Investigation of flow structures in a turbulent separating flow using hybrid RANS-LES model

Kumar, Ghanendra; De, Ashoke; Gopalan, Harish

doi:10.1108/hff-03-2016-0134

Cited by 18 publications

(9 citation statements)

References 38 publications

(70 reference statements)

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“…The airflow around the model can be regarded as the 3D incompressible viscous isothermal flow. In consideration of its accuracy in studies (Ahoward and Pourquie, 2002;Kumar et al, 2017;Garcia et al, 2017), the LES model is introduced. Filtered Navier-Stokes' equations are shown as follows:…”

Section: Governing Equations and Discretizationmentioning

confidence: 99%

Research on transient aerodynamic characteristics of windshield wipers of vehicles

Chen

Gu²,

Jiang

2019

HFF

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Purpose The main purpose of this paper is to gain a better understanding of the transient aerodynamic characteristics of moving windshield wipers. In addition, this paper also strives to illustrate and clarify how the wiper motion impacts the airflow structure; the aerodynamic interaction of two wipers is also discussed. Design/methodology/approach A standard vehicle model proposed by the Motor Industry Research Association and a pair of simplified bone wipers are introduced, and a dynamic mesh technique and user-defined functions are used to achieve the wiper motion. Finite volume methods and large eddy simulation (LES) are used to simulate the transient airflow field. The simulation results are validated through the wind tunnel test. Findings The results obtained from the study are presented graphically, and pressure, velocity distributions, airflow structures, aerodynamic drag and lift force are shown. Significant influences of wiper motion on airflow structures are achieved. The maximum value of aerodynamic lift and drag force exists when wipers are rotating and there is a certain change rule. The aerodynamic lift and drag force when wipers are rotating downward is greater than when wipers are rotating upward, and the force when rotating upward is greater than that when steady. The aerodynamic lift and drag forces of the driver-side wiper is greater than those of the passenger-side wiper. Originality/value The LES method in combination with dynamic mesh technique to study the transient aerodynamic characteristics of windshield wipers is relatively new.

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Section: Governing Equations and Discretizationmentioning

confidence: 99%

Research on transient aerodynamic characteristics of windshield wipers of vehicles

Chen

Gu²,

Jiang

2019

HFF

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“…( 14). This non-linear correction to SST model is adopted from Abe et al [22] and more details on the exact expression used in this study can be found in Kumar et al [23,24].…”

Section: Non-linear Shear Stress Transport Model (Nsst)mentioning

confidence: 99%

Prediction of separation induced transition on thick airfoil using non-linear URANS based turbulence model

Mishra

Kumar

2019

J Mech Sci Technol

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Most of the turbulence models in practice are based on the assumption of a linear relation between Reynolds stresses and mean flow strain rates which generally provides a good approximation in case of attached and fully turbulent flows. However, this is seldom the need in most of the engineering problems; the majority of the engineering problems observe flow separation or flow transition. Recent developments in non-linear turbulence models have proven significant improvement in prediction of separated flow due to better resolution of anisotropy in modeled Reynolds stress. The domain of application of this improved RANS model can be extended to flow transitions as well, where the resolution of anisotropy in Reynolds stress is required. For a validation of such kind, a two-dimensional numerical study has been carried out over NACA 0021 with k- SST model with non-linear correction at Re = 120,000 for various angles of attack which experiences the formation of a Laminar Separation Bubble (LSB). A correct prediction of LSB requires an accurate resolution of anisotropy in Reynolds stresses. For comparison with other linear models, the simulations are also performed with k-kl- (a 3equation linear transition model), k- SST (a 2-equation linear model) and Spalart-Allmaras (a 1-equation model). The performance of these models is assessed through aerodynamic lift, drag, pressure and friction coefficients. It is found that the non-linear k- SST and kkl- transition model provide comparable quality of prediction in lift and drag coefficients (in spite of the fact that non-linear k- SST involves solving less number of transport equation than the transition model) as observed in the experiments whereas k- SST and SA models under predict the drag coefficient value at low angle of attack due to inability to capture the separation induced transition. It is also observed that the location of laminar separation bubble is captured accurately when non-linear or transition model is used as opposed to the SA or linear SST models, which lack in the ability to predict the same.

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“…where ' ̅ 'denotes averaging over time. Further details regarding the computation of POD modes and reconstruction can be found in the published literature [18][19][20][21][22] .…”

Section: B Proper Orthogonal Decompositionmentioning

confidence: 99%

Investigation of mixing characteristics in strut injectors using modal decomposition

Soni

2018

Physics of Fluids

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Effect of large-scale vortical structure on mixing and spreading of shear layer is numerically investigated. Two strut configurations namely Straight & Tapered strut at two convective Mach numbers (Mc = 1.4 & 0.37) for two jet heights (0.6 & 1mm) are investigated. Hydrogen jet is injected through a two-dimensional slot in oncoming coflow at Mach 2. Excellent agreement between simulated and experimental data is witnessed, whereas the instantaneous data reveal the presence of various large-scale structures in the flow field. From the instantaneous field, it becomes apparent that both the geometries have different vortical breakdown locations. It is also noticed that an early onset of vortex breakdown manifests itself into the mixing layer thickness enhancement, effect of which is reflected in overall mixing characteristics. It becomes evident that the shear strength plays an important role in the near field mixing. The higher shear strength promotes the generation of large vortices. The analysis shows that SS-0.6 case offers highest mixing efficiency being dominated by relatively large-scale structures. Eigenmodes obtained through Proper Orthogonal Decomposition (POD) confirm the presence of dominating structures and shed light into the series of events involved in vortex pairing/merging and breakdown. Dynamic modal decomposition (DMD) also strengthens the observation made through the POD. I. INTRODUCTIONThe very notion of atmospheric flight at hypervelocity regime may appear fascinating and appealing but there are certain intrinsic challenges that need to be addressed. The concept of Scramjet was conceived as an air-breathing propulsion system, which is capable of propelling in high Mach number regime. But before the concept is realized certain questions need to be answered related to the design and technological issues. Although the proposed design may appear simple but achieving a stable and sustainable combustion efficiently at these speeds is an engineering marvel. The recent interest in Scramjet has promoted research towards the understanding of supersonic mixing phenomenon. The residence time being exceptionally short and need for efficient combustor has motivated research community to explore the underlying physics governing the mixing in these flow regimes.Various injector configurations have been explored and studied, most popular being normal, oblique and parallel each of them is having their own pros and cons, while the detailed discussion can be found in [1][2][3] . Due to the simplicity of the ____________________________

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Investigation of flow structures in a turbulent separating flow using hybrid RANS-LES model

Cited by 18 publications

References 38 publications

Research on transient aerodynamic characteristics of windshield wipers of vehicles

Research on transient aerodynamic characteristics of windshield wipers of vehicles

Prediction of separation induced transition on thick airfoil using non-linear URANS based turbulence model

Investigation of mixing characteristics in strut injectors using modal decomposition

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