Reynolds Stress Turbulence Model Research Articles

Ship Flow of the Ryuko-maru Calculated by the Reynolds Stress Model Using the Roughness Function at the Full Scale

The k-omega SST turbulence model is extensively employed in Reynolds-averaged Navier–Stokes (RANS)-based Computational Fluid Dynamics (CFD) calculations. However, the accuracy of the estimation of viscous resistance and companion flow distribution for full-sized vessels is not sufficient. This study conducted a computational analysis of the flow around the Ryuko-maru at model-scale and full-scale Reynolds numbers utilizing the Reynolds stress turbulence model (RSM). The obtained Reynolds stress distribution from the model-scale computation was compared against experimental measurements to assess the capability of the RSM. Furthermore, full-scale computations were performed, incorporating the influence of hull surface roughness, with the resulting wake distributions juxtaposed with the actual ship measurements. The full-scale calculation employed the sand-grain roughness function, and an optimal roughness length scale was determined by aligning the computed wake distribution with Ryuko-maru’s measured data. The results of this study will allow for the direct performance estimation of full-scale ships and contribute to the design technology of performance.

CFD Simulation of an Industrial Dust Cyclone Separator: A Comparison with Empirical Models: The Influence of the Inlet Velocity and the Particle Size on Performance Factors in Situation of High Concentration of Particles

The present work is dedicated to the study of multiphase turbulent and three-dimensional rotational flow in dust cyclones, a contribution to air pollution control. Cyclones are widely used devices for the separation of constituents from solid-gas mixtures in industry. In order to improve the filtration efficiency of cyclones, and to reduce the pressure drop, parametric numerical simulation studies using the Fluent code have been conducted to characterise the effects of the parameters affecting the operation of these devices through their performance indicators. In this work, the effect of inlet velocity and the particle size on the turbulent flow air in the cyclone is presented. Numerical simulation of the flow by Fluent code using three numerical models: the first based on the dissipation of kinetic energy by viscosity (RNG) K-epsilon and standard K-epsilon as well as the last based on the solution of Reynolds stress equations (RSM), combined with the multiphase mixing model, gave interesting results in terms of the pressure and flow field in the separator, the variation of inlet velocity, and the variation of particle size. Validation with experimental and empirical results showed the advantage of the Reynolds stress turbulence model (RSM) over the standard K-epsilon and RNG K-epsilon. The RSM model better captures physical phenomena in an intense vortex flow in the presence of walls. But it is characterised by a very long calculation time and requires large machine resources. An alternative to this model is RNG K-epsilon model, which offers a reasonable calculation time with acceptable results (maximum deviation of 5 %) for speed values below 10 m/s. In the absence of numerical resources, certain empirical models such as those of First (for the evaluation of pressure drop) and Iozia and Leith (for evaluation of efficiency) may well be useful for the dimensioning of the cyclone.

Surface Currents Effect in the Explicit Algebraic Reynolds Stress Turbulence Model for Simulation of Lateral Buoyant Jets in Cross-Flow

Surface Currents Effect in the Explicit Algebraic Reynolds Stress Turbulence Model for Simulation of Lateral Buoyant Jets in Cross-Flow

Numerical simulation of gas-solid flow in a cyclone separator with additional inlet

In this study, an additional inlet was added to the gas-solid cyclone separator to enhance the separation efficiency. Four different heights were tested, including 0.95D, 1.4D, 1.5D, and 1.95D (D is the diameter of the cylindrical section). The investigation involved two inlet flow conditions: increasing and dividing the inlet flow rate. The finite volume method and Reynolds stress turbulence model were used to solve the averaged Navier–Stokes equations, whereas the Eulerian–Lagrangian approach and discrete phase model (DPM) were applied to track particles with a uniform diameter of 0.5–1.8 microns as the discrete phase. Owing to the low Stokes number and small and low-volume-fraction particles, a one-way coupling method was employed between air and the particles. The addition of an additional inlet reduced the static pressure in the center and downstream areas and increased the reverse flow velocity at the end of the cyclone. The installation of an additional inlet at 0.95D had the most positive effect on the separation efficiency, with an increase of 28.8% in the increasing flow rate case and 19.6% in the dividing flow rate case compared with the cyclone without an additional inlet. Furthermore, the increase in the separation efficiency of the submicron particles was greater than that of the larger particles in both flow distribution cases.

The effects of inlet number and positions on the flow pattern and performance of a Stairmand cyclone

This study conducts numerical investigations to analyze the influence of inlet number and vertical positioning on flow patterns, collection efficiency, pressure drop, and efficiency of Stairmand cyclones. The maximum displacement of inlets is considered approximately equal to the cyclone diameter, and the inlets are arranged in a gradual manner. The Reynolds Stress Turbulence model (RSM) was employed to calculate flow properties in turbulent conditions. Out of the 44 cases examined, the four-inlet cyclone with L4=0.1 exhibited the smallest cut-size diameter, while the single-inlet cyclone with L1=0.9 displayed the lowest pressure drop. Notably, shifting one of the inlets of the two-inlet cyclone by 20% relative to the cyclone diameter resulted in higher pressure levels on the cyclone wall compared to other geometries explored in this study. Collection efficiency in cyclones is generally enhanced by an increase in tangential velocity, but it is also influenced by the position of the inlet(s).

Numerical investigation of cooling performance of 3D-printable cooling structure for aero-engine combustor

Thermal protection is an essential technology for gas turbine hot components to cope with the unprecedented thermal loads, and to ensure their enduring and efficient operation. A 3D-printable hybrid cooling cellular structure is suggested in this paper, the cooling property of which in a Can-type combustion chamber with chemical reaction considered is evaluated in detail. Reynolds Stress Turbulence Model together with the non-premixed combustion model are used to resolve the detailed flow structures and turbulence-chemistry interactions. Cases of cooling cellular with various film hole inclined angles are compared and analyzed. Results show that the cooling cellular can reduce the temperature of combustor liner noticeably, especially at the region near the second row of dilution holes. Meanwhile, the cooling performance is improved as the decrease of inclined angle, with an improvement of 29.1% as the inclined angle range from 90° to 30°, because the smaller incline angle is more resilient to coolant lift-off. A comparation with effusion cooling scheme is also made and concluded that the case of hybrid cooling exhibits a 673%-1409% higher porosity ratio, while the cooling effectiveness is reduced about 3.6%-8.3%. The lower performance of the hybrid cooling is explored further with a flat plate conjugate heat transfer numerical test, and ultimately attributed to the relative lower flow rate of coolant air induced by higher pressure loss of hybrid cooling cellular. Finally, the compound angle is further introduced into the hybrid cooling cellular. Results show that the impact of compound angle on cooling property depends highly on the angle between the film outflow and the swirling main-flow. The performance of compound angle cases will only increase when cooling cellular deflects in opposite directions of swirling flow, not vice versa. Overall, the hybrid cooling cellular shows a great potential in the cooling design of combustor liner. A smaller incline angle with compound angle deflected in the opposite direction of the swirling main-flow are also recommended for increased cooling performance.

Sensitive analyses of flow property to turbulence model in swirls simulation within aquaculture tanks

Water swirls in tanks with bottom drain(s), which is observed in aquaculture tanks. Numerical simulation of the swirling field with the general two-equation turbulence models fails to describe the swirling phenomenon and the investigating results are less convincing. This study simulates the swirling flow fields with four categories of turbulence models, they are the laminar model, the turbulent-viscosity model, the Reynolds stress model, and the Large Eddy Simulation model. Results show that the swirling phenomenon is successfully numerically reproduced except for the turbulent-viscosity model. Although the flow properties predicted with the turbulent-viscosity model are different from other turbulence models, the results are meaningful from the perspective of statistical items (mean, standard variation, uniformity, PDF, CFD). For cases with swirls, the flow field can be divided into a forced vortex and a free vortex, and their tangential velocity profiles can be described with a theoretical formula. Considering the numerical cost and the reproduction of experiments, the Reynolds stress turbulence model is preferable in studies of the flow properties of aquaculture tanks.

Analysis of the effect of rigid vegetation patches on the hydraulics of an open channel flow with Realizable k-ε and Reynolds stress turbulence models

In this study, the effect of vegetation patches naturally located in the river and stream bed on flow characteristics was observed under laboratory conditions by using representative rigid vegetation. Then, the behavior of rigid vegetation was compared with two different (Realizable k-ε and Reynolds Stress) turbulence models using a CFD software (ANSYS-Fluent). Firstly, our use of models was validated. Then, they were used for numerical simulation. The velocity distributions energy dissipation, and turbulent intensities, at the determined points for the patches located in the downstream part, were analyzed with graphics and simulations. The vertical distribution of the average velocities was calculated at typical locations downstream. The magnitude of flow velocities was observed to decrease within the vegetation patch zone. The minimum values of the velocity magnitude were observed just behind the vegetation structures. Higher velocities were simulated in the vegetation patch regions compared with the gap regions. This identifies that the gap areas are appropriate for the deposition of sediments and advantageous for aquatic living beings in terms of physical atmosphere and nutriment. A maximum of 7 % energy dissipation difference occurred between the highest and lowest SVF values. For equal SVF values, a 1 % energy dissipation difference was obtained. This situation can be associated with the number of rods, and rod spacing being equal to the rod diameter. The 3-D turbulence intensity was only numerically measured and compared. Between the Realizable k-ε model and the RES model, the maximum 0.05 %turbulence density difference was observed (for SC1 and SC3 scenarios). We can associate this situation with the vortex and complex turbulent flow, which is formed from the channel bottom to the water surface, depending on the diameter of the rigid vegetation and the rod sequence. It was observed that there are effective methods to predict the flow model within both models.

Effect of a curved turning vane on the heat transfer and fluid flow of four-pass internal cooling channels of gas turbine blades

This numerical study examined the effects of a curved turning vane on the heat transfer and pressure loss of a four-pass internal cooling channel. Three-dimensional omega-based Reynolds stress (RSM-ω) turbulence model equations were used in the computation process. Three different curved turning vane configurations were studied using a simple, without a turning vane under stationary and rotating conditions for Reynolds numbers between 20,000 and 60,000 and a rotation number of 0.042. The numerical results showed good agreement with previous experimental data. Under both stationary and rotating conditions, the curved turning vane in a hub turn reduced the pressure drop significantly compared to the conventional turning vanes. Although a curved turning vane attenuated overall heat transfer, the local heat transfer increased it in particular regions, such as the hub turn and the fourth turn of cooling passages, particularly in cases with smaller radii. Coolant flow through the hub turn of the serpentine channel can reduce recirculation, separation, and flow impingement, which are unfavorable factors of pressure loss, owing to the semi-circular configuration of the curved turning vane. Regarding the rotating conditions, four-pass channels with a smaller radius of a curved turning vane provide better overall cooling performance.

Dynamic Stall Control for a Vertical-Axis Wind Turbine Using Plasma Actuators

Dynamic stall is a major challenge for vertical-axis wind turbines (VAWTs) as it negatively impacts the aerodynamic performance of VAWTs, resulting in a reduction in net power output from the turbines. This study explores the use of alternating current dielectric barrier discharge plasma actuators for controlling dynamic stall on a VAWT. The flow control process is resolved using a two-dimensional unsteady Reynolds-averaged Navier–Stokes equations simulation with a Reynolds stress turbulence model adopted. The macro-effect of the plasma discharge on mean flow is modeled by an empirical body force model. The detailed flow actuation procedure is simulated. Numerical results show that the flow control process is dominated by the spanwise vortices, which result from the interaction between the plasma discharge and separated flow. The spanwise vortices not only prevent the development of a leading-edge separation bubble into a dynamic stall vortex, but also suppress the flow separation at the trailing edge. The application of plasma forcing has been found to greatly enhance the aerodynamic performance of the turbine in terms of the moment coefficient and averaged power coefficient of the turbine blades. Furthermore, we examine how the positioning of the plasma actuators and the freestream wind velocity affect flow control. The optimal actuation location is determined, and the plasma actuators are seen to be able to substantially enhance the net power output of the blades at all freestream speeds.

Realizability-preserving time-stepping for the differential Reynolds stress turbulence models

In the context of incompressible turbulence modelling, differential Reynolds stress models allow a better representation of turbulence anisotropy than classical linear eddy viscosity models and are less expensive than large eddy simulations in terms of computational cost. They rely on a modelled transport equation for the Reynolds stress tensor, which is by definition a covariance tensor and must remain symmetric positive semi-definite. However, the solution of the modelled and discretized transport equation may not preserve these mathematical properties. In the present article, a methodology to time-split Reynolds stress R__ terms in the transport equation is proposed using a decomposition theorem which proves the realizability of R__ provided realizable initial conditions. Realizability-preserving time-steppings are designed for several differential Reynolds stress models. The numerical schemes are presented in a finite volume context but may be used with others space discretization schemes. The realizability, precision and robustness of the numerical scheme is verified through the anisotropy time evolution in homogeneous shear-flow simulations with various initial conditions.

Оцінка впливу канавок у дифузорі на втрати повного тиску

The subject of the study is the total pressure in the diffuser channel with passive control of the boundary layer. The object of this research is a diffuser channel with riblets. The mechanism of total pressure reduction due to the presence of longitudinal grooves on the streamlined surface is related to the strengthening of viscous forces acting in the transverse direction caused by them. These forces generate a relatively calm flow inside the riblets, which pushes out the turbulent flow, which causes surface friction, pushing it away from the surface. Thus, the process of generation and growth of elongated wall turbulent formations. In addition, in the presence of riblets, a change in the pressure field in the transverse direction is possible, as well as the creation of a quasi-two-dimensional flow in the immediate vicinity of the wall. In this work, the aim of research to investigate the influence of riblets on total pressure loss in the diffuser channel with the purpose of evaluating the influence of riblets on the change in the nature of the flow and the change in pressure, using numerical modeling. To study the nature of the flow in the diffuser channel, we resolved the following tasks: a diffuser channel was modeled with the following dimensions: length L=50 mm, hydraulic diameter at the inlet X=25 mm, hydraulic diameter at the outlet Y=40 mm, riblets diameter d=4 mm, number of riblets n =4 and n=8. The study was compared with a diffuser with the following dimensions: length L=50 mm, diameter at the inlet X=25 mm, diameter at the outlet Y=40 mm. To research the flow in the diffuser, the method of numerical experiment was chosen. An unstructured calculation grid was used in the diffuser for the research. The calculation of the turbulent gas flow was performed by numerically solving the averaged Navier-Stokes equations. During the numerical simulation of the flow, the Reynolds stress turbulent viscosity model will be used. As a result, using a diffuser with riblets increases the coefficient of hydraulic resistance compared to a smooth diffuser. The resistance reduction mechanism does not work due to the relatively short length of the diffuser and small longitudinal vortices of the riblets scale do not have time to form. There are pressure increasing instead of laminization of the flow and pressure decreasing. Scientific novelty - received new data on the effect of riblets in the diffuser channel on the total pressure loss coefficient. Practical significance - the obtained results can be used to control the boundary layer in diffuser channels (in diffuser compressor grates) to improve their characteristics.

Тестова задача моделювання течії у ступені компресора Rotor 37

The subject of the study is the dependence of the degree of pressure increase on the airflow in the impeller of the axial compressor degree. The object of study is the Rotor 37 axial compressor. The purpose of this study was to select a turbulent viscosity model when conducting a test task in the Rotor 37 compressor. To achieve this goal, the following tasks were solved: to create a three-dimensional model of the object under study; develop a grid model of the object under study; to simulate the flow in a certain range of air flow; to compare the data of numerical and physical experience; evaluate the flow visualization in the Rotor 37 axial compressor stage for all studied turbulent viscosity models. When studying the flow in the stage of the axial compressor Rotor 37, the numerical experiment method was used. The flow simulation was carried out by solving the system of Navier-Stokes equations, which was closed by the turbulent viscosity model. The study used seven turbulent viscosity models: k-ε, k-ε EARSM, SST, BSL, BSL Reynolds Stress, SSG Reynolds Stress, and QI Reynolds Stress. For simulation, a computational grid was built with the adaptation of the boundary layer. This study presents the results of a flow simulation test problem in the Rotor 37 compressor. The results of the study show that all the tested turbulent viscosity models can be used to simulate the flow in an axial compressor. However, the flow calculation with the SSG Reynolds Stress turbulent viscosity model has the smallest error. An analysis of the visualization of streamlines in the interblade channel of the Rotor 37 compressor showed that in all cases, the flow pattern with all turbulent viscosity models is similar. Some differences are observed when modeling the flow with the BSL Reynolds Stress and SST turbulence models. An important factor that should also be taken into account when modeling is the calculation time. In this case, the shortest calculation time was observed for simulation with SST model. Scientific novelty and practical significance is that new data were obtained when testing the following turbulent viscosity models: k-ε, k-ε EARSM, SST, BSL, BSL Reynolds Stress, SSG Reynolds Stress, QI Reynolds Stress. The results obtained made it possible to choose a turbulent viscosity model for further research.

Numerical modeling of body shape effect on the performance of a square cyclone separator

This study aims to determine the effect of a square cyclone body shape on the performance of a square cyclone separator. To achieve this goal, four square cyclone separators with square lengths 0, 1, 2, and 3 times the hydraulic diameter of the cyclone body were considered. The simulation of the gas-solid flow was carried out using the Euler-Lagrange approach, while the gas flow was modeled by Navier–Stokes equations and the Reynolds stress turbulent model (RSTM), and the injected solid particle was solved using the Newton equation. The pressure drop, separation efficiency, and flow pattern were investigated to evaluate the performance of square cyclone separators. The results revealed that the pressure drop and separation efficiency decreased as the relative square length increased. In the case with a lower relative square length, the vortex core penetration is less than that in the other cases, which leads to a decrease in the entrainment phenomena and separation efficiency enhancement. At an inlet velocity of 16 m/s, an increase in the relative square length from 0 to 3 reduced the pressure drop by approximately 35%. At an inlet velocity of 24 m/s and a particle diameter of 8 µm, with an increase in the relative square length from 0 to 3, the efficiency decreased from 88.7 to 77.4%.

Analysis of the vortical flow in a cyclone using four vortex identification methods

This paper analyzes the vortex flow field and performance of a solid-gas cyclone separator using computational fluid dynamics (CFD) by employing the Reynolds stress turbulence model (RSM) and Eulerian-Lagrangian particle tracking scheme for particle diameter (d) range of 0.1 to 8 μm. The complex structure of vortices is analyzed using the vorticity method, λ2-criterion, Q-criterion, and Ω-method. The results demonstrate that the presence of helical guide vanes (HGVs) enhances the centrifugal force applied to the solid particles and fluid velocity up to 4.4 times compared to the conventional cyclone. It is revealed that the λ2, Q, and Ω methods provide more details of eddy structure in the inner and outer layers of the isovortex surfaces than the vorticity method. Besides, the vortex core diameter can be estimated by all vortex identification methods.

Flow Control in a Rectangular Open Channel using Two Impermeable Spur Dikes: A Numerical Study

The present study examines how adjusting vegetation patches in a rectangular open channel with two impermeable spur dikes alters the displacement of the recirculation region. The Reynolds stress turbulence model is implemented via the 3D numerical code FLUENT (ANSYS). Mean stream-wise velocity profiles were drawn at selected positions and at mid of flow depth i.e., 3.5 cm, a horizontal plane is cut through the open channel for analyzing velocity contours and streamline flow. The findings indicate that the stream-wise velocity profiles showed fluctuations in the presence of different shapes and arrangement of cylindrical patch discussed and the maximum velocity within the field of spur dike is of the order of 0.018 m/s due to the prism shape. By changing the position of the cylindrical patch, the location of the recirculation region displaces within the field of impermeable spur dike.

Fineness Ratio Effects on the Flow Past an Axisymmetric Body at High Incidence

The flow past an axisymmetric body at a sufficiently high angle of attack becomes asymmetric and unsteady. Several authors identified three different flow regions for bodies of large fineness ratio at low subsonic flow and high incidence: a steady region in the forebody and two unsteady regions in the rear body. Unsteady Reynolds Averaged Navier–Stokes (URANS) codes with eddy viscosity turbulence models or Reynolds stress turbulence models fail to capture the unsteady flow region. These methods are overly dissipative and resolve only frequencies far lower than turbulent fluctuations. Scale-Adaptive-Simulation (SAS) provides an alternative method to afford the problem of these massively separated flows at high Reynolds numbers without addressing the problem to Large Eddy Simulation (LES). This paper applies SAS to study the effect of slenderness on the flow. The numerical solutions show that the flow becomes more unstable as the fineness ratio increases, and the three flow regions are clearly recognizable. For low fineness ratios, only one of the two unsteady regions is visible. The good agreement between the sectional forces and pressure coefficients with their corresponding experimental data for an ogive-cylinder configuration allows an analysis of the flow structure with a fair degree of confidence.

Numerical simulation of jet impingement relaminarization using nonlinear eddy viscosity turbulence models

This numerical study investigated a single air jet impingement at a constant temperature. Different RANS turbulence models, namely the v2-f model and four Reynolds stress turbulence models (the linear pressure-strain model, the quadratic pressure-strain model, the stress-omega model and the stress-BSL model) were employed to simulate and compare the numerical results with other published measurement data. Here, we show that the v2-f model has better numerical precision in simulating the local Nusselt number and velocity profiles and is in good agreement with a variety of Reynold numbers. These findings can assist scientists or engineers to improve mathematical turbulence modeling and industrial equipment for further development and to enable innovation.

A novel idea to increase the performance of a wheat flour cyclone separator: Controlling the reverse flow

AbstractIn this study, as a novelty, the reverse flow effect on a wheat flour cyclone performance was evaluated. A computational fluid dynamics (CFD) simulation was realized using a Reynolds stress turbulence model. Also, particle–air interactions were modeled applying a discrete phase model. Besides the experimental measurement, the numerical simulation was conducted in a main (without reverse flow) and six various reverse flow levels (I = 0.0385 m3 s−1, II = 0.0396 m3 s−1, III = 0.0484 m3 s−1, IV = 0.0583 m3 s−1, V = 0.0704 m3 s−1, and VI = 0.0836 m3 s−1) by CFD. The validation between pressure drop in experimental data and numerical results revealed a good agreement with a maximum deviation of 8.2%. Cyclone performance including pressure drop and separation efficiency was assessed in the mentioned reverse flow levels. Moreover, velocity field, centrifugal force, and turbulence parameter were evaluated, comprehensively. It was found that the flour separation efficiency increased with enhancing the reverse flow level to IV = 0.0583 m3 s−1, but decreased with a sharp slope in the reverse levels of V = 0.0704 m3 s−1 and VI = 0.0836 m3 s−1.Practical ApplicationsCyclone separators are widely used in various industries such as flour and cement. The various parameters of cyclones in a food processing unit effectively affect cyclone efficiency. Therefore, an innovative method for increasing cyclone performance is presented in this study. Computational fluid dynamics (CFD) is a powerful tool for simulation of the food processing phenomenon. Validation could be guaranteed by the usage of numerical results that are obtained from CFD simulations. The innovative methods can play a key role in decreasing energy usage by reducing the pressure drop and enhancing separation efficiency.

Numerical Investigation of Flow Separation Control over Rotor Blades Using Plasma Actuator

The flow separation control over rotating rotor blades in hover using an alternating current dielectric barrier discharge (AC-DBD) plasma actuator is investigated through numerical simulation, possibly for the first time. Three-dimensional unsteady Reynolds-averaged Navier–Stokes calculation with a Reynolds stress turbulence model is adopted to resolve the airflow. The impact of the AC-DBD plasma discharge on the airflow is modeled by an empirical body force model. The objective of this work is to characterize the separated flow over the rotating blades, resolve the flow control procedure, reveal the flow control mechanism, and evaluate the control authority. Compared with the experiment, the numerical simulation can provide satisfactory predictions of the baseline flow over the rotor for the qualitative flow pattern and quantitative aerodynamic features. The good agreement between the simulation and experiment lends credibility to the observations made from the numerical result. It is found that in the baseline flow, the flow separation occurs in the vicinity of the blade tips and exhibits strong three-dimensional characteristics under the influence of centrifugal force. The plasma excitation can significantly inhibit the flow separation over the blades at large angles of attack (AOAs). The flow control is seen to be dominated by the spanwise vortices induced by the plasma discharges, for which the strong entrainment effect makes the separated flow fully or partially reattach to the blade surfaces. The resulting forced flow pattern is influenced by the AOA of the blades. At each high AOA under consideration, the controlled flow is a significant improvement over the baseline case, and the aerodynamic characteristics of the rotor blades are appreciably enhanced.