Showing papers on "K-epsilon turbulence model published in 2020"

Comparison between a Conventional and a New IRS Device in Terms of Air Entrainment: An Experimental and Numerical Analysis

Abstract: An experimental study was conducted on a laboratory-scale new infrared suppression (IRS) device to assess the mass entrainment of ambient air into it under various operating conditions. A numerical analysis was also undertaken to assess the mass entrainment rate against pertinent input parameters independently. The numerical results were validated against the experimental data to ensure the reliability of the numerical analysis of the new IRS device at real scales. The numerical method solves the three-dimensional, incompressible Navier-Stokes equations; the mass continuity equation; and the two-equation-based eddy viscosity model for the turbulent k-epsilon equations in the flow field. Numerical assessment of the air entrainment was performed for the conventional and the newly proposed IRS devices. A number of experiments on the new IRS device were carried out under various operating conditions. From the numerical study, it was observed that the conventional IRS device performs better than the new IRS device up to a geometric ratio of 1.4 (which is the ratio of diameters of the successive funnels used in an IRS device). Beyond the geometric ratio of 1.4, the newly proposed IRS device outperforms the conventional one significantly. For the new IRS device, the maximum mass entrainment was found to occur when four funnels were used and the nozzle was kept in flush condition with the lower opening of the bottom-most funnel. Mass entrainment increases with the nozzle-exit Reynolds number for the range of values considered in the study.

Numerical simulation of wind turbine wake based on extended k-epsilon turbulence model coupling with actuator disc considering nacelle and tower

Abstract: The Reynolds-averaged Navier–Stokes (RANS) method coupling with the actuator disc model (ADM) is considered as a promising numerical simulation technology of wind turbine wake, and it is widely utilised in the aerodynamics of wind turbines and optimal layout of wind farms. The k − e turbulence model is widely adopted, among the RANS-based turbulence models. However, the k − e turbulence model easily overestimates the turbulence viscosity in the wake, which results in fast recovery of wake velocity and failure in wake forecasting. In addition, ADM with the oversimplified geometrical structure ignores the effects of nacelle and tower on the wind turbine wake, which further lowers the accuracy of wake simulation. Therefore, the numerical simulation of wind turbine wake based on the extended k − e turbulence model of EI Kasmi coupling with ADM considering nacelle and tower is proposed. Comparing the results of Marchwood Engineering Laboratories (MEL) ABL wind tunnel measurements and TNO wind tunnel experiments, it has been found that the proposed model improves the simulation effect for the near wake and has a certain contribution to the wake prediction accuracy overall.

Parametric Study of Turbulent Couette Flow over Wavy Surfaces Using RANS Simulation: Effects of Aspect-Ratio, Wave-Slope and Reynolds Number

Abstract: A turbulent Couette flow over a wavy surface is subject to a detailed parametric study in which three parameters—Aspect Ratio, Wave Slope and Reynolds number—are independently varied over an order of magnitude to investigate their influence on the flow. Stdk−e turbulence model with enhanced wall functions is used to simulate all cases in the study and the results are validated against experimental data as well as analytical theories pertaining to flow over wavy surfaces. Gross flow properties such as mean velocity profiles, mass flow rate, shear stress and pressure on the walls, as well as turbulent flow characteristics such as inner-wall coordinates, log-law fit, eddy viscosity profiles and turbulence kinetic energy across the domain, are presented and their corroboration with existing literature is discussed. The effect of the three parameters on the flow variables is investigated. It is observed that while all response flow variables scale monotonically with a progressive change in the parameters, there are certain flow characteristics that can be ascribed exclusively to one of the three parameters. The study also discusses the influence of the top plate, a much-needed discussion that seems to be absent in most literature pertaining to Couette flow in wavy channels.