RNG K-epsilon Turbulence Model Research Articles

Numerical Simulation of Pressure Fluctuation around the Tongue Region in a Centrifugal Pump

Pressure fluctuation near the tongue is one of the primary sources of pump vibration and noise. In order to investigate the effect of pressure fluctuation near the tongue, the RANS equations and the RNG k-epsilon turbulence model are employed to simulate the flow in the pump. The SIMPLE algorithm is applied to couple the solutions of the system of equations. Flow field within the centrifugal pump under different flow rates are obtained by simulation. The simulation results are compared with the experimental data to verify the reliability of the calculation model. It is found that the pressure fluctuation at each monitor point is a periodic wave but non-uniform under small flow rate. When the flow rate is larger than the design flow rate, average pressure and standard deviation at monitor points is relative uniform. The dominate frequency of pressure fluctuation is the blade passing frequency and the amplitude of pressure fluctuation is regular. At small flow rate, complex unstable flow makes average pressure and standard deviation at monitor points increasing obviously. Amplitude of pressure fluctuation is larger than that of design flow rate conditions and the maximum amplitude of pressure fluctuation in frequency domain exists at the monitor point just behind the tongue along the impeller rotation direction.

Human induced flow field and resultant particle resuspension and transport during gait cycle

Particle resuspension from flooring is believed to be an important source of particulate matter (PM) in the indoor environment. It is hypothesized that the high speed airflow generated between the flooring and the foot during the gait cycle is the main cause of particle resuspension. The simulation results show that particles are detached from the substrate during the downward motion of the foot. Furthermore, during the upward motion of the foot, additional particles may also be resuspended because of the suction flow generated by lifting the foot. These resuspended particles are then dispersed in the room by the airflow turbulence.In this study a combined experimental and computational studies were performed to shed light on the mechanisms of particle resuspension from flooring during the gait cycle. A mechanical foot experimental setup which mimics the human walking was developed and used to measure the rate of resuspension. In addition, to investigate the airflow field during walking, a three dimensional numerical model of a moving shoe during the gait cycle was generated using the ANSYS-FLUENT™ CFD package. A RANS approach with the RNG k-epsilon turbulence model was used for simulating the unsteady airflow field around and under the shoe. To include the shoe motion in the analysis, a user defined function (UDF) was developed and the dynamic mesh technique was used. A resuspension model was applied for the resuspension of pre-deposited particles from the flooring. The predicted particle resuspension were compared with the corresponding experimental results and good agreement was found.

Investigation on Characteristics Behavior on Aerosol Spray at Exit Nozzle Based on ANSYS-CFX Simulation

A new generation of aerosol technology is expanded rapidly where the research and development are focused on the analysis of pressure involved in the propellants, packaging and ingredients to make the aerosol as a high performance with fine spray product. There are few problems in replacing Volatile Organic Compound (VOC) with water and developing quality fine spray with pressurised aerosol spray. Therefore, this study is focused on developing an internal nozzle by analysed the characteristics of spray using ANSYS-CFX simulation with RNG k-epsilon turbulence model. The analysis were on various pressure supply from 1 bar up to 9 bar, where the n-butane and water are applied as a single liquid phases material. The simulation are based on plain nozzle design where the geometry and physical properties were carefully scale based on actual condition. As a result, it shows the widening of the jet downstream of the gap and increased in Reynolds stresses in the region of high turbulence intensity. Furthermore, the spectra of turbulent kinetic energy were also investigated, indicating that, increased in turbulent kinetic energy is mainly due to an increase in energy of eddies. Consequently, the use of water is acceptable as an alternative to substitute the n-butane liquid phase in producing an aerosol spray product.

Numerical Simulation of Marine Propeller Hydrodynamic Performance in Uniform Inflow with Different Turbulence Models

In general, marine propellers have complicated geometries and as a consequence complicated flow around propeller. The aim of this work is to find an appropriate method and assess the turbulence model to approach the open water hydrodynamic characteristics of the marine propellers. In this work, a numerical modeling using a finite volume commercial code (FVM) for different turbulence models has been applied on the well known conventional screw propeller DTRC P4119. The 3-D solid model of P4119 is established using pro/E software and for the mesh generation ANSYS-ICEM has been used. Steady Reynolds-Averaged Navier Stokes (RANS) simulations are accomplished using FLUENT software with unstructured mesh in the rotating computational domain and structured mesh for the rest of the domain. The open water performance coefficients, thrust (KT), torque (KQ) and efficiency (η) have been calculated and compared with available experimental data to assess the applicability of different turbulence models for the open water study of propeller. This paper shows that, the accuracy of the CFD based on RANS equations is dependent on the used turbulence model and the RNG K-epsilon turbulence model yields to provide the most accurate results. Also, all the turbulence models via FLUENT software behave the same behavior for the total span of the advance coefficient (J) with two types of result accuracy. All the turbulence models shows high accuracy at low advance coefficient and this accuracy decreases but with an acceptable error till it decreases suddenly at the maximum advance coefficient.

最小流量阀的数值分析及结构优化

对最小流量阀在不同开度下进行了三维数值模拟研究。采用RNG k-epsilon湍流模型封闭N-S方程组以求解阀门内部流场，得到了各个开度下的阀门压力和流速的分布情况。根据阀门的损失系数和流量随开度的变化曲线，研究了阀门的特性。通过对压力分析确定了主要压力损失发生的部位，并提出改进方案。结果表明改进后的阀门，其压力损失得到明显的降低，流体对阀门的冲击也得到明显改善。 Based on three-dimensional numerical simulation results, the minimum flow valve is studied under different opening level. The flow inside the valve was controlled by the Reynolds averaged Navier-Stokes equations together with the continuity equation. The RNG k-epsilon turbulence model was selected to govern the turbulence characteristics. Pressure and velocity distributions in the flow fields were obtained and analyzed under every opening level. The varia- tion curves of the loss coefficient and the flow rate along with the opening level were obtained to study the valve per- formance. The location where the major pressure loss happening was found by analyzing the pressure distribution. Then, the improvement method was proposed. The results of the valve with the new structure show that the pressure loss is decreased and the impaction of the fluid to the valve is alleviated.

Hydraulic design and performance analysis of low specific speed centrifugal pump

Since low specific speed centrifugal pump with long narrow flow divergent channels has positive slope of head-capacity characteristic curve, low flow rate instability and high flow rate power overload, special events about its hydraulic design are still under study. This paper demonstrates a method for hydraulic design of low specific speed centrifugal pump complex impeller (with splitter blades) which is based on 2D flow theory. In this method, obtain the basic geometry parameters by empirical correlation, adjust impeller profile according to given flow cross section area distribution and wrapping angles distribution, relate the position of splitter blades to slip factor. Based on this method, low specific speed centrifugal pump impellers have been designed using the same design parameters (Head, Capacity, Rotation Speed, etc) with different factors. And 3D turbulent flow fields in design pumps have been solved by using RANS equations with RNG k-epsilon turbulence model. The investigation to the effects of different splitter blades on velocity distributions and pressure distributions along the flow channels and hydraulic performance of centrifugal pumps are presented. The result shows that properly placed splitter blades by choosing suitable design factors will improve the flow in the pump and enhance the hydraulic performance of it.

Numerical investigation on flow and convective heat transfer of aviation kerosene at supercritical conditions

avier-Stokes equations were solved using RNG k-epsilon turbulence model with low Reynolds number correction. The thermophysical and transport properties of the China RP-3 kerosene were calculated with a 10-species surrogate and the extended corresponding state method (ECS) combined with Benedict-Webb-Rubin equation. The independence of grids was first studied and the numerical results were then compared with experimental data for validation. Under flow conditions given in the paper, the results show that deterioration of convective heat transfer occurs when the wall temperature is slightly higher than the pseudo-critical temperature of kerosene for cases with wall heat flux of 1.2 and 0.8 MW/m(2). The degree of the heat transfer deterioration is weakened as the heat flux decreases. The deterioration, however, does not happen when the heat flux on the pipe wall is reduced to 0.5 MW/m(2). Based on the analysis of the near-wall turbulent properties, it is found that the heat transfer deterioration and then the enhancement are attributed partly to the change in the turbulent kinetic energy in the vicinity of pipe wall. The conventional heat transfer relations such as Sieder-Tate and Gnielinski formulas can be used for the estimation of kerosene heat convection under subcritical conditions, but they are not capable of predicting the phenomenon of heat transfer deterioration. The modified Bae-Kim formula can describe the heat transfer deterioration. In addition, the frictional drag would increase dramatically when the fuel transforms to the supercritical state.

The Fan Blade Velocity Field Analysis of Scenery Tower Power Generation Device Based on FLUENT

Based on field theory and air dynamics theory, two kinds of different curvature blade rotation of velocity and its distribution area were simulated, through the establishment of the three-dimensional flow model for the scenery tower fan blade generator and the adoption of RNGK-epsilon turbulence model. Then reach a conclusion from comparison: Smaller curvature leaf has a higher wind speed than the bigger one, which is easy to wind energy conversion under the common function of the force in the rotating area.

Development and experimental validation of a simulation model for open joint ventilated façades

The investigation of the thermal and fluid dynamical behaviour of open joint ventilated façades is a challenging task due to the complex airflows generated inside of the naturally ventilated cavity by the existence of open joints. For this reason, the use of advanced fluid measurement and simulation techniques is highly recommended. This paper focuses in the development and experimental validation of a simulation model for these façade systems. More specifically, different turbulence and radiation models available in the commercial computational fluid dynamic codes have been tested on a three-dimensional model and the results have been compared to particle image velocimetry measurements. The correlation between experimental and numerical data has been used in order to select the simulation procedure for this type of façades. Best fittings have been found when using the RNG k-epsilon turbulence model and the Discrete Ordinate radiation model. Using the selected scheme, parametrical simulations have been performed to investigate the effect of increasing the cavity height, and correspondingly, the number of slabs. Results show that ventilation air flow inside the cavity is enhanced by incident radiation as well as by the height of the façade.

Numerical Investigation of Flow Friction and Heat Transfer in a Channel with Various Shaped Ribs Mounted on Two Opposite Ribbed Walls

Heat transfer and fluid flow characteristics through a channel with two - dimensional transverse ribs are numerically investigated. The effects of different shaped ribs (rectangular rib, triangular rib, cylindrical rib, concave-concave rib, convex-concave rib, long convex-short concave rib and long concave-short concave rib) are examined. The investigation is performed for the ribs mounted on top and bottom walls with rib pitch to height ratio (P/e) of 6.67, in Reynolds number between 3000 and 7000, under constant wall temperature condition. For the present case, the data predicted by SST k-omega turbulence model show better agreement with the experimental data, than those predicted by RNG k-epsilon turbulence model. The mean heat transfer, flow friction, temperature fields and the local heat transfer coefficients as well as the flow structure behaviors are reported. For the ribs considered, the channel with triangular-ribs yields the highest Nusselt number, the one with concave-concave rib provides the highest friction and the one with cylindrical rib show the best thermal enhancement. At the similar condition, the triangular rib gives higher Nusselt number than that provided by the cylindrical one by around 29.3 percent, while the cylindrical rib offers the highest thermal enhancement factor of 1.4 which is higher than that of the cylindrical one by around 1.33 percent while the cylindrical rib offers the highest thermal enhancement factor of 1.33 which is higher than that of the triangular one by around 9.6 percent. In addition, in spite of their high heat transfer, the concave-concave rib and long concave-concave rib yield low thermal performance factors, due to the prominent effect of high friction factor.

Numerical Investigation of Flow Friction and Heat Transfer in a Channel with Various Shaped Ribs Mounted on Two Opposite Ribbed Walls

Heat transfer and fluid flow characteristics through a channel with two - dimensional transverse ribs are numerically investigated. The effects of different shaped ribs (rectangular rib, triangular rib, cylindrical rib, concave-concave rib, convex-concave rib, long convex-short concave rib and long concave-short concave rib) are examined. The investigation is performed for the ribs mounted on top and bottom walls with rib pitch to height ratio (P/e) of 6.67, in Reynolds number between 3000 and 7000, under constant wall temperature condition. For the present case, the data predicted by SST k-omega turbulence model show better agreement with the experimental data, than those predicted by RNG k-epsilon turbulence model. The mean heat transfer, flow friction, temperature fields and the local heat transfer coefficients as well as the flow structure behaviors are reported. For the ribs considered, the channel with triangular-ribs yields the highest Nusselt number, the one with concave-concave rib provides the highest friction and the one with cylindrical rib show the best thermal enhancement. At the similar condition, the triangular rib gives higher Nusselt number than that provided by the cylindrical one by around 29.3 percent, while the cylindrical rib offers the highest thermal enhancement factor of 1.4 which is higher than that of the cylindrical one by around 1.33 percent while the cylindrical rib offers the highest thermal enhancement factor of 1.33 which is higher than that of the triangular one by around 9.6 percent. In addition, in spite of their high heat transfer, the concave-concave rib and long concave-concave rib yield low thermal performance factors, due to the prominent effect of high friction factor.

Numerical investigations of circular tube fitted with helical screw-tape inserts from the viewpoint of field synergy principle

3-D numerical simulations are performed for heat transfer and fluid flow characteristics of the tubes fitted with helical screw-tape inserts. The comparison between the RNG k-epsilon turbulence model and the SST k-omega turbulence model in prediction of swirling flow shows that the latter has better qualitative and quantitative agreements with the experimental results than the former. The simulation results show that the novel helical inserts with right and left twists alternately have better heat transfer performance than that of the helical inserts with uniformly right twists. The simulation results are analyzed from the viewpoint of field synergy principle, it is found that the principle could explain well the mechanism of heat transfer enhancement of the helical twist inserts. The smaller the mean intersection angle between the temperature gradient and velocity vector, the larger the Nusselt number; in addition, the smaller local intersection angle also implies the higher local heat transfer coefficient.

Numerical modeling of pulsatile turbulent flow in stenotic vessels.

Pulsatile turbulent flow in stenotic vessels has been numerically modeled using the Reynolds-averaged Navier-Stokes equation approach. The commercially available computational fluid dynamics code (CFD), FLUENT, has been used for these studies. Two different experiments were modeled involving pulsatile flow through axisymmetric stenoses. Four different turbulence models were employed to study their influence on the results. It was found that the low Reynolds number k-omega turbulence model was in much better agreement with previous experimental measurements than both the low and high Reynolds number versions of the RNG (renormalization-group theory) k-epsilon turbulence model and the standard k-epsilon model, with regard to predicting the mean flow distal to the stenosis including aspects of the vortex shedding process and the turbulent flow field. All models predicted a wall shear stress peak at the throat of the stenosis with minimum values observed distal to the stenosis where flow separation occurred.

Numerical investigation of cavitating flow behind the cone of a poppet valve in water hydraulic system

Computational Fluid Dynamics (CFD) simulations of cavitating flow through water hydraulic poppet valves were performed using advanced RNGk-epsilon turbulence model. The flow was turbulent, incompressible and unsteady, for Reynolds numbers greater than 43000. The working fluid was water, and the structure of the valve was simplified as a two dimensional axisymmetric geometrical model. Flow field visualization was numerically achieved. The effects of inlet velocity, outlet pressure, opening size as well as poppet angle on cavitation intensity in the poppet valve were numerically investigated. Experimental flow visualization was conducted to capture cavitation images near the orifice in the poppet valve with 30° poppet angle using high speed video camera. The binary cavitating flow field distribution obtained from digital processing of the original cavitation image showed a good agreement with the numerical result.

Three-dimensional combustion modelling of a biomass fired pulverized fuel boiler

A Computational fluid dynamic (CFD) model was applied for a 200 MW pulverised fuel boiler. Peat, demolition wood and wood residuals were used as fuel. The computer code FLUENT was used for the modelling of the combustion process inside the boiler. The RNG k-epsilon turbulence model together with wall functions was adapted for characterization of the flue gas behaviour. Reaction between fuel and oxidizer was modelled using the mixture-fraction/PDF approach. The CFD calculations were compared with acoustic pyrometry measurements and process data.