CFX Model Research Articles

1D-3D co-simulation pipe resonance induced by cavitating vortex shedding

Abstract Hydraulic systems may experience excitation caused by complex flow patterns within various components of the system. A computational effective way to predict the interaction between the hydraulic system and the excitation source is to conduct a co-simulation using two independent simulation codes. One code models the fluid pipe system using a one-dimensional compressible approach, while the other code simulates the excitation source with a three-dimensional model. Recognized as a standard communication protocol for linking two simulation codes that solve a system of ordinary differential equations, the Functional Mockup Interface, FMI, protocol has been implemented in SIMSEN to couple with the Ansys CFX software solution. Localized hydrodynamic instabilities including cavitation are prone to interact with the entire system. A cavitating case study has been investigated to assess robustness and accuracy of the co-simulation performed with the FMI protocol. The case study consists in a straight pipe connecting two constant pressure tanks with a bluff body placed at 3/4 of the pipe length. The vortex shedding is the excitation which frequency is proportional to the flow velocity. Measurements are available for resonant and non-resonant conditions in cavitating and free cavitating flow regimes. Co-simulations are performed between SIMSEN 1D model of the pipe and a pseudo 3D CFX model of the bluff body, reduced to one cell in the width direction. The comparisons with measurements show good agreement despite the pseudo 3D approach to simulate bluff body-induced excitation. This demonstrates that this approach is valid to address complex unsteady, compressible and cavitating flow phenomena.

SIMULATION OF TRANSIENT PROCESS ON WWER-1000 USING COUPLED APPROACH

Research and modeling of thermohydraulic processes in NPP equipment is necessary for a deep and improved justification of reliable and safe operation of nuclear installations. Taking into account the accumulated experience and the latest technologies, the study of thermohydraulic processes is developing in the direction of applying innovative approaches to conducting both experimental studies and expanding the calculation capabilities of thermohydraulic codes. The article presents an approach to the decomposition of the thermohydraulic model of the WWER-1000 reactor plant on submodels, which are calculated in coupling with separate instances of the system thermohydraulic code RELAP5/Mod 3.2. Coupling is implemented using a specially developed module. This approach allows you to "bypass" the internal limitations of RELAP5 in the number of components (hydrodynamic volumes, thermal structures, "trips" and control variables) that can be used for computational analysis. As a result, it becomes possible to achieve a higher degree of detail for the entire reactor installation. In addition, the article confirms the possibility of applying the previously developed coupling module to such a non-equilibrium model as a nuclear reactor model. At the same time, the use of the RELAP5 model as a reactor model makes it possible to avoid inaccuracies that arise when applying assumptions about the transverse profiles of the input variables of the CFX model, as well as to perform the validation of the RELAP5 model of the RU loops. Coupled calculation of stationary and transient mode of reactor installation WWER-1000 is performed. The reliability of calculation results obtained in conjugation is evaluated by comparing them with the results of autonomous calculations in RELAP5. The analysis of the results of computational modeling confirms the possibility of applying the developed coupling module to such a non-equilibrium model as a model of a nuclear reactor, and also confirms the correctness of the RELAP5 model of the loops of the reactor plant obtained on the basis of the modification of the full-fledged RELAP5 model.

An experimental and numerical study to evaluate performance parameters of GIS circuit breaker during low current interruption

Abstract The basic philosophy of two-stage blast interrupter is combination of self-blast and puffer-interrupter principles. Gas circuit breaker (GCB) with two-stage blast interrupter has two gas chambers. High gas pressure in one chamber generates by using arc energy and in other chamber, by mechanical compression. In such type of breakers, interruption becomes quite difficult at low currents and hence optimization of gas chambers design is essential. In view of above, a numerical program has been developed to calculate SF6 gas pressure-rise in various interrupter volumes and gas flow rates across different passages of interrupter w.r.t. time. To validate model developed in the study, an experimental set-up is established and measured transient gas pressure-rise generated during 420 kV GCB operation. The effect of speed-time characteristics, stroke length and piston diameter on performance parameters of 420 kV GCB model is analyzed. Further, to understand gas flow pattern across insulated nozzle during GCB operation, authors developed a CFX model. By using this numerical model, effect of nozzle profile, gas flow passage areas and profile of gas discharge vents on transient gas pressure and Mach number distribution across inter-electrode gap and gas flow rates through various outlets has been discussed in detail in the paper.

Study on the Effect of the Guide Vane Opening on the Band Clearance Sediment Erosion in a Francis Turbine

Sediment erosion is a negative phenomenon for the water turbine. The purpose of this paper is to study the effect of the guide vane opening on the particle motion and sediment erosion in the band chamber using the Euler–Lagrangian approach. The software Ansys CFX and Tabakoff erosion model are used to simulate the sediment laden flow in the full flow passage of the hydraulic turbine. The results are in good agreement with the actual erosion character on site. Results show that the guide vane opening has a positive correlation with the flow in the non-clearance channel. The increase of the guide vane opening will increase the erosion of the runner blade head, but the friction wear on the outlet side of the blade surface will decrease. The rotating action of the runner makes the sediment particles in the band chamber rotate rapidly around the center of the runner and constantly collide with the band chamber wall. Under the small opening, the smaller the opening, the easier the leakage of the band clearance occurs. The unsteady flow in the band chamber will disturb the motion trajectory of particles, change the impact angle of particles, and affect the wear in the band chamber. Under different openings, the change law of the erosion in the band clearance is closely related to the change law of clearance leakage.

UNIDIRECTIONAL COUPLED FINITE ELEMENT SIMULATION OF THERMOELASTIC TCP-DISPLACEMENT THROUGH MILLING PROCESS CAUSED HEAT LOAD

The paper presents a numerical simulation of thermal induced tool displacement during milling oper-ation. An unidirectional finite element model is developed which consists of two sections. A CFX model and a thermal transient model. With the aid of CFX module, the conjugated heat transfer be-tween milling tool and coolant fluid is described. The result of these efforts is the body temperature field of the end mill cutter due to thermal load, which is the thermal fingerprint of the cutting process. Subsequently the calculated body temperature field is linked with a transient-structural module to cal-culate the resulting thermal elastic displacement of the milling cutter. The thermo-elastic displace-ment of the tool is determined by examining a pilot node at the tip of the end mill, whose displace-ment is calculated in relation to the global coordinate system of the model.

CFD simulation for the internal pressure characteristics of an oil-injected twin-screw refrigeration compressor

3• A 3D model of an oil-injected twin-screw compressor was simulated with CFX. 3• The CFD model accounted well for the pressure in both time and frequency domains. 3• The highest pressure pulsation acted on the inner surface of the rotor housing. 3• The fluid hammer effect was found at the oil injection outlets. The internal pressure characteristics of an oil-injected twin-screw refrigeration compressor was studied using a full 3D CFX model, and the hexahedral moveable meshes of the twin-screw domain were generated by the professional mesh tool SCORG. The gas pressure throughout the whole working process was investigated to disclose its distribution feature. The working pressure at different locations, such as the inner surface of the screw rotor housing, the oil injection paths, the male screw groove, the internal suction and discharge flowing paths, were all captured and analyzed. The simulated pressure inside the screw working chamber agreed well with the experimental results in both time and frequency domains. The pressure pulsations in the compression section acting on the inner surface of the screw rotor housing presented higher levels than the data in the other domains. The highest pulsation level occurred on the location where could record the whole discharge process of the internal ports. Under the high oil flowrate conditions, due to the different influences of the fluid hammer effect, the pressure pulsation increment of the axial oil injection outlet was much larger than that of the radial oil injection outlet. The orifice on the oil path could help reduce the influence of the fluid hammer. Finally, several suggestions were given based on the simulation findings.

Hydraulic modeling of combined sewers overflow integrating the results of the SWMM and CFX models.

This study proposes a methodology for the calibration of combined sewer overflow (CSO), incorporating the results of the three-dimensional ANSYS CFX model in the SWMM one-dimensional model. The procedure consists of constructing calibration curves in ANSYS CFX that relate the input flow to the CSO with the overflow, to then incorporate them into the SWMM model. The results obtained show that the behavior of the flow over the crest of the overflow weir varies in space and time. Therefore, the flow of entry to the CSO and the flow of excesses maintain a non-linear relationship, contrary to the results obtained in the one-dimensional model. However, the uncertainty associated with the idealization of flow methodologies in one dimension is reduced under the SWMM model with kinematic wave conditions and simulating CSO from curves obtained in ANSYS CFX. The result obtained facilitates the calibration of combined sewer networks for permanent or non-permanent flow conditions, by means of the construction of curves in a three-dimensional model, especially when the information collected in situ is limited.

Conceptual design of small modular reactor driven by natural circulation and study of design characteristics using CFD & RELAP5 code

A detailed computational fluid dynamics (CFD) simulation analysis model was developed using ANSYS CFX 16.1 and analyzed to simulate the basic design and internal flow characteristics of a 180 MW small modular reactor (SMR) with a natural circulation flow system. To analyze the natural circulation phenomena without a pump for the initial flow generation inside the reactor, the flow characteristics were evaluated for each output assuming various initial powers relative to the critical condition. The eddy phenomenon and the flow imbalance phenomenon at each output were confirmed, and a flow leveling structure under the core was proposed for an optimization of the internal natural circulation flow. In the steady-state analysis, the temperature distribution and heat transfer speed at each position considering an increase in the output power of the core were calculated, and the conceptual design of the SMR had a sufficient thermal margin (31.4 K). A transient model with the output ranging from 0% to 100% was analyzed, and the obtained values were close to the Thot and Tcold temperature difference value estimated in the conceptual design of the SMR. The K-factor was calculated from the flow analysis data of the CFX model and applied to an analysis model in RELAP5/MOD3.3, the optimal analysis system code for nuclear power plants. The CFX analysis results and RELAP analysis results were evaluated in terms of the internal flow characteristics per core output. The two codes, which model the same nuclear power plant, have different flow analysis schemes but can be used complementarily. In particular, it will be useful to carry out detailed studies of the timing of the steam generator intervention when an SMR is activated. The thermal and hydraulic characteristics of the models that applied porous media to the core & steam generators and the models that embodied the entire detail shape were compared and analyzed. Although there were differences in the ability to analyze detailed flow characteristics at some low powers, it was confirmed that there was no significant difference in the thermal hydraulic characteristics' analysis of the SMR system's conceptual design.

Potential of Utilizing Solar Chimney as an Energy Efficiency Measure in Malaysian Hospitals

Many energy efficiency measures were proposed to reduce the high energy demand in hospitals. Solar chimney is a form of passive solar heating and cooling system that can be used for temperature regulation and ventilation of a building This paper explores the solar chimney’s performance in terms of air changes per hour (ACH) in Malaysian tropical climate were thus, investigated for its feasibility in Malaysian hospitals. A 2D CFX model is simulated at four different times (8 am, 10 am, 2pm and 4 pm). Openings provided at the bottom and top of the chimney and at the right of the cabin with dimension of 1 m located 1 m from the floor level to allow air with room temperature to enter the cabin and towards the solar chimney. Simulations were validated form previous study and the study use solar irradiance from previous study to simulate Malaysia’s solar irradiance and outside temperature. Steady state and laminar flow were used in this study to model air turbulence in the cabin to the solar chimney. The results show that the simulations have been validated and all 4 of different time have been simulated. 2 pm with the highest solar irradiance have the most air changes per hour (ACH), while 8 am with the lowest solar irradiance have the least ACH. Further experimental study is currently ongoing.

Leakage Estimate in Nonuniformly Compressed Packing Rings

Abstract Characterizing the permeation performance of nanoporous material is an initial step toward predicting microflows and achieving acceptable designs in sealing and filtration applications. This study deals with analytical, numerical, and experimental studies of gaseous leaks through soft packing materials subjected to nonuniform axial compression in valve stuffing boxes. A new analytical model that accurately predicts gaseous leak rates through nanoporous packing materials assumed made of capillaries having an exponentially varying section. Based on Navier–Stokes equations with the first-order velocity slip condition for tapered cylinder capillaries, the analytical model is used to estimate gas flow through soft packing materials. In addition, computational fluid dynamic modeling using cfx software is used to test its capacity to estimate the permeation of compression packing ring materials assuming the fluid flow to follow Darcy's law. Helium gas is used as a reference gas in the experiments to characterize the porosity parameters. The analytical and cfx numerical leak predictions are compared to leak rates measured experimentally using different gas types (helium, nitrogen, air, and argon) at different pressures and gland stresses. The analytical and numerical models account for the porosity change with the stem axial distance because the packing ring set is subjected to an exponentially varying radial compression. The predictions from analytical model are in close agreement with the cfx model and in better agreement with experimental measurements.

Coupled Monte Carlo-CFD analysis of heat transfer phenomena in a supercritical water reactor fuel assembly

In this paper coupled calculations with the CFD code ANSYS-CFX-19.0 and the Monte Carlo neutronics code MCNP6 were performed to analyze the heat transfer in supercritical water flowing through the typical fuel assembly of the high-performance light water reactor (HPLWR), in order to improve the characterization of the heat transfer phenomena in supercritical water under non-uniform axial heat flux distributions that is characteristic of this type of reactor. To check the capability of the CFX model to predict the thermal-hydraulic behavior of supercritical water, the computational results were compared with two experimental data. The Shitsmańs experiment in the presence of heat transfer deterioration (HTD) using four low-Re turbulence models (SST, k-ω, BSL-k-ω, and ω-Reynolds Stress) and the Wanǵs experiment in absence of HTD, using the low-Re-SST and the scalable-wall-function-SSG turbulence models. In the presence of the HTD phenomenon, results showed the high dependency of the wall temperature with the turbulence model and the turbulent Prandtl number selected. In the absence of HTD, both turbulence models studied adequately predicted the behavior of the wall temperature distribution.For the coupled neutronic/thermal-hydraulic analysis of the typical HPLWR fuel assembly, the low-Re SST turbulence model and the Prt = 1.5 were used. Different axial profiles of heat flux generated in the fuel rods were obtained for the different power values studied. For the analyzed conditions, the presence of HTD in the lower zone of the fuel assembly was observed. In addition, the results showed a strong non-uniformity of the circumferential surface cladding temperature distribution in the sub-channel located at the corner of the fuel assembly; a new curvature radius of the assembly box corner was proposed to obtain a well homogenized circumferential wall temperature distribution.

CFD study on flow approach angle of a bi-directional velocity probe for fire testing

The present study examines the flow characteristics near the bi-directional velocity probe and estimates the probe constant associated with the Reynolds number and flow approach angle. A series of numerical experiments using CFX model are conducted to simulate the 3D flow field near the probe. The CFD model was validated with the best fit polynominal of the experimental data of McCaffrey and Heskestad. The calculated probe constants for a Reynolds number higher than 3000 are almost constant at 1.07 and match well with the conventionally-accepted asymptotic value of 1.08. Using the validated numerical code, a series of parameter studies were conducted. The angular sensitivity of the bi-directional probe increases when increasing the flow approach angle from 0 to 30 degrees, and the maximum angular sensitivity was observed near the flow approach angle of 30 degree. Based on the detailed analysis of flow structure, the present study shows that the pressure at the rear hole of the probe is more affected by the flow approach angle and influenced by the asymmetric wake flow behind the probe body. It is expected that this study can contribute to enhancing the reliability of velocity measurement in fire testing and be utilized as a preliminary study for design optimization of the bi-directional probe based on the understanding of detailed flow characteristics.

Turbulent flow investigation of the vacuum boiler at boiling

Viscosity coefficient defining methods taking into account the turbulent component under the boiler various operating conditions at the subatmospheric pressureare considered in the paper. Currently, addressing this problem is of particular relevance for the vacuum boilers heat-exchange problems solution. The viscosity coefficient dependences in a wide range of the specific heat fluxes at the free convection and bubble boiling are obtained. The study results were obtained by means of the software complex ANSYS CFX and RPI model.

Cooling efficiency of gas turbine blade leading edge with a closed whirler

The high temperature gas turbine vane has the leading edge convective cooling. This study discloses investigation of thermal and hydraulic performance of closed whirler, or cyclone edge cooling. Its mass and heat transfer are simulated with the ANSYS CFX model of the leading edge with closed whirler dome. Changes in air supply and discharge orifice areas change the heat transfer distribution. Test results show the influence of the whirler configuration parameters on heat transfer intensity. The obtained criteria equations allow calculations of local and mean heat transfer coefficients with 8% accuracy.

CFD simulation of a TES tank comprising a PCM encapsulated in sphere with heat transfer enhancement

Phase change materials (PCMs) are known to have a critical drawback of low thermal conductivity that resulted to an ineffective thermal storage system. This paper aims to investigate the effect of the heat transfer enhancement in a thermal energy storage (TES) system comprising a PCM encapsulated in sphere. To enhance the performance, the design modification method by the employment of pins and copper plating were adopted and carried out by computational fluid dynamics (CFD) and experimental studies. The phase change times (PCTs) of the systems were analysed as a performance measure. Consistent with the experimental results, simulation analysis in ANSYS CFX showed that utilising pins for heat transfer enhancement reduced the PCT of the PCM by 27% while design modification with copper coating and embedded pins reduced the PCT by 37% relative to a plain sphere. Good correlation of the PCT was found between the graphs plotted from CFD analysis and experimental data. This study prescribes that the CFX model developed can accurately predict the PCM behaviour of the sphere, with and without modification. These improved results facilitate the use of a conductor and copper plates as an alternative technique for the performance improvement of a PCM encapsulated in a sphere.

A computational design method for bio-mimicked horizontal axis tidal turbines

PurposeThe purpose of this paper is to conduct a comparative analysis between a straight blade (SB) and a curved caudal-fin tidal turbine blade (CB) and to examine the aspects relating to geometry, turbulence modelling, non-dimensional forces lift and power coefficients.Design/methodology/approachThe comparison utilises results obtained from a default horizontal axis tidal turbine with turbine models available from the literature. A computational design method was then developed and implemented for “horizontal axis tidal turbine blade”. Computational fluid dynamics (CFD) results for the blade design are presented in terms of lift coefficient distribution at mid-height blades, power coefficients and blade surface pressure distributions. Moving the CB back towards the SB ensures that the total blade height stays constant for all geometries. A 3D mesh independency study of a “straight blade horizontal axis tidal turbine blade” modelled using CFD was carried out. The grid convergence study was produced by employing two turbulence models, the standard k-ε model and shear stress transport (SST) in ANSYS CFX. Three parameters were investigated: mesh resolution, turbulence model, and power coefficient in the initial CFD, analysis.FindingsIt was found that the mesh resolution and the turbulence model affect the power coefficient results. The power coefficients obtained from the standard k-ε model are 15 to 20 per cent lower than the accuracy of the SST model. Further analysis was performed on both the designed blades using ANSYS CFX and SST turbulence model. The variation in pressure distributions yields to the varying lift coefficient distribution across blade spans. The lift coefficient reached its peak between 0.75 and 0.8 of the blade span where the total lift accelerates with increasing pressure before drastically dropping down at 0.9 onwards due to the escalating rotational velocity of the blades.Originality/valueThe work presents a computational design methodological approach that is entirely original. While this numerical method has proven to be accurate and robust for many traditional tidal turbines, it has now been verified further for CB tidal turbines.

A Study on the Flow Characteristics According to the Structure Change of Filtration in a Pressurized Type Filtration System Using Numerical Model

In this study, a prototype was constructed and a field experiment was conducted to develop the water supply system that can purify polluted water quickly and efficiently. As a result of water quality analysis on the filtered water treated by a prototype, it could be used for living water, graywater and drinking water. There is the pressurized type filtration system that plays an important role in the water supply and production system. A filtration filter in the pressurized type filtration system absorbs pollutants and produces clean water. Filtration filter that can filter out contaminants is closely related to flow phenomena. Since it is impossible to observe in the vicinity of the filtration filter, the flow phenomenon is analyzed using CFX model. As the inner structure of the filtration was changed, the flow phenomenon in the filtration filter was examined. After changing the angle of the filter plate inside the filtration from 15º to 20º, the velocity distribution was analyzed. The standard deviation was reduced from 0.0575 to 0.0154. A uniform flow velocity distribution was formed around the filter. As a result, filtration efficiency is expected to increase. Keywords: Water Supply System, Pressurized Type Filtration System, Filtration, Filtration Filter, 3D Numerical Method, CFX

Theoretical investigation and prototype design for non-parallel squeeze film movement platform driven by standing waves

Abstract In order to realize contactless levitation and movement of precision components, a new kind of acoustic prototype driven by standing waves utilizing reverse hydrodynamic effects of non-parallel squeeze film was proposed in this paper. Its mechanism of movement and levitation was revealed by the viscous fluid mechanics and dynamic lubrication theory. It is amazing that the reverse hydrodynamic effects made the levitated plate move along the opposite direction of gravitational tangential component, which was proved in the experiments. The bearing and pushing capacity is predicted by numerical calculation of Reynolds equation and a CFX model. A dimensionless parameter 'voltage difference ratio' was proposed to evaluate the deflection angle of a non-parallel squeeze film, which can guide the prototype design.

Development of a Model for Long-Term Storage Container for VVER-1000 Spent Fuel Assemblies in ANSYS CFX

This paper evaluates the thermohydraulic aspects of modeling multi-purpose container (MPC-31) with VVER-1000 spent nuclear fuel (SNF) during its long-term storage in HI-STORM container (designed by Holtec International). The paper describes the main approaches and assumptions applied for the development of correspondent ANSYS CFX model, as well as provides the main calculation results for one of the cases of MPC-31 loading with SNF. The results of calculations were used in the regulatory review of technical specifications of MPC-31 and correspondent safety analysis reports.

Effects of Width Ratios and Deviation Angles on the Mean Velocity in Inlet Channels Using Numerical Modeling and Artificial Neural Network Modeling

Dividing open channels are varied types of open channel structures used to provide water for irrigation channels, agriculture and wastewater networks. In the present study, artificial neural network (ANN) and computational fluid dynamic models are used to calculate the mean velocity in different dividing angles within branch channels. First, the ANSYS-CFX model is used to simulate the flow pattern within the branch at a 90° angle. Results of the CFX model correspond fairly well to the results of the experimental model with a mean absolute percentage error (MAPE) of 5 %. After verification, two CFX models are generated in 30° and 60° angles in different width ratios of 0.6, 0.8, 1, 1.2, and 1.4, and the mean velocities are obtained by a flowmeter. The ANN model is then trained and tested by a set of experimental and CFX data. The ANN model presented an acceptable level of accuracy in predicting the dividing open channel mean flow velocity with a mean value R 2 of 0.93. A comparison of the results indicated that the ANN model with 1.8 % MAPE performs better under 0.8 m width ratio. The MAPE within the 0.8 width is equivalent to the ratios 1.58, 1.87, and 2.04 % in 30°, 60°, and 90° deviation angles, respectively, and therefore the model performs better at the 30° angle.