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.

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.

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 Tailings Filtration Using Viper Filtration Technology—a Case Study

2021 ◽  
Author(s):  
Oliver Whatnall ◽  
Kevin Barber ◽  
Peter Robinson
Keyword(s):  
Large Scale ◽  
Full Scale ◽  
Plant Design ◽  
Design Data ◽  
Pilot Testing ◽  
Performance Improvements ◽  
Wide Range ◽  
Vacuum Belt ◽  
Filtration Technology

AbstractInvestigation and uptake of filtered tailings continues to grow throughout the globe. This is driven by a wide range of site-specific considerations, which include such factors as tailings characteristics (e.g., amenability to filtration), production rates, climate, water availability, cost drivers, environmental requirements, and social factors. Despite the aforementioned technological growth, the currently available filtration technology is not able to meet the needs of many operations and projects that would otherwise adopt the technology. Experience with large-scale industrial filtration shows that vacuum belt filter systems meet the needs of many modern users, exceptions being the inability to effectively dewater tailings at altitude and/or with a fine particle size distribution: a potential fatal flaw. This paper presents a case study on the utilization of the patented Viper Filtration technology on gold tailings to overcome this challenge and shares the resultant full-scale plant design, highlighting the features designed to overcome cost and scalability deterrents. This technology is a novel mechanical process which complements the vacuum pressure in dewatering the filter cake as it travels along the belt filter. This project commenced with a pilot testing program, which successfully met the objective to rigorously test, measure and record any performance improvements achieved when engaging the Viper technology. Of the two tailings products tested, gross improvements of 4.2%w/w and 5.7%w/w were achieved when compared to the conventional vacuum belt filter operation. This pilot testing facilitated measurement of operating and design data, which forms the basis of the full-scale system design and resultant equipment supply of three vibration roller assemblies for retro-fitting on the existing vacuum belt filter.

scholarly journals Assessment of Discretization Uncertainty Estimators Based On Grid Refinement Studies

2021 ◽  
Author(s):  
Luis Eca ◽  
Guilherme Vaz ◽  
Martin Hoekstra ◽  
Scott Doebling ◽  
Robert Singleton ◽  
...  
Keyword(s):  
Incompressible Flows ◽  
Turbulence Models ◽  
Double Precision ◽  
Grid Refinement ◽  
Convergence Criteria ◽  
Data Set ◽  
Local Flow ◽  
Uncertainty Estimates ◽  
Wide Range ◽  
Naca 0012

Abstract This paper presents the assessment of the performance of 9 discretization uncertainty estimates based on grid refinement studies including methods that use grid triplets and others that use a largest number of data points, which in the present study was set to five. The uncertainty estimates are performed for the data set proposed for the 2017 ASME Workshop on Estimation of Discretization Errors including functional and local flow quantities from the two-dimensional incompressible flows over a flat plate and the NACA 0012 airfoil. The data were generated with a RANS solver using three eddy-viscosity turbulence models with double precision and sufficiently tight iterative convergence criteria to ensure that the numerical error is dominated by the discretization error. The use of several geometrically similar grid sets with different near-wall cell sizes lead to a wide range of convergence properties for the selected flow quantities. The evaluation of uncertainty estimates is based on the ratio of the estimated uncertainty over the "exact error" that is obtained from an "exact solution" obtained from extra grid sets significantly more refined than those used to generate the Workshop data. Although none of the methods tested fulfilled the goal of bounding the "exact error" 95 times out of 100 that was tested, the results suggest that the methods tested are useful tools for the assessment of the numerical uncertainty of practical numerical simulations even for cases where it is not possible to generate data in the "asymptotic range".

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.

The impact of storage conditions on heat losses of HT-ATES systems

2021 ◽  
Author(s):  
Stijn Beernink ◽  
Martin Bloemendal ◽  
Niels Hartog
Keyword(s):  
Large Scale ◽  
Energy Use ◽  
Waste Heat ◽  
Ghg Emissions ◽  
Storage Conditions ◽  
Heat Losses ◽  
Transport Processes ◽  
Heating And Cooling ◽  
Wide Range ◽  
The Impact

<p>Heating and cooling is responsible for about 50% of the European total energy use. Therefore, renewable sources of heat are needed to reduce GHG emissions (e.g. solar, geothermal, waste-heat). Due to a temporal and spatial mismatch between availability and demand of heat, large scale heat storage facilities are needed. High Temperature Aquifer Thermal Energy Storage (HT-ATES) systems are one of the cheapest and most adequate ways to store large amounts of sensible heat. Regular/Low-T ATES systems are considered a proven technology with currently more than 3 000 systems operable world-wide. However, at higher storage temperatures (e.g. 40-100 °C) temperature dependent water properties (density, viscosity) more strongly affect physical processes, resulting in higher and unpredictable heat losses. While first applications and research on this subject started more than 50 years ago, many uncertainties still remain. In this research we study the (hydrogeological) storage conditions that affect the heat losses of HT-ATES systems. Numerical simulations of a wide range of storage conditions, are done to obtain generic insights in the performance of HT-ATES systems. These insights allow to identify which heat transport processes dominate in contribution to heat losses. Results show that conduction always contributes to heat losses for HT-ATES systems and relate to geometric storage conditions. While buoyancy flow (free convection) may also contribute considerable to heat losses under specific conditions.</p>

A Methodology for Simulating Compressible Turbulent Flows

2003 ◽  
Author(s):  
Hermann F. Fasel ◽  
Dominic A. von Terzi ◽  
Richard D. Sandberg
Keyword(s):  
Turbulent Flows ◽  
Compressible Flows ◽  
Flow Behavior ◽  
Flow Simulation ◽  
Turbulence Models ◽  
Fine Grid ◽  
Local Flow ◽  
Wide Range ◽  
Unsteady Rans ◽  
Grid Points

A Flow Simulation Methodology (FSM) is presented for computing the time-dependent behavior of complex compressible turbulent flows. The development of FSM was initiated in close collaboration with C. Speziale (then at Boston University). The objective of FSM is to provide the proper amount of turbulence modelling for the unresolved scales while directly computing the largest scales. The strategy is implemented by using state-of-the-art turbulence models (as developed for RANS) and scaling of the model terms with a “contribution function”. The contribution function is dependent on the local and instantaneous “physical” resolution in the computation. This “physical” resolution is determined during the actual simulation by comparing the size of the smallest relevant scales to the local grid size used in the computation. The contribution function is designed such that it provides no modelling if the computation is locally well resolved so that it approaches a DNS in the fine-grid limit and such that it provides modelling of all scales in the coarsegrid limit and thus approaches an unsteady RANS calculation. In between these resolution limits, the contribution function adjusts the necessary modelling for the unresolved scales while the larger (resolved) scales are computed as in traditional LES. However, FSM is distinctly different from LES in that it allows for a consistent transition between (unsteady) RANS, LES, and DNS within the same simulation depending on the local flow behavior and “physical” resolution. As a consequence, FSM should require considerably fewer grid points for a given calculation than would be necessary for a traditional LES. This conjecture is substantiated by employing FSM to calculate the flow over a backward-facing step at low Mach number and a supersonic, axisymmetric baseflow. These examples were chosen such that they expose, on the one hand, the inherent difficulties of simulating (physically) complex flows, and, on the other hand, demonstrate the potential of the FSM approach for a wide range of compressible flows.

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.

On the Impact of Blade Count Reduction on Aerodynamic Performance and Loss Generation in a Three-Stage LP Turbine

2001 ◽  
Author(s):  
Jochen Gier ◽  
Sabine Ardey
Keyword(s):  
Low Pressure ◽  
Aerodynamic Performance ◽  
Point Of View ◽  
Navier Stokes ◽  
Viscous Effects ◽  
Local Flow ◽  
Wide Range ◽  
Separation Bubbles ◽  
Flow Phenomena ◽  
The Impact

Reducing the number of blades in low pressure turbines is a desirable option for decreasing total operation costs. From an aerodynamical point of view this directly leads to an increased blade load. However, increasing the blade load above a certain level results in viscous effects like separation bubbles and finally full separation. This becomes especially significant for aero engine turbines, which operate at high altitudes and thus low Reynolds numbers. The underlying local flow phenomena and the effect on the aerodynamic performance of such configurations are addressed in this paper. This investigation is based on a three-stage low pressure turbine typical for aero engines. Different setups are employed with different number of guide vanes in certain stages. Furthermore, the Reynolds number is varied within a wide range. These configurations are investigated numerically using a modern steady-state transitional Navier-Stokes solver and experimental results from the same turbine. Based on this information, a detailed analysis of the viscous flow phenomena is performed with focus on the influence of separation bubbles on the loss production after the transition. These results are discussed with respect to blade count reduction.

Large-scale motions and inner/outer layer interactions in turbulent Couette–Poiseuille flows

2011 ◽  
Vol 680 ◽  
pp. 534-563 ◽  
Author(s):  
SERGIO PIROZZOLI ◽  
MATTEO BERNARDINI ◽  
PAOLO ORLANDI
Keyword(s):  
Large Scale ◽  
Flow Mode ◽  
Modulation Effect ◽  
Wide Range ◽  
Flow Features ◽  
The Mean ◽  
Flow Configurations ◽  
Nonlinear Modulation ◽  
High Reynolds ◽  
Poiseuille Flows

We investigate the organization of the momentum-carrying eddies in turbulent Couette–Poiseuille flows. The study relies on a direct numerical simulation (DNS) database covering a wide range of flow configurations from pure Couette to pure Poiseuille flows, at Reτ ≈ 250 (based on the flow properties at the stationary wall). The study highlights the occurrence of streaky patterns of alternating high and low momentum throughout the channel for all flow configurations, except near zeros of the mean shear, where streaks are suppressed. The mean streak spacing shows a relatively universal distribution in the core of the channel, where it ranges from 50 to 100 local viscous units. The validity of the local viscous scaling in collapsing flow features at different wall distances is confirmed by the analysis of the spanwise velocity spectra, which also highlights (in the case of Couette-like flows) the onset of a secondary low-wavenumber flow mode, superposed on the high-wavenumber flow mode that is responsible for the inner-layer dynamics. The effect of the former mode on the latter is studied by means of the two-point amplitude modulation coefficient, which brings to light a nonlinear modulation phenomenon. Physical mechanisms to explain the modulation effect are proposed, based on the interpretation of the conditional average events. Note that, although similar mechanisms have been previously observed in high-Reynolds-number turbulent boundary layers and channels, the modulation effect is here rather associated with the intrinsic large-scale dynamics of Couette-like flows, and takes place at DNS-accessible Reynolds numbers. We thus believe that the study of Couette-like flows may give an alternative avenue for probing inner/outer interaction effects than canonical channel flows.

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