3D Computational Fluid Dynamics Analysis Research Articles

New insights in twin screw expander performance for small scale ORC systems from 3D CFD analysis

Twin screw expanders are widely used for power generation in small scale Organic Rankine Cycles (ORC). In order to increase the efficiency and maximize the generated power, an optimized design and appropriate operating conditions should be used. The use of Computational Fluid Dynamics (CFD) allows the analysis of the flow inside these machines which is impossible to investigate experimentally but which is influencing the performance of the expander. Some of the challenges when performing CFD analysis in these machines are the complexity of the rotors’ motion and the properties of the refrigerant. In this paper a 3D CFD analysis of a twin screw expander is presented. The 3D block-structured grid for the twin screw expander is constructed from the solution of Laplace problems in two-dimensional sections on an unstructured grid of the same geometry. During the transient calculations, grid nodes are moved while keeping the mesh topology. The properties of the refrigerant R245fa have been evaluated using the ideal gas Equation of State (EoS), the Aungier Redlich–Kwong EoS and the CoolProp. 3D CFD analysis of the screw expander showed that the difference in power output between the ideal gas EoS and the Aungier Redlich–Kwong EoS is 8% and between Aungier Redlich–Kwong EoS and CoolProp is negligible for operating conditions of interest. To investigate the performance of the expander, different pressure ratios and rotational speeds were studied for two different designs of the twin screw expander. The flow analysis inside the clearances that are forming leakage paths gives more insight in the performance of the expander. It is concluded that the biggest pressure drop is caused by a throttling loss at the inlet port and therefore an optimized design of the inlet port is necessary.

Influence of Aortic Outflow Cannula Orientation on Epiaortic Flow Pattern During Pulsed Cardiopulmonary Bypass

Cerebral hypoperfusion that may occur during linear cardiopulmonary bypass (CPB) is often responsible for mnemonic problems, loss of neural functions, or coma. Pulsed CPB might provide better organ protection, especially to the brain. The present work numerically investigates how the CPB cannula orientation influences blood flow in aortic and epiaortic vessels during pulsed CPB, realized using the intra-aortic balloon pump (IABP). The computational fluid dynamics (CFD) model consisted of a three-dimensional (3D) patient-specific aorta with three epiaortic vessels, a 40-cm3 intra-aortic balloon, and a 24 Fr arterial cannula in the traditional position and orientation (tilt angle of 45°, case I) and with a greater inclination (tilt angle of 60°, case II). Comparative multi-scale studies, realized by coupling a 3D CFD analysis and a lumped-parameters model, were carried out to establish the hemodynamic modifications due to changes in the cannula orientation. A comparison between the two cases revealed that when the cannula flow was directed to the epiaortic vessels (case I), the mean flows of the left subclavian artery and the thoracic aorta increased by about 2.08 and 7.50 %, respectively. When the flow cannula collided with the aortic arch concavity (case II), this area presented high wall shear stress (WSS) values and a greater amount of blood occurred in the ascending aorta, where it stagnated, although the mean flows of the innominate and left common carotid arteries increased by about 6.25 and 3.13 %, respectively. Pulsed CPB may reduce brain damage during heart surgery, so the evaluation of epiaortic flow during the extracorporeal circulation with various arterial cannula orientations is useful for the analysis of hemodynamic modifications.

3D CFD Analysis of a Vertical Axis Wind Turbine

To analyze the complex and unsteady aerodynamic flow associated with wind turbine functioning, computational fluid dynamics (CFD) is an attractive and powerful method. In this work, the influence of different numerical aspects on the accuracy of simulating a rotating wind turbine is studied. In particular, the effects of mesh size and structure, time step and rotational velocity have been taken into account for simulation of different wind turbine geometries. The applicative goal of this study is the comparison of the performance between a straight blade vertical axis wind turbine and a helical blade one. Analyses are carried out through the use of computational fluid dynamic ANSYS® Fluent® software, solving the Reynolds averaged Navier–Stokes (RANS) equations. At first, two-dimensional simulations are used in a preliminary setup of the numerical procedure and to compute approximated performance parameters, namely the torque, power, lift and drag coefficients. Then, three-dimensional simulations are carried out with the aim of an accurate determination of the differences in the complex aerodynamic flow associated with the straight and the helical blade turbines. Static and dynamic results are then reported for different values of rotational speed.

3D CFD analysis of the effect of inlet air flow maldistribution on the fluid flow and heat transfer performances of plate-fin-and-tube laminar heat exchangers

Plate fin-and-tube heat exchangers are widely used in several areas such as heating, ventilating, air conditioning and refrigeration systems. Nonuniformity of the inlet air flow in heat exchangers is first order importance and has decisive influence on their efficiency because it can intensify longitudinal wall heat conduction and the maldistribution of interior temperature.This study presents the results of three-dimensional (3D) Computational Fluid Dynamics (CFD) simulations aim to investigate the effect of inlet air flow maldistribution on the thermo-hydraulic performance of heat exchangers. Validation of the computation results with experimental data found in the literature has shown a very good agreement.Different computation test cases with a variety of inlet air flow distributions on in-line and staggered plate-fin-and-tube heat exchangers were run to systematically analyse their effects on system performance. The CFD results confirmed the importance of the influence of inlet fluid flow nonuniformity on heat exchanger efficiency. Results indicate that up to 50% improvement or deterioration in the Colburn j-factor are found compared to the baseline case of a heat exchanger with a uniform inlet air velocity profile. Moreover, the present investigation with respect to inlet flow maldistribution demonstrates that 3D CFD simulation is a useful tool for analysing, designing and optimising heat exchangers. Finally, the results of this study can be also of significant value for the optimum design of header and distributor configurations of heat exchangers to minimise maldistribution.

Buffeting Analysis of a Cable-Stayed Bridge Using Three-Dimensional Computational Fluid Dynamics

In recent years, a number of studies have been conducted to analyze wind-induced vibrations of a bridge using computational fluid dynamics (CFD). Previous studies have been limited to analyzing two-dimensional sections only, and three-dimensional (3D) analyses of entire bridges have not yet been performed. In this study, a CFD program with fluid-structure interaction is developed to perform buffeting analysis of a 3D cable-stayed bridge. The FEM formulated by the Galerkin least-squares method and arbitrary Lagrangian-Eulerian method are used to perform fluid-structure interaction CFD. The spectral representation method is used to generate the time series turbulence, which is applied to the inlet boundary condition. A supercomputer is used to reduce the large computing time. The analysis model of an existing cable-stayed bridge, which contains an ambient atmospheric region, has been used to calculate the dynamic responses of bridges and the detailed flow of wind. The results of the 3D CFD analysis of the bridge are compared with the results of conventional frequency domain buffeting analysis. The results are essentially in good agreement with those of the conventional analysis. The numerical method developed in this study will be an efficient alternative to wind tunnel tests for verifying wind flow, wind loading, and structural vibrations.

A comprehensive 3D analysis of polymer flow through a conical spiral extrusion die

Several restrictions which are related to extruder machinery and nature of process material exist in the design of plastic extrusion dies. To this respect, it is very important to consider design criteria and limitations in order to operate extrusion dies at desired production rate and temperature. In the current study, flow field characteristics through a conical spiral mandrel die are analysed in detail by 3D Computational Fluid Dynamics (CFD) simulations. The effects of operating conditions such as production rate and temperature on pressure drop through the spiral mandrel die and the occurence of melt fracture are investigated. The temperature dependent viscosity versus shear rate data for grade QB79P (CarmelTech) polypropylene (PP) melt under study are measured by use of rotational and capillary rheometers. Stress terms in the momentum equations are modeled by Generalized Newtonian Fluid (GNF) Model. For this, Bird-Carreau Model is employed as the viscosity model for the polymer melt. 3D CFD analyses provide comprehensive data and understanding with regard to flow behaviour through complex extrusion dies.

Study on Thermal Performance of Energy Textile in Tunnel

터널 내부의 지열을 활용하여 지열 냉난방 시스템 가동에 필요한 열에너지를 얻을 수 있는 텍스타일 형태의 지중열교환기(에너지 텍스타일)를 충남 서천군 일대의 철도 폐터널 벽면에 시험 시공하였다. 현장에 설치된 에너지 텍스타일의 성능을 평가하기 위해 냉방 운영과 난방 운영에 대한 일일 냉난방 모사 시험을 수행하였다. 일일 냉난방 모사 시험을 진행하는 동안 터널 벽면에 설치된 지중 열교환기로 유입/유출되는 순환수의 온도, 순환 유량, 터널 벽면 내부 지반의 온도, 터널 내부의 온도를 지속적으로 측정하였다. 시험을 통해 현장에 설치된 에너지 텍스타일은 난방가동에서 에너지 텍스타일 유닛당 57.6~143.5 W의 열교환률을 보였고 냉방가동에서는 362.3~558.4 W의 열교환률을 보였다. 또한, 시험결과로부터 터널에 설치된 지중열교환기의 열교환 성능은 터널 내부 기온의 변화에 큰 영향을 받는 것으로 나타났다. 또한, 전산유체 수치해석을 통하여 터널 내부 기온 변화를 고려한 현장 시험을 모사하여 적용된 수치해석 모델을 검증하였다. 검증된 수치해석 모델을 이용하여 콘크리트 라이닝 내부의 유도 배수재 설치 유무에 따른 에너지 텍스타일의 열적 거동에 대한 매개변수 연구를 수행하였다. Textile-type heat exchangers installed on the tunnel walls for facilitating ground source heat pump systems, so called "energy textile", was installed in an abandoned railroad tunnel around Seocheon, South Korea. To evaluate thermal performance of the energy textile, a series of long-term monitoring was performed by artificially applying daily intermittent cooling and heating loads on the energy textile. In the course of the experimental measurement, the inlet and outlet fluid temperatures of the energy textile, pumping rate, temperature distribution in the ground, and air temperature inside the tunnel were continuously measured. From the long-term monitoring, the heat exchange rate was recorded as in the range of 57.6~143.5 W per one unit of the energy textile during heating operation and 362.3~558.4 W per one unit during cooling operation. In addition, the heat exchange rate of energy textile was highly sensitive to a change in air temperature inside the tunnel. The field measurements were verified by a 3D computational fluid dynamics analysis (FLUENT) with the consideration of air temperature variation inside the tunnel. The verified numerical model was used to evaluate parametrically the effect of drainage layer in the energy textile.

Nonlinear finite amplitude vibrations of sharp-edged beams in viscous fluids

In this paper, we study flexural vibrations of a cantilever beam with thin rectangular cross section submerged in a quiescent viscous fluid and undergoing oscillations whose amplitude is comparable with its width. The structure is modeled using Euler–Bernoulli beam theory and the distributed hydrodynamic loading is described by a single complex-valued hydrodynamic function which accounts for added mass and fluid damping experienced by the structure. We perform a parametric 2D computational fluid dynamics analysis of an oscillating rigid lamina, representative of a generic beam cross section, to understand the dependence of the hydrodynamic function on the governing flow parameters. We find that increasing the frequency and amplitude of the vibration elicits vortex shedding and convection phenomena which are, in turn, responsible for nonlinear hydrodynamic damping. We establish a manageable nonlinear correction to the classical hydrodynamic function developed for small amplitude vibration and we derive a computationally efficient reduced order modal model for the beam nonlinear oscillations. Numerical and theoretical results are validated by comparison with ad hoc designed experiments on tapered beams and multimodal vibrations and with data available in the literature. Findings from this work are expected to find applications in the design of slender structures of interest in marine applications, such as biomimetic propulsion systems and energy harvesting devices.

Modeling the Effects of Coolant Application in Friction Stir Processing on Material Microstructure Using 3D CFD Analysis

The ability to generate nano-sized grains is one of the advantages of friction stir processing (FSP). However, the high temperatures generated during the stirring process within the processing zone stimulate the grains to grow after recrystallization. Therefore, maintaining the small grains becomes a critical issue when using FSP. In the present reports, coolants are applied to the fixture and/or processed material in order to reduce the temperature and hence, grain growth. Most of the reported data in the literature concerning cooling techniques are experimental. We have seen no reports that attempt to predict these quantities when using coolants while the material is undergoing FSP. Therefore, there is need to develop a model that predicts the resulting grain size when using coolants, which is an important step toward designing the material microstructure. In this study, two three-dimensional computational fluid dynamics (CFD) models are reported which simulate FSP with and without coolant application while using the STAR CCM+ CFD commercial software. In the model with the coolant application, the fixture (backing plate) is modeled while is not in the other model. User-defined subroutines were incorporated in the software and implemented to investigate the effects of changing process parameters on temperature, strain rate and material velocity fields in, and around, the processed nugget. In addition, a correlation between these parameters and the Zener-Holloman parameter used in material science was developed to predict the grain size distribution. Different stirring conditions were incorporated in this study to investigate their effects on material flow and microstructural modification. A comparison of the results obtained by using each of the models on the processed microstructure is also presented for the case of Mg AZ31B-O alloy. The predicted results are also compared with the available experimental data and generally show good agreement.

Computational Flow Dynamics Study in Severe Carotid Bulb Stenosis with Ulceration

Purpose: Computational fluid dynamics (CFD) applications for atherosclerotic carotid stenosis have not been widely used due to limited resolution in the severely stenotic lumen as well as small flow dimension in the stenotic channel. Materials and Methods: CT data in DICOM format was transformed into 3 dimensional (3D) CFD model of carotid bifurcation. For computational analysis of blood flow in stenosis, commercial finite element software (ADINA Ver. 8.5) was used. The blood flow was assumed to be laminar, viscous, Newtonian, and incompressible. The distribution of wall shear stress (WSS), peak velocity and pressure across the average systolic and diastolic blood pressures permitted construction of a contour map of the velocity in each cardiac cycle. Results: Computer simulation of WSS, flow velocity and wall pressure could be demonstrated three dimensionally according to flow vs. time dimension. Such flow model was correlated with angiographic finding related to maximum degree of stenosis associated with ulceration. Combination of WSS map and catheter angiogram indicated that the highest WSS corresponded to the most severely stenotic segment at systolic phase, whereas ulceration, which is the weakest point of the plaque, appeared at the downstream side of the carotid bulb stenosis. Conclusion: Our preliminary study revealed that 3D CFD analysis in carotid stenosis was feasible from CT angiography source image and could reveal WSS, flow velocity and wall pressure in the severe carotid bulb stenosis with ulceration. Further CFD analysis is warranted to apply such hemodynamic information to the atherosclerotic lesion in the more practical way.

Modeling of friction stir processing using 3D CFD analysis

Friction Stir Processing (FSP) has emerged as an effective tool for enhancing sheet metal properties through microstructural modification of processed materials. Despite the large number of studies, most of the work that has been done in the FSP field focuses primarily on experimental work. Only limited modeling attempts on temperature distribution and strain rate analysis have been conducted. In this work, a three dimensional Computational Fluid Dynamics (CFD) model was developed to simulate FSP using the STAR CCM+ CFD commercial software. User-defined subroutines were developed and implemented to investigate the effects of process parameters on temperature, strain rate, flow stress and material velocity fields in, and around, the processed nugget. In addition, a correlation between process parameters and the Zener-Holloman parameter was developed to predict the grain size distribution in the processed zone. Different stirring conditions were incorporated in this study to investigate their effects on material flow and microstructural modification. The modeling results were compared with the available experimental data and showed good agreement.

3D CFD Analysis of an Abnormally Rapid Combustion Phenomenon in Downsized Gasoline Engines

Soaring oil prices combined with increased environmental awareness maintain the drive for fuel-efficient and CO2-friendly powertrains. Even if hybrids seem to be the media friendly solution, there is still much work to be done on combustion systems. For gasoline engines aggressive downsizing seems promising and IFP proposes an innovative approach. However, new difficulties arise as specific power outputs are increased. Various combustion phenomena are encountered from simple knock to rumble and must be understood and mastered in order to fully optimize the combustion system. Abnormally rapid yet non destructive and seemingly stable combustion is one of these new phenomena. 3D CFD (Computational Fluid Dynamics) simulation tools were used in order to investigate and under- stand what lies behind this particular combustion.

3D CFD analysis of the hydrogen releases and dispersion around storage facilities

Unexpected hazards often arise from hydrogen storage and distribution facilities, and latent dangers induced by handling of hydrogen. This paper represents the results of CFD (computational fluid dynamics) modeling of hydrogen releases and dispersion at model storage facilities with simple geometries. Numerical results for model storage facility were compared with the reported data on the hydrogen dispersion. In addition, the hydrogen concentration in a real industrial environment, such as in the hydrogen energy station (HES), was estimated with 3D CFD modeling. The risk assessment was achieved under hypothetical hydrogen leakage scenarios.

Numerical simulations of homogeneous charge compression ignition engines with high levels of residual gas

In order to account for the effect of mixture inhomogeneity in HCCI engines utilizing high levels of residual gas and to estimate accurate initial conditions, a sequential numerical procedure was devised. A one-dimensional (1D) engine cycle simulation and a three-dimensional (3D) CFD analysis were used to calculate the residual gas overall level and its spatial distribution. A Monte-Carlo method for the probability density function (PDF) of the mass fraction and temperature, assuming negligible spatial inhomogeneity in the mean quantities but including finite small-scale fluctuations, was used to allow for micro-mixing in the evolution of the chemical reactions. The computational fluid dynamics (CFD) analysis confirmed that substantial scalar inhomogeneity persists up to top dead centre (TDC). The result from the procedure showed a close prediction of the pressure profile from the experiment. However, the u HC level is underpredicted, attributed to the assumed spatial homogeneity of the mean quantities in the Monte-Carlo simulation, which causes an overprediction of the scalar fluctuation decay. Parametric studies of the initial mixture inhomogeneity and turbulence timescale showed that they affect both the ignition timing and combustion duration. A comparison of three mixing models (IEM, modified Curl, and EIEM) showed that the EIEM model predicts a later ignition. The results suggested that accurate prediction of pollutant emission in HCCI engines with high levels of residual gas can be achieved only by a fully 3D calculation incorporating turbulence-chemistry interactions, although combustion phasing and duration can be predicted with adequate accuracy with a volume-averaged representation of the initial residual gas fluctuations.

Three-dimensional thermal boundary layer corrections for circular heat flux gauges mounted in a flat plate with a surface temperature discontinuity

Three-dimensional Navier–Stokes computational fluid dynamics (CFD) analysis has been performed in an effort to determine thermal boundary layer correction factors for circular convective heat flux gauges (such as Schmidt–Boelter and plug type) mounted flush in a flat plate subjected to a stepwise surface temperature discontinuity. Turbulent flow solutions with temperature-dependent properties are obtained for a freestream Reynolds number of 1E6, and freestream Mach numbers of 2 and 4. The effect of gauge diameter and the plate surface temperature have been investigated. The 3D CFD results for the heat flux correction factors are compared to quasi-2D results deduced from constant property integral solutions and also 2D CFD analysis with both constant and variable properties. The role of three-dimensionality and of property variations on the heat flux correction factors has been demonstrated.

2D CFD analysis and experimental analysis on the effect of hub to tip ratios on the performance of 0.6 m impulse turbine

The objective of this paper is to present the performance comparison of 2D Computational Fluid Dynamics (CFD) analysis with experimental analysis of 0.6 m impulse turbine with fixed guide vanes for both 0.6 and 0.7 hub to tip ratio (H/T). Also the comparison of 2D CFD analysis of the said turbine with different values of H/T ranging from 0.5 to 0.7. A 2D-cascade model was used for CFD analysis while uni-directional steady flow was used for experimental analysis. The blade and guide vane geometries are based on 0.6 m rotor diameter, with optimum profile, and different H/T of 0.5, 0.6 and 0.7. It was concluded from 2D CFD analysis that 0.5 H/T ratio performances was higher than that of 0.6 and 0.7 H/T at peak efficiency and the operational flow range for 0.5 H/T was found to be wider than that of 0.6 and 0.7 H/T ratio.

Formula 1 car wheel aerodynamics

A detailed project has been carried out to investigate the aerodynamic performance of a Formula 1 car front wheel. Experimental drag measurements were carried out on a 40% scale rig representing the front right-hand quarter of a generic Formula 1 car, with features such as the front wing and car body modelled accurately to generate a suitable flowfield around the wheel. Smoke flow visualization gave valuable insights into the major flow features and enabled understanding of how the wheel aerodynamic perform- ance might be improved. Further visualization was carried out using a fully 3D CFD (Computational Fluid Dynamics) analysis of the test rig geometry, using state-of-the-art in-house geometry handling and CFD facilities based around an unstructured Navier–Stokes solver. Drag measurements were successfully obtained for a large range of typical car configurations, including front wing endplate variations. The experimental and computational flow visualization enabled a new front wing geometry to be designed, which gave a significant reduction in the drag of the wheel.