Detached Eddy Simulation Approach Research Articles

A comprehensive assessment on detached eddy simulation and delayed detached eddy simulation approaches in large-scale rotating separated flow in a centrifugal impeller under small flow rate

This work performed a comprehensive comparative assessment on the capabilities and performances of detached-eddy simulation (DES) and delayed detached-eddy simulation (DDES) approaches in revealing the flow physics in a six-blade centrifugal impeller under a small flow rate. The numerical results are well validated by the experimental data of a similar configuration and are compared with the benchmark data generated by an additional large-eddy simulation investigation. The results are presented and analyzed in terms of the time-averaged flow field, the transient flow, and momentum transport characteristics. The capabilities of DES and DDES approaches in predicting the rotating turbulent flow are compared and assessed. The numerical results show that DES performs better in the pressure distribution, while DDES is superior in resolving the transient evolution of velocity field, especially the fluctuation quantities and turbulent statistical quantities. It is also emphasized that both approaches perform distinctly in quantifying the patterns of internal flow in different regions within the centrifugal impeller.

RANS-DES Comparison on the Numerical Modelling of a Downforce Generating Wing Moving over a Solid Surface

Present paper covers the numerical modelling of a 3D wing operating near a solid surface using Reynolds Averaged Navier Stokes (RANS) and Detached Eddy Simulation (DES). The characteristics of the flow over a wing near a surface is significantly different from the free flight. Capturing the changing aerodynamics of an object moving close to a surface have importance for flight and vehicle aerodynamics. This study aims to investigate the reliability of RANS and DES turbulence modelling approaches on the numerical solution of the challenging ground effect flow physics of the downforce generating (or inverted) wings. For this purpose, a 3D symmetrical wing moving in the close proximity of a solid surface is numerically modelled in fully turbulent flow conditions. The results show that, DES approach predicts the lift force slightly better than RANS. On the other hand, tip leakage flow capturing and the separating vortex field modelling of the DES approach is clearly superior. Comparison of velocity, vorticity and the vortex visualization results are presented for the better understanding of the performance of the two modelling approaches.

Horizontal Axis Wind Turbine Weather Vane Aerodynamic Characteristics: Delayed Detached Eddy Simulation and Experimental Approach

The known differential yaw error of horizontal axis wind turbines is clearly linked to weather vane fluctuations, arising out of the deflection of the onrushing wind flow from the rotating blades. Since the problem has not been resolved as the control systems still present this problem, it should be considered as an actual difficulty requiring deeper studies of the weather vane’s aerodynamic features, including the modeling of its deviations. This paper focuses on the computational fluid dynamics and experimental study of the aerodynamic characteristics of the weather vane located on the nacelle top of horizontal axis wind turbines. Computational fluid dynamics simulation is based on the k-ω Shear Stress Transport turbulence model and the Delayed Detached Eddy Simulation. The numerical simulation and laboratory experiment arrangements are demonstrated in detail. The new scientific results obtained during the research include the validation of the numerical experiment, demonstration of the differences in forming the wake structures for the used models on the studied angles of attack and comparison of the mean values of the moment and power spectral densities for all cases, which demonstrated a good correlation between the Delayed Detached Eddy Simulation data and the experiment. The time spent on the preparation of numerical experiments using different models was accurately estimated, to give an understanding of man-hour resources. The obtained moment values for the weather vane are applied for further mathematical modeling of the systems intended for the reduction in the differential yaw error. The applicability of the Delayed Detached Eddy Simulation approach was proved by the simulation of the aerodynamic characteristics of complexly streamlined bodies, but at the same time, it showed an extended calculation period. The results obtained during the study expand upon the experience of using numerical simulation when studying horizontal axis wind turbines and may be used to build mathematical models of yaw control systems.

Improved Delayed Detached Eddy Simulation of Combustion of Hydrogen Jets in a High-Speed Confined Hot Air Cross Flow

The paper deals with the self-ignition and combustion of hydrogen jets in a high-speed transverse flow of hot vitiated air in a duct. The Improved Delayed Detached Eddy Simulation (IDDES) approach based on the Shear Stress Transport (SST) model is used, which in this paper is applied to a turbulent reacting flow with finite rate chemical reactions. An original Adaptive Implicit Scheme for unsteady simulations of turbulent flows with combustion, which was successfully used in IDDES simulation, is described. The simulation results are compared with the experimental database obtained at the LAERTE experimental workbench of the ONERA—The French Aerospace Laboratory. Comparison of IDDES with experimental results shows a strong sensitivity of the simulation results to the surface roughness and temperature of the duct walls. The results of IDDES modeling are in good agreement with experimental pressure distributions along the wall and with the results of videoregistration of the excited radical chemiluminescence.

Performance of a vehicle-mounted anemometer under crosswind: Simulation and experiment

Abstract Environmental wind measurements are essential for ensuring the operational safety of rail vehicles. In our previous work, an anemometer that can be mounted on the top of a train to achieve real-time measurements of wind speed and direction was proposed based on the pressure distributions around the cylindrical anemometer. However, the flow field on the top of the train is significantly influenced by the train; thus, the measured data might differ from the actual environmental wind parameters, particularly when trains are subjected to windbreak walls. In this study, simulations considering flow fields around trains installed with the proposed anemometer were conducted, and an improved delayed detached eddy simulation approach was adopted. Through simulations, the flow field at the top of the train was analysed, and the aerodynamic characteristics of the anemometer were investigated. Accordingly, relationships between the measured wind characteristics and environmental wind characteristics are presented under various situations herein. Field experiments were performed for the proposed anemometer installed on a certain type of high-speed train along the Nanjiang Railway in China. The results obtained from both the numerical and experimental studies show that the proposed method has high accuracy for measuring environmental wind speed and direction when mounted on the top of a train.

Numerical investigation of 3D unsteady flow around a rotor of vertical axis wind turbine darrieus type H

This article presents an analysis of the complex and unsteady flow a ssociated with the functioning of the rotor of a vertical axis wind turbine Darrieus - H. In this study, the influence of different numerical aspects on the accuracy of the simulation of the flow around a rotor of three straight blades in rotation is performed, which are the effect of the turbulence modeling, and the effects of the mesh and the time step. The Delayed Detached Eddy Simulation (DDES) approach is used. The aim of this article is to describe and analyze the unsteady flow in 3D predicted numerically considering the effects of arms like blade-arms interference, blade-wake interactions around the Darrieus rotor and the effect of tip vortices. Two-dimensional simulations are used in a preliminary numerical configuration. Then, three-dimensional simulations a re performed t o p recisely determine the characteristics of the complex aerodynamic flow associated with the operation of the wind turbine rotor. The flow field around the rotor is studied for several values of the tip speed ratio, dynamic quantities, such as the torque and the power of the rotor that are presented and analyzed. From the results obtained, it is clear that the approach of the Detached Eddy Simulation with the SST K-ω model can be considered as a reliable prediction. A comparison of the performance of the results showed that the predicted coefficients of performance are very close to the experimental data from the bibliography.

Evaluation of Enhanced Gray Area Mitigation Approaches Based on Jet Aeroacoustics

An investigation of various eddy viscosity models for accurate scale-resolving simulation of aerodynamics and aeroacoustics of a turbulent jet is presented. The models are considered from the perspective of solving the so-called gray area problem. This problem is related to nonphysical delay in the transition from Reynolds-averaged Navier–Stokes (RANS) to large-eddy simulation (LES) in hybrid RANS–LES approaches such as detached eddy simulation (DES) when applied to shear-layer flows. The performance of recently developed dynamic adapting subgrid length scales (, , and ) and subgrid LES models ( and S3QR) separately and together is demonstrated. The object of the investigation is an immersed subsonic turbulent jet. The simulations are carried out on a set of refining meshes using two different scale-resolving numerical algorithms with basic and higher-accuracy schemes on unstructured meshes. The evaluation of various eddy-viscosity models within the DES approach is mostly focused on the analysis of far-field noise. The study has clearly demonstrated the importance of both a numerical scheme and a subgrid turbulence model. The results show that some of the considered techniques provide the necessary accuracy to predict the noise generated by a turbulent jet. The features of the considered approaches are identified and discussed. Recommendations are formulated for the choice of the LES model and subgrid length scale for this kind of problem.

The energy equation for modeling reacting flows on RANS, LES and DES approaches

Computational Fluid Dynamics (CFD), through high-performance computing and robust codes, has proven to be an invaluable tool for the simulation of combustion processes, ranging from low speeddiffusive flames up to detonations. This work intends to provide a review of details needed in modeling asReynolds-averaged Navier–Stokes (RANS), large eddy simulation (LES) or Detached eddy simulation (DES)energy equation in CFD codes used for solving chemically reacting turbulent flows. When the density is variable, traditional Reynolds averages introduce many open correlations between any quantity f and density fluctuations which are difficult to close. Therefore, Favre’s mass-weighted average technique must be preferred.

Numerical investigation of transonic buffet on a prescribed-pitching OAT15A airfoil

The transonic buffet over a prescribed-pitching OAT15A airfoil was numerically investigated using a well-validated delayed detached eddy simulation approach. The present approach successfully reproduced self-sustained shock wave oscillations. The computational results show that the amplitude of the lift fluctuations in the pitching case is approximately six times that of the fixed case. Compared to the fixed case, the presence of a larger shock motion region, two shock wave interactions, and severe boundary separation give rise to higher pressure and velocity fluctuation levels on the whole upper surface in the pitching case. In particular, the highly disordered flow replaces the periodic vortex shedding in the wake, resulting in the disappearance of the secondary fluctuation in unsteady lift coefficients, which is observed at 2274 Hz in the fixed case. A proper orthogonal decomposition analysis shows that the buffet flow in the fixed case exhibits the feature of regular motion, which is closely related to the coherent flow structure of shock oscillations and Karman vortices. Strong interactions between the Karman vortex structure and the shock oscillations are also observed. Compared to those in the fixed case, the fluctuation amplitudes of the coefficients of the first mode pair and the second to fourth mode pairs in the pitching case are 2.5 times and 5 times larger, respectively, and the energy ratio of the nonlinear component in the total mode energy is significantly increased. Furthermore, the main frequencies of modes 1–10 in the pitching case are all located at the shock buffet frequency or its higher-order harmonics.

Estimation of pollutant dispersion around a building within non-isothermal boundary-layer using detached eddy simulation

The paper presents the numerical results of modelling pollutant transport from a low source behind a bluff-body imitating a building within a non-isothermal boundary-layer. The main goal of the study is to estimate the tracer gas dispersion in a complex turbulent separated flow behind a building in the presence of interference of the atmospheric boundary-layer and local flows. In the first part of the study we compare numerical approaches URANS and IDDES for turbulent flow prediction on a configuration for which experimental data are available. It is shown that detached eddy simulation approach predicts correctly the main separated flow features and demonstrates a reliable correlation with the experimental data on mean velocity, pollutant concentration and temperature fields. In the second part of the study, the influence of unstable thermal stratified flow on the tracer gas transport around a building is analyzed using IDDES method. The unstable thermal flow regime considered in the study affects the distribution of the pollutant concentration in the re-circulation zone behind the building. The presence of additional buoyancy effects leads to an increase in the gas concentration on the leeward wall of the body and gas transport from a ground region to a height greater than in the case with the neutral boundary-layer.

Flow Field and Heat Transfer of an Impinging Synthetic Jet in the Presence of Cross-Flow: Application of SAS and DES Approaches

Nowadays, synthetic jets have various applications such as cooling enhancement and active flow control. In the present paper, the capability of two turbulence modelling approaches in predicting thermal performance of an impinging synthetic jet is investigated. These two approaches are scale adaptive simulation (SAS) and detached eddy simulation (DES). Comparisons between numerical data and experimental studies reveal that the ability of DES in predicting the asymmetrical trend of heat transfer profiles is better than SAS in almost all the study cases. Although, near the stagnation zone, the performance of SAS is superior. Results show that the effects of parameters such as frequency, cross-flow velocity and suction duty cycle factor are well predicted by both approaches. An increase of cross-flow velocity from 1.81 m/s to 2.26 m/s results in an improvement of [Formula: see text] near the stagnation point by almost 16.3% and 9.2% using DES and SAS, respectively.

Delayed detached eddy simulation method for breaking bow waves of a surface combatant model with different trim angle

Sailing attitudes vary with different loading conditions for ships sailing in open sea, and the trim angle, either by bow or by stern, exerts considerable impact on the flow field around the ship. Currently, attention has primarily been focused on hull resistance and wave patterns while few studies have touched upon breaking bow wave under different trim conditions. This study aims to analyze the breaking bow wave of a surface combatant model with a length of 5.72 m DTMB (name of a surface combatant model) under different sailing attitudes at Fr = 0.35. The Delayed Detached Eddy Simulation (DDES) approach was adopted to study the breaking bow wave features such as plunging jet and air entrainment. The interface-compression algebraic Volume Of Fluid (VOF) method in OpenFOAM was used to capture the free surface. The Computational Fluid Dynamics (CFD) approach was firstly validated by comparing hull resistance and wave contour with the available experimental data. The study then delves into the influence of trim angles on breaking bow waves through simulations of the different conditions, i.e., 1 deg trim by bow, test condition and 1 deg trim by stern. The wave contour, breaking wave profile, vorticity field and the wake field at several transverse sections are then compared in three trim conditions, followed by an analysis of the initial evolution of bow wave breaking based on the turbulent kinetic energy and the vorticity field at four cross sections. The results suggest that trim by bow makes free surface sharper and wave amplitude larger in the breaking bow wave region. The reason is that trim by bow enlarges the attack angle of the bow, thus energizing the bow wave and generating a more violent free surface of bow wave breaking.

Influence of roughness on propeller performance with a view to mitigating tip vortex cavitation

This study explored the effects of uniformly and non-uniformly distributed biofouling roughness on hydrodynamic performance, particularly on the tip vortex cavitation (TVC) for model and full-scale marine propellers. The effect of roughness was investigated on a benchmark propeller belongs to the research catamaran, ‘The Princess Royal’. The investigation also explored the potential use of the roughness effect to mitigate this propeller's tip vortex cavitation with uniform, inclined and non-uniform flow conditions. In the numerical calculations, DES (Detached Eddy Simulation) approach was used to simulate the cavitating flow around the propeller. The Schneer-Sauer cavitation model was used to model the sheet and tip vortex cavitation. An advanced meshing technique called V-AMR (Vorticity-based Adaptive Mesh Refinement) was proposed to model the TVC in the propeller slipstream. The modified wall-function approach was utilised to implement the roughness effects in the calculations using the experimentally obtained roughness functions based on one of the authors' recent study. The results showed that the velocity components decreased inside the tip vortex due to roughness, resulting in a pressure increase and TVC mitigation. The suction side of the propeller blade tips was found to be an effective roughness application area for the TVC mitigation with a moderate level of loss in the propeller efficiency. The findings indicated that the cavitation volume reduction, mainly due to the TVC mitigation, was by approximately 6–38%, with a 5–10% efficiency loss in the model scale, while these figures were 4–10% and 2–5%, respectively, for the full-scale propeller under the uniform and non-uniform flow conditions.

The Influence of Front Wing Pressure Distribution on Wheel Wake Aerodynamics of a F1 Car

The present study focuses on investigating the aerodynamic interaction between a three-element wing and wheel in ground effect, following the Formula One regulation change set for 2022, among which is the simplification of the front wing. This was accomplished by conducting a three-dimensional computational fluid dynamics analysis, using a Detached-Eddy Simulation approach, on a simplified one-quarter model of a Formula One racing car. The main goal was to examine how changing the front wing pressure distribution, by changing the incidence of the second flap, affected the wheel wake. The flow investigation indicated that the wheel wake is influenced by the flap configuration, which is mainly due to the fact that different flap configurations produce different upwash flow fields, leading to a variation of the separation point on top of the tire. As the separation point moves rearwards, the downwash generated in the central region (for a vertical plane) of the wheel wake increases incrementally, leading to a resultant wake that is shorter and further apart. The force investigation showed that the proximity between the region of instability (i.e., vortex breakdown) and the wing’s trailing edge influences the behavior of the transient oscillations, regarding the forces acting on the wing: detecting higher drag force fluctuations, when compared to downforce fluctuations.

On the coupling of wall-model immersed boundary conditions and curvilinear body-fitted grids for the simulation of complex geometries

One of the main limitations in computational aerodynamics lies in the ability of CFD solvers to handle complex geometries while maintaining their accuracy. Among the currently available strategies, the Zonal Immersed Boundary Conditions (ZIBC) has shown its capability to introduce complex geometrical details for the simulations of high Reynolds turbulent flows. In this context, this work aims to extend the ZIBC framework, initially adapted to reproduce blockage effects, to take into account configurations where the influence of spatially developing boundary layers has to be accurately predicted. For this purpose, a compact sharp interface immersed boundary method has been developed for curvilinear grids. Moreover, a Thin Boundary Layer Equations (TBLE) wall model based on one-dimensional RANS Spalart-Allmaras equations is coupled with the IBC to model the inner part of compressible turbulent boundary layers. The coupling with the Zonal Detached Eddy Simulation (ZDES) approach is improved and permits to simulate turbulent flows capturing accurately the wall-normal gradients with a limited grid resolution. This strategy is applied to the simulation of a generic missile configuration (FG5) with an angle of attack of 10∘ using RANS and ZDES approaches. For the first time, wall quantities such as unsteady loads, including the viscous contribution, are accuratly reproduced on surfaces modelled with IBC using hybrid RANS/LES (ZDES) computations and for a realistic configuration at high Reynolds number. Such a reconstruction of physical quantities at the wall is achieved thanks to a precise reconstruction procedure using a TBLE wall model.

Numerical study of supercavitating flow around high-speed underwater projectile near different seabed obstacles

In this paper, several shape obstacle models are built to observe the characteristics of the cavity around the axisymmetric projectile near different obstacles. Numerical simulations using a detached eddy simulation approach, the Schnerr–Sauer cavitation model, and the olume of fluid method are performed to present details and mechanisms at different distances between the projectile and obstacles (0.5 ≤ h/D ≤ 4). The shape and length of the supercavity are in good agreement with the experimental observation, which guarantees the accuracy of the numerical methods. The study shows that the cavity around the projectile is primarily affected by three key factors: the size and slope of the obstacle and the distance between the projectile and obstacles. At the same distance, the larger the size of the obstacle, the greater the impact on the cavity. At the projectile arrival stage, the smaller the slope of the obstacle edge, the lesser the damage it will cause to the cavity. However, at the projectile leaving stage, the small slope will hinder the regeneration of the cavity. As the distance increases, the impact of obstacles on cavitation gradually decreases.

A numerical study of aerodynamic characteristics of a high-speed train with different rail models under crosswind

The CFD (Computational Fluid Dynamics) numerical simulation method with the DES (detached eddy simulation) approach was adopted in this paper to investigate and compare the aerodynamic performance, pressure distributions of the train surface, and flow fields near the train model placed above the subgrade with non-rail, realistic rail, and simplified rail models under crosswind. The numerical methods were verified with the wind tunnel tests. Significant differences in aerodynamic performances of the train body and bogie were found in the cases with and without a rail model as the presence of the rail model had significant impacts on the flow field underneath the vehicle. A larger yaw angle can result in a more significant difference in aerodynamic coefficients. The deviations of the train aerodynamic forces and the pressure distribution on the train body with the realistic and simplified rail models were not significant. It was concluded that a rail model is necessary to get more realistic results, especially for large yaw angle conditions. Moreover, a simplified rectangular rail model is suggested to be employed instead of the realistic rail and is capable to get accurate results.

Effect of different typical high speed train pantograph recess configurations on aerodynamic noise

For high-speed trains, the aerodynamic noise becomes an essential consideration in the train design. The pantograph and pantograph recess are recognised as important sources of aerodynamic noise. This paper studies the flow characteristics and noise contributions of three typical high-speed train roof configurations, namely a cavity, a ramped cavity and a flat roof with side insulation plates. The Improved Delayed Detached-Eddy Simulation approach is used for the flow calculations and the Ffowcs Williams & Hawkings aeroacoustic analogy is used for far-field acoustic predictions. Simulations are presented for a simplified train body at 1/10 scale and 300 km/h with these three roof configurations. In each case, two simplified pantographs (one retracted and one raised) are located on the roof. Analysis of the flow fields obtained from numerical simulations clearly shows the influence of the train roof configuration on the flow behaviour, including flow separations, reattachment and vortex shedding, which are potential noise sources. A highly unsteady flow occurs downstream when the train roof has a cavity or ramped cavity due to flow separation at the cavity trailing edge, while vortical flow is generated by the side insulation plates. For the ramped cavity configuration, moderately large pressure fluctuations appear on the cavity outside walls in the upstream region due to unsteady flow from the upstream edge of the plate. The raised pantograph, roof cavity, and ramped cavity are identified as the dominant noise sources. When the retracted pantograph is located in the ramped roof cavity, its noise contribution is less important. Furthermore, the insulation plates also generate tonal components in the noise spectra. Of the three configurations considered, the roof cavity configuration radiates the least noise at the side receiver in terms of A-weighted level.

Towards DES/DDES computation of the flow field and heat transfer adopting elliptic relaxation and local correlation based transition approaches

As Large–Eddy Simulation (LES) shall remain too expensive in the following few decades for the ever increasing number of engineering complexities, researches have shifted much of the attention and effort to hybrid formulations incorporating Reynolds–Averaged Navier– Stokes (RANS) equations and LES in a certain ways. The long term goal of this research activity is to develop accurate hybrid RANS/LES methods. These approaches are particularly appealing in massively separated flows since they offer good prediction performance and they can be considered a good trade–off, in terms of computational resources, if compared with standard LES techniques. In particular with this work we want to deeply investigate Detached–Eddy Simulation (DES) based on: (i) elliptic relaxation turbulence model; (ii) Spalart Allmaras local correlation based transition model (LCTM). Specifically, we analyze v2–f DES approach for the convective heat transfer around a sphere at Re = 5000 (with Pr = 0.71) and we compare these results with the so called delayed version of the model. At the same time we also investigate the LCTM version of the SA model, in the DES context.

A study of fan-distortion interaction within the fan rotor

Boundary-layer-ingesting fans and compressors in the next-generation turbofan engines require high-performance operations under distorted inflow. The aim of this work is to study the effects of inlet distortions including inlet stagnation pressure and temperature distortion, on the aerodynamic performance of a transonic axial fan. Firstly, the validated full-annulus, unsteady, three-dimensional computational fluid dynamic code in conjunction with detached Eddy simulation approach is used here to simulate the fan flows assembly with individual inlet stagnation pressure/temperature distortion. Then, the propagation process of the inlet distortion waves is analyzed to understand how the aerodynamic performance degradation is triggered. The simulation results show that the fan performance is remarkably degraded when the inlet distortion is introduced. The leading-edge spillage, the trailing edge back flow and the “tornado vortex” occur when parts of fan blades encounter the incoming distorted flows. Finally, the responses of fan to the combined inlet stagnation distortion effects are discussed in this paper. It is found that the combined distortion effects can be predicted based on the sum of the performance responses to the individual constituent distortions. Furthermore, the relative location of the constituent distortions shows a non-ignorable influence on the overall fan performance, especially for the intensified inlet distortion.