A Periodically Perturbed Backward-Facing Step Flow by Means of LES, DES and T-RANS: An Example of Flow Separation Control

2005 ◽  
Vol 127 (5) ◽  
pp. 879-887 ◽  
Author(s):  
S. Šarić ◽  
S. Jakirlić ◽  
C. Tropea
Keyword(s):  
Navier Stokes ◽  
Detached Eddy Simulation ◽  
Reattachment Length ◽  
Backward Facing Step ◽  
Inlet Channel ◽  
Flow Separation Control ◽  
Eddy Simulation ◽  
Sst Model ◽  
Perturbation Frequency ◽  
Zero Net Mass Flux

Turbulent flow over a backward-facing step, perturbed periodically by alternative blowing∕suction through a thin slit (0.05H width) situated at the step edge, was studied computationally using (LES) large eddy simulation, (DES) detached eddy simulation, and (T-RANS) transient Reynolds-averaged Navier–Stokes techniques. The flow configuration considered (ReH=UcH∕ν=3700) has been investigated experimentally by Yoshioka et al. (12). The periodic blowing∕suction with zero net mass flux is governed by a sinusoidal law: ve=0.3Ucsin(2πfet), Uc being the centerline velocity in the inlet channel. Perturbation frequencies fe corresponding to the Strouhal numbers St=0.08, 0.19, and 0.30 were investigated (St=feH∕Uc). The experimental observation that the perturbation frequency St=0.19 represents the most effective case, that is the case with the minimum reattachment length, was confirmed by all computational methods. However, the closest agreement with experiment (the reattachment length reduction of 28.3% compared to the unperturbed case) was obtained with LES (24.5%) and DES (35%), whereas the T-RANS computations showed a weaker sensitivity to the perturbation: 5.9% when using the Spalart–Allmaras model and 12.9% using the k-ω SST model.

A Periodically Perturbed Backward-Facing Step Flow by Means of LES, DES and T-RANS: An Example of Flow Separation Control

2004 ◽  
Author(s):  
Sanjin Sˇaric´ ◽  
Suad Jakirlic´ ◽  
Cameron Tropea
Keyword(s):  
Navier Stokes ◽  
Reattachment Length ◽  
Backward Facing Step ◽  
Inlet Channel ◽  
Flow Separation Control ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Sst Model ◽  
Perturbation Frequency ◽  
Length Reduction

Turbulent flow over a backward-facing step perturbed periodically by an alternating blowing/suction through a thin slit situated at the step edge was studied computationally using the LES (Large Eddy Simulation), DES (Dettached Eddy Simulation) and T-RANS (Transient Reynolds-Averaged Navier-Stokes) techniques. The flow configuration considered (ReH = UcH/ν = 3700) has been investigated experimentally by Yoshioka et al. (2001). The periodical blowing/suction with zero mass flux is governed by a sinusoidal law: ve = 0.3Ucsin(2πfet), Uc being the centerline velocity in the inlet channel. Perturbation frequencies fe corresponding to the Strouhal numbers St = 0.08, 0.19 and 0.30 were investigated (St = feH/Uc). The experimental observation, that the perturbation frequency St = 0.19 represents the most effective case, that is the case with the minimum reattachment length, was confirmed by all computational methods applied. However, the closest agreement with experiment (the reattachment length reduction of 28.3% compared to the unperturbed case) was obtained with the LES (24.5%) and DES (35%) methods whereas the T-RANS computations show a weak sensitivity to the perturbation: 5.9% when using the Spalart-Allmaras model and 12.9% using the k–ω SST model.

A New Hybrid RANS/LES Modeling Methodology for CFD Applications

2011 ◽  
Author(s):  
Mohammad F. Alam ◽  
D. Keith Walters ◽  
David S. Thompson
Keyword(s):  
Turbulence Models ◽  
Detached Eddy Simulation ◽  
Backward Facing Step ◽  
Mean Velocity ◽  
New Model ◽  
Rans Model ◽  
Eddy Simulation ◽  
Modeling Methodology ◽  
Sst Model ◽  
Les Model

The primary weakness of current hybrid RANS/LES (HRL) models lies in the treatment of the “transition zone,” where the value and the physical interpretation of the eddy viscosity changes from LES to RANS, or vice versa. In order to address this problem, the initial version of a new HRL modeling methodology has been developed that incorporates two separate turbulent stress parameters (one from the LES model and the other from the RANS model). In this paper, the viability of the new model is demonstrated by predictions of the flow over a backward facing step, which is one of the canonical test cases used for the validation of turbulence models. The simulation results of backward facing step flow at ReH = 37,000 provided by Menter’s Shear Stress Transport (SST) model, a new version of Detached Eddy Simulation (DES) i.e. delayed DES model, and the new model are compared with experiments. Mesh sensitivity of the models is also studied employing two different types of mesh, in order to test the wide applicability of the HRL models in various realistic flow simulations. Pressure and skin friction distributions and mean velocity profiles obtained with the new HRL model show improved agreement with the experimental measurements versus DES, and less sensitivity to the mesh details. Turbulent kinetic energy profiles of both the new model and the RANS model show qualitatively good agreement with experiments.

Numerical study of the flow over the modified simple frigate shape

2020 ◽  
pp. 095441002097775
Author(s):  
Tong Li ◽  
Yibin Wang ◽  
Ning Zhao
Keyword(s):  
Bluff Body ◽  
Recirculation Zone ◽  
Numerical Study ◽  
Reference Value ◽  
Flow Fields ◽  
Navier Stokes ◽  
Detached Eddy Simulation ◽  
Eddy Simulation ◽  
Delayed Detached Eddy Simulation ◽  
Simulation Results

The simple frigate shape (SFS) as defined by The Technical Co-operative Program (TTCP), is a simplified model of the frigate, which helps to investigate the basic flow fields of a frigate. In this paper, the flow fields of the different modified SFS models, consisting of a bluff body superstructure and the deck, were numerically studied. A parametric study was conducted by varying both the superstructure length L and width B to investigate the recirculation zone behind the hangar. The size and the position of the recirculation zones were compared between different models. The numerical simulation results show that the size and the location of the recirculation zone are significantly affected by the superstructure length and width. The results obtained by Reynolds-averaged Navier-Stokes method were also compared well with both the time averaged Improved Delayed Detached-Eddy Simulation results and the experimental data. In addition, by varying the model size and inflow velocity, various flow fields were numerically studied, which indicated that the changing of Reynolds number has tiny effect on the variation of the dimensionless size of the recirculation zone. The results in this study have certain reference value for the design of the frigate superstructure.

Detached Eddy Simulation of Transonic Rotor Stall Flutter Using a Fully Coupled Fluid-Structure Interaction

2011 ◽  
Author(s):  
Hongsik Im ◽  
Xiangying Chen ◽  
Gecheng Zha
Keyword(s):  
Stokes Equations ◽  
Rotating Stall ◽  
Rotor Blades ◽  
Tip Clearance ◽  
Weno Scheme ◽  
Navier Stokes ◽  
Detached Eddy Simulation ◽  
Eddy Simulation ◽  
Stall Flutter ◽  
Fully Coupled

Detached eddy simulation of an aeroelastic self-excited instability, flutter in NASA Rotor 67 is conducted using a fully coupled fluid/structre interaction. Time accurate compressible 3D Navier-Stokes equations are solved with a system of 5 decoupled modal equations in a fully coupled manner. The 5th order WENO scheme for the inviscid flux and the 4th order central differencing for the viscous flux are used to accurately capture interactions between the flow and vibrating blades with the DES (detached eddy simulation) of turbulence. A moving mesh concept that can improve mesh quality over the rotor tip clearance was implemented. Flutter simulations were first conducted from choke to stall using 4 blade passages. Stall flutter initiated at rotating stall onset, grows dramatically with resonance. The frequency analysis shows that resonance occurs at the first mode of the rotor blade. Before stall, the predicted responses of rotor blades decayed with time, resulting in no flutter. Full annulus simulation at peak point verifies that one can use the multi-passage approach with periodic boundary for the flutter prediction.

Detached-Eddy Simulations Over a Simplified Landing Gear

2002 ◽  
Vol 124 (2) ◽  
pp. 413-423 ◽  
Author(s):  
L. S. Hedges ◽  
A. K. Travin ◽  
P. R. Spalart
Keyword(s):  
Stokes Equations ◽  
Separated Flow ◽  
Flow Fields ◽  
Equation Model ◽  
Landing Gear ◽  
Navier Stokes ◽  
Detached Eddy Simulation ◽  
Navier Stokes Equations ◽  
Instantaneous Flow ◽  
Eddy Simulation

The flow around a generic airliner landing-gear truck is calculated using the methods of Detached-Eddy Simulation, and of Unsteady Reynolds-Averaged Navier-Stokes Equations, with the Spalart-Allmaras one-equation model. The two simulations have identical numerics, using a multi-block structured grid with about 2.5 million points. The Reynolds number is 6×105. Comparison to the experiment of Lazos shows that the simulations predict the pressure on the wheels accurately for such a massively separated flow with strong interference. DES performs somewhat better than URANS. Drag and lift are not predicted as well. The time-averaged and instantaneous flow fields are studied, particularly to determine their suitability for the physics-based prediction of noise. The two time-averaged flow fields are similar, though the DES shows more turbulence intensity overall. The instantaneous flow fields are very dissimilar. DES develops a much wider range of unsteady scales of motion and appears promising for noise prediction, up to some frequency limit.

Numerical Investigation of Energy Saving Device Effects on Ships With Propeller-Hull Interactions

2018 ◽  
Author(s):  
Ravi Chaithanya Mysa ◽  
Le Quang Tuyen ◽  
Ma Shengwei ◽  
Vinh-Tan Nguyen
Keyword(s):  
Energy Saving ◽  
Full Scale ◽  
Navier Stokes ◽  
Detached Eddy Simulation ◽  
Propulsion Efficiency ◽  
Operational Conditions ◽  
Ship Resistance ◽  
The Past ◽  
Eddy Simulation ◽  
Flow Features

Energy saving devices (ESD) such as propeller ducts, pre-swirl stators, pre-nozzles, etc have been explored as a more economic and reliable approach to reduce energy consumption for both in-operation and newly design ships over the past decades. Those energy saving devices work in the principle of reducing ship resistance and improving propulsion efficiency as well as hull-propeller interactions. Potential saving from various types of ESD have been reported in literature from the range of 3–9% [1] for propulsion efficiency dependent on different measures. Deployment of those devices on actual full-scale ships has been limited over the past years. One of the key obstacles in application of ESD is the lack of confidence in measuring its efficiency on full-scale ships in actual operational conditions. Advances in computational fluid dynamics (CFD) has provided an alternative approach from model scale test to better understand uncertainties in prediction of ESD efficiency in full-scale ship operations [Shin et al, 2013]. In this work a high fidelity CFD model is presented for investigation effects of pre-nozzles on propulsion efficiency and ship resistance. The model is based on the Reynolds Average Navier-Stokes (RANS) solver with different turbulent models including a hybrid detached eddy simulation (DES) approach for predictions of complex near body flow features as well as in the wake regions from hull and propeller. The model is validated with model test for both towing and self-propulsion conditions. Finally a study of pre-nozzle effects on propeller efficiency as well as hull-propeller interaction is presented and compared with available experimental data (Tokyo 2015 Workshop). The current work constitutes a fundamental approach towards designing more efficient ESD for a specific hull form and propeller.

Current Capabilities of DES and LES for Submarines at Straight Course

2010 ◽  
Vol 54 (03) ◽  
pp. 184-196 ◽  
Author(s):  
N. Alin ◽  
R.E. Bensow ◽  
C. Fureby ◽  
T. Huuva ◽  
U. Svennberg
Keyword(s):  
Statistical Moments ◽  
Navier Stokes ◽  
Detached Eddy Simulation ◽  
Complex Flow ◽  
First Order ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Actuator Disc ◽  
Rans Models ◽  
Coarse Grids

The flow around an axisymmetric hull, with and without appendages, is investigated using large eddy simulation (LES), detached eddy simulation (DES), and Reynolds averaged Navier Stokes (RANS) models. The main objectives of the study is to investigate the effect of the different simulation methods and to demonstrate the feasibility of using DES and LES on relatively coarse grids for submarine flows, but also to discuss some generic features of submarine hydrodynamics. For this purpose the DARPA Suboff configurations AFF1 (bare hull) and AFF8 (fully appended model) are used. The AFF1 case is interesting because it is highly demanding, in particular for LES and DES, due to the long midship section on which the boundary layer is developed. The AFF8 case represents the complex flow around a fully appended submarine with sail and aft rudders. An actuator disc model is used to emulate some of the effects of the propulsor for one of the AFF8 cases studied. Results for the AFF8 model are thus presented for both "towed" and "self-propelled" conditions, where as for the bare hull, only a "towed" condition is considered. For the AFF1 and the "towed" AFF8 cases experimental data are available for comparison, and the results from both configurations show that all methods give good results for first-order statistical moments although LES gives a better representation of structures and second-order statistical moments in the complex flow in the AFF8 case.

A Comparative Study of DES and URANS in a Two-Pass Internal Cooling Duct With Normal Ribs

2005 ◽  
Author(s):  
Aroon K. Viswanathan ◽  
Danesh K. Tafti
Keyword(s):  
Heat Transfer ◽  
Secondary Flows ◽  
Navier Stokes ◽  
Internal Cooling ◽  
Detached Eddy Simulation ◽  
Mean Flow ◽  
Streamline Curvature ◽  
Eddy Simulation ◽  
Flow And Heat Transfer ◽  
Developing Flow

The capabilities of the Detached Eddy Simulation (DES) and the Unsteady Reynolds Averaged Navier-Stokes (URANS) versions of the 1988 κ-ω model in predicting the turbulent flow field and the heat transfer in a two-pass internal cooling duct with normal ribs is presented. The flow is dominated by the separation and reattachment of shear layers; unsteady vorticity induced secondary flows and strong streamline curvature. The techniques are evaluated in predicting the developing flow at the entrance to the duct and downstream of the 180° bend, fully-developed regime in the first pass, and in the 180° bend. Results of mean flow quantities, secondary flows, friction and heat transfer are compared to experiments and Large-Eddy Simulations (LES). DES predicts a slower flow development than LES, while URANS predicts it much earlier than LES computations and experiments. However it is observed that as fully developed conditions are established, the capability of the base model in predicting the flow and heat transfer is enhanced by switching to the DES formulation. DES accurately predicts the flow and heat transfer both in the fully-developed region as well as the 180° bend of the duct. URANS fails to predict the secondary flows in the fully-developed region of the duct and is clearly inferior to DES in the 180° bend.

Merging Near-Wall RANS Models With LES for Separating and Reattaching Flows

2006 ◽  
Author(s):  
Suad Jakirlic´ ◽  
Bjo¨rn Kniesner ◽  
Sanjin Sˇaric´ ◽  
Kemal Hanjalic´
Keyword(s):  
Reynolds Number ◽  
Equation Model ◽  
Navier Stokes ◽  
Model Parameters ◽  
Wall Region ◽  
Detached Eddy Simulation ◽  
Rans Model ◽  
Eddy Simulation ◽  
Moderate Reynolds Number ◽  
Near Wall

A method of coupling a low-Reynolds-number k–ε RANS (Reynolds-Averaged Navier-Stokes) model with Large-Eddy Simulation (LES) in a two-layer Hybrid LES/RANS (HLR) scheme is proposed in the present work. The RANS model covers the near-wall region and the LES model the remainder of the flow domain. Two different subgrid-scale (SGS) models in LES were considered, the Smagorinsky model and the one-equation model for the residual kinetic energy (Yoshizawa and Horiuti, 1985), combined with two versions of the RANS ε equation, one governing the “isotropic” (ε˜; Chien, 1982) and the other the “homogeneous” dissipation rate (εh; Jakirlic and Hanjalic, 2002). Both fixed and self-adjusting interface locations were considered. The exchange of the variables across the interface was adjusted by smoothing the turbulence viscosity either by adjusting the RANS model parameters, such as Cμ (Temmerman et al., 2005), or by applying an additional forcing at the interface using a method of digital-filter-based generation of inflow data for spatially developing DNS and LES due to Klein et al. (2003). The feasibility of the method was illustrated against the available DNS, fine- and coarse grid LES, DES (Detached Eddy Simulation) and experiments in turbulent flow over a backward-facing step at a low (Yoshioka et al., 2001) and a high Re number (Vogel and Eaton, 1985), periodic flow over a series of 2-D hills (Fro¨hlich et al., 2005) and in a high-Re flow over a 2-D, wall-mounted hump (Greenblat et al, 2004). Prior to these computations, the method was validated in a fully-developed channel flow at a moderate Reynolds number Rem ≈ 24000 (Abe et al., 2004).

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