Numerical Investigation of a Banki Turbine in Transient State: Reaction Ratio Determination

2012 ◽  
Author(s):  
Sergio D. Croquer ◽  
Jesus de Andrade ◽  
Jorge Clarembaux ◽  
Freddy Jeanty ◽  
Miguel Asuaje
Keyword(s):  
Numerical Models ◽  
Flow Characteristics ◽  
Cross Flow ◽  
Turbulence Models ◽  
Transient State ◽  
Major Influence ◽  
Small Scale ◽  
Complex Flow ◽  
Impulse Turbine ◽  
Reaction Ratio

Cross-Flow Turbines (CFT) also known as Banki Turbines, are often considered for small scale hydroelectric generation. They are known for their simple construction, maintenance and operation, which means they incur in lower CAPEX and OPEX when compared to other types of turbines. However, they also tend to have a modest efficiency (82% [1–3]), hence they are not considered for big scale operations. Little is known about the flow characteristics inside the runner of the CFT. The objective of this investigation is to better understand the flow inside CFTs using Computational Fluid Dynamics (CFD) tools. Steady and Transient State simulations were performed for a CFT at an specific speed NS = 45. SST and κ–ε turbulence models were compared in terms of simulation requirements and obtained results. A proposed runner-nozzle interface, considering real CFT existent gap between these two components (free space) was evaluated as well. Results were compared to available experimental data. Maximum, numerically calculated efficiency deviation from reported experimental global efficiency was 15%. Pressure and velocity profiles along nozzle outlet, energy transfer stages location and CFT reaction ratio values were addressed. Results were compared in terms of runner-nozzle interface (gap vs no-gap), turbulence model (SST vs κ–ε) and calculation regime (steady vs transient regime). Only calculation state (steady vs transient) was found to have major influence over results. Transient state calculations better representing complex flow inside the CFT. Obtained degrees of reaction (no runner-nozzle gap, SST, transient state) were 0.12 and 0.08, for 1st and 2nd stages respectively. Hence the CFT is defined, according to this numerical models, as an impulse turbine.

Prediction of Unsteady Flow around a Square Cylinder Using RANS

2011 ◽  
Vol 52-54 ◽  
pp. 1165-1170
Author(s):  
Fu You Xu ◽  
Xu Yong Ying ◽  
Zhe Zhang
Keyword(s):  
Standard Model ◽  
Unsteady Flow ◽  
Flow Characteristics ◽  
Turbulence Models ◽  
Surface Flow ◽  
Two Dimensional ◽  
Square Cylinder ◽  
Complex Flow ◽  
Near Surface ◽  
Sst Model

The results of unsteady Reynolds averaged Navier-Stokes (URANS) simulations of flow around a square cylinder using two-dimensional hybrid meshes were presented in this paper. The first part examined the accuracy of various RANS turbulence models, i.e. the standard model, RNG model, realizable model, standard model, SST model, and RSM, by comparing their results with available experimental data. Despite the limits imposed by the RANS approach and the relatively inexpensive two-dimensional computations, the main features of this complex flow can be predicted reasonably well. Among the computations using various RANS models compared here, the SST model shows the best agreement with the experiment. The second part investigated the effects of corner cutoffs on unsteady flow characteristics around a square cylinder by using the SST model. Especially the detailed near-surface flow structure around the cylinder was focused on, aiming at giving an explanation for the drastic modification of the aerodynamic characteristics as the corner shape is slightly changed.

Influence of PIG Mass, Launching Time and Turbulence Model on 3-D CFD Transient Simulation of PIG Motion

2016 ◽  
Author(s):  
Diego Jaimes Parilli ◽  
Armando Blanco ◽  
Janneth García
Keyword(s):  
Pressure Drop ◽  
Numerical Models ◽  
Control Volume ◽  
Asymptotic Relation ◽  
Fluid Pressure ◽  
Turbulence Models ◽  
Transient State ◽  
Terminal Velocity ◽  
Transient Simulation ◽  
Transient Pressure

Pigging procedures are common maintenance operations used to perform cleaning, draining and pipeline inspection in order to improve flow efficiency and operation cost. Despite these procedures are commonly used, questions still remain regarding the flow and the PIG motion features due to the complex interaction among pig, wall and flow, and the changes in internal fluid pressure and local fluid density. Currently, the PIG dynamic predictions are based on experimental data from short scale laboratory experiments and numerical models founded on physical simplification. So far, the transient of PIG motion calculated by methods that combine CFD and fluid-structure interaction in a 3D model and the influence of the physic and numerical features over the pig dynamics has not been analyzed yet. To provide a better understanding of pigging runs, this paper proposes a CFD methodology to obtain a 3D transient simulation of PIG motion. A moving control volume attached to the PIG let to solve the governing equation in a stationary mesh. This methodology is used to obtain the transient simulation of a PIG launched in a straight water pipeline for different PIG mass, launching time and turbulence models in order to study its influence over the PIG dynamics. The numerical results show a linear relation between the mass and the pressure drop in the transient state, but with no influence over the final stationary state. Also, an asymptotic relation between the transient pressure drop and the launching time was observed with no influence over the PIG terminal velocity. Besides, it is exposed the influence of the turbulence models (κ-ε, SST and BSL Reynolds Stress) in the results of pig motion; appreciable difference between the drop pressure of Omega-Based Stress Models (SST and BSL) and κ-ε turbulent model at steady state is shown, and, finally, a comparison of the velocity profiles at the interstice for each model was developed, this one shows an inaccuracy of the κ-ε model to describe the velocity profile in the walls proximities.

An Experimental Study of Detailed Flow and Heat Transfer Analysis in a Single Row Narrow Impingement Channel

2014 ◽  
Author(s):  
Jahed Hossain ◽  
Lucky V. Tran ◽  
Jayanta S. Kapat ◽  
Erik Fernandez ◽  
Rajan Kumar
Keyword(s):  
Heat Transfer ◽  
Flow Characteristics ◽  
Cross Flow ◽  
Turbulence Models ◽  
Heat Transfer Analysis ◽  
Temperature Sensitive ◽  
Single Row ◽  
Flow Physics ◽  
Flow And Heat Transfer ◽  
Target Wall

An experimental investigation of detailed flow and heat transfer in a narrow impingement channel was studied; the channel included 15 inline jets in a single row with a jet-to-target wall distance of 3 jet diameters. The spanwise length of the channel was 4 jet diameters, and a streamwise jet spacing of 5 jet diameters was considered for the current study. Both the flow physics and heat transfer tests were run at an average jet Reynolds number of 30,000. Temperature sensitive paint was used to study heat transfer at the target wall. Along with other parameters, jet-to-jet interaction in a narrow row impingement channel plays a significant role on heat transfer distribution at the side and target walls as the self-induced jet cross flow tends to bend the downstream jets. The present work shows detailed information of flow physics using Particle Image Velocimetry (PIV). PIV measurements were taken at planes normal to the target wall along the jet centerline for several jets. The flow field and heat transfer data was compared between the experiment and CFD in order to understand the relationship between flow characteristics and heat transfer. The experimental data gathered from PIV can be used as benchmark data for validating the current state of the art RANS turbulence models as well as for Large Eddy Simulation (LES).

Internal Flow Characteristics of Cross-Flow Hydraulic Turbine With the Variation of Nozzle Shape

2007 ◽  
Author(s):  
Young-Do Choi ◽  
Jea-Ik Lim ◽  
You-Taek Kim ◽  
Young-Ho Lee
Keyword(s):  
Flow Characteristics ◽  
Cross Flow ◽  
Internal Flow ◽  
Close Relation ◽  
Hydraulic Turbine ◽  
Impulse Turbine ◽  
Runner Blade ◽  
Turbine Performance ◽  
Nozzle Shape ◽  
The Cross

The purpose of this study is to examine the optimum configuration of nozzle shape to further optimize the cross-flow hydraulic turbine structure and improve the performance. The results show that CFD analysis for the cross-flow turbine can be adopted as a useful method to examine the internal flow and turbine performance in detail. Pressure on the runner blade in Stage 1 and velocity at nozzle outlet have close relation to the turbine performance. The performance characteristics of cross-flow turbine have both impulse turbine and reaction turbine simultaneously.

Compressible flow characteristics in bent duct with constant flow section

2020 ◽  
pp. 095441002095859
Author(s):  
Xiao-lin Sun ◽  
Shan Ma ◽  
Zhan-xue Wang ◽  
Jing-wei Shi ◽  
Li Zhou
Keyword(s):  
Shock Wave ◽  
Flow Characteristics ◽  
Turbulence Models ◽  
Stress Transfer ◽  
Oblique Shock Wave ◽  
Flow Section ◽  
Formation Mechanisms ◽  
Constant Flow ◽  
Complex Flow ◽  
Large Curvature

The components with large curvature features are widely applied in aero-engines. Complex flow features are induced due to large curvature under high-subsonic even transonic incoming flow condition. In this study, the formation mechanisms of local acceleration in bent duct are investigated. To this end, the cold fluid test of a 60° bent duct with constant flow section was conducted. The surface static pressures and the schlieren flow visualizations were obtained. Then the three-dimensional numerical simulations based on the experimental model were computed using computational fluid dynamics software. The simulations were conducted using five different turbulence models to compare with the experimental data. The validation study shows that the shear stress transfer (SST) κ-ω turbulence model is suitably used for the simulations. Results show that three different flow situations were shown for the bent duct at diverse nozzle pressure ratios (NPRs). One situation was shown by the case at NPR = 1.5, in which the whole flow field is subsonic, and just two jet edges are shown by the schlieren images. One situation was shown by the case at NPR = 1.8, in which a local supersonic region is induced near the lower wall at the hind side of the bent section, and a small shock wave is observed. The other one situation was shown by the cases at NPR = 2.0, 2.5 and 3.0, in which the air flow in the whole passage reaches supersonic speeds and an oblique shock wave is shown for each case.

Evaluation of Turbulence Modeling Approaches for Cross-Flow in a Helical Tube Bundle

2018 ◽  
Author(s):  
Adam R. Kraus ◽  
Haomin Yuan ◽  
Elia Merzari
Keyword(s):  
Pressure Drop ◽  
Turbulence Modeling ◽  
Tube Bundle ◽  
Cross Flow ◽  
Turbulence Models ◽  
Computational Time ◽  
High Fidelity ◽  
Complex Flow ◽  
Helical Tube ◽  
Flow Phenomena

Helical steam generators are proposed for use in a number of advanced nuclear reactor designs. The cross-flow around the helical tubes is a complex flow-field, and accurate knowledge of this flow is necessary for estimating pressure drop, heat transfer, and risk of flow-induced vibration. However, legacy data for helical tube cross-flow are scarce, and building new large-scale experiments that investigate relevant phenomena can be costly. Thus large uncertainties must currently be taken into account in the design of these systems. Numerical modeling with CFD can provide improved insight into the flow phenomena to reduce this uncertainty, but choosing a methodology can prove difficult. LES methods provide high-fidelity data, but require immense computational time to perform even an investigatory calculation for a moderate-sized sector, let alone for many design iterations. URANS methods offer significantly lower computational time, but it can be difficult to confidently justify the accuracy of a particular model without validation, particularly given the highly three-dimensional and complex flow-field present here. To better establish a basis for URANS turbulence modeling, an LES simulation was performed using Nek5000, a massively-parallel spectral element code developed at Argonne National Laboratory, for the geometry of a legacy helical tube bundle experiment. Data from this high-fidelity LES simulation were compared with URANS simulations using a number of turbulence models with the commercial code STAR-CCM+. Turbulent kinetic energy in the flow channels as well as bundle pressure drop were compared. The values of these key parameters were found to vary significantly between different turbulence models, with some models predicting pressure drops and kinetic energies well below those seen in LES. Some models were identified that showed good potential for predicting helical tube bundle flow phenomena. Further work, at a wider range of flow velocities, will be useful to further solidify the range of applicability of these models.

Computational Analysis of Fluid Flow in Pebble Bed Modular Reactor Using Different Turbulence Models

2010 ◽  
Author(s):  
Akshay Gandhir ◽  
Yassin Hassan
Keyword(s):  
Fluid Flow ◽  
Pressure Drop ◽  
Flow Structure ◽  
Computational Study ◽  
Vortex Formation ◽  
Flow Characteristics ◽  
Turbulence Models ◽  
Packed Bed ◽  
Complex Flow ◽  
Fluid Flow Characteristics

A steady state computational study was done to obtain the pressure drop estimation in different packed bed geometries, and describe the fluid flow characteristics for such complex structures. Two out of the three Bravais lattices were analyzed, namely, simple cubic (symmetric) and body centered cubic (staggered). STARCCM+ commercial CFD software from CD-ADAPCO was used to simulate the flow. To account for turbulence effects standard k-epsilon and realizable k-epsilon models were used. Various cases were analyzed with Modified Reynolds number ranging from 10,000 to 50,000. Each model showed different results as far as the velocity and flow structure is concerned. However, for each case the flow structure showed similar features such as vortex formation downstream and between pebbles due to complex flow separation [1]. The pressure drop obtained from each model was found to be in reasonable agreement with the existing data.

Use of CFD Tools in Internal Deflector Design for Cross Flow Turbine Efficiency Improvement

2012 ◽  
Author(s):  
Sergio D. Croquer ◽  
Jesus de Andrade ◽  
Jorge Clarembaux ◽  
Freddy Jeanty ◽  
Miguel Asuaje
Keyword(s):  
Power Plants ◽  
Large Scale ◽  
Numerical Models ◽  
Fluid Dynamic ◽  
Cross Flow ◽  
Small Scale ◽  
Efficiency Improvement ◽  
Hydropower Generation ◽  
Turbine Efficiency ◽  
Starting Point

Cross Flow Turbines (CFT), also known as Banki or Ossberger turbines are broadly used in small scale hydropower generation. Easy construction and operation, low CAPEX and OPEX and fairly independent efficiency from flow rate are the main characteristics of the CFT. However, they also tend to have a modest efficiency (80%), hence they are not considered for large scale power plants. Previous work have focused on use of Internal Deflectors (ID) for CFT efficiency improvement. However experimental flow observation and characterization inside CFT is hard to achieve. This work proposes use of Computational Fluid Dynamic (CFD) tools as an aid in ID design. A transient regime, two-dimensional, numerical model of a CFT without any internal deflectors was carried out. Deviation from experimental results at BEP was close to 5%. CFT w/o ID results were used as ID design starting point. Parameters: Upper Blade Position and ID Length were defined and varied obtaining six different ID versions. Numerical models were carried out for evaluation of ID effect on CFT. CFT hydraulic efficiency improvement was achieved for all ID versions studied (range 0.5%–3%, average:1.9%). Output power was also augmented (range 0.3%–4%, average:2.5%)for all cases.

Numerical Analysis of a Multiple Jet Impingement System

2009 ◽  
Author(s):  
G. Arvind Rao ◽  
Myra Kitron-Belinkov ◽  
Yeshayahou Levy
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Flow Behavior ◽  
Flow Characteristics ◽  
Turbulence Models ◽  
Jet Impingement ◽  
Impinging Jets ◽  
Turbulent Regime ◽  
Transfer Coefficients ◽  
Complex Flow

Jet impingement is known to provide higher heat transfer coefficients as compared to other conventional modes of single phase heat transfer. Jet impingement has been a subject of research for a long time. Single jets have been studied extensively for their heat transfer and flow characteristics. However, for practical usage, multiple jets (in the form of arrays) have to be used for increasing the total heat transfer over a given area. Most of the research on multiple impinging jets have focused on evaluating heat transfer correlations for such arrays in the turbulent regime (Re >2500). The focus of the present paper is on experimental investigation of a large array of impinging jets in the low Reynolds number regime (<1000) and subsequently numerically modeling the same array by using existing Computational Fluid Dynamics tools in order to study the physical phenomena within such a complex system. Different turbulence models were used for modeling the fluid flow within these impinging jets and it was found that the SST k-ω model is the most suitable. Results obtained from CFD analysis are in reasonable agreement with experimental values. It was observed that CFD simulations over predicted the Nusselt number and pressure drop when compared to the experimentally obtained values. It was also observed that the decrease in Nusselt number along the streamwise direction of the array was not monotonic. This could be due to the complex flow field resulting from interaction between the crossflow and the impinging jets in the wall jet region. It is anticipated that results obtained from the present work will provide greater insight into the flow behavior and the heat transfer mechanism occurring in multiple impinging jets.

scholarly journals Towards viable flow simulations of small-scale rotors and blade segments

2021 ◽  
pp. 8-8
Author(s):  
Jelena Svorcan ◽  
Aleksandar Kovacevic ◽  
Dragoljub Tanovic ◽  
Mohammad Hasan
Keyword(s):  
Turbulence Modeling ◽  
Turbulence Models ◽  
Operating Conditions ◽  
Flight Mechanics ◽  
Small Scale ◽  
Viscous Effects ◽  
Complex Flow ◽  
Thrust Coefficient ◽  
Spatial And Temporal Scales ◽  
Flow Models

The paper focuses on the possibilities of adequately simulating complex flow fields that appear around small-scale propellers of multicopter aircraft. Such unmanned air vehicles (UAVs) are steadily gaining popularity for their diverse applications (surveillance, communication, deliveries, etc.) and the need for a viable (i.e. usable, satisfactory, practical) computational tool is also surging. From an engineering standpoint, it is important to obtain sufficiently accurate predictions of flow field variables in a reasonable amount of time so that the design process can be fast and efficient, in particular the subsequent structural and flight mechanics analyses. That is why more or less standard fluid flow models, e.g. Reynolds-averaged Navier-Stokes (RANS) equations solved by the finite volume method (FVM), are constantly being employed and validated. On the other hand, special attention must be given to various flow peculiarities occurring around the blade segments shaped like airfoils since these flows are characterized by small chords (length-scales), low speeds and, therefore, low Reynolds numbers (Re) and pronounced viscous effects. The investigated low-Re flows include both transitional and turbulent zones, laminar separation bubbles (LSBs), flow separation, as well as rotating wakes, which require somewhat specific approaches to flow modeling (advanced turbulence models, fine spatial and temporal scales, etc). Here, the conducted computations (around stationary blade segments as well as rotating rotors), closed by different turbulence models, are presented and explained. Various qualitative and quantitative results are provided, compared and discussed. The main possibilities and obstacles of each computational approach are mentioned. Where possible, numerical results are validated against experimental data. The correspondence between the two sets of results can be considered satisfactory (relative differences for the thrust coefficient amount to 15%, while they are even lower for the torque coefficient). It can be concluded that the choice of turbulence modeling (and/or resolving) greatly affects the final output, even in design operating conditions (at medium angles-of-attack where laminar, attached flow dominates). Distinctive flow phenomena still exist, and in order to be adequately simulated, a comprehensive modeling approach should be adopted.

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