Prediction of Transition and Losses in Compressor Cascades Using Large-Eddy Simulation

2016 ◽  
Vol 138 (12) ◽  
Author(s):  
Gorazd Medic ◽  
Vicky Zhang ◽  
Guolei Wang ◽  
Jongwook Joo ◽  
Om P. Sharma
Keyword(s):  
Large Eddy Simulation ◽  
Pressure Coefficient ◽  
Computational Cost ◽  
Predictive Tool ◽  
Laminar Separation ◽  
Eddy Simulation ◽  
Air Inlet ◽  
Large Eddy ◽  
Inlet Angle ◽  
Rapid Pressure

In the 1950s, NACA conducted a series of low-speed cascade experiments investigating the performance of NACA 65-series compressor cascades with tests covering multiple airfoils of varying camber and with variations in solidity and air inlet angle. Most of the configurations show transition via laminar separation—both on suction and pressure side—characterized by a relatively flat region in pressure distribution, while turbulent reattachment is characterized by a rapid pressure recovery just downstream of the separated region. In the current study, wall-resolved large-eddy simulation (LES) has been used to predict transition via laminar separation in such compressor configurations as well as the resulting airfoil losses. Six different cascades with local diffusion factor varying from 0.14 to 0.56 (NACA 65-010, 65-410, 65-(12)10, 65-(15)10, 65-(18)10, and 65-(21)10 cascades) were analyzed at design conditions. In addition, the loss bucket for various angles of attack off-design conditions has been computed for the NACA 65-(18)10 cascade. Chord-based Reynolds number for all the experiments considered here was held at 250,000. This allows sufficient grid resolution in these LES analyses at an acceptable computational cost, i.e., up to 20,000 CPU hours per case. Detailed comparisons to test data are presented in the form of surface pressure coefficient, drag coefficient, losses, and momentum thickness ratio. The results show that LES is capable of capturing transition via laminar separation relatively well for most of the cases, and consequently, may constitute a predictive tool for assessing losses of different compressor airfoils.

Large eddy simulation study of turbulent flow around smooth and rough domes

2013 ◽  
Vol 227 (12) ◽  
pp. 2686-2700 ◽  
Author(s):  
N Kharoua ◽  
L Khezzar
Keyword(s):  
Large Eddy Simulation ◽  
Turbulent Flow ◽  
Flow Behavior ◽  
Pressure Coefficient ◽  
Horseshoe Vortex ◽  
Scale Model ◽  
Stream Velocity ◽  
Mean Velocity ◽  
Eddy Simulation ◽  
Large Eddy

Large eddy simulation of turbulent flow around smooth and rough hemispherical domes was conducted. The roughness of the rough dome was generated by a special approach using quadrilateral solid blocks placed alternately on the dome surface. It was shown that this approach is capable of generating the roughness effect with a relative success. The subgrid-scale model based on the transport of the subgrid turbulent kinetic energy was used to account for the small scales effect not resolved by large eddy simulation. The turbulent flow was simulated at a subcritical Reynolds number based on the approach free stream velocity, air properties, and dome diameter of 1.4 × 105. Profiles of mean pressure coefficient, mean velocity, and its root mean square were predicted with good accuracy. The comparison between the two domes showed different flow behavior around them. A flattened horseshoe vortex was observed to develop around the rough dome at larger distance compared with the smooth dome. The separation phenomenon occurs before the apex of the rough dome while for the smooth dome it is shifted forward. The turbulence-affected region in the wake was larger for the rough dome.

scholarly journals Numerical Framework for the Computation of Urban Flux Footprints Employing Large-eddy Simulation and Lagrangian Stochastic Modeling

2017 ◽  
Author(s):  
Mikko Auvinen ◽  
Leena Järvi ◽  
Antti Hellsten ◽  
Üllar Rannik ◽  
Timo Vesala
Keyword(s):  
Large Eddy Simulation ◽  
Urban Landscape ◽  
Computational Cost ◽  
Source Area ◽  
Target Volume ◽  
Particle Analysis ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Flux Measurements ◽  
Urban Footprint

Abstract. Conventional footprint models cannot account for the heterogeneity of the urban landscape imposing a pronounced uncertainty on the spatial interpretation of eddy-covariance (EC) flux measurements in urban studies. This work introduces a computational methodology that enables the generation of detailed footprints in arbitrarily complex urban flux measurements sites. The methodology is based on conducting high-resolution large-eddy simulation (LES) and Lagrangian stochastic (LS) particle analysis on a model that features a detailed topographic description of a real urban environment. The approach utilizes an arbitrarily sized target volume set around the sensor in the LES domain, to collect a dataset of LS particles which are seeded from the potential source-area of the measurement and captured at the sensor site. The urban footprint is generated from this dataset through a piecewise post-processing procedure, which divides the footprint evaluation into multiple independent processes that each yield an intermediate result that are ultimately selectively combined to produce the final footprint. The strategy reduces the computational cost of the LES-LS simulation and incorporates techniques to account for the complications that arise when the EC sensor is mounted on a building instead of a conventional flux tower. The presented computational framework also introduces a result assessment strategy which utilizes the obtained urban footprint together with a detailed land cover type dataset to estimate the potential error that may arise if analytically derived footprint models were employed instead. The methodology is demonstrated with a case study that concentrates on generating the footprint for a building-mounted EC measurement station in downtown Helsinki, Finland, under neutrally stratified atmospheric boundary layer.

Validation of Species-Based Extended Coherent Flamelet Model in a Large Eddy Simulation of a Homogeneous Charge Spark Ignition Engine

2020 ◽  
Author(s):  
Y. See ◽  
M. Wang ◽  
J. Bohbot ◽  
O. Colin
Keyword(s):  
Large Eddy Simulation ◽  
Computational Cost ◽  
Spark Ignition ◽  
Spark Ignition Engine ◽  
Cylinder Pressure ◽  
Flamelet Model ◽  
Progress Variable ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Homogeneous Charge

Abstract The Species-Based Extended Coherent Flamelet Model (SB-ECFM) was developed and previously validated for 3D Reynolds-Averaged Navier-Stokes (RANS) modeling of a spark-ignited gasoline direct injection engine. In this work, we seek to extend the SB-ECFM model to the large eddy simulation (LES) framework and validate the model in a homogeneous charge spark-ignited engine. In the SB-ECFM, which is a recently developed improvement of the ECFM, the progress variable is defined as a function of real species instead of tracer species. This adjustment alleviates discrepancies that may arise when the numerical treatment of real species is different than that of the tracer species. Furthermore, the species-based formulation also allows for the use of second-order numeric, which can be necessary in LES cases. The transparent combustion chamber (TCC) engine is the configuration used here for validating the SB-ECFM. It has been extensively characterized with detailed experimental measurements and the data are widely available for model benchmarking. Moreover, several of the boundary conditions leading to the engine are also measured experimentally. These measurements are used in the corresponding computational setup of LES calculations with SB-ECFM. Since the engine is spark ignited, the Imposed Stretch Spark Ignition Model (ISSIM) is utilized to model this physical process. The mesh for the current study is based on a configuration that has been validated in a previous LES study of the corresponding motored setup of the TCC engine. However, this mesh was constructed without considering the additional cells needed to sufficiently resolve the flame for the fired case. Thus, it is enhanced with value-based Adaptive Mesh Refinement (AMR) on the progress variable to better capture the flame front in the fired case. As one facet of model validation, the ensemble average of the measured cylinder pressure is compared against the LES/SB-ECFM prediction. Secondly, the predicted cycle-to-cycle variation by LES is compared with the variation measured in the experimental setup. To this end, the LES computation is required to span a sufficient number of engine cycles to provide statistical convergence to evaluate the coefficient of variation (COV) in peak cylinder pressure. Due to the higher computational cost of LES, the runtime required to compute a sufficient number of engine cycles sequentially can be intractable. The concurrent perturbation method (CPM) is deployed in this study to obtain the required number of cycles in a reasonable time frame. Lastly, previous numerical and experimental analyses of the TCC engine have shown that the flow dynamics at the time of ignition is correlated with the cycle-to-cycle variability. Hence, similar analysis is performed on the current simulation results to determine if this correlation effect is well-captured by the current modeling approach.

scholarly journals Scale-Adaptive Simulation of Unsteady Cavitation Around a Naca66 Hydrofoil

2019 ◽  
Vol 9 (18) ◽  
pp. 3696 ◽  
Author(s):  
Víctor Hidalgo ◽  
Xavier Escaler ◽  
Esteban Valencia ◽  
Xiaoxing Peng ◽  
José Erazo ◽  
...  
Keyword(s):  
Large Eddy Simulation ◽  
Pressure Coefficient ◽  
Experimental Results ◽  
Navier Stokes ◽  
Naval Academy ◽  
Eddy Simulation ◽  
Hydraulic Machinery ◽  
Adaptive Simulation ◽  
Large Eddy ◽  
Sas Model

The present paper focuses on the numerical simulation of unsteady cavitation around a NACA66 hydrofoil to improve the understanding of the cavitation effects on hydraulic machinery. For this aim, the Zwart–Gerber–Belamri cavitation model was updated and uploaded as a library file for OpenFOAM’s solvers using C++ language. Furthermore, the hybrid Reynold average Navier–Stokes (RANS)–large eddy simulation (LES) model k - ω SST scale adaptive simulation (SAS) was implemented as a turbulence model for the present study of scale adaptive simulation. For validation, numerical results were compared with experimental results obtained by Leroux at the Naval Academy Research Institute in France. In order to highlight the benefits in terms of computational consumption and reproduction of the phenomenon the k - ω SST SAS model was compared against implicit large eddy simulation (ILES). Results show that the cavitation evolution including the maximum vapor length, the detachment and the oscillation frequency were reproduced satisfactorily using k - ω SST SAS. Moreover, k - ω SST SAS results predicted a lower total vapor volume on time than ILES, which is related to observed pulses of pressure coefficient, C p , and those match fairly well with the experimental results. To summarize, the k - ω SST SAS model predicts with good accuracy unsteady cavitation behavior around hydrofoils and shows improved versatility over the ILES approach.

Detailed Numerical Characterization of the Suction Side Laminar Separation Bubble for a High-Lift Low Pressure Turbine Blade by Means of RANS and LES

2016 ◽  
Author(s):  
Fabio Bigoni ◽  
Stefano Vagnoli ◽  
Tony Arts ◽  
Tom Verstraete
Keyword(s):  
Large Eddy Simulation ◽  
Separation Bubble ◽  
Suction Side ◽  
Reynolds Numbers ◽  
Laminar Separation Bubble ◽  
High Lift ◽  
Laminar Separation ◽  
Low Pressure Turbine ◽  
Eddy Simulation ◽  
Large Eddy

The scope of this work is to obtain a deep insight of the occurrence, development and evolution of the laminar separation bubble which occurs on the suction side of the high-lift T106-C low pressure turbine blade operated at correct engine Mach and Reynolds numbers. The commercial codes Numeca FINE/Turbo and FINE/Open were used for the numerical investigation of a set of three different Reynolds numbers. Two different CFD approaches, characterized by a progressively increasing level of complexity and detail in the solution, have been employed, starting from a steady state RANS analysis and ending with a Large Eddy Simulation. Particular attention was paid to the study of the open separation occurring at the lowest Reynolds number, for which a Large Eddy Simulation was performed in order to try to correctly capture the involved phenomena and their characteristic frequencies. In addition, the potentialities of the codes employed for the analysis have been assessed.

Large Eddy Simulation for Turbines: Methodologies, Cost and Future Outlooks

2013 ◽  
Vol 136 (6) ◽  
Author(s):  
James Tyacke ◽  
Paul Tucker ◽  
Richard Jefferson-Loveday ◽  
Nagabushana Rao Vadlamani ◽  
Robert Watson ◽  
...  
Keyword(s):  
Large Eddy Simulation ◽  
Computational Cost ◽  
Quality Data ◽  
Real Surface ◽  
Internal Cooling ◽  
Design Environment ◽  
Roughness Effects ◽  
Eddy Simulation ◽  
Wide Range ◽  
Large Eddy

Flows throughout different zones of turbines have been investigated using large eddy simulation (LES) and hybrid Reynolds-averaged Navier–Stokes-LES (RANS-LES) methods and contrasted with RANS modeling, which is more typically used in the design environment. The studied cases include low and high-pressure turbine cascades, real surface roughness effects, internal cooling ducts, trailing edge cut-backs, and labyrinth and rim seals. Evidence is presented that shows that LES and hybrid RANS-LES produces higher quality data than RANS/URANS for a wide range of flows. The higher level of physics that is resolved allows for greater flow physics insight, which is valuable for improving designs and refining lower order models. Turbine zones are categorized by flow type to assist in choosing the appropriate eddy resolving method and to estimate the computational cost.

Large-Eddy Simulation of Atomizing Spray With Stochastic Modeling of Secondary Breakup

2003 ◽  
Author(s):  
Sourabh V. Apte ◽  
Mikhael Gorokhovski ◽  
Parviz Moin
Keyword(s):  
Large Eddy Simulation ◽  
Droplet Size ◽  
Particle Tracking ◽  
Hybrid Approach ◽  
Computational Cost ◽  
Fuel Injector ◽  
Combustion Dynamics ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Secondary Breakup

Large-eddy simulation (LES) of reacting multi-phase flows in practical combustor geometries is essential to accurately predict complex physical phenomena of turbulent mixing and combustion dynamics. This necessitates use of Lagrangian particle-tracking methodology for liquid phase in order to correctly capture the droplet evaporation rates in the sparse-liquid regime away from the fuel injector. Our goal in the present work is to develop a spray-atomization methodology which can be used in conjuction with the standard particle-tracking schemes and predict the droplet-size distribution accurately. The intricate process of primary atomization and lack of detailed experimental observations close to the injector requires us to model its global effects and focus on secondary breakup to capture the evolution of droplet sizes. Accordingly, a stochastic model for LES of atomizing spray is developed. Following Kolmogorov’s idea of viewing solid particle-breakup as a discrete random process, atomization of liquid blobs at high relative liquid-to-gas velocity is considered in the framework of uncorrelated breakup events, independent of the initial droplet size. Kolmogorov’s discrete model of breakup is represented by Fokker-Planck equation for the temporal and spatial evolution of droplet radius distribution. The parameters of the model are obtained dynamically by relating them to the local Weber number. A novel hybrid-approach involving tracking of individual droplets and a group of like-droplets known as parcels is developed to reduce the computational cost and maintain the essential features and dynamics of spray evolution. The present approach is shown to capture the complex fragmentary process of liquid atomization in idealized and realistic Diesel and gas-turbine combustors.

Large eddy simulation as a fast and accurate engineering approach for the simulation of rotary blood pumps

2021 ◽  
pp. 039139882110416
Author(s):  
Jia-Dong Huo ◽  
Peng Wu ◽  
Liudi Zhang ◽  
Wei-Tao Wu
Keyword(s):  
Large Eddy Simulation ◽  
Turbulence Modeling ◽  
Computational Cost ◽  
Cost Effective ◽  
Design And Optimization ◽  
Engineering Approach ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Blood Pumps ◽  
Rotary Blood Pumps

An accurate representation of the flow field in blood pumps is important for the design and optimization of blood pumps. The primary turbulence modeling methods applied to blood pumps have been the Reynolds-averaged Navier–Stokes (RANS) or URANS (unsteady RANS) method. Large eddy simulation (LES) method has been introduced to simulate blood pumps. Nonetheless, LES has not been widely used to assist in the design and optimization of blood pumps to date due to its formidable computational cost. The purpose of this study is to explore the potential of the LES technique as a fast and accurate engineering approach for the simulation of rotary blood pumps. The performance of “Light LES” (using the same time and spatial resolutions as the URANS) and LES in two rotary blood pumps was evaluated by comparing the results with the URANS and extensive experimental results. This study showed that the results of both “Light LES” and LES are superior to URANS, in terms of both performance curves and key flow features. URANS could not predict the flow separation and recirculation in diffusers for both pumps. In contrast, LES is superior to URANS in capturing these flows, performing well for both design and off-design conditions. The differences between the “Light LES” and LES results were relatively small. This study shows that with less computational cost than URANS, “Light LES” can be considered as a cost-effective engineering approach to assist in the design and optimization of rotary blood pumps.

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