Transient Flow Behavior Research Articles

Effect on the drag coefficient of various spiked cylinders during buzz phenomenon subjected to hypersonic flows

Pulsation mode of transient flow behavior may occur in a violent manner in case of spiked cylinders depending on the geometry, type of spikes, and free stream conditions. Drastic pressure fluctuations near the face of the afterbody have been observed in most cases of pulsating flow mode and thus resulting in drastic variations in the coefficient of drag of the spiked body. The transient analysis of variations in Cd with spike length for various spiked cylinders have been carried out in the current work. The variations in Cd during one complete cycle as well as variations in time-averaged value of Cd with increase in L/D ratios have been analyzed. These variations have been explained with respect to the localized pressure fluctuations, shift in foreshock–aftershock interaction region, effect of effective shielding, and increasing spike lengths. It was found that aerodisk spiked cylinder had the least time-averaged Cd. The Cd for various other spiked bodies has also been summarized over a range of feasible spike lengths and an optimum design of the spiked body in terms of the spike shape and L/D has also been suggested.

An Alternative BEM for Simulating the Flow Behavior of a Leaky Confined Fractured Aquifer With the Use of the Semianalytical Approach

AbstractThis study developed an alternative boundary element method (BEM) to simulate the transient flow behavior of groundwater induced by well extraction in a confined fractured aquifer containing a network of discrete or connected fractures. The matrix flow, network‐fracture flow, and matrix‐fracture fluid exchange were considered. The aquifer was treated as a heterogeneous whole that consisted of fracture and matrix blocks with locally homogeneous hydraulic properties. The fractures were explicitly represented to be of true finite volume rather than nonrepresentational line sources. A semianalytical solution was developed based on the theory of a BEM in the Laplace transform domain, but the analytical Green's function was used for the bounded domain rather than the free‐space Green's function in a conventional BEM. Case studies were presented in order to investigate the flow exchange behavior between the matrix and fractures and the corresponding transient drawdown response. The results showed that (1) exchange flux distribution calculated with the classical infinitesimal fracture model was consistent with the difference of the normal drawdown derivative values on both sides of the fracture body in our model. (2) When the well was in the matrix, the fractures acted as both highly conductive conduits and leaky faults, and the drawdown derivative behaviors resembled the characteristics of a dual‐porosity reservoir model. (3) When the well was in the network fracture and when the volume of fracture was of the same order of magnitude as the matrix, the drawdown derivative might exhibit the look‐alike behavior of a dual‐porosity model.

Analysis of a Multi-Porthole Injector Array in a Supersonic Crossflow

Computational fluid dynamic (CFD) simulations of hydrogen injection through a multi-porthole injector array into a Mach 10 enthalpy supersonic crossflow are presented and compared to experimental data. Reynolds-averaged Navier–Stokes simulations using a Menter shear-stress transport turbulence model are performed with the CFD code CFD++. The experimental results showed transient flow behavior in the boundary-layer separation upstream of the injector past the measurable test time. This complicated the validation process of the steady-state simulations to the experimental data. A hybrid simulation, which provides a laminar inflow boundary layer and turbulence production at the injector, matched the upstream separation length as measured from the experimental data. The simulation near-field shock structures and fuel penetration matched experimental schlieren photographs. The close jet-to-jet spacing leads to a blockage of injector-generated vortices. The simulations show that including three-dimensional spillage effects reduced the injection-induced separation length by 20%, and they resulted in a better match with the experimental data. The results also showed the injection-induced separation has a significant spanwise flow and alters the mixing process downstream of the multi-porthole injector array by enabling trailoff vortices to develop.

Integration of Pressure Transient Data into Reservoir Models Using the Fast Marching Method

SummaryCalibration of reservoir model properties by integration of well-test data remains an important research topic. Well-test data have been recognized as an effective tool to describe transient flow behavior in petroleum reservoirs. It is also closely related to the drainage volume of the well and the pressure-front propagation in the subsurface. Traditional analytic means of estimating reservoir permeability relies on an interpretation of the diagnostic plot of the well pressure and production data, which usually leads to a bulk average estimation of the reservoir permeability. When more detailed characterization is needed, a forward model that is sensitive to the reservoir heterogeneity needs to be established, and a numerical inversion technique is required.We use the concept of the diffusive time of flight (DTOF) to formulate an asymptotic solution of the diffusivity equation that describes transient flow behavior in heterogeneous petroleum reservoirs. The DTOF is obtained from the solution of the Eikonal equation using the fast marching method (FMM). It can be used as a spatial coordinate that reduces the 3D diffusivity equation to an equivalent 1D formulation. We investigate the drainage-volume evolution as a function of time in terms of the DTOF. The drainage volume might be directly related to the well-test derivative, which can be used in an inversion calculation to calibrate reservoir model parameters.The analytic sensitivity coefficients of the well-test derivative with respect to reservoir permeability are derived and incorporated into an objective function to perform model calibration. The key to formulating the sensitivity coefficients is to use the functional derivative of the Eikonal equation to derive the analytic sensitivity of the DTOF to reservoir permeability. Its solution is implemented by tracking the characteristic trajectory of the local Eikonal solver within the FMM. The major advantage of calculating the sensitivity coefficients using the FMM is its significant computational efficiency during the iterative inversion process.This inverse-modeling approach is tested on a 2D synthetic heterogeneous reservoir model and then applied to the 3D Brugge Field, where a single well with constant flow rate is simulated. The well-test derivative is shown to be inversely proportional to the drainage volume and is treated as the objective function for inversion. With an additional constraint to honor the prior model, our inverse-modeling approach will adjust the reservoir model to obtain permeability as a function of distance from the well within the drainage volume. It provides a modification of reservoir permeability both within and beyond the depth of investigation (DOI).

Simulation model size reduction using volume of investigation by fast marching method

The numerical methods have been widely utilized to conduct history matching work in the formations with complex in-situ conditions. Due to the fact that the history matching process normally requires running numerous models to find the best match between the history production data and the simulated production data, it is necessary to improve the computational efficiency of the numerical method in order to reduce the computational time. In this work, the author introduces a dynamic-volume-of-investigation (DVOI) implicit-finite-difference (IMFD) method to increase the computational efficiency of the conventional IMFD method. In the DVOI-IMFD method, the computational efficiency has been improved by reducing the simulation model size using volume of investigation (VOI) by fast marching method (FMM).This proposed DVOI-IMFD method is developed based on the concept of VOI. The VOI initiates at the wellbore and extends to the further region of the reservoir as production proceeds. Beyond the VOI, the pressure disturbance in the reservoir is regarded as negligible. Following this scenario, the author assumes that, at each timestep, the pressure response in the region that is beyond the VOI can be neglected, and we only study the pressure response in the region that is within the VOI to approximately characterize the transient flow behavior in the reservoir. Therefore, this proposed numerical approach is composed of two parts, namely, predicting the VOI at each timestep and applying the IMFD within the VOI. In this work, the DVOI is captured with a boundary tracking technique which is called FMM. The author applies this proposed DVOI-IMFD method to different scenarios and compares the simulation outputs and computational time of the DVOI-IMFD method to those of the conventional IMFD method. The calculated results show that the outputs of this proposed method exhibit negligible difference from those of the conventional IMFD method, whereas the computational speed of this proposed method can be significantly faster than that of the conventional IMFD method.

Gradual contraction of pipe cross-section effects on transient behavior of air–water slug flow

The current experimental investigation was aimed at understanding the influence of reducing sections on the transient behavior of slug flow. Experiments were carried out using two concentric area cross-section reducers with 160 mm lengths; the first one was shaped as a conical frustum with a 44 mm inlet diameter reducing to a 30 mm outlet diameter and the second one as a frustum with the same inlet diameter converting to a rectangular cross-section (34 mm × 21 mm). Four different water superficial velocities (0.43, 0.55, 0.72 & 0.84 m s−1) and three different air superficial velocities (2.5, 3.6 & 4.9 m s−1) were applied in the course of the experiments. Visualization studies, as well as frequency distribution analyses, were used to observe flow field changes. The visualization study showed that the gas slug tail, liquid slug, and gas slug subsequent to passing through the reducers converted to non-homogeneous bubbly flow, several small slugs, and pseudo-slugs, respectively. The obtained frequency distributions, which were calculated using a Fourier transform tool, showed that unlike that of the dominant frequency, the power of other frequencies was amplified in the low-frequency range owing to the high formation rate of pseudo-slugs and small slugs. This change indicates that intermittent air–water slug flow with a specified dominant frequency subsequent to passing reducers varies to an uncertain flow with semi-uniform distribution in the low-frequency range. Estimation of Shannon entropy also showed that entropy increased by almost five times downstream of the reducers, which confirms that energy is distributed uniformly in a broad frequency bandwidth. Analyses of the essential bandwidth showed that the reducing section acted as a frequency distribution modifier whose performance decreased with liquid flow rate increments. Based on this achievement, it was found that both the circular and the rectangular reducers were able to generate the named conditions.

Investigation of the influence of various numbers of impeller blades on internal flow field analysis and the pressure pulsation of an axial pump based on transient flow behavior

AbstractIn the current study, the flow behavior in an axial pump through changing the number of impeller blades is analyzed. Due to the number of blades being very important geometrical parameters in the pump, the study of the influence of various numbers of blades on flow and pressure pulsation in the pump is carried out using the computational fluid dynamics technique. The sliding mesh with the standard turbulence k‐ε model is used to investigate the unsteady flow with several flows and impeller blades. Pump performance prediction results with available experimental data indicate reasonable and good agreement with each other. Static pressure, shear stress, and different velocity compounds are qualitatively analyzed. Moreover, the fluctuation pressure and average pressure under different operating conditions and impeller blades are quantitatively investigated. The numerical results show that the impeller blade has a high impact on pressure, shear stress, magnitude velocity, axial velocity, radial velocity, tangential velocity, and average pressure. Furthermore, this numerical study provides good and useful information for the hydraulic design of axial pumps.

Transient flow and mold flux behavior during ultra-high speed continuous casting of billet

Ultra-high casting speed is an important development feature for efficient continuous casting of billet. A mathematical model which addresses the high flow rate of molten steel in the billet mold is presented, coupling slag flow with heat flux and solidification. The model is then applied to investigate the correlation between transient steel flow, slag infiltration and heat transfer in the mold-shell gap during ultra-high casting speed. The results show that the meniscus level experiences a hump near the mold wall and a valley near the nozzle as a result of the recirculating flow in the upper mold. The liquid slag around the mold wall infiltrates preferentially into the gap to be consumed quickly, whereas those near the SEN flows to the mold with a low speed. Severe fluctuations in meniscus level will disturb the slag infiltration, which in turn causes the formation of uneven slag films, leading to intensified heat flux fluctuations in the mold-shell gap, especially in the area of 20−60 mm from the mold corner.

Transient flow behavior in serpentine curved microchannel of inertial microfluidic devices

The serpentine microchannel or bent microchannel has been identified as one of the essential elements for inertial microfluidic devices. Understanding the transient flow of liquid is important in predicting flow time and evaluating device performance. In this paper, based on the unsteady Bernoulli equation, the inertial transient flow model was derived by analyzing the microchannel resistance factor using back propagation (BP) artificial neural network (ANN). In order to train the ANN, an improved BP algorithm was used to make the resistance model more accurate. A centrifugal test platform was employed to measure flow time in the microchannel with different structure sizes. The results show that the transient flow model has a good agreement with the experiment values, the results also show that the method using BP neural network can also be used to solve the problem of nonlinear inertial flow.

Investigation on the control of multiphase flow behavior in a continuous casting tundish during ladle change

The transient multiphase flow behavior in a single-strand tundish during ladle change was studied using physical modeling. The water and silicon oil were employed to simulate the liquid steel and slag. The effect of the turbulence inhibitor on the slag entrainment and the steel exposure during ladle change were evaluated and discussed. The effect of the slag carry-over on the water-oil-air flow was also analyzed. For the original tundish, the top oil phase in the impact zone was continuously dragged into the tundish bath and opened during ladle change, forming an emulsification phenomenon. By decreasing the liquid velocities in the upper part of the impact zone, the turbulence inhibitor decreased considerably the amount of entrained slag and the steel exposure during ladle change, thereby eliminating the emulsification phenomenon. Furthermore, the use of the TI-2 effectively lowered the effect of the slag carry-over on the steel cleanliness by controlling the movement of slag droplets. The results from industrial trials indicated that the application of the TI-2 reduced considerably the number of linear inclusions caused by ladle change in hot-rolled strip coils.

Numerical analysis of nitrogen condensation heat transfer enhancement with liquid film fluctuation at cryogenic temperature

Film condensation is the main condensation mode for cryogenic fluids with extremely low surface tension. Deep understanding of how fluctuating liquid film affects heat transfer is of great significance to the design and optimization of cryogenic condensers. In this study, a numerical model of nitrogen condensation on a vertical plate is established which adopts an accurate condensation mass transfer model, and the simulation results match well with the experimental data. The transient flow behaviors like thickness, temperature field, velocity field of liquid nitrogen film and various heat transfer coefficients are analyzed. Results show that the condensed liquid nitrogen film undergoes a flow pattern evolution from laminar flow to sinusoidal-like wave flow and then solitary wave flow. Compared to water condensation, nitrogen condensation has a more intense fluctuating flow pattern due to the lower latent heat. Large local heat transfer coefficient could be found at both the trough and peak areas of the film waves, while the lowest value occurs at the front of the wave peak. The analysis shows that the liquid film in the laminar flow zone between the two peaks is thinned to below Nusselt's theoretical value, and the convection effect at the peak is enhanced due to a sharp increase in the wave velocity. Finally, the time domain characteristics of the local heat transfer coefficients reveal that the synergistic effect of intermittent thinning of film thickness and enhanced convection in solitary waves improves the heat transfer coefficient up to 30% compared with the Nusselt's theoretical value for laminar flow.

Multiphase modelling of the transient flow for Sn-15Pb and 357.0 alloys in semi-solid die casting process

Abstract The transient flow behavior of the semi-solid slurries for Sn-15Pb and 357.0 alloys during die casting process is investigated by experimental and numerical methods. A model for the transient-state three-dimensional multiphase flow based on the kinetic theory of granular flow is developed. This model is applied to investigate the distribution of solid concentration, flow state, pressure variation of the semi-solid slurry in the die casting process. The three important aspects of the multiphase flow, flow regime, particle-particle interaction and particle-liquid interaction, are interpreted according to the characteristic of the system. The model is verified by partial filling and in-situ observation experiments. Then it is applied for the phase segregation study of an elbow cavity encountered in practice. Results indicate that the 3D multiphase model can depict the flow characteristics of the semi-solid slurry very well. The inner arc side of the elbow cavity is easier to have liquid phase segregation than the outer arc side for the lower velocity gradients of the solid and liquid phases.

A fourth-order accurate finite difference method to evaluate the true transient behaviour of natural convection flow in enclosures

PurposeModelling accurately the transient behaviour of natural convection flow in enclosures been a challenging task because of a variety of numerical errors which have limited achieving the higher order temporal accuracy. A fourth-order accurate finite difference method in both space and time is proposed to overcome these numerical errors and accurately model the transient behaviour of natural convection flow in enclosures using vorticity–streamfunction formulation.Design/methodology/approachFourth-order wide stencil formula with appropriate one-sided difference extrapolation technique near the boundary is used for spatial discretisation, and classical fourth-order Runge–Kutta scheme is applied for transient term discretisation. The proposed method is applied on two transient case studies, i.e. convection–diffusion of a Gaussian Pulse and Taylor Vortex flow having analytical solution.FindingsError magnitude comparison and rate of convergence analysis of the proposed method with these analytical solutions establish fourth-order accuracy and prove the ability of the proposed method to truly capture the transient behaviour of incompressible flow. Also, to test the transient natural convection flow behaviour, the algorithm is tested on differentially heated square cavity at high Rayleigh number in the range of 103-108, followed by studying the transient periodic behaviour in a differentially heated vertical cavity of aspect ratio 8:1. An excellent comparison is obtained with standard benchmark results.Research limitations/implicationsThe developed method is applied on 2D enclosures; however, the present methodology can be extended to 3D enclosures using velocity–vorticity formulations which shall be explored in future.Originality/valueThe proposed methodology to achieve fourth-order accurate transient simulation of natural convection flows is novel, to the best of the authors’ knowledge. Stable fourth-order vorticity boundary conditions are derived for boundary and external boundary regions. The selected case studies for comparison demonstrate not only the fourth-order accuracy but also the considerable reduction in error magnitude by increasing the temporal accuracy. Also, this study provides novel benchmark results at five different locations within the differentially heated vertical cavity of aspect ratio 8:1 for future comparison studies.

CFD Simulation of Natural Convection Flow and Heat Transfer Process in Rectangular Cavity

In this paper we investigate the natural convective heat transfer process inside a ventilated rectangular cavity with a projected heat source. The heat source block is mounted on the bottom wall and a horizontal vent is provided on the top wall of the rectangular cavity. The flow is induced due to the density difference which arises due to the variations in temperature between the heat source block and the surrounding ambient fluid. A FORTRAN 90 CFD solver is developed to simulate the natural convection phenomena by solving the Navier-stokes equation, energy equation coupled with Realizable k-ε turbulence model. The transient flow behavior inside the cavity is simulated by varying the heat source aspect ratios, Grashof number and the heat source locations. It is found that the heat source aspect ratio and its locations significantly influences the flow and heat transfer characteristics inside the cavity. The bidirectional exchange rate across the horizontal opening increases linearly with Grashof number and heat source aspect ratio. A chaotic flow behavior pattern is observed across the opening and the strength of the instabilities increases linearly with heat source aspect ratio. It is identified that by varying the aspect ratio 0.1 ≤ β ≤ 3, the average Nusselt number and mass flow rates are increased by 28% and 43% respectively.

Experimental and numerical investigation of lubrication system for reciprocating compressor

Sufficient lubrication of the moving parts in a variable capacity inverter compressor is vital since it can directly affect the performance and expected lifetime. In this study, the lubrication system of a compact inverter compressor (CIC) is numerically and experimentally investigated. In the numerical modeling, a finite volume-based algorithm is used to model two-phase (air–oil) flow inside the compressor using Volume of Fluid Method (VoF) method. Transient behavior of the oil flow under laminar flow conditions is both simulated by imposing Sliding Mesh (SM) and the Moving Reference Frame (MRF) methods at various crankshaft speeds varying between 1200 and 4500 rpm. The measurements are taken using an experimental setup to compare/validate CFD results obtained from SM and MRF methods. Flow visualizations are performed with a high-speed camera to determine the oil climbing and required time for sufficient lubrication precisely. Moreover, the acceleration of the crankshaft is determined via high-speed camera and employed as a user-defined function to model the start-up period of the compressor. It is shown that with increasing crankshaft speeds, the average oil mass flow rate released from the upper part of the crankshaft is increasing almost linearly. It is also shown numerically that with increasing oil viscosity, the mass flow rate decreases. The comparison of experimental and CFD results reveals that the MRF solutions are in a better agreement with the measurements up to 2800 rpm. The SM method became favorable as a CFD method due to better agreement with measurements between 3000 and 4500 rpm.

Study of the Transient Flow Behavior of Complex Fractures by Use of Semi-Analytical Models

Study of the Transient Flow Behavior of Complex Fractures by Use of Semi-Analytical Models

Real‐time monitoring and estimation of the discharge of flash floods in a steep mountain catchment

AbstractSynchronously and accurately estimating the flood discharges and dynamic changes in the fluid density is essential for hydraulic analysis and forecasting of flash floods, as well as for risk assessment. However, such information is rare for steep mountain catchments, especially in regions that are hotspots for earthquakes. Therefore, six hydrological monitoring sites were established in the main stream and tributaries of the 78.3‐km2 Longxi River catchment, an affected region of the Wenchuan earthquake region in China. Direct real‐time monitoring equipment was installed to measure the flow depths, velocities, and fluid total pressures of the flood hydrographs. On the basis of field measurements, real‐time mean cross‐sectional velocities during the flood hydrographs could be derived from easily obtainable parameters: cross‐sectional maximum velocities and the calibrated dimensionless parameter Kh. Real‐time discharges were determined on the basis of a noncontact method to establish the effective rating curves of this mountainous stream, ranging from 1.46 to 386.34 m3/s with the root mean square errors of ≤10.22 m3/s. Compared with the traditional point‐velocity method and empirical Manning's formula, the proposed noncontact method was reliable and safe for monitoring whole flood hydrographs. Additionally, the real‐time fluid density during the flood hydrographs was calculated on the basis of the direct monitoring parameters for fluid total pressures and water depths. During the flood hydrograph, transient flow behaviour with higher fluid density generally occurred downstream during the flood peak periods when the flow was in the supercritical flow regime. The observed behaviour greatly increased the threat of damage to infrastructure and human life near the river. Thus, it is important to accurately estimate flood discharge and identify for fluid densities so that people at risk from an impending flash flood are given reliable, advanced warning.

Performance of horizontal wells in composite tight gas reservoirs considering stress sensitivity

Tight gas reservoir (TGR) plays an important role in unconventional oil and gas resources. The existing seepage models for TGR rarely consider the effects of heterogeneity, stress-sensitivity, and the unsteady fluid exchange between matrix and fracture. Heterogeneity is common for tight gas reservoir which should be carefully considered in geological model. The stress-sensitivity effect of fracture is an important factor influencing the transient flow behavior of TGR. Ultra-low porosity and permeability cause the unsteady flow between matrix and fractures systems. So this paper introduced a mathematical model for the horizontal well in a dual-porosity composite tight gas reservoir with considering the stress-sensitivity effect and unsteady flow between matrix and fractures systems. Some mathematical methods including the finite Fourier cosine transform, perturbation technique, Laplace transform, superposition principle, Stehfest numerical inversion algorithm are used to solve the nonlinear partial differential equation. Different flow regimes are divided based on pressure transient analysis curves. The sensitivity analysis of related parameters is studied according to pressure transient analysis and rate transient analysis curves. The presented model and obtained results in this paper give better understanding on pressure and rate transient behaviors of composite TGR. Cited as : Zhao, K., Du, P. Performance of horizontal wells in composite tight gas reservoirs considering stress sensitivity. Advances in Geo-Energy Research, 2019, 3(3): 287-303, doi: 10.26804/ager.2019.03.07

Investigation of the influence of heat source orientation on the transient flow behavior during PCM melting using particle image velocimetry

• Investigated the influence of heat source orientation on the transient flow behavior in the liquid PCM. • The heat source orientation has shown to influence the flow behavior. • Discussed how the flow behavior influences the transient melting and heat transfer. The present study reports the characterization of transient flow and thermal behavior of phase change material (PCM) during solid-liquid phase change (melting) through experimental investigation. Two specific aspects of the current work, both important in the field of latent heat thermal energy storage, are to investigate the influence of the flow behavior within liquid PCM on the melting and heat transfer processes, and the impact of heat source orientation on the underlying melting and heat transfer processes. Particle image velocimetry (PIV) was used to measure the velocity fields in the liquid PCM, while thermocouples were used to measure the temperature fields. During PCM melting, three distinct phases of heat transfer were found: strong conduction, strong natural convection and weakening natural convection. The transient Nusselt number characterized the underlying physical behavior observed through transient flow and temperature fields. The findings show that the fluid velocity plays a critical role in the transportation of heat within the liquid domain, which in turn regulates the melting trend and hence, the overall heat transfer. These results further extended the understanding of phase change and the associated heat transfer processes in the PCM and provide comprehensive benchmark data for the improvement of numerical models simulating the solid-liquid phase change process.

Numerical investigation of flow characteristics through simple support grids in a 1 x 3 rod bundle

Abstract This paper investigated the influence of simple support girds on flow, irrespective of having mixing vanes, in a 1 x 3 array rod bundle by using CFD methodology and the most accurate turbulence model which could reflect the actual physics of the flow was determined. In this context, a CFD model was created simulating the experimental studies on a single-phase flow [1] and the results were compared with the experimental data. In the first part of the study, influence of mesh was examined. Tetra, hybrid and poly type meshes were analyzed and convergence study was carried out on each in order to determine the most appropriate type and density. k − e Standard and RSM LPS turbulence models were used in this section. In the second part of the study, the most appropriate turbulence model that could reflect the physics of the actual flow was investigated. RANS based turbulence models were examined using the mesh that was determined in the first part. Velocity and turbulence intensity results obtained on the upstream and downstream of the spacer grid at –3dh, +3dh and +40dh locations were compared with the experimental data. In the last section of the study, the behavior of flow through the spacer grid was examined and its prominent aspects were highlighted on the most appropriate turbulence model determined in the second part. Results of the study revealed the importance of mesh type. Hybrid mesh having the largest number of structured elements performed remarkably better than the other two on results. While comparisons of numerical and experimental results showed an overall agreement within all turbulence models, RSM LPS presented better results than the others. Lastly, physical appearance of the flow through spacer grids revealed that springs has more influence on flow than dimples and induces transient flow behaviors. As a result, flow through a simple support grid was examined and the most appropriate turbulence model reflecting the actual physics of the flow was determined.