scholarly journals Numerical and Physical Modelling of the Performance of the Pro-vortex Vanes in Shaft Spillways

2021 ◽  
Vol 1203 (3) ◽  
pp. 032082
Author(s):  
Miroslav Broucek ◽  
Ladislav Satrapa ◽  
Martin Kralik ◽  
Jiri Soucek
Keyword(s):  
Pressure Fluctuations ◽  
Turbulence Models ◽  
Physical Modelling ◽  
Complete Removal ◽  
Developed Countries ◽  
Climate Change Scenarios ◽  
Cfd Modelling ◽  
Existing Structures ◽  
Hydraulic Conditions ◽  
Spillway Tunnel

Abstract The paper focuses on the analysis of hydraulic conditions in the proximity of the intake part of high shaft spillways equipped with pro-vortex vanes and discusses recent enhancements in modelling of the shaft spillways and compares the acquired results of the performance of the spillway after complete removal or rehabilitation of the vanes in context of capacity and overall hydraulic conditions. Increasing requirements on safety of embankment dams during floods with respect to anticipated effect of the climate change scenarios on parameters of design floods demand further assessment of capabilities of outlet structures to meet the updated needs. Such dam safety assessments often conclude in the need of designing additional measures to improve existing structures. Despite different approach to the evaluation of the uncertainties and subsequent risk assessment the goal of improving safety of large dams remains consistent in the effort of all developed countries. Adjustments of the intake part of shaft spillways can present a valid design option for increasing capacity of the complex spillway/tunnel structure if supported by solid analysis of hydraulic conditions inside these structures. As the governing idea of the pro-vortex vanes is to ensure spiral flow inside the shaft and to minimize the pressure fluctuations the paper presents results from physical model of several designs of the pro-vortex vanes which approximated possible adjustment of tower like shaft spillway of existing large dam in Czech Republic and also results from CFD modelling illustrating the importance of combination of both modelling approaches. For the CFD part, different turbulence models are discussed.

A Road Map for CFD Modelling of Forced Cooled Packages

2006 ◽  
Author(s):  
Emre O¨ztu¨rk ◽  
Ilker Tari
Keyword(s):  
Heat Transfer ◽  
Numerical Models ◽  
Turbulence Models ◽  
Thermal Design ◽  
Heat Sinks ◽  
Convergence Criteria ◽  
Cfd Modelling ◽  
Road Map ◽  
Discretization Schemes ◽  
Cfd Analyses

In this study, Computational Fluid Dynamics, which has taken its position in the thermal design of electronic packages, was used in order to draw a CFD road map for forced cooling conjugate heat transfer analyses in heat generating electronic systems. The main sources of error in CFD analyses arise from inappropriate numerical models including turbulence models, radiation modeling and discretization schemes, insufficient grid resolution, and lack of convergence. A complete computer chassis model with heat sinks and fans inside was created and parametric analyses were performed to compare the effects of different turbulence models, discretization schemes, mesh resolutions, convergence criteria, and radiative heat transfer. Two commercially available CFD software packages were used, Icepak™ for pre-processing, Fluent™ for solution and post-processing. The road map was applied to three different heat sinks modeled into the full chassis. Numerical results were compared with the available experimental data and they were in good agreement.

CFD Analysis of Industrial Gas Turbine Exhaust Diffusers

2002 ◽  
Author(s):  
V. Vassiliev ◽  
S. Irmisch ◽  
S. Florjancic
Keyword(s):  
Gas Turbine ◽  
Measurement Data ◽  
Turbulence Models ◽  
Cfd Analysis ◽  
Cfd Modelling ◽  
Gas Turbine Exhaust ◽  
Key Aspects ◽  
Industrial Gas Turbine ◽  
Turbine Exhaust

The key aspects for the reliable CFD modelling of exhaust diffusers are addressed in this paper. In order to identify adequate turbulence models a number of 2D diffuser configurations have been simulated using different turbulence models and results have been compared with measurements. An automated procedure for a time- and resource-efficient and accurate prediction of complex diffuser configuration is presented. The adequate definitions of boundary conditions for the diffuser simulation using this procedure are discussed. In the second part of this paper, the CFD procedure is being applied to investigate the role of secondary flow on axial diffusers. Prediction results are discussed and compared with available measurement data.

Numerical simulations for swirlmeter on flow fields and metrological performance

2016 ◽  
Vol 40 (4) ◽  
pp. 1072-1081 ◽  
Author(s):  
Desheng Chen ◽  
Baoling Cui ◽  
Zuchao Zhu
Keyword(s):  
Vortex Core ◽  
Reverse Flow ◽  
Pressure Fluctuations ◽  
Flow Characteristics ◽  
Turbulence Models ◽  
Internal Flow ◽  
Industrial Applications ◽  
Throat Region ◽  
Vortex Precession ◽  
Metrological Performance

Measurements of flow rates of fluids are important in industrial applications. Swirlmeters (vortex precession meters) are widely used in the natural gas industry because of their advantage in having a large measurement range and strong output signal. In this study, using air as a working medium, computational fluid dynamics (CFD) simulations of a swirlmeter were conducted using the Reynolds-averaged Navier–Stokes (RANS) and renormalization group (RNG) k–ε turbulence models. The internal flow characteristics and the influence of the tube structure (geometric parameter of flow passage) on metrological performance were studied, with a particular focus on the meter factor. Calibration experiments were performed to validate the CFD predictions; the results show good agreement with those from simulations. From the streamline distributions, a clear vortex precession is found in the throat region. At the end of throat, the pressure fluctuation reached a maximum accompanied by the largest shift in the vortex core from the centreline. There exists a large reverse flow zone in the vortex core region in the convergent section. To mitigate the influence of reverse flow on vortex precession, a suitable length of throat is required. For a larger convergent angle, the fluid undergoes higher acceleration leading to an increase in velocity that produces more intensive pressure fluctuations. The minor diameter of the throat also produces a higher velocity and larger meter factor. Compared with both divergent angle and throat length, the convergent angle and throat diameter play a more important role in determining precession frequency.

3D Quasi-Unsteady Flow Simulation in a Centrifugal Pump: Comparison With the Experimental Results

2004 ◽  
Author(s):  
Miguel Asuaje ◽  
Farid Bakir ◽  
Andres Tremante ◽  
Ricardo Noguera ◽  
Robert Rey
Keyword(s):  
Unsteady Flow ◽  
Centrifugal Pump ◽  
Cfd Simulation ◽  
Pressure Fluctuations ◽  
Pressure Sensors ◽  
Flow Simulation ◽  
Turbulence Models ◽  
Numerical Predictions ◽  
Radial Thrust ◽  
Unsteady Flow Simulation

A 3D-CFD simulation of the impeller and volute casing of a centrifugal pump has been performed using commercial codes CFX 5.5 and CFX-TASCflow 2.12. The pump has an specific speed of 32 (metric units) and an outside impeller diameter of 400 mm. First, a 3D-flow simulation for the isolated impeller with a structured grid is presented. A sensitivity analysis regarding grid quality and turbulence models were also performed. A 3D quasi-unsteady flow simulation of the impeller-volute assembly is presented, as well. This flow simulation was carried out for several impeller blades and volute tongue relative positions. As a result, the radial thrust on the pump shaft were calculated for different flow rates. Experimental test were carried out in order to compare theoretical pressure fluctuations with the experimental ones measured by various unsteady pressure sensors placed on the impeller shroud and volute. The qualitative and quantitative results ratify numerical predictions.

scholarly journals CFD Modelling of Naturally Ventilated Double Skin Façades: Comparisons among 2D and 3D Models

2021 ◽  
Vol 65 (2-4) ◽  
pp. 330-336
Author(s):  
Camilla Lops ◽  
Nicola Germano ◽  
Sabino Matera ◽  
Valerio D’Alessandro ◽  
Sergio Montelpare
Keyword(s):  
Energy Requirement ◽  
Three Dimensional ◽  
Turbulence Models ◽  
3D Models ◽  
Computational Effort ◽  
Correct Prediction ◽  
Cfd Modelling ◽  
Double Skin ◽  
Cfd Analyses ◽  
Double Skin Facades

Nowadays, Double Skin Façades (DSFs) are popular technologies adopted for both new and existing buildings. Since their introduction, new configurations and materials started to be tested to improve the DSF energy behaviour and function. Such complex technologies, able to improve comfort conditions of occupied spaces and decrease building energy requirement, are strictly related to the design phase that should be carefully evaluated. The correct prediction of air fluxes inside the DSF cavity, in fact, is highly influenced by the adopted analysis hypothesis and settings. Moreover, the absence of multiple experimental campaigns and empirical validations in the sector represents the major concerns for scientists and researchers. Among the possible numerical approaches for studying DSFs, Computational Fluid Dynamics (CFD) analyses confirm to be the most suitable solution. The CFD modelling activity presented in this paper intends to compare various Double Façade configurations by adopting bi- and three-dimensional domains and different turbulence models. According to the obtained results, 2D simulations can predict airflows inside and around the DSF channel with good approximation and reasonable computational effort. Moreover, the velocity profiles estimated by the turbulence formulations are in good accordance, underling only a few slight variations in proximity to the DSF layers.

Multiphase Flow Induced Vibrations at High Pressure: CFD Analysis of Multiphase Forces

2021 ◽  
Author(s):  
Paul Emmerson ◽  
Mike Lewis ◽  
Neil Barton ◽  
Steinar Orre ◽  
Knud Lunde ◽  
...  
Keyword(s):  
High Pressure ◽  
Multiphase Flow ◽  
Gas Flow ◽  
Production Systems ◽  
Pressure Fluctuations ◽  
High Amplitude ◽  
Operating Pressure ◽  
Cfd Analysis ◽  
Cfd Modelling ◽  
Test Loop

Abstract CFD analysis of a high pressure 2” pipe test loop with water-gas flow was undertaken using three different solvers. Multiphase flow induced forces were predicted on the bends at a range of operating pressures between 10 and 80 barg and compared with forces reconstructed from vibration measurements. Overall the three different CFD solvers predicted consistent results. The fluid forces predicted on the bends of the double U-loop test rig have a good range of values compared to the test reconstructed forces. The forces predicted at low pressure were in line with the experimental reconstructed values, whilst at high pressure all three CFD solvers predicted higher forces. The trend of the forces reducing with increased operating pressure, evident in test, was matched by one of the CFD methods, but less well by the other two. At low operating pressure the forces are dominated by the momentum of the liquid in the multiphase flow, whilst at high pressure the pressure fluctuations and turbulent effects will be more important. All three CFD solvers use VOF methods and above about 40 barg it is possible that they struggle to fully resolve the flow behaviour, which will be more influenced by bubble and droplet entrainment and turbulence. Multiphase flow can induce high amplitude vibrations in piping systems, potentially leading to fatigue failures. CFD modelling offers a potentially powerful tool to provide the flow induced forces required for assessing and diagnosing multiphase flow induced pipework vibration problems in hydrocarbon production systems.

POD and Extended-POD Analysis of Pressure Fluctuations and Vortex Structures Inside a Steam Turbine Control Valve

2018 ◽  
Author(s):  
Peng Wang ◽  
Hongyu Ma ◽  
Yingzheng Liu
Keyword(s):  
Steam Turbine ◽  
Pressure Fluctuation ◽  
Pressure Field ◽  
Pressure Fluctuations ◽  
Turbulence Models ◽  
Control Valve ◽  
Vortex Structures ◽  
Detached Eddy Simulation ◽  
Eddy Simulation ◽  
Pod Analysis

In steam turbine control valves, pressure fluctuations coupled with vortex structures in highly unsteady three-dimensional flows make essential contributions to aerodynamic forcing on the valve components, and are major sources of flow-induced vibration and acoustic effects. Advanced turbulence models, such as scale adaptive simulation (SAS), detached eddy simulation (DES) and large eddy simulation (LES), can capture detailed flow information of the control valve, but it is challenging to identify the primary flow structures due to the massive flow database. The present study used state-of-the-art data-driven analysis, namely proper orthogonal decomposition (POD) and extended-POD, to extract the energetic pressure fluctuations and dominant vortex structures of the control valve. To this end, the typical annular attachment flow inside a steam turbine control valve was investigated by performing a DES study. Subsequently, the energetic pressure fluctuation modes were extracted by performing POD analysis on the valve’s pressure field. The vortex structures contributing to these energetic pressure fluctuation modes were extracted by performing extended-POD analysis on the pressure-velocity coupling field. Finally, the dominant vortex structures were revealed directly by POD analysis of the valve’s velocity field. The results demonstrated that the flow instabilities inside the control valve were mainly induced by oscillations of the annular wall-attached jet and the derivative flow separations and reattachments. In POD analysis of the pressure field, the axial, antisymmetric and asymmetric pressure modes occupied most of the pressure fluctuation intensity. By further conducting extended-POD analysis, the vortex structures’ incorporation with the energetic pressure modes was identified as mainly attributed to the synchronous, alternating and single-sided oscillation behaviors of the annular attachment flow. However, based on POD analysis of the unsteady velocity fields, the vortex structures, buried in the dominant modes at St = 0.017, were found to result from alternating oscillations of the annular wall-attached jet.

Facing the Challenges in CFD Modelling of Multistage Axial Compressors

2017 ◽  
Author(s):  
Lorenzo Cozzi ◽  
Filippo Rubechini ◽  
Michele Marconcini ◽  
Andrea Arnone ◽  
Pio Astrua ◽  
...  
Keyword(s):  
Steady State ◽  
Axial Compressor ◽  
Turbulence Models ◽  
Operating Conditions ◽  
Tip Clearance ◽  
Cfd Modelling ◽  
Main Research ◽  
Axial Compressors ◽  
Rotor Stator Interaction ◽  
The Impact

Multistage axial compressors have always been a great challenge for designers since the flow within these kind of machines, subjected to severe diffusion, is usually characterized by complex and widely developed 3D structures, especially next to the endwalls. The development of reliable numerical tools capable of providing an accurate prediction of the overall machine performance is one of the main research focus areas in the multistage axial compressor field. This paper is intended to present the strategy used to run numerical simulations on compressors achieved by the collaboration between the University of Florence and Ansaldo Energia. All peculiar aspects of the numerical setup are introduced, such as rotor/stator tip clearance modelling, simplified shroud leakage model, gas and turbulence models. Special attention is payed to the mixing planes adopted for steady-state computations because this is a crucial aspect of modern heavy-duty transonic multistage axial compressors. In fact, these machines are characterized by small inter-row axial gaps and transonic flow in front stages, which both may affect non-reflectiveness and fluxes conservation across mixing planes. Moreover, the high stage count may lead to conservation issues of the main flow properties form inlet to outlet boundaries. Finally, the likely occurrence of partspan flow reversal in the endwall regions affects the robustness of non-reflecting mixing plane models. The numerical setup has been validated on an existing machine produced and experimentally tested by Ansaldo Energia. In order to evaluate the impact on performance prediction of the mixing planes introduced in the steady-state computation, un-steady simulations of the whole compressor have been performed at different operating conditions. These calculations have been carried out both at the compressor design point and close to the surge-line to evaluate the effect of rotor/stator interaction along the compressor working line.

3D CFD Investigation of Air Flow Behind a Porous Fence Using Different Turbulence Models

2014 ◽  
Author(s):  
Yizhong Xu ◽  
Mohamad Y. Mustafa ◽  
Geanette Polanco
Keyword(s):  
Velocity Profile ◽  
Turbulence Model ◽  
Air Flow ◽  
Turbulence Models ◽  
Experimental Results ◽  
Turbulence Structure ◽  
Cfd Modelling ◽  
Lack Of Information ◽  
Vertical Velocity Profile ◽  
Flow Through

Even after many years of the application of numerical CFD techniques to flow through porous fences, still there is disagreement between researchers regarding the best turbulence model to be implemented in this field. Moreover, different sources claim to have achieved good agreement between numerical results and experimental data; however, it is not always possible to compare numerical and experimental results due to the lack of information or variations in test conditions. In this paper, five different turbulence models namely; K-ε models (standard, RNG and Realizable) and K-ω models (Standard and SST), have been applied through a 3D CFD model to investigate air flow behind a porous panel, under the same conditions (boundary conditions and numerical schemes). Results are compared with wind tunnel experiments. Comparison is based on the vertical velocity profile at a location 925 mm downstream of the fence along its center line. All models were capable of reproducing the velocity profile, however, some turbulence models over-predicted the reduction of velocity while it was under-predicted by other models, however, discrepancy between CFD modelling and experimental results was kept around 20%. Comprehensive description of the turbulence structure and the streamlines highlight the fact that the criterion for selecting the best turbulence model cannot rely only on the velocity comparison at one location, it must also include other variables.

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