performed with the Scale-Adaptive Simulation turbulence model (SAS model) using the two commercial CFD solvers, ANSYS-FLUENT and ANSYS-CFX. Both the KSKL-SAS and the SST-SAS model variants have been tested, although most cases have been computed with the second. The turbulence-resolving capability of the SAS method has been validated with a representative set of test cases, covering both underlying generic flows as well as practical engineering applications. In addition to the purely aerodynamic flows with massive separation and heat transfer they include also such physical phenomena as turbulent combustion and aeroacoustics. The illustrating results show the potentials of the SAS approach for industrial flow simulations. Most of the test case simulations were conducted during the recent EU project “DESider”.

Application of the SAS turbulence model to predict the unsteady flow field behaviour in a forward centrifugal fan

In the current study, the unsteady flow in a centrifugal fan is carried out using Computational Fluid Dynamics calculation based on the Scale Adaptive Simulation (SAS) approach to model the turbulence phenomenon. The SAS concept is based on the introduction of the von Karman length scale into the turbulence scale equation. The information provided by the von Karman length scale allows SAS models to dynamically adjust to resolved structures in an Unsteady Reynolds-Averaged Navier–Stokes (URANS) simulation, which results in a Large Eddy Simulation-like behaviour in unsteady regions of the flow field. At the same time, the model provides standard RANS capabilities in stable flow regions. The introduction of the von Karman length scale is based on the reformulation of Rottas's equation for the integral length scale. To validate the numerical results, the overall performances of the fan and the wall pressure fluctuations computed upon the volute casing surface are compared with the unsteady measured data.