scholarly journals Large Eddy Simulation of Turbulent Attached Cavitating Flows around Different Twisted Hydrofoils

Energies ◽  
2018 ◽  
Vol 11 (10) ◽  
pp. 2768 ◽  
Author(s):  
Changli Hu ◽  
Guanghao Chen ◽  
Long Yang ◽  
Guoyu Wang
Keyword(s):  
Large Eddy Simulation ◽  
Dynamic Behavior ◽  
Lift Force ◽  
Computational Method ◽  
Cavitating Flows ◽  
Suction Surface ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Time Fluctuation ◽  
Cavity Shedding

In this paper, the turbulent attached cavitating flows around two different twisted hydrofoils, named as NACA0009 and Clark-y, are studied numerically, with emphasis on cavity shedding dynamic behavior and the turbulence flow structures. The computational method of large eddy simulation (LES) coupled with a homogeneous cavitation model is applied and assessed by previous experimental data. It was found that the predicted results were in good agreement with that of the experiment. The unsteady cavity morphology of the two hydrofoils undergoes a similar quasi-periodic process, but has different shedding dynamic behavior. The scale of the U-type shedding structures forming on the suction surface of NACA0009 is larger than that of Clark-y. This phenomenon is also present in the iso-surface distributions of Q-criterion. Otherwise, the time-averaged cavity morphology is dramatically different for the two hydrofoils, and it is found that the attached location of the cavity is closely related to the hydrofoil geometry. The time fluctuation of the lift force coefficients is affected significantly by the cavity shedding dynamics. Compared with NACA0009, the lift force of Clark-y shows more fluctuation, due to its complicated shedding behavior. Further analysis of the turbulent structure indicates that the more violent shedding behaviors can induce higher levels of turbulence velocity fluctuations.

Large Eddy Simulation of Wake-Shear Layer Interactions Over a Multi-Element Aerofoil

2020 ◽  
Author(s):  
Souvik Naskar ◽  
S. Sarkar
Keyword(s):  
Large Eddy Simulation ◽  
Shear Layer ◽  
Separation Bubble ◽  
Turbine Blades ◽  
Leading Edge ◽  
Aerodynamic Characteristics ◽  
Suction Surface ◽  
Free Stream Turbulence ◽  
Eddy Simulation ◽  
Large Eddy

Abstract Modern commercial airliners use multi-element aerofoils to enhance take-off and landing performance. Further, multielement aerofoil configurations have been shown to improve the aerodynamic characteristics of wind turbines. In the present study, high resolution Large Eddy Simulation (LES) is used to explore the low Reynolds Number (Re = 0.832 × 104) aerodynamics of a 30P30N multi-element aerofoil at an angle of attack, α = 4°. In the present simulation, wake shed from a leading edge element or slat is found to interact with the separated shear layer developing over the suction surface of the main wing. High receptivity of shear layer via amplification of free-stream turbulence leads to rollup and breakdown, forming a large separation bubble. A transient growth of fluctuations is observed in the first half of the separation bubble, where levels of turbulence becomes maximum near the reattachment and then decay depicting saturation of turbulence. Results of the present LES are found to be in close agreement with the experiment depicting high vortical activity in the outer layer. Some features of the flow field here are similar to those occur due to interactions of passing wake and the separated boundary layer on the suction surface of high lift low pressure turbine blades.

Large-Eddy Simulation of Unsteady Surface Pressure Over a LP Turbine Blade Due to Interactions of Passing Wakes and Inflexional Boundary Layer

2005 ◽  
Author(s):  
S. Sarkar ◽  
Peter R. Voke
Keyword(s):  
Large Eddy Simulation ◽  
Turbine Blade ◽  
Coherent Structures ◽  
Pressure Fluctuations ◽  
Time Dependent ◽  
Suction Surface ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Grid Points ◽  
Lp Turbine

The unsteady pressure over the suction surface of a modern low-pressure (LP) turbine blade subjected to periodically passing wakes from a moving bar wake generator is described. The results presented are a part of detailed Large-Eddy Simulation (LES) following earlier experiments over the T106 profile for a Reynolds number of 1.6×105 (based on the chord and exit velocity) and the cascade pitch to chord ratio of 0.8. The present LES uses coupled simulations of cylinder for wake, providing four-dimensional inflow conditions for successor simulations of wake interactions with the blade. The three-dimensional, time-dependent, incompressible Navier-Stokes equations in fully covariant form are solved with 2.4×106 grid points for the cascade and 3.05×106 grid points for the cylinder using a symmetry-preserving finite difference scheme of second-order spatial and temporal accuracy. A separation bubble on the suction surface of the blade was found to form under the steady state condition. Pressure fluctuations of large amplitude appear on the suction surface as the wake passes over the separation region. Enhanced receptivity of perturbations associated with the inflexional velocity profile is the cause of instability and coherent vortices appear over the rear half of the suction surface by the rollup of shear layer via Kelvin-Helmholtz (K-H) mechanism. Once these vortices are formed, the steady-flow separation changes remarkably. These coherent structures embedded in the boundary amplify before breakdown while traveling downstream with a convective speed of about 37 percent of the local free-stream speed. The vortices play an important role in the generation of turbulence and thus to decide the transitional length, which becomes time-dependent. The source of the pressure fluctuations on the rear part of the suction surface is also identified as the formation of these coherent structures. When compared with experiments, it reveals that LES is worth pursuing as an understanding of the eddy motions and interactions is of vital importance for the problem.

Large Eddy Simulation of Boundary Layer Transition Mechanisms in a Gas-Turbine Compressor Cascade

2018 ◽  
Author(s):  
Ashley D. Scillitoe ◽  
Paul G. Tucker ◽  
Paolo Adami
Keyword(s):  
Boundary Layer ◽  
Large Eddy Simulation ◽  
Boundary Layer Transition ◽  
Bypass Transition ◽  
Suction Surface ◽  
Layer Transition ◽  
Turbulent Spots ◽  
Pressure Surface ◽  
Eddy Simulation ◽  
Large Eddy

Large Eddy Simulation (LES) is used to explore the boundary layer transition mechanisms in two rectilinear compressor cascades. To reduce numerical dissipation, a novel locally adaptive smoothing scheme is added to an unstructured finite-volume solver. The performance of a number of Sub-Grid Scale (SGS) models is explored. With the first cascade, numerical results at two different freestream turbulence intensities (Ti’s), 3.25% and 10%, are compared. At both Ti’s, time-averaged skin-friction and pressure coefficient distributions agree well with previous Direct Numerical Simulations (DNS). At Ti = 3.25%, separation induced transition occurs on the suction surface, whilst it is bypassed on the pressure surface. The pressure surface transition is dominated by modes originating from the convection of Tollmien-Schlichting waves by Klebanoff streaks. However, they do not resembled a classical bypass transition. Instead, they display characteristics of the “overlap” and “inner” transition modes observed in the previous DNS. At Ti = 10%, classical bypass transition occurs, with Klebanoff streaks incepting turbulent spots. With the second cascade, the influence of unsteady wakes on transition is examined. Wake-amplified Klebanoff streaks were found to instigate turbulent spots, which periodically shorten the suction surface separation bubble. The celerity line corresponding to 70% of the free-stream velocity, which is associated with the convection speed of the amplified Klebanoff streaks, was found to be important.

Large Eddy Simulation of Bypass Transition in Vane Passage With Freestream Turbulence

2020 ◽  
Vol 142 (6) ◽  
Author(s):  
Yousef Kanani ◽  
Sumanta Acharya ◽  
Forrest Ames
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Large Eddy Simulation ◽  
Bypass Transition ◽  
Freestream Turbulence ◽  
Turbulent Spot ◽  
Suction Surface ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Inflow Turbulence

Abstract High Reynolds flow over a nozzle guide-vane with elevated inflow turbulence was simulated using wall-resolved large eddy simulation (LES). The simulations were undertaken at an exit Reynolds number of 0.5 × 106 and inflow turbulence levels of 0.7% and 7.9% and for uniform heat-flux boundary conditions corresponding to the measurements of Varty and Ames (2016, “Experimental Heat Transfer Distributions Over an Aft Loaded Vane With a Large Leading Edge at Very High Turbulence Levels,” ASME Paper No. IMECE2016-67029). The predicted heat transfer distribution over the vane is in excellent agreement with measurements. At higher freestream turbulence, the simulations accurately capture the laminar heat transfer augmentation on the pressure surface and the transition to turbulence on the suction surface. The bypass transition on the suction surface is preceded by boundary layer streaks formed under the external forcing of freestream disturbances which breakdown to turbulence through inner-mode secondary instabilities. Underneath the locally formed turbulent spot, heat transfer coefficient spikes and generally follows the same pattern as the turbulent spot. The details of the flow and temperature fields on the suction side are characterized, and first- and second-order statistics are documented. The turbulent Prandtl number in the boundary layer is generally in the range of 0.7–1, but decays rapidly near the wall.

Large Eddy Simulation and CDNS Investigation of T106C Low-Pressure Turbine

2017 ◽  
Vol 140 (1) ◽  
Author(s):  
Site Hu ◽  
Chao Zhou ◽  
Zhenhua Xia ◽  
Shiyi Chen
Keyword(s):  
Large Eddy Simulation ◽  
Flow Separation ◽  
Separated Flow ◽  
Low Pressure ◽  
Secondary Flows ◽  
Computational Domain ◽  
Suction Surface ◽  
Low Pressure Turbine ◽  
Eddy Simulation ◽  
Large Eddy

This study investigates the aerodynamic performance of a low-pressure turbine, namely the T106C, by large eddy simulation (LES) and coarse grid direct numerical simulation (CDNS) at a Reynolds number of 100,000. Existing experimental data were used to validate the computational fluid dynamics (CFD) tool. The effects of subgrid scale (SGS) models, mesh densities, computational domains and boundary conditions on the CFD predictions are studied. On the blade suction surface, a separation zone starts at a location of about 55% along the suction surface. The prediction of flow separation on the turbine blade is always found to be difficult and is one of the focuses of this work. The ability of Smagorinsky and wall-adapting local eddy viscosity (WALE) model in predicting the flow separation is compared. WALE model produces better predictions than the Smagorinsky model. CDNS produces very similar predictions to WALE model. With a finer mesh, the difference due to SGS models becomes smaller. The size of the computational domain is also important. At blade midspan, three-dimensional (3D) features of the separated flow have an effect on the downstream flows, especially for the area near the reattachment. By further considering the effects of endwall secondary flows, a better prediction of the flow separation near the blade midspan can be achieved. The effect of the endwall secondary flow on the blade suction surface separation at the midspan is explained with the analytical method based on the Biot–Savart Law.

The Characteristics Research of Tube Vortex Based on Large Eddy Simulation

2011 ◽  
Vol 121-126 ◽  
pp. 3657-3661
Author(s):  
Dun Zhang ◽  
Yuan Zheng ◽  
Ying Zhao ◽  
Jian Jun Huang
Keyword(s):  
Large Eddy Simulation ◽  
Turbulent Flow ◽  
Complex Geometry ◽  
Initial Conditions ◽  
Three Dimensional ◽  
Flow Simulation ◽  
Computational Method ◽  
Francis Turbine ◽  
Eddy Simulation ◽  
Large Eddy

Numerical simulation of three-dimensional transient turbulent flow in the whole flow passage of a Francis turbine were based upon the large eddy simulation(LES) technique on Smargorinsky model and sliding mesh technology. The steady flow data simulated with the standard k-εmodel was used as the initial conditions for the unsteady simulation. The results show that LES can do well transient turbulent flow simulation in a Francis turbine with complex geometry. The computational method provides some reference for exploring the mechanism of eddy formation in a complex turbulent of hydraulic machinery.

Large Eddy Simulation of Bypass Transition in Vane Passage With Freestream Turbulence

2019 ◽  
Author(s):  
Yousef Kanani ◽  
Sumanta Acharya ◽  
Forrest Ames
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Large Eddy Simulation ◽  
Bypass Transition ◽  
Freestream Turbulence ◽  
Turbulent Spot ◽  
Suction Surface ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Inflow Turbulence

Abstract High Reynolds flow over a nozzle guide-vane with elevated inflow turbulence was simulated using wall-resolved large eddy simulation (LES). The simulations were undertaken at an exit Reynolds number of 0.5×106 and inflow turbulence levels of 0.7% and 7.9% and for uniform heat-flux boundary conditions corresponding to the measurements of (Varty, J. W., and Ames, F. E., 2016, ASME Paper No. IMECE2016-67029). The predicted heat transfer distribution over the vane is in excellent agreement with measurements. At higher freestream turbulence, the simulations accurately capture the laminar heat transfer augmentation on the pressure surface and the transition to turbulence on the suction surface. The bypass transition on the suction surface is preceded by boundary layer streaks formed under the external forcing of freestream disturbances which breakdown to turbulence through inner mode secondary instabilities. Underneath the locally formed turbulent spot, heat transfer coefficient spikes and generally follows the same pattern as the turbulent spot. The details of the flow and temperature fields on the suction side are characterized and first and second order statistics are documented. The turbulent Prandtl number in the boundary layer is generally in the range of 0.7–1, but decays rapidly near the wall.

Leading Edge Contamination of a C-D Compressor Blade Using Large Eddy Simulation

2020 ◽  
Author(s):  
S. Katiyar ◽  
S. Sarkar
Keyword(s):  
Boundary Layer ◽  
Large Eddy Simulation ◽  
Separation Bubble ◽  
Leading Edge ◽  
Adverse Pressure Gradient ◽  
Suction Surface ◽  
Local Flow ◽  
Flow Acceleration ◽  
Eddy Simulation ◽  
Large Eddy

Abstract A large-eddy simulation (LES) is employed here to predict the flow field over the suction surface of a controlled-diffusion (C-D) compressor stator blade following the experiment of Hobson et al. [1]. When compared with the experiment, LES depicts a separation bubble (SB) in the mid-chord region of the suction surface, although discrepancies exist in Cp. Further, the LES resolves the growth of boundary layer over the mid-chord and levels of turbulence intensity with an acceptable limit. What is noteworthy that LES also resolves a tiny SB near the leading-edge at the designed inflow angle of 38.3°. The objective of the present study is to assess how this leading-edge bubble influences the transition and development of boundary layer on the suction surface before the mid-chord. It appears that the separation at leading-edge suddenly enhances the perturbation levels exciting development of boundary layer downstream. The boundary layer becomes pre-transitional followed by a decay of fluctuations up to 30% of chord attributing to the local flow acceleration. Further, the boundary layer appears like laminar after being relaxed from the leading edge excitation near the mid-chord. It separates again because of the adverse pressure gradient, depicting augmentation of turbulence followed by the breakdown at about 70% of chord.

Large Eddy Simulation of a Compressor Stage

2017 ◽  
Author(s):  
Pranab Mondal ◽  
Joseph Mathew
Keyword(s):  
Large Eddy Simulation ◽  
Tangential Velocity ◽  
Surface Boundary ◽  
Blade Surface ◽  
Suction Surface ◽  
Time Step ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Scale Modelling ◽  
Grid Points

A methodology for large eddy simulation (LES) of a turbomachine stage is presented. Computations of mean fields (RANS) of stages may be performed separately of rotor and stator rows by providing an averaged solution as input to the down-stream row. In unsteady simulations, unsteady field information must be exchanged in both directions after every time step. Here a procedure for linear cascade simulations of a stage has been implemented in a high-resolution compressible flow solver for LES. The LES uses an explicit filtering method for sub-grid-scale modelling. Grids overlap at the interface between blade rows. Field data is transferred in both directions. Rotor velocity is added or subtracted as needed to tangential velocity component during this transfer. The relative movement of the rotor and stator grids is accounted for by suitable periodic tangential shifting of the paired grid points in the overlap for the transfer. The method has been tested against a published DNS of a statorrotor stage. The Reynolds number based on blade chord and mean axial velocity at inflow was 40000. Solution fields show the wake vortex street of the upstream blade row impinging on downstream blades and being convected through the downstream blade passage. The LES captured transition on rotor blade surface boundary layers. Blade surface pressure distributions agree closely on pressure surfaces. Separation and transition on downstream blade suction surface is delayed slightly at the present resolution, but this will improve with grid refinement, monotonically, for this LES method.

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