Reynolds-averaged Naiver-Stokes Research Articles

Experimental investigation of the turbulent flow in a rod bundle channel with spacer grids

The performance of the CFD prediction of the flow details in the fuel assembly using Reynolds-averaged Naiver-Stokes (RANS) model is still poor. Evaluation and understanding of the complicated turbulent flow structure in the rod bundle channel with mixing devices are essential to optimize turbulence models. Therefore, the current study used the time-resolved particle image velocimetry (TR-PIV) as the measurement tool and combined with the matching index refractive (MIR) technology to obtain high-fidelity experimental data in pressurized water reactor (PWR) based 5 × 5 rod bundle channel. Mean flow properties, turbulent parameters, and spectral analysis are presented in this paper. The results show that a large velocity gradient appears downstream of the spacer grid. The turbulence intensity has been decayed sharply about 45 mm (about 4.5Dh) downstream of the spacer grid, indicated that the mixing effect of the spacer grid becomes weakened after 4.5Dh. Besides, the fluctuating velocity and instantaneous swirl strength are utilized to present the transport characteristics of the eddies downstream of the spacer grid. Combined with the power spectral density spectrum analysis of the transverse fluctuating velocity, the vortex shedding frequency of the mixing layer downstream of the spacer grid is obtained. These results indicate the existence of the quasi-periodic oscillations in the rod bundle channel. Finally, the integral scale on the rod bundle channel is calculated using the cross-correlation function of two reference points. This result reveals that the turbulence in the rod bundle channel is anisotropic.

Ship Manoeuvring Prediction Based on Numerical Towing Tank Technique

A practical procedure is proposed in this paper to predict ship manoeuvrability. A three degrees of freedom MMG (Japanese Manoeuvring Mathematical Modelling Group)-type model is established to simulate rudder manoeuver. Propeller thrust and rudder loads are calculated by empirical formulas, whereas the hull forces as well as moment are determined with hydrodynamic derivatives which are derived from CFD (Computational Fluid Dynamics) computations. An own developed RANS (Reynolds-Averaged Naiver-Stokes) solver on the base of OpenFOAM is applied to simulate a range of PMM (Planar Motion Mechanism) tests and Fourier analyses of the computed results are carried out to obtain the required derivatives. In order to demonstrate the effectivity of the whole procedure and the RANS computations, the US (United States) combatant DTMB 5415 is taken as a sample for an application. Forced motions of surge, sway, yaw and yaw with drift for the bare hull with bilge keels are simulated. Thereafter, simulations of standard rudder manoeuvers, i.e. turning and zigzag, are performed by applying the computed derivatives. The results are compared with available measured data. It has been shown that the present procedure together with the RANS method can be used to evaluate the manoeuvrability of a ship since general good agreements between the simulated results and measured data are achieved.

Turbulent Spray Combustion Modeling Using Various Kinetic Solvers and Turbulence Models

Turbulent spray combustion of n-dodecane was modeled at relevant engine conditions using two combustion models (direct integration of chemistry (DIC) and flamelet generated manifolds (FGM)) and multifidelity turbulence models (dynamic structure large eddy simulation (LES) and renormalization group (RNG) Reynolds-averaged Naiver–Stokes (RANS)). The main objective of this work is to study the effect of various combustion and turbulence models on spray behavior and quantify these effects. To reach these objectives, a recently developed kinetic mechanism and well-established spray models were utilized for the three-dimensional turbulent spray simulation at various combustion chamber initial gas temperature and pressure conditions. Fine mesh with a size of 31 μm was utilized to resolve small eddies in the periphery of the spray. In addition, a new methodology for mesh generation was proposed and investigated to simulate the measured data fluctuation in the CFD domain. The pressure-based ignition delay, flame lift-off length (LOL), species concentrations, spray, and jet penetrations were modeled and compared with measured data. Differences were observed between various combustion and turbulence models in predicting the spray characteristics. However, these differences are within the uncertainties, error, and variations of the measured data.

Model- and Full-Scale RANS Simulations for a Drift Tanker

The flow around a full scale (FS) ship can be simulated by mean s of Reynolds Averaged Naiver Stokes (RANS) method, which provides a way to obtain more knowledge about scale effect s on ship hydrodynamics. In this work, the viscous flow around a static drift tanker in full scale is simulated by using the RANS solver based on the open source platform OpenFOAM. The 𝑘−𝜔 SST model is employed to approximate the eddy viscosity. To reduce computational time, wall function approach is applied for the FS simulation. The flow around the ship in model scale is simulated as well, but without using any wall function, i.e. using Low Reynolds number mode. In order to verify the computations, de-tailed studies on the computational grid including investigation of the sensitivity of computed forces to 𝑦+ (dimension-less distance of first grid point to wall) and grid dependency study are carried out. The computed forces are compared with available measured data The scale effect s are analysed and discussed by comparisons.

Aerodynamic Performance Prediction of a Profile in Ground Effect With and Without a Gurney Flap

A very detailed experimental case of a reversed profile in ground effect has been selected in the open literature where available experimental data have been used as reference data for the computational fluid dynamics (CFD) analysis. The CFD approach has been used to predict aerodynamic performance of the profile at different distances with respect to the ground: in the freestream case, there is no ground effect whereas in the low height the profile operation is limited by the stall on the suction surface. Moreover, the effect of a Gurney flap addition on flow distribution and performance has been numerically investigated. The experimental data have been used to setup and test the capabilities of the computational approach. With the addition of a Gurney flap, a significant flow unsteadiness is introduced that needs to be considered in the numerical approach. In this case, the configurations investigated are used to highlight the capabilities of CFD using Reynolds-averaged Naiver–Stokes (RANS) approach for its effective application as a tool for the detailed design of aerodynamic components to generate downforce for race cars.

Wave-induced seabed response around an offshore pile foundation platform

In this paper, a three-dimensional integrated numerical model including the wave and seabed sub-model is developed to investigate the wave induce seabed response around a pile foundation platform. The wave sub-model is based on Volume-Averaged Reynolds-Averaged Naiver-Stokes (VARANS) equations with k-ε turbulence closure scheme, and the volume of fluid (VOF) method is applied to track water free surface. The seabed is treated as an isotropic and homogeneous porous medium and characterized by Biot's partly dynamic equations (u-p model). The proposed model is verified with the previous analytical results. Based on the numerical results, the distribution of flow field around pile foundation will be investigated. Then, a comprehensive comparison between a pile foundation platform model and a pile foundation without platform model will be performed to examine the effects of platform to the pile foundation. Finally, the effects of wave, pile foundation, and seabed characteristics, such as wave depth, wave height, pile diameter, pile insertion ratio, soil permeability and degree of saturation on the wave-induced seabed and pile foundation platform response will be studied.

Numerical and experimental investigation on the diffuser optimization of a reactor coolant pump with orthogonal test approach

The diffuser of a reactor coolant pump was optimized using an orthogonal approach with numerical simulation to improve the pump hydraulic performance. Steady simulation was conducted by solving Reynolds-averaged Naiver-Stokes equations with the SST k-ω turbulence model using CFX code. The influence of the diffuser geometric parameters, namely, S, φ, α 4, b 4, δ 2, R t and R 4, on the pump performance were determined. L18 (37) orthogonal table was chosen for the optimization process. Best indicators were determined, and range analysis of energy losses, head, and efficiency at the rated condition was performed. Optimal parameters of the diffuser were S = 490 mm, φ = 36°, α 4 = 30°, b 4 = 200 mm, δ 2 = 20 mm, R t = 5 mm and R 4 = 565 mm. The final design was experimentally tested. Simulation results showed more remarkable performance than the experimental result. However, the numerical predictions and experimental results were consistent, validating the design procedure. Loading of the impeller and diffuser blades was analyzed to investigate the direct impact on the hydrodynamic flow field. The head was 14.74 m, efficiency was 79.6 %, and efficiency of the prototype pump was 83.3 % when the model pump functioned at the rated conditions. Optimization results showed that efficiency and head were improved at the design condition.

Study on the effect of the impeller and diffuser blade number on reactor coolant pump performances

In this paper, CFD approach was employed to study how the blade number of impeller and diffuser influences reactor coolant pump performances. The three-dimensional pump internal flow channel was modelled by pro/E software, Reynolds-averaged Naiver-Stokes equations with the k-ε turbulence model were solved by the computational fluid dynamics software CFX. By post-processing on the numerical results, the performance curves of reactor coolant pump were obtained. The results are as follows, with the blade number of the impeller increasing, the head of the pump with different diffuser universally increases in the 8Qn∼1.2Qn conditions, and at different blade number of the diffuser, the head increases with the blade number of the impeller increasing. In 1.0Qn condition, when the blades number combination of impeller and diffuser chooses 4+16, 7+14 and 6+18, the head curves exist singular points. In 1.2Qn condition, the head curve still exists singular point in 6+18. With the blade number of the impeller increasing, the efficiency of the pump with different diffuser universally decreases in the 0.8Qn and 1.0Qn conditions, but in 1.2Qn condition, the efficiency of the pump with different diffuser universally increases. In 1.0Qn condition, the impellers of 4 and 5 blades are better. When the blade number combination of impeller and diffuser choose 4+11, 4+17, 4+18, 5+12, 5+17 and 5+18, the efficiencies relatively have higher values. With the blade number of the impeller increasing, the hydraulic shaft power of the pump with different diffuser universally increases in the 0.8Qn∼1.2Qn conditions, and with the blade number of the diffuser increasing, the power of different impeller overall has small fluctuation, but tends to be uniform. This means the increase of the diffuser blade number has less influence on shaft power.The influence on the head and flow by the matching relationship of the blades number between impeller and diffuser is very complicated, which still need further research.This paper provides a reference for exploring the match relationship between the impeller and diffuser blade number of reactor coolant pump.

기울어진 타원형 딤플이 부착된 냉각 유로에 대한 열전달 성능해석

This paper deals with a parametric study on inclined elliptical dimples to enhance heat transfer in a channel. Three-dimensional Reynolds-averaged Naiver-Stokes equations are solved to estimate flow and heat transfer in dimpled channel. As turbulence closure, the low-Re shear stress transport model is employed. Two non-dimensional geometric variables, dimple ellipse diameter ratio and angle of main diameter to flow direction are selected for the parametric study. The inclined elliptical dimples show higher heat-transfer performance but with higher pressure drop compared to the circular dimples. And there is an optimum inclination angle that gives the maximum heat transfer.

Numerical and experimental study of internal flow field for a carbon fiber tow pneumatic spreader

In this study, a three-dimensional (3-D) mathematical model of a fiber pneumatic spreader was successfully developed in the physical phenomena of the internal flow field by a far-field treatment at boundary conditions. The 3-D numerical analysis was carried out on incompressible fluid flows in the pneumatic spreader by using finite volume method combined with the k-ɛ turbulence model which solves Reynolds-averaged Naiver-Stokes equations. Characteristics of the flow field in the spreader at different service conditions are investigated by velocity and pressure distributions. Comparisons of numerical results with measured velocity and pressure distributions were made to determine the accuracy of the employed method. A good agreement was found in both qualitative and quantitative analysis. Fibers were spread on 1:1-scale model of the pneumatic spreader at various fiber transporting rates and air flow rates. Photography techniques were simultaneously used to record the procedures of fibers spread. The carbon fiber tow was easily spread out at service conditions. The performance was better than prior studies in one-dimensional orifice formulation. The results revealed details of the fiber spreading processes. Agreement among those results validated the assumptions inherent to the computational calculation and gave confidence to more complex geometries as well as flow fields. In other words, the use of numerical analysis in the internal flow field was useful for the fiber pneumatic spreader design.