Computational Flow Analysis Research Articles

Computational analysis of magnetohydrodynamic Sisko fluid flow over a stretching cylinder in the presence of viscous dissipation and temperature dependent thermal conductivity

Present communication presents numerical investigation of magnetohydrodynamic Sisko fluid flow over linearly stretching cylinder along with combined effects of temperature depending thermal conductivity and viscous dissipation. The arising set of flow govern equations are simplified under usual boundary layer assumptions. A set of variable similarity transforms are employed to shift the governing partial differential equations into ordinary differential equations. The solution of attained highly nonlinear simultaneous equations is computed by an efficient technique (shooting method). Numerical computations are accomplished and interesting aspects of flow velocity and temperature are visualized via graphs for different parametric conditions. A comprehensive discussion is presented to reveal the influence of flow parameters on wall shear stress and local Nusselt number via figures and tables.Furthermore, it is observed that magnetic field provides noticeable resistance to the fluid motion while both material parameter and curvature accelerates it. The progressing values of both Eckert number and thermal conductivity parameter have qualitively same effects i.e. they rise the temperature. Additionally, material parameter and curvature parameter increase the coefficient of skin friction absolutely and qualitively similar effects are noticed for Nusselt number against variations in Prandtl number and curvature parameter. On the other hand local Nusselt diminishes for larger values of Eckert number and power law index. The present results are compared with existing literature via tables, they have good covenant with previous results.

Computational fluid dynamic analysis of the exhaust gas flow through absorptive and reactive mufflers: some case studies

This paper aims to study comprehensively the flow characteristics of exhaust gases through different types of muffler (e.g. absorptive, reactive and resonating). Geometric models were designed using PRO-E and analysed using ANSYS FLUENT 14. The contours for the pressure, the velocity and the turbulence were plotted for optimization of the muffler design based on the known thermodynamic parameters. On the basis of the variation in these parameters, various hybrid designs were proposed for a muffler and even for a combination of mufflers.

Three-dimensional computations of the hydrodynamics and mass transfer during solution growth of KDP crystal with a planetary motion

Computational analysis of the three-dimensional flow and mass transfer involved in the growth of KDP crystal with a planetary motion (PM) was conducted, in which the crystal executes an orbital revolution with a constant revolution rate during its self-rotation together with periodically changing the direction of crystal rotation. Compared with the conventional KDP growth method which conducts centric rotation (CR), this new configuration can avoid the sharp fluctuation of surface supersaturation during the phases of crystal spin down, stalling and spin up, and brings about an oscillatory fluid field during the steady self-rotation phase, all of that being able to promote the morphological stability of the growing crystal. By increasing the self-rotation rate, the frequency of the oscillatory fluid field will increase, and the morphological stability will be enhanced. The time-averaged supersaturation fields of the crystal surfaces are obtained, which are greatly affected by the orbital revolution rate and the orbital radius. For a higher orbital revolution rate or larger orbital radius, higher time-averaged value and better homogeneity of the surface supersaturation could be obtained.

Mesh convergence study for hydraulic turbine draft-tube

Computational flow analysis is an essential tool for hydraulic turbine designers. Grid generation is the first step in the flow analysis process. Grid quality and solution accuracy are strongly linked. Even though many studies have addressed the issue of mesh independence, there is still no definitive consensus on mesh best practices, and research on that topic is still needed. This paper presents a mesh convergence study for turbulence flow in hydraulic turbine draft- tubes which represents the most challenging turbine component for CFD predictions. The findings from this parametric study will be incorporated as mesh control rules in an in-house automatic mesh generator for turbine components.

Slocum 수중 글라이더의 유영 받음각에 대한 전산유동해석 및 항력계수 연구

An underwater glider makes it easy to explore a wide area with low power. However, an underwater glider is difficult to use for rapid collection, because the surfacing location cannot be predicted after a dive. Thus, simulation research is needed to predict the swimming path. In this paper, based on research, a linearized equation is derived for the drag coefficient at each angle of attack by assuming the boundary conditions for the Slocum underwater glider and performing a computational flow analysis.

The capillary bed offers the largest hemodynamic resistance to the cortical blood supply

The cortical angioarchitecture is a key factor in controlling cerebral blood flow and oxygen metabolism. Difficulties in imaging the complex microanatomy of the cortex have so far restricted insight about blood flow distribution in the microcirculation. A new methodology combining advanced microscopy data with large scale hemodynamic simulations enabled us to quantify the effect of the angioarchitecture on the cerebral microcirculation. High-resolution images of the mouse primary somatosensory cortex were input into with a comprehensive computational model of cerebral perfusion and oxygen supply ranging from the pial vessels to individual brain cells. Simulations of blood flow, hematocrit and oxygen tension show that the wide variation of hemodynamic states in the tortuous, randomly organized capillary bed is responsible for relatively uniform cortical tissue perfusion and oxygenation. Computational analysis of microcirculatory blood flow and pressure drops further indicates that the capillary bed, including capillaries adjacent to feeding arterioles (d < 10 µm), are the largest contributors to hydraulic resistance.

Computational analysis of two-phase flow and heat transfer in parallel and counter flow double-pipe evaporators

A computational study is carried out to compare the two-phase flow and heat transfer characteristics of a double-pipe evaporator operating under parallel and counter flow configurations for use in waste heat recovery and low grade geothermal applications. The heat exchanger considered uses low boiling point fluid FC-72 to recover thermal energy from water that is at a temperature greater than the boiling point of FC-72 through forced convective boiling. The simulations are carried out at steady state using the SST-k-ω Reynolds-Averaged-Navier-Stokes equations, and by employing the Eulerian two-fluid formulation for the region of the heat exchanger where multiphase flow with phase-change occurs. The net heat flux from the wall during nucleate boiling is evaluated using the Rensselaer Polytechnic Institute wall heat flux partitioning model with appropriate empirical and mechanistic closures for the underlying physical mechanisms such as ebullition characteristics. The present computational methodology is extensively validated by comparison of the predicted fluid and wall temperatures, local vapor fractions and heat transfer coefficients against experimental data in the literature. For the range of parameters considered, contrary to that generally expected in single phase double-pipe heat exchangers, under two-phase conditions (boiling), the parallel flow configuration is found to result in a greater thermal effectiveness as compared to the counter flow. This is observed irrespective of whether FC-72 flows in the tube or annulus, and can be attributed to the greater vapor generation relatively upstream and for most of the length of the heat exchanger during parallel flow conditions. For the heat exchanger considered, the net FC-72 vapor generation is also greater when FC-72 flows in the tube-side as compared to that in the annulus under both parallel and counter flow configurations, although with marginal variation in the overall heat transfer rates.

Turbocharger flow computations with the Space–Time Isogeometric Analysis (ST-IGA)

Abstract We focus on turbocharger computational flow analysis with a method that possesses higher accuracy in spatial and temporal representations. In the method we have developed for this purpose, we use a combination of (i) the Space–Time Variational Multiscale (ST-VMS) method, which is a stabilized formulation that also serves as a turbulence model, (ii) the ST Slip Interface (ST-SI) method, which maintains high-resolution representation of the boundary layers near spinning solid surfaces by allowing in a consistent fashion slip at the interface between the mesh covering a spinning surface and the mesh covering the rest of the domain, and (iii) the Isogeometric Analysis (IGA), where we use NURBS basis functions in space and time. The basis functions are spatially higher-order in all representations, and temporally higher-order in representation of the solid-surface and mesh motions. The ST nature of the method gives us higher-order accuracy in the flow solver, and when combined with temporally higher-order basis functions, a more accurate representation of the surface motion, and a mesh motion consistent with that. The spatially higher-order basis functions give us again higher-order accuracy in the flow solver, a more accurate, in some parts exact, representation of the surface geometry, and better representation in evaluating the second-order spatial derivatives. Using NURBS basis functions with a complex geometry is not trivial, however, once we generate the mesh, the computational efficiency is substantially increased. We focus on the turbine part of a turbocharger, but our method can also be applied to the compressor part and thus can be extended to the full turbocharger.

Rheological problems and alternatives for existing oxidation ponds

A trace test and computational flow analysis were carried out in order to identify the flow characteristics of mine drainage in an existing oxidation pond. Consequently, despite the need for sufficient retention time of mine drainage to purify the mine drainage, the effective volume of an oxidation pond without any structure is too small and the time for mine drainage required to reach the outlet is also too short. To deal with this problem, computational flow analysis was carried out after systematically arranging the baffles in an oxidation pond. The initial arrival time to the outlet with baffles was more than 360 times compared to the case without baffles. Furthermore, exchange efficiency was also significantly increased from 14.5 to 82.7 %. Thus, adding baffles to an oxidation pond resulted in an increase in the volume of the oxidation pond in the flow range of mine drainage, enhancing the flow efficiency and retention time as well.

Experimental and Computational Analysis of Single Phase Flow Coiled Flow Inverter Focusing on Number of Transfer Units and Effectiveness

Abstract The coiled flow inverter (CFI) is an enhanced heat exchanger. This device uses the principle of flow inversion to increase heat transfer and has potential for industrial applications. A mathematical model based on experimental and numerical data was developed for the case of single phase flow with water as working fluids. This model includes (ε-NTU) Effectiveness Number of Transfer Units curves, Nusselt correlations, for this specific neither parallel nor counter flow setup. A range of Reynolds numbers from 2,000 to 18,000 in the tube side, and 500 to 2,000 in the shell side was considered. The coiled flow inverter is made of coils and 90◦ bends, inserted in a closed shell. The shell side is cylindrical. The average temperatures at input and output of the heat exchanger were reported for different tube and shell side flow rates. Overall heat-transfer coefficients (Uf) were calculated as well as the Number of Transfer Units (NTU) and Effectiveness (ε) at various process conditions. A Nusselt correlation was proposed for the shell side of this configuration. The ε-NTU curves of the selected heat exchanger have a high resemblance to the parallel flow tube heat exchanger, with a maximum of 2.1 % error. The coiled flow inverter has increases of 200 %, 300 % and 500 %, respectively for effectiveness, number of transfer units and overall heat transfer coefficient compared to a regular parallel flow heat exchanger at the same conditions. Correlations for the CFI in its shell were proposed. This heat exchanger provides higher Uf, reduces cumbersomeness and length of piping.

진동형 히트 파이프에서 튜브의 지름과 개수에 따른 전산 열유동해석

In this paper, heat transfer characteristics of pulsating heat pipes are investigated with the diameter and the number of tubes through the computational analysis of thermal flow. The numerical simulation includes the phase change precess with VOF model using OpenFOAM software. The numerical code is modified for the phase change to occur with saturation temperature. The numerical results are compared with the previous ones to validate the present code. The resonable results have been obtained based on the mass transfer time relaxation parameter considering the density ratio. When the ratio of length to diameter and the number of tubes are on the decrease, the thermal resistances also tends to decrease in the pulsating heat pipes. These numerical results will supply the base line data to design and to manufacture the pulsating heat pipe.

파이롯 규모 SI 공정 시험 설비에서의 헬륨 가열 장치 설계

In this study, researchers performed preliminary design and numerical analysis for a pilot-scale helium heating system in- tended to support full-scale construction for a sulfur-iodine (SI) cycle. The helium heat exchanger used a liquefied petroleum gas (LPG) combustor. Exhaust gas velocity at the heat exchanger outlet was approximately 40 m/s based on computational thermal and flow analysis. The maximum gas temperature was reached with six baffles in the design; lower gas temperatures were observed with four baffles. The amount of heat transfer was also higher with six baffles. Installation of additional baffles may reduce fuel costs because of the reduced LPG exhausted to the heat exchanger. However, additional baffles may also increase the pressure dif- ference between the exchanger's inlet and outlet. Therefore, it is important to find the optimum number of baffles. Structural analy- sis, followed by thermal and flow analysis, indicated a 3.86 mm thermal expansion at the middle of the shell and tube type heat exchanger when both ends were supported. Structural analysis conditions included a helium flow rate of 3.729 mol/s and a helium outlet temperature of 910°C. An exhaust gas temperature of 1300°C and an exhaust gas rate of 52 g/s were confirmed to achieve the helium outlet temperature of 910°C with an exchanger inlet temperature of 135°C in an LPG-fueled helium heating system.

Role of the Accessory Parotid Gland in the Etiology of Parotitis: Statistical Analysis of Sialographic Features.

This retrospective study aimed to identify if the existence of the accessory parotid gland correlated with the etiology of parotitis. This may aid the development of better treatment strategies in the future. Sialographic features of cases with parotitis and healthy subjects were reviewed. The chi-square test was used to compare the incidence of accessory parotid gland between the groups. The Student’s t test was used to compare the length of Stensen’s duct, the length from the orifice to the confluence of the accessory duct, and the angle between the accessory duct and Stensen’s duct between the groups. The incidence of accessory parotid gland in patients with parotitis was 71.8% (28/39), which was significantly higher than that in healthy subjects (P = 0.005). Patients with parotitis had a longer Stensen’s duct than healthy subjects (P = 0.003). There was no significant difference in the length from the orifice to the confluence of the accessory duct or the angle between the accessory duct and Stensen’s duct (P = 0.136 and 0.511, respectively) between the groups.The accessory parotid gland might play a role in the pathogenesis of parotitis. The existence of an accessory parotid gland is likely to interfere with salivary flow. Computational fluid dynamics analysis of salivary flow in the ductal system would be useful in future etiologic studies on parotitis.

The Relationship Between Flow Paths and Water Quality in Mine Water Oxidation Ponds in South Korea

Tests were carried out at passive mine water treatment sites in South Korea to determine how flow and pH affected other water quality parameters. Computational flow analysis and tracer tests revealed that the water took surprisingly direct flow routes in the oxidation ponds, while other areas remained stagnant. Furthermore, ferrous iron concentration, dissolved oxygen, pH, electrical conductivity, total dissolved solids, turbidity, and water depth were all directly affected by the flow patterns due to the relationship between retention time and iron precipitation.

Analytical and Computational Analysis of Flow Splitting in Multiple, Parallel Channels Systems

Previous analytical results on flow splitting are generalized to consider multiple boiling channels systems. The analysis is consistent with the approximations usually adopted in the use of systems codes (like RELAP5 and TRACE5, among others) commonly applied to perform safety analyses of nuclear power plants. The problem is related to multiple, identical, parallel boiling channels, connected through common plena. A theoretical model limited in scope explains this flow splitting without reversal. The unified analysis performed and the confirmatory computational results found are summarized in this paper. New maps showing the zones where this behavior is predicted are also shown considering again twin pipes. Multiple pipe systems have been found not easily amenable for analytical analysis when dealing with more than four parallel pipes. However, the particular splitting found (flow along N pipes dividing in one standalone pipe flow plus N -1 identical pipe flows) has been verified up to fourteen pipes, involving calculations in systems with even and odd number of pipes using the RELAP5 systems thermal-hydraulics code.

Spiral blood flow in aorta–renal bifurcation models

The presence of a spiral arterial blood flow pattern in humans has been widely accepted. It is believed that this spiral component of the blood flow alters arterial haemodynamics in both positive and negative ways. The purpose of this study was to determine the effect of spiral flow on haemodynamic changes in aorta–renal bifurcations. In this regard, a computational fluid dynamics analysis of pulsatile blood flow was performed in two idealised models of aorta–renal bifurcations with and without flow diverter. The results show that the spirality effect causes a substantial variation in blood velocity distribution, while causing only slight changes in fluid shear stress patterns. The dominant observed effect of spiral flow is on turbulent kinetic energy and flow recirculation zones. As spiral flow intensity increases, the rate of turbulent kinetic energy production decreases, reducing the region of potential damage to red blood cells and endothelial cells. Furthermore, the recirculation zones which form on the cranial sides of the aorta and renal artery shrink in size in the presence of spirality effect; this may lower the rate of atherosclerosis development and progression in the aorta–renal bifurcation. These results indicate that the spiral nature of blood flow has atheroprotective effects in renal arteries and should be taken into consideration in analyses of the aorta and renal arteries.

A computational analysis of heat transfer and fluid flow in high-speed scanning of laser micro-welding

A transient three-dimensional model is numerically developed using computational fluid dynamics (CFD) method to understand some critical criteria such as temperature fields and melt pool formation by considering the heat source and the material interaction and the effect of laser welding parameters on laser micro-welding process. To gain more implicit insight of fluid dynamics, the issue of circulation of molten metal assisted by the surface tension, buoyancy and recoil pressure forces in the weld pool has been investigated Assuming that atmospheric and vaporised material pressures are balanced at the front of the laser beam. The governing equations from the Navier–Stokes for Newtonian fluid are prepared to estimate the melt flow that influences the rate of temperature distribution in a 3-D domain. The simulation results have been compared with two sets of experimental research to predict the weld bead geometry and solidification pattern which laser welds are made on thin stainless steel sheet (SUS304). The shape comparison describes those parameters relevant to any changes in the melt dynamics and temperatures are of great importance on the formation of weld pool and heat distribution during laser micro-welding. The fair agreement between simulated and experimental results, demonstrates the reliability of the computed model.

Exploiting active subspaces to quantify uncertainty in the numerical simulation of the HyShot II scramjet

We present a computational analysis of the reactive flow in a hypersonic scramjet engine with focus on effects of uncertainties in the operating conditions. We employ a novel methodology based on active subspaces to characterize the effects of the input uncertainty on the scramjet performance. The active subspace identifies one-dimensional structure in the map from simulation inputs to quantity of interest that allows us to reparameterize the operating conditions; instead of seven physical parameters, we can use a single derived active variable. This dimension reduction enables otherwise infeasible uncertainty quantification, considering the simulation cost of roughly 9500 CPU-hours per run. For two values of the fuel injection rate, we use a total of 68 simulations to (i) identify the parameters that contribute the most to the variation in the output quantity of interest, (ii) estimate upper and lower bounds on the quantity of interest, (iii) classify sets of operating conditions as safe or unsafe corresponding to a threshold on the output quantity of interest, and (iv) estimate a cumulative distribution function for the quantity of interest.

리버스 엔지니어링을 통한 디젤엔진 흡기포트의 성능 비교

In this paper, we built a three-dimensional model by applying reverse engineering techniques on targeting the intake port of 2900cc class diesel engine before that three-dimensional design technique is applied. The performance of the intake port is predicted and analysed using the computational flow analysis. Flow Coefficient and Swirl Ratio have been analyzed for two intake port models. One is the intake port for the diesel engine with plunger-type fuel system, and the other is for the diesel engine with CRDI fuel system. Computational result shows that the Flow Coefficient of the intake port with CRDI fuel system is increased upto 10 percentage compared with that with plunger-type. Also, the intake port with plunger-type has high Swirl Ratio at high valve lift, and the intake port with CRDI fuel system has high Swirl Ratio at relatively low valve lift. It is believed that because of high performance of the fuel injector, the intake port with CRDI fuel system is designed for more air amount and not much swirl flow at high valve lift. However, high swirl flow is required at low valve lift for initial fuel and air mixing. The result of this study may be useful for the re-manufacturing industry of automotive parts.

Power Flow Analysis of Simulink IEEE 57 Bus Test System Model using PSAT

In this paper, we have developed an IEEE 57 bus test system model for conducting the power flow analysis. Simulink library based editor in Power System Analysis Toolbox (PSAT) is used for designing the model. MATLAB is used as a platform for running the PSAT software package. Default Newton-Raphson method in PSAT is used for conducting the power flow analysis. The algorithm for designing the Simulink IEEE 57 bus test system model is developed and the power flow has conducted. All the results are tabulated and the necessary graphs were drawn for the voltage, angle, active, and the reactive power for all the 57 buses. All the results are analyzed and the conclusion has given for the validity of this computational power flow analysis.