scholarly journals Verification of the accuracy of CFD simulations in small-scale tunnel and atrium fire configurations

2011 ◽  
Vol 46 (4) ◽  
pp. 186-193 ◽  
Author(s):  
Nele Tilley ◽  
Pieter Rauwoens ◽  
Bart Merci
Keyword(s):  
Small Scale ◽  
Cfd Simulations ◽  
Atrium Fire

scholarly journals Numerical CFD simulations on a small-scale ORC expander using a customized grid generation methodology

2017 ◽  
Vol 129 ◽  
pp. 843-850 ◽  
Author(s):  
Giuseppe Bianchi ◽  
Sham Rane ◽  
Ahmed Kovacevic ◽  
Roberto Cipollone ◽  
Stefano Murgia ◽  
...  
Keyword(s):  
Grid Generation ◽  
Small Scale ◽  
Cfd Simulations

Fully-Coupled Turbojet Engine CFD Simulations and Cycle Analyses Along the Equilibrium Running Line

2020 ◽  
Author(s):  
Alejandro Briones ◽  
Andrew W Caswell ◽  
Brent Rankin
Keyword(s):  
Flow Rate ◽  
Fluid Dynamic ◽  
Thermodynamic Cycle ◽  
Angular Speed ◽  
Small Scale ◽  
Cfd Simulations ◽  
Fuel Flow ◽  
Turbojet Engine ◽  
Design Cycle ◽  
Fully Coupled

Abstract This work presents fully-coupled computational fluid dynamic (CFD) simulations and thermodynamic cycle analyses of a small-scale turbojet engine at several conditions along the equilibrium running line. The CFD simulations use a single mesh for the entire engine, from the intake to the exhaust, allowing information to travel in all directions. The CFD simulations are performed along the equilibrium running line by using the iterative Secant method to compute the fuel flow rate required to match the compressor and turbine power. The freestream pressure and temperature and shaft angular speed are the only inputs needed for the CFD simulations. To evaluate the consistency of the CFD results with thermodynamic cycle results, outputs from the CFD simulations are prescribed as inputs to the cycle model. This approach enables on-design and off-design cycle calculations to be performed without requiring turbomachinery performance maps. In contrast, traditional off-design cycle analyses require either scaling, calculating, or measuring compressor and turbine maps with boundary condition assumptions. In addition, the CFD simulations and the cycle analyses are compared with measurements of the turbojet engine. The CFD simulations, thermodynamic cycle analyses, and measurements agree in terms of total temperature and pressure at the diffuser-combustor interface, air and fuel mass flow rate, equivalence ratio, and thrust. The developed methods to perform CFD simulations from the intake to the exhaust of the turbojet engine are expected to be useful for guiding the design and development of future small-scale gas turbine engines.

Development of Efficient Small Scale Axial Turbine for Solar Driven Organic Rankine Cycle

2016 ◽  
Author(s):  
Ayad Al Jubori ◽  
Raya K. Al-Dadah ◽  
Saad Mahmoud ◽  
Khalil M. Khalil ◽  
A. S. Bahr Ennil
Keyword(s):  
Large Scale ◽  
Renewable Energy Sources ◽  
Cycle Performance ◽  
Working Fluid ◽  
Small Scale ◽  
Cfd Simulations ◽  
Axial Turbine ◽  
Working Fluids ◽  
Wide Range ◽  
Inlet Conditions

Recently, the increase in fossil fuel consumption and associated adverse impact on the environment led to significant interest in renewable energy sources like solar. This paper presents a new methodology that integrates the ORC cycle analysis with modeling of an efficient small scale subsonic axial turbine at low temperature heat sources using wide range of organic working fluids like R123, R134a, R141b, R152a, R245fa, R290 and isobutene. The work involves detailed turbine analysis including 1D mean line approach, extensive 3D CFD simulations and ORC cycle analysis at inlet total pressure ranging from 2–5 bar corresponding to temperature range from 275K–365K to achieve the best turbine and cycle performance. This work provides a more reliable data base for small scale organic working fluids instead of using the map of large scale gas turbine. The numerical simulation was performed using 3D RANS with SST turbulence model in ANSYS-CFX. Using iterative CFD simulations with various working fluids with subsonic inlet conditions, Mach number ranging from 0.6–0.65, results showed that using working fluid R123 for a turbine with mean diameter of 70mm, the maximum isentropic efficiency was 82% and power output 5.66 kW leading to cycle efficiency of 9.5%.

scholarly journals Numerical analysis on the performance of Dual Rotor wind turbine

2020 ◽  
Vol 8 (03) ◽  
pp. 352-368
Author(s):  
Hazem Ali Abdel Karim ◽  
Ahmed Reda El-Baz ◽  
Nabil Abdel Aziz Mahmoud ◽  
Ashraf Mostafa Hamed
Keyword(s):  
Wind Turbine ◽  
Rotational Speed ◽  
Pitch Angle ◽  
Numerical Study ◽  
Three Dimensional ◽  
Scale Model ◽  
Power Coefficient ◽  
Peak Performance ◽  
Small Scale ◽  
Cfd Simulations

This study investigates the aerodynamic performance of wind turbines aiming to maximize the power extracted from the wind. The study is focusing on the effect of introducing a second rotor to the main rotor of the wind turbine in what is called a dual rotor wind turbine (DRWT).  The numerical study took place on the performance of small-scale model of wind turbine of 0.9 m diameter using S826 airfoil. Both the Co-rotating and Counter rotating configurations were investigated at different tip speed ratios (TSR) and compared with the performance of the single rotor wind turbine (SRWT). Many parameters were studied for dual rotor turbines. These include the spacing between the two rotors, the pitch angle of the rear rotor and the rotational speed of ratio rear to front rotor. Three-dimensional simulations performed and employed using CFD simulations with Multi Reference Frame (MRF) technique. The Co Rotating Wind Turbine (CWT) and Counter Rotating Wind Turbine (CRWT) found to have better performance compared to that of the SRWT with an increase ranging from 12 to 14% in peak power coefficient. Moreover, the effect of changing the pitch angle of the rear rotor on the overall performance found to be of a negligible effect between angles 0⁰ until 2⁰ degrees tilting toward the front rotor. On the other hand, the ratio of rotational speed of the rear rotor to the front rotor found to cause a further increase in the peak performance of the CWT and CRWT ranging from 3 to 5%.

scholarly journals Validation of CFD Predictions of Urban Wind - Developing a Methodology

2021 ◽  
Author(s):  
◽  
Riley Willis
Keyword(s):  
Wind Tunnel ◽  
City Council ◽  
Wind Tunnels ◽  
Small Scale ◽  
Cfd Model ◽  
Validation Process ◽  
Cfd Simulations ◽  
Entire Area ◽  
Cfd Models ◽  
Wind Tunnel Measurements

<p>“Good mental health in a fluid or CFD modeller is always indicated by the presence of a suspicious nature, cynicism and a ‘show me’ attitude. These are not necessarily the best traits for a life mate or a best friend, but they are essential if the integrity of the modelling process is to be maintained.” (Meroney, 2004)  Over the past 50 years, Computational Fluid Dynamics (CFD) computer simulation programs have offered a new method of calculating the wind comfort and safety data for use in pedestrian wind studies. CFD models claim to have some important advantages over wind tunnels; which remain the most common method of wind calculation. While wind tunnels provide measurements of selected points, CFD simulations provide whole-flow field data for the entire area under investigation (Blocken, 2014; Blocken, Stathopoulos, & van Beeck, 2016). Similarly, wind tunnel measurements must consider the similarity requirements involved with testing a model at small scale, while CFD simulations can avoid this as they are conducted at full scale (Ramponi & Blocken, 2012a).  However, CFD simulations can also often be misleading; and they should only be trusted once they can be proven to be accurate. To appease the requirements for this cynical view- referenced in the above quote- proper verification and validation of a model is imperative.  This thesis investigated and tested the current best practice guidelines around CFD model validation, using existing wind tunnel measurements of generic urban arrays. The goal of the research was to determine whether the existing data and guidance around the validation process was sufficient for a consultant user to trust that a CFD model they created was sufficiently accurate to base design decisions from.  The CFD code Autodesk CFD was used to simulate two configurations first tested as wind tunnel models by the Architectural Institute of Japan, and Opus labs in Wellington. The Wellington City Council wind speed criteria were used to determine whether the CFD simulations met the required accuracy criteria for council consent.  Results from the study found that the CFD models could not meet the accuracy criteria. It concluded that while the validation process provided sufficient guidance, there is a lack of available data which is relevant to CFD validation for urban flows.  It was recommended that at least one improved dataset was required, to build a system by which a consultant can identify what the requirements of a CFD model are to provide accurate CFD analysis of the site under investigation. To accommodate the range of sites likely to be present in urban wind studies, it was recommended that the new dataset provided data for a variety of wind flows likely to be found in cities.</p>

scholarly journals Experimental Study and Simulation of a Small-Scale Horizontal-Axis Wind Turbine

2017 ◽  
Vol 139 (5) ◽  
Author(s):  
Randall S. Jackson ◽  
Ryoichi Amano
Keyword(s):  
Wind Turbine ◽  
High Speed ◽  
Wind Farm ◽  
Reynolds Stress Model ◽  
Turbulence Closure ◽  
Small Scale ◽  
Stress Model ◽  
Horizontal Axis Wind Turbine ◽  
Cfd Simulations ◽  
Velocity Deficit

The advancement of wind energy as an alternative source to hydrocarbons depends heavily on research activities in turbulence modeling and experimentation. The velocity deficit behind wind turbines affects the power output and efficiency of a wind farm. Being able to simulate the wake dynamics of a wind turbine effectively can result in optimum spacing, longer wind turbine life, and shorter payback on the wind farm investment. Two-equation turbulence closure models, such as k–ε and k–ω, are used extensively to predict wind turbine performance and velocity deficit profiles. The application of the Reynolds stress model (RSM) turbulence closure method has been limited to few studies where the rotor is modeled as an actuator disk (AD). The computational cost associated with RSM has made it challenging for simulations where the rotor is discretized directly; however, with advances in computer speed and power coupled with parallel computing architecture, RSM may be a better turbulence closure option. In this research, wind tunnel experiments were conducted, using hot-wire anemometry, to measure the velocity deficit profiles at different wake locations behind a small-scale, three-bladed, horizontal-axis wind turbine (HAWT). Experiments were also performed with two and three HAWTs in series to evaluate the change in velocity deficit and turbulence intensity (TI). High-speed imaging with an oil-based mist captured the vortices produced at the blade tips and showed the vortices dissipated approximately three rotor diameters downstream. Computational fluid dynamics (CFD) simulations were performed to predict the velocity deficit at wake locations matching the experiments. The Reynolds stress model was applied to a fully discretized rotor with a tower and nacelle included in the simulation. A steady-state moving reference frame (MRF) model was created with the computational domain subdivided into rotating and stationary domains. The MRF results were used as an initial condition for time-accurate rigid body motion (RBM) simulations. The RBM CFD simulations showed excellent agreement with experimental measurements for velocity deficit after properly accounting for experimental boundary effects. Isosurfaces of the Q-criterion highlighted the vortices produced at the blade tips and were consistent with high-speed images.

Experimental and Numerical Investigations of Temperature Stratification Phenomena in Passive Safety Systems for Decay Heat Removal

2009 ◽  
Author(s):  
Eckhard Krepper ◽  
Matthias Beyer
Keyword(s):  
Nuclear Power ◽  
Natural Circulation ◽  
Heat Removal ◽  
Temperature Stratification ◽  
Small Scale ◽  
Passive Systems ◽  
Nuclear Power Reactor ◽  
Cfd Simulations ◽  
Decay Heat ◽  
Passive Safety Systems

Modern concepts of nuclear power reactor systems are equipped with passive systems for decay heat removal. Examples are the pool of the emergency condenser (BWR-1000) or the pool of the ESBWR. These systems operate without active influence from outside. The questions arise: How reliable are the based physical mechanisms? Are they understood completely? Are actual models able to describe the phenomena? In different passive systems the energy is transferred by natural circulation into large pools which are considered as infinite heat sink. The paper deals with experiments and with CFD simulations to investigate the capability of actual CFD codes to describe these phenomena. In the FZ Dresden-Rossendorf at the facility TOPFLOW heating-up tests of an emergency condenser were performed. During these tests also the temperature courses on the secondary side of the pool were recorded. The data recording comprises periods starting from single phase liquid until steam on the secondary pool side was found. During these experiments temperature stratification phenomena were observed, which were found in earlier small scale tests. In the paper also these small scale experiments are described. A detailed CFD analysis of these experiments was performed. An explanation of the observed phenomena on the basis of the small scale tests and the CFD simulations is presented.

scholarly journals Numerical CFD Simulations and Indicated Pressure Measurements on a Sliding Vane Expander for Heat to Power Conversion Applications

Designs ◽  
2019 ◽  
Vol 3 (3) ◽  
pp. 31
Author(s):  
Giuseppe Bianchi ◽  
Sham Rane ◽  
Fabio Fatigati ◽  
Roberto Cipollone ◽  
Ahmed Kovacevic
Keyword(s):  
Power Output ◽  
Cfd Simulation ◽  
Mechanical Efficiency ◽  
Specific Power ◽  
Working Fluid ◽  
Small Scale ◽  
Pressure Measurements ◽  
Cfd Simulations ◽  
Large Power ◽  
Specific Power Output

The paper presents an extensive investigation of a small-scale sliding vane rotary expander operating with R245fa. The key novelty is in an innovative operating layout, which considers a secondary inlet downstream of the conventional inlet port. The additional intake supercharges the expander by increasing the mass of the working fluid in the working chamber during the expansion process; this makes it possible to harvest a greater power output within the same machine. The concept of supercharging is assessed in this paper through numerical computational fluid dynamics (CFD) simulations which are validated against experimental data, including the mass flow rate and indicated pressure measurements. When operating at 1516 rpm and between pressures of 5.4 bar at the inlet and 3.2 bar at the outlet, the supercharged expander provided a power output of 325 W. The specific power output was equal to 3.25 kW/(kg/s) with a mechanical efficiency of 63.1%. The comparison between internal pressure traces obtained by simulation and experimentally is very good. However, the numerical model is not able to account fully for the overfilling of the machine. A comparison between a standard and a supercharged configuration obtained by CFD simulation shows that the specific indicated power increases from 3.41 kW/(kg/s) to 8.30 kW/(kg/s). This large power difference is the result of preventing overexpansion by supercharging. Hence, despite the greater pumping power required for the increased flow through the secondary inlet, a supercharged expander would be the preferred option for applications where the weight of the components is the key issue, for example, in transport applications.

Evaluation of the Effectiveness of a Coastal Wave Reduction and Sediment Retention Structure Using CFD Simulations

2017 ◽  
Author(s):  
Steven Dabelow ◽  
Ning Zhang
Keyword(s):  
Sediment Transport ◽  
Small Scale ◽  
Sediment Retention ◽  
Cfd Simulations ◽  
Coastal Waves ◽  
Shoreline Protection ◽  
Current Design ◽  
Flow And Sediment Transport ◽  
Louisiana Coast ◽  
Wave Reduction

The Louisiana coast experiences significant erosion due to wave actions. There are wetlands and marshes located in the coastal areas, however loss of these wetlands is a major threat. Although coastal waves and floods cause erosion, they do carry sediments, which can potentially counter-act some of the wetland losses. Innovative shoreline protection designs that reduce the wave actions but still allow sediments to travel through could be very beneficial. This research aims to evaluate the effectiveness of the wave reduction and sediment retention of several such designs using CFD simulations. CFD simulations were used to determine the alternations of the wave characteristics and the sediment transport with the designed structures. Small scale experiments of such designs will be conducted in a wave tank facility to validate the modeling results. The research aims to disclose the detailed physics of the flow and sediment transport in this complicated flow-structure interaction problems, and, based on the discoveries, we will provide suggestions to improve the current design to enhance the performance significantly.

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