Papers by Keyword: Turbulence

Abstract: Turbulence is a highly complex and challenging phenomenon to study, especially in the field of fluid dynamics, where many applications rely on accurate predictions of turbulent flow behavior. Due to its random and chaotic nature, turbulence is difficult to model precisely, but achieving reliable results is essential for solving numerous engineering problems. Various turbulence models, each with specific strengths and limitations, have been developed to address this challenge. This study focuses on comparing three widely used turbulence models (k−ϵ, k−ω, and the Reynolds Stress Model (RSM)) to evaluate their accuracy in simulating turbulent flow within a corrugated channel. The aim of this study is to simulate and achieve better result accuracy while minimizing computational cost in this geometry, both with and without vortex generators. The investigation begins with a trapezoidal channel, after which vortex generators are introduced to assess their impact on flow behavior. Vortex generators are known to enhance heat transfer by promoting flow separation and modifying the flow direction, making their effect critical in such simulations. The computational analysis is conducted using ANSYS Fluent, a commercial software for computational fluid dynamics (CFD) and heat transfer modeling, which operates on the finite volume method to ensure conservation of physical properties. Results will be presented through detailed graphical representations and contour plots, followed by a comprehensive discussion of the comparative performance of each model.

Abstract: This study proposes a numerical investigation of turbulent flow and heat transfer properties within an air channel featuring a 7-shaped baffle affixed to the lower wall. The main objective of this computational investigation is to assess how the Reynolds number influences the enhancement of heat transfer across a range of Reynolds values from 18000 to 33000. To solve the governing equations, the QUICK numerical scheme and the SIMPLE discretization algorithm are employed. The numerical results are presented through variations in mean velocity and temperature, as well as profiles of local Nusselt number, friction coefficient, Nusselt number and friction factor. These representations facilitate a comprehensive exploration of the aerodynamic and thermal flow properties.

Abstract: This work presents the development of a computational model for the simulation of an Oscillating Water Column device that converts wave flow into electrical energy. The device is placed into a wave channel and a Savonius turbine is inserted in the inlet/outlet duct of the converter. The modeling of the turbine is performed with a rotational moving mesh that simulates the turbine movement in stabilized operating conditions. This coupling provides the minimization of simplifying assumptions, addressing in a single problem the two phenomena inherent to the device approach: the two-phase, incompressible and turbulent flow of air and water in a wave channel containing the oscillating water column device and the incompressible and turbulent airflow passing through a rotational turbine. The computational model was verified/validated for a free stream turbulent flow over a Savonius turbine and verified for the case of wave flow over a converter without the inserted turbine. Results showed that the coupled model allowed obtaining not only available power but also mechanical power in the turbine. For the rotation imposed in the domain, the turbine did not affect the behavior of the wave flow that impinges on the chamber of the OWC device. An augmentation of the power coefficient of the turbine in comparison with turbines subjected to free stream flows was obtained, showing that the fairing of turbine can led to increased power takeoff.

Abstract: The present study investigates numerically the heat transfer process based forced convective flow of an incompressible fluid in a two-dimensional rectangular channel. Two baffles are imposed periodically on the lower and upper walls. The study mainly focused on the influence of the arrangement and spacing separating the baffles on the heat transfer's intensification. The values of the Reynolds number for the present turbulent flow regime were chosen in the range of 10⁴ to 8.73 × 10⁴. The equations resulting from the three conservation laws, namely continuity, Navier-Stokes, and energy equations, are solved numerically based on the finite volume method. SIMPLE algorithm is used to overcome the pressure-velocity coupling, and k-ε model is used for the computation of turbulent patterns. Numerical simulations are carried out to study the dynamic and thermal behavior influenced by the control parameters. The physical quantities calculated are the axial velocity, the local, mean Nusselt numbers and the friction coefficient. The obtained results show that the friction coefficient decreases proportionally with the increase of Re number, and the local Nusselt number increases with the Reynolds number. As the spacing between the baffles decreases, the N_R ratio increases, and as the Reynolds number increases, N_R decreases N_R = 6.13, 5.31, 4.62, and 4.30 for case P₁, N_R = 5.1, 4.5, 3.89, and 3.64, for case P₂, N_R = 5.00, 4.45, 8.83, and 3.51, for case P₃, for equal Reynolds number, 10⁴, 2×10⁴, 4×10⁴, 8.73×10⁴, respectively.

Abstract: This paper deals with studying numerically two circular turbulent jets impinging on a flat surface with a low velocity cross flow by using ANSYS CFX 16.2, with the aim of proving the effect ofReynolds number on the flow demeanor in a vertical circular free turbulent jet with cross flow. Five turbulence models of the RANS (Reynolds Averaged Navier–Stokes) approach were tested and the k -ω SST model was chosen to validate CFD results with the experimental data. Average velocity profiles, velocity and turbulent kinetic energy contours and streamlines are presented for four case configurations. In the first three cases, the following parameters have been varied: Reynolds number at the level of the two jets ( ), wind velocity at the level of the cross-flow ( ), and the distance between the two jets (S = 45mm, 90mm and 135mm). In the last case, a new configuration of the phenomenon not yet studied so far was treated, where horizontal cross-flows were introduced from both sides in order to simulate gusts of wind disrupting a VSTOL aircraft which tries to operate close to the ground. This case was carried out for Reynolds number based on the crossflow of 4 10⁴, 10 10⁴ and 20 10⁴ .The numerical results obtained show that the deflection of the jets is minimal when the Reynolds number at the level of the jets is greater than that of the cross-flow. The increase of Reynolds number at the level of the cross-flow reveals a significant deviation of the two jets with an intensity which always remains less for the second jet. As for the space parameter between the two jets, it turns out that the fact of further spacing the two jets makes the first jet even more vulnerable and leads to a greater deflection. Finally, the simulation of the wind gusts from the front and the back caused a zone of turbulence which resulted from a form of "interlacing" of the two jets under the effect of the transverse current imposed by the two sides.

Abstract: The new duster is used to remove the coal dust from the coal conveying system of thermal power plant. Many of plastic globules are filled into the duster. The water is sprayed from the upper of duster. The airflow of containing coal dust flows through the filler from bottom to top, and change to clean air. The application of the turbulent duster in the coal conveying system of the thermal power plant shows: the efficiency of dust collection is 99%. In particular, it can remove 67% of coal dust smaller than 5 microns. The duster adopts fully automatic control technology. The amount of water consumed is very low. It can be effectively used for coal conveying system of thermal power plant. After air purification with coal dust, the air quality meets the requirements of the health standard.

Abstract: Wind climate influencing wind loads on buildings and other structures, as well as the dispersion of pollutants from various surfaces is essentially determined by small-scale motions and processes occurring in the atmospheric boundary layer (ABL). The physical and thermal properties of the underlying surface, in conjunction with the dynamics and thermodynamics of the lower atmosphere influence the distribution of wind velocity in thermally stratified ABL. Atmospheric turbulence is characterized by a high degree of irregularity, three-dimensionality, diffusivity, dissipation, and a wide range of motion scales. This article describes a change of selected turbulent variables in the surroundings of flow around a thermally loaded object. The problem is solved numerically in Ansys Fluent 13.0 software using LES (Large eddy simulation) models as well as the Transition SST (Shear Stress Transport) model that is able to take into account the difference between high and low turbulence at the interface between the wake behind an obstacle and the free stream. The results are mutually compared and verified with experimental measurements in the wind tunnel.

Abstract: One of the major components of axial-flow compressors and turbines are the diffusers, employed for the conversion of fluid velocity to pressure. They are used in gas turbines, pumps, wind tunnels and other fluid flow devices. Diffusers are used in jet engines, aircraft engines for various purposes. Usually a diffuser is considered as an isolated component for the ease of computation. However, when there is upstream machinery, the effect of flow separation cannot be neglected and hence considering a diffuser as an isolated component would not suffice. The effect of swirl on the performance of a conical diffuser is taken into consideration. Pressure recovery co-efficient indicates the performance of the system and its values are studied under various inlet condition still ideal case is reached and various flow parameters for this ideal case are noted. Ideal condition is the one in which the energy losses along the sections of a diffuser are minimum. This paper provides a holistic view of the flow through a diffuser, laying primary emphasis on the effect of inlet swirl.

Abstract: This works centers on the design of a De Laval (convergent - Divergent) nozzle to accelerate the flow to supersonic or hypersonic speeds and computational analysis of the same. An initial design of the nozzle is made from the method of characteristics. The coding was done in Matlab to obtain the contour of the divergent section for seven different exit Mach numbers viz. 2.5,3,3.5,4,4.5,5 and 5.5.To quantify variation in the minimum length of the nozzle divergent section with respect to the exit mach number, a throat of constant height (0.005m) and width (0.05m) was chosen for all the design. The area exit required for each mach no varying from 1 to 5.5 was plotted using isentropic relations and was also used to verify the exit area of the nozzle for each of those mach numbers. An estimate of the exit pressure ratio is obtained by using isentropic and normal shock relations. With this exit pressure ratio, a more refined verification is done by computational analysis using ANSYS Fluent software for a contour nozzle with exit Mach number 5.5. The spalart Allmaras and k-epsilon model were used for turbulence modeling.

Abstract: Turbulence is a flow regime characterized by chaotic property changes. Randomness, fluctuations, vorticity and large Reynolds number (Re) are the basic characteristics of turbulent flows. In this contribution is Computer Fluid Dynamic simulation of air-flow over an obstacle in shape of “quarter-circular” object compared to the data from previous work. This comparison is focused on mean values of pressure in 16 selected points at different elevations. k-ω turbulence model performed well (convergence, time, CPU) and the overall error is 13.61 %.