Visualization and Validation of Ejector Flow Field With Computational and First-Principles Analysis

2015 ◽  
Vol 137 (5) ◽  
Author(s):  
Adrienne B. Little ◽  
Yann Bartosiewicz ◽  
Srinivas Garimella
Keyword(s):  
Flow Field ◽  
First Principles ◽  
Large Scale ◽  
Turbulence Models ◽  
Ideal Gas ◽  
Analytical Models ◽  
Local Flow ◽  
Flow Features ◽  
Flow Phenomena ◽  
Air Ejector

Passive, heat actuated ejector pumps offer simple and energy-efficient options for a variety of end uses with no electrical input or moving parts. In an effort to obtain insights into ejector flow phenomena and to evaluate the effectiveness of commonly used computational and analytical tools in predicting these conditions, this study presents a set of shadowgraph images of flow inside a large-scale air ejector and compares them to both computational and first-principles-based analytical models of the same flow. The computational simulations used for comparison apply k-ε renormalization group (RNG) and k-ω shear stress transport (SST) turbulence models to two-dimensional (2D), locally refined rectangular meshes for ideal gas air flow. A complementary analytical model is constructed from first principles to approximate the ejector flow field. Results show that on-design ejector operation is predicted with reasonable accuracy, but accuracy with the same models is not adequate at off-design conditions. Exploration of local flow features shows that the k-ω SST model predicts the location of flow features, as well as global inlet mass flow rates, with greater accuracy. The first-principles model demonstrates a method for resolving the ejector flow field from relatively little visual data and shows the evolving importance of mixing, momentum, and heat exchange with the suction flow with distance from the motive nozzle exit. Such detailed global and local exploration of ejector flow helps guide the selection of appropriate turbulence models for future ejector design purposes, predicts locations of important flow phenomena, and allows for more efficient ejector design and operation.

Optical Validation of Ejector Flow Characteristics Predicted by Computational Analysis

2012 ◽  
Author(s):  
Adrienne B. Little ◽  
Yann Bartosiewicz ◽  
Srinivas Garimella
Keyword(s):  
Large Scale ◽  
Waste Heat ◽  
Turbulence Models ◽  
Ideal Gas ◽  
Computational Simulations ◽  
Design Data ◽  
Local Flow ◽  
Wide Range ◽  
Flow Features ◽  
Flow Phenomena

Passive, heat actuated devices can offer simple and energy-efficient options for a variety of end uses. An ejector pump is one such device that provides reasonable pressure head with no electrical input or moving parts. Useful for a wide range of applications from nuclear reactor cooling to vapor compression in waste-heat-driven heat pumping and work recovery systems, the flow phenomena inside an ejector must be understood to achieve improvements in component design and efficiency. In an effort to obtain insights into the flow phenomena inside an ejector, and to evaluate the effectiveness of commonly used computational tools in predicting these conditions, this study presents a set of shadowgraph images of flow inside a large-scale air ejector, and compares them to computational simulations of the same flow. On-design and off-design conditions are considered where the suction flow is choked and not choked, respectively. The computational simulations used for comparison apply k-ε RNG and k-ω SST turbulence models available in ANSYS FLUENT to 2D, locally-refined rectangular meshes for ideal gas air flow. Experimental and computational results show that on-design ejector operation is predicted with reasonable accuracy, but accuracy with the same models is not adequate at off-design conditions. This is attributed to an inability of turbulence models to predict shock/expansion interaction with the motive jet boundary, as well as the strength and position of flow features. Exploration of local flow features shows that the k-ω SST model predicts the location of flow features, as well as global inlet mass flow rates, with greater accuracy. It is concluded that to provide a rigorous validation of turbulence models for the application of modeling ejector flow, it is necessary to rely on off-design data where more complex phenomena occur, such as flow separation, strong boundary layer/shock interaction, and unsteady flow. Such validation will help refine turbulence models for future ejector design purposes, and allow for more efficient ejector operation.

Numerical Simulation of the Resistance and Self-Propulsion Model Tests

2018 ◽  
Author(s):  
Adrian Lungu
Keyword(s):  
Complex Structure ◽  
Turbulence Models ◽  
Numerical Approach ◽  
Local Flow ◽  
Complex Investigation ◽  
Grid Convergence ◽  
Flow Features ◽  
Sinkage And Trim ◽  
Thrust And Torque ◽  
Resistance Coefficients

The paper proposes a series of numerical investigations performed to test and demonstrate the capabilities of a RANS solver in the area of complex ship flow simulations. Focus is on a complete numerical model for hull, propeller and rudder that can account for the mutual interaction between these components. The paper presents the results of a complex investigation of the flow computations around the hull model of the 3600 TEU MOERI containership (KCS hereafter). The resistance for the hull equipped with rudder, the POW computations as well as the self-propulsion simulation are presented. Comparisons with the experimental data provided at the Tokyo 2015 Workshop on CFD in Ship Hydrodynamics are given to validate the numerical approach in terms of the total and wave resistance coefficients, sinkage and trim, thrust and torque coefficients, propeller efficiency and local flow features. Verification and validation based on the grid convergence tests are performed for each computational case. Discussions on the efficiency of the turbulence models used in the computations as well as on the main flow features are provided aimed at clarifying the complex structure of the flow around the stern.

scholarly journals Turbulence and Wake Effects in Tidal Stream Turbine Arrays

2018 ◽  
Author(s):  
Martin Nuernberg ◽  
Longbin Tao
Keyword(s):  
Flow Field ◽  
Electricity Generation ◽  
Large Scale ◽  
Numerical Models ◽  
Turbulence Models ◽  
Ambient Flow ◽  
Wake Effects ◽  
Tidal Turbine ◽  
Turbine Arrays ◽  
Good Agreement

Electricity generation from tidal current can provide a reliable and predictable addition to a reduced carbon energy sector in the future. Following the deployment of the first multi-turbine array, significant cost reduction can be achieved by moving beyond demonstrator projects to large scale tidal turbine arrays. The interactions between multiple turbines installed in close proximity can affect the total electricity generation and thus require knowledge of the resulting flow field within and downstream of the array. Results are presented for experimental and numerical studies investigating the flow field characteristics in terms of velocity deficit and turbulence intensity in a staggered tidal turbine array section. Multiple configuration with varying longitudinal and transverse spacing between devices in a three-turbine array are tested. Comparison between numerical and experimental flow characteristics shows that open source numerical models with dynamic mesh features achieve good agreement and can be used for the investigation of array wake effects. The standard k–ω SST shows good agreement with experiments at reduced computational efficiency compared to higher order turbulence models (RSM). The importance of mixing with ambient flow is highlighted by identifying areas of significantly reduced velocity recovery within closely spaced arrays where ambient flow does not penetrate between adjacent wakes.

Numerical Simulation of the Resistance and Self-Propulsion Model Tests1

2019 ◽  
Vol 142 (2) ◽  
Author(s):  
Adrian Lungu
Keyword(s):  
Complex Structure ◽  
Turbulence Models ◽  
Open Water ◽  
Numerical Approach ◽  
Navier Stokes ◽  
Navier Stokes Equation ◽  
Local Flow ◽  
Complex Investigation ◽  
Flow Features ◽  
Thrust And Torque

Abstract The paper proposes a series of numerical investigations performed to test and demonstrate the capabilities of a Reynolds-averaged Navier–Stokes equation (RANSE) solver in the area of complex ship flow simulations. The focus is on a complete numerical model for hull, propeller, and rudder that can account for the mutual interaction between these components. The paper presents the results of a complex investigation of the flow computations around the hull model of the 3600 TEU MOERI containership (KCS hereafter). The resistance for the hull equipped with a rudder, the propeller open-water (POW hereafter) computations, as well as the self-propulsion simulation are presented. Comparisons with the experimental data provided at the Tokyo 2015 Workshop on Computational Fluid Dynamics (CFD) in Ship Hydrodynamics are given to validate the numerical approach in terms of the total and wave resistance coefficients, sinkage and trim, thrust and torque coefficients, propeller efficiency, and local flow features. Verification and validation based on the grid convergence tests are performed for each computational case. Discussions on the efficiency of the turbulence models used in the computations as well as on the main flow features are provided aimed at clarifying the complex structure of the flow around the ship stern.

CFD analysis of a supersonic air ejector. Part II: Relation between global operation and local flow features

2009 ◽  
Vol 29 (14-15) ◽  
pp. 2990-2998 ◽  
Author(s):  
Amel Hemidi ◽  
François Henry ◽  
Sébastien Leclaire ◽  
Jean-Marie Seynhaeve ◽  
Yann Bartosiewicz
Keyword(s):  
Cfd Analysis ◽  
Local Flow ◽  
Flow Features ◽  
Air Ejector

On the Reliability of RANS Turbulence Models for Endwall Cooling Prediction

2017 ◽  
Author(s):  
Xueying Li ◽  
Jing Ren ◽  
Hongde Jiang
Keyword(s):  
Heat Transfer ◽  
Flow Field ◽  
Film Cooling ◽  
Conjugate Heat Transfer ◽  
Large Scale ◽  
Turbulence Models ◽  
Secondary Flows ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Rans Turbulence Models

The large scale coherent structures in the flow field of film cooling makes it difficult for the modeling of film cooling flow and heat transfer. The interaction between the complex secondary flows near the endwall and the film cooling jets makes it even worse. A typical flat vane endwall with/without film cooling is investigated experimentally and numerically. The aerodynamic and heat transfer of the endwall is measured. Adiabatic film cooling effectiveness is measured using PSP technique and conjugate overall cooling effectiveness is measured by TSP technique for different conditions. The coolant to mainstream massflow ratio (MFR) is varied from 0.5% to 1.5% in the experiment. Several RANS turbulence models are tested in the prediction of endwall aerodynamics, heat transfer, film cooling and conjugate heat transfer. Detailed analyses of the computational results are performed. The algebraic anisotropic turbulence model proposed previously aiming at a more accurate modeling of the Reynolds stress and turbulent scalar flux is employed in the study. The SST with transition model shows advantage in the prediction of endwall flow field and film cooling with high blowing ratios which is detached from the surface. The Realizable k-epsilon model is more suitable for predicting attached film cooling and conjugate heat transfer of the endwall. The algebraic anisotropic models show better agreement with the experimental data qualitatively and quantitatively for both adiabatic and conjugate situations.

CFD Study of Ejector Efficiencies

2014 ◽  
Author(s):  
Giorgio Besagni ◽  
Riccardo Mereu ◽  
Emanuela Colombo
Keyword(s):  
Thermal Field ◽  
Turbulence Models ◽  
Navier Stokes ◽  
Validation Process ◽  
Local Flow ◽  
Convergent Nozzle ◽  
Flow Parameters ◽  
Rans Turbulence Models ◽  
Flow Phenomena ◽  
Computational Fluid Dynamics Cfd

This paper presents a method to evaluate ejector efficiency in function of local flow parameters. The paper is divided into two parts. In the first part, a Computational Fluid-Dynamics (CFD) approach for convergent nozzle ejectors is presented and computational results are validated using experimental velocity and temperature profiles at different sections. The validation process includes the evaluation of seven Reynolds-Averaged Navier–Stokes (RANS) turbulence models: the Spalart-Allmaras and the k–omega SST models show better performance in terms of convergence capability and flow and thermal field prediction. In the second part, local flow phenomena and their influence on ejector component efficiencies are investigated. The validated CFD approach is used to determine the efficiencies of the ejector primary nozzle, suction chamber, and mixing zone. Efficiency maps, regressing equation linking efficiencies, and local flow quantities are proposed and discussed. Finally, global ejector performance is mapped and considerations are outlined.

scholarly journals A Comparison of Experimental With Computational Results in an Annular Turbine Cascade With Emphasis on Losses

1998 ◽  
Author(s):  
C. Casciaro ◽  
M. Treiber ◽  
M. Sell ◽  
A. P. Saxer ◽  
G. Gyarmathy
Keyword(s):  
Flow Field ◽  
Turbulence Models ◽  
Test Case ◽  
Data Sets ◽  
Computational Results ◽  
Efficient Computation ◽  
Free Stream Turbulence ◽  
Wide Range ◽  
Flow Phenomena ◽  
Exit Mach Number

Recent discussions in the industrial CFD community have identified a need for guidelines covering the accurate and efficient computation of a range of flow field classes. This paper addresses some of these issues for a standard turbomachinery test case, by investigating the flow through on annular blade row of a generic turbine profile, operating at an exit Mach number of 0.5. The joint experimental and CFD works have focused upon identifying and quantifying the loss sources and loss development. This has been achieved by the acquisition of dense data sets of a known, high and repeatable experimental accuracy, where, concentrating primarily upon the investigation of the secondary flow phenomena, optimised experimental methods have been employed to measure the pressure distributions in the annuls and the development of the flow field, particularly the loss structures, downstream of the trailing edge. On the CFD side, the flow field has been computed using commercial codes. Adopting the loss distribution as a primary marker for the quality of the CFD results, the performance and efficacy of the codes and the implemented viscous models can be assessed. The flow has been computed both 2D and 3D, from inviscid to laminar to turbulent with different turbulence models, with and without transition. According to the model, the flow has been investigated considering a wide range of parameters influencing its turbulent state. Through this study, guidelines concerning numerical smoothing and free-stream turbulence parameters are proposed for the computation of such flows. The need of a transition model within 3D schemes, rather than an improvement of the turbulence model, to predict accurate loss levels has been recognized. However, through the cross analysis of the different computational results, a good estimate of the loss magnitude and distribution is feasible with the currently used models.

Accelerated Discovery of High-Refractive-Index Polyimides via First-Principles Molecular Modeling, Virtual High-Throughput Screening, and Data Mining

2019 ◽  
Author(s):  
Mohammad Atif Faiz Afzal ◽  
Mojtaba Haghighatlari ◽  
Sai Prasad Ganesh ◽  
Chong Cheng ◽  
Johannes Hachmann
Keyword(s):  
Data Mining ◽  
Refractive Index ◽  
High Throughput ◽  
First Principles ◽  
High Throughput Screening ◽  
Large Scale ◽  
Computational Study ◽  
High Refractive Index ◽  
Structural Features ◽  
Learning Program

<div>We present a high-throughput computational study to identify novel polyimides (PIs) with exceptional refractive index (RI) values for use as optic or optoelectronic materials. Our study utilizes an RI prediction protocol based on a combination of first-principles and data modeling developed in previous work, which we employ on a large-scale PI candidate library generated with the ChemLG code. We deploy the virtual screening software ChemHTPS to automate the assessment of this extensive pool of PI structures in order to determine the performance potential of each candidate. This rapid and efficient approach yields a number of highly promising leads compounds. Using the data mining and machine learning program package ChemML, we analyze the top candidates with respect to prevalent structural features and feature combinations that distinguish them from less promising ones. In particular, we explore the utility of various strategies that introduce highly polarizable moieties into the PI backbone to increase its RI yield. The derived insights provide a foundation for rational and targeted design that goes beyond traditional trial-and-error searches.</div>

Sign in / Sign up

Export Citation Format

Share Document