SST Turbulence Model Research Articles

Численное моделирование горения в камере модельного ракетного двигателя малой тяги на газообразных компонентах кислород – метан

The paper provides numerical study of the working process in a model low-thrust rocket engine operating on the gaseous oxygen-methane components based on results of the preliminary computational analysis of the component supply system efficiency. Combustion of the oxygen-methane unprepared preliminary mixture was numerically simulated carried using the fast chemistry approaches, including eddy dissipation models (EDM), chemical equilibrium and flamelet. To describe the chemical processes occurring during combustion, the Westbrook and Dreyer quasi-global two-stage mechanism, the reduced Jones—Lindstedt kinetic mechanism with the Frassoldati corrections and the GRI Mech 3.0 mechanism were used. Calculations were performed in the two-dimensional and three-dimensional formulations of the gaseous oxygen and methane diffusion combustion. Results of the parametric study (concentration and temperature fields) are presented for the oxidizer excess coefficients of α = 0.7; 1; 1.2. It is shown that using a mathematical model based on the Reynolds-averaged Navier-Stokes equations closed by the k—ω SST turbulence model, supplemented with the flamelet model based on the GRI Mech 3.0 mechanism taking into account the radiative heat transfer makes it possible to obtain satisfactory convergence with results of the experimental study and to qualitatively assess the workflow in this type of engine.

A Comparative Study of Film Cooling with Combined Impingement and Film Cooling

In order to cool the gas turbine vane or blade and raise the operating temperature, two standard convective cooling methods are used: jet impingement cooling and film cooling. The current study uses computational analysis to analyze and compare film cooling effectiveness with and without multi-jet impingement cooling on a flat plate. Ansys Fluent software is used to perform computational analysis on a flat plate. The computational results were compared with the experimental result using K-ω SST turbulence model and validated with literature data. The flat plate is used for the conjugate heat transfer study on the hot surface (named interaction surface), cold surface (called target surface), and inside the film hole. Different heat transfer parameters such as heat flux, Nusselt's number, and effectiveness are compared for the two cases, i.e., film cooling with impinging jets (IFC) and film cooling without impingement cooling (FC). It is observed that the FC case shows lower effectiveness as compared to the IFC case. The average Nusselt number for the IFC cases is almost three times larger than FC. The film exit temperature values are higher FC case, but it is more uniform in the IFC case. Interaction surface heat flux and Nusselt number values show higher values on the upstream wall of the film hole for IFC than in the FC case.

Instabilities identification based on a new centrifugal 3D impeller outflow model

Previous research works have shown that the inflow boundary conditions have a significant effect on the behavior of diffusers in a centrifugal machine. To better understand the vaneless diffuser instability mechanism and save computing resources, several numerical works are planned to be conducted for the solely vaneless diffuser, excluding the rest of the centrifugal machine from the flow domain to simulate. Previous reduced-order models used either two-dimensional approaches that focused exclusively on the core-flow instability or three-dimensional models tested for a few inflow conditions. To obtain the more realistic diffuser inlet boundary conditions, a modeling method is here developed by fitting the diffuser inflow velocity derived from numerical simulations of the entire machine. The classic fitting methods used to approximate inflow profiles by algebraic polynomials or Gaussian functions are observed to introduce numerical artifacts that significantly affect the flow and therefore its stability. The multi-stage scale-matching fitting approach developed in this study is designed as a robust successive-order approximation of the inflow conditions. Our objective is to demonstrate its robust capability of taking into account the main physical features of the inlet velocity profiles, which, in turn, allows us to significantly improve the prediction of the flow instability occurring in the pump diffuser. Firstly, the RANS and URANS simulations of the entire machine are carried out by OpenFOAM using the k−ω SST turbulence model. The simulation results show that the RANS simulation is efficient in correctly capturing the diffuser inlet velocity profile except for developed stall conditions. The RANS simulations are carried out for cases with three different kinds of leakage configurations between the impeller and the diffuser. For each case, five flow rates were simulated to get the basic data for fitting the inlet profiles for a total of 125 simulations. The diffuser inlet velocity profiles are averaged in the azimuthal direction and fitted such to obtain an explicit function for the azimuthally-averaged velocity profile that varies with the flow rate Q. The fitting results are very close to the original data, and using our fits to predict the diffuser flow instabilities we show that our modeling approach compares well against the URANS simulations of the whole machine.

Optimization of Outer Diameter Bernoulli Gripper with Cylindrical Nozzle

Gripping and manipulating objects using non-contact and low-contact technologies is becoming increasingly necessary in manufacturing. One of the promising contactless gripping technologies is Bernoulli gripping devices for industrial robots. They have many advantages, but when changing the nozzle geometry, it is difficult to find the optimal parameters of the outer diameter of the gripper and its operating parameters. Therefore, the article presents a model for numerical simulation of the dynamics of airflow in the nozzle of the Bernoulli gripping device and in the radial gap between its active surface and the surface of the object of manipulation. Reynolds-averaged Navier–Stokes equations of viscous gas dynamics, SST-model of turbulence, and γ-model of laminar-turbulent transition were used for this purpose. The technical requirements for the design of the nozzle of Bernoulli jet gripping nozzles are determined and variants of their constructive improvement are offered. According to the results of numerical simulation in the Ansys-CFD software environment, the optimal diameter of the Bernoulli gripping device and the influence of the geometric parameters of the nozzle on the nature of the pressure distribution in the radial gap and its lifting force were determined. Determined the optimal parameters of the height of the gap between the object of manipulation and the Bernoulli gripping device using C—Factor, which will allow efficient operation of Bernoulli gripping devices during automated handling operations using industrial robots.

Numerical simulation of compound wings wind tunnel test for wig effect vehicle

This paper presents the comparison of numerical simulation results and wind tunnel experiment for compound WIG's wing. Numerical simulation was performed in the ANSYS Fluent software. The choice of the turbulence model and the computational mesh parameters, including the resolution of the boundary layer, are substantiated. Comparison of the results of the experiment and numerical simulation showed good convergence for middle density mesh about 7 million cells and first layer height 0.0001 m. Additional study for k-ε realizable and k-ω SST turbulence models was done. Its result founded much efficiency k-ε realizable model than k-ω SST turbulence models for compound WIG's wing. Numerical simulation takes less time and ensures the same accuracy. The results can be argued that the selected parameters of numerical simulation can be used to obtain the aerodynamic characteristics of various layout solutions for "type C" WIG craft.

Altitude-compensating axisymmetric supersonic nozzle design and flow analysis

Altitude-adapted nozzles are designed to facilitate flow adaptation during rocket ascent in the atmosphere, without requiring mechanical activation. As a consequence, the performance of the nozzle is significantly improved. The aim of this study is to develop a new profile of axisymmetric supersonic nozzles adapted at altitude (Dual Bell Nozzle with Central Body), which is characterized by an E-D nozzle as a basic profile. The performances obtained for this nozzle (E-D Nozzle) are then compared to those of a Plug nozzle. The E-D nozzle shows significant performance advantages over the Plug nozzle, including a 13.02% increase in thrust, knowing that the length of the E-D nozzle is half that of the Plug nozzle under the same design conditions. Finally, viscous calculations using the k-ω SST turbulence model were conducted to compare the performance of the dual bell nozzle with central body (DBNCB) and the E-D nozzle with the same cross-sectional ratio, and to assess the impact of nozzle pressure ratio (NPR) variations on the operation mode of the DBNCB. The results obtained show that the DBNCB offers the best performance in most phases of flight.

PATTERNS OF GAS FLOW IN A HIGH-PRESSURE CENTRIFUGAL COMPRESSOR

The development of three-dimensional modeling and analysis of the flow based on the solution of Reynolds-averaged Navier–Stokes equations allows to better determine the characteristics and flow parameters, but requires significantly more time spent on simulation and proof or verification of mathematical models in order to obtain minimal calculation errors. The aim of the work is to determine gas flow patterns in a high-pressure centrifugal compressor based on numerical methods for calculating the flow and to compare the integral characteristics with experimental data. The adequacy of the mathematical model with a displacement of the mass flow rate by 0.3 kg/s was confirmed. Nevertheless, the maximum mismatch of the determination of the total pressure ratio is equal to 8% in the zone of optimal values with flow displacement. The maximum error of determining efficiency is 9%. In the zone of optimal values, if the flow rate characteristic is shifted, the error of efficiency calculating does not exceed 2%. The pressure distribution along the impeller blades and the diffuser blades showed ways to optimize the blade shape to increase the compressor efficiency: there is an intersection of the lines for the optimal mode of the rotor blade; the splitter blade works in normal mode, but the distribution can be improved by changing the blade shape in the initial section; the intersection of the pressure lines for the optimal mode indicates the insufficient quality of the diffuser, which can be improved by changing the shape of the blade. For a more qualitative mathematical description of the flow patterns in the compressor, it is advisable to use the SST turbulence model, with a larger number of elements. The compressor characteristics were obtained numerically and the integral parameters of operation were determined. Keywords: high-pressure centrifugal compressor, numerical simulation, mathematical modeling, performances, adequacy

Optimized Ristorcelli’s Compressibility Correction to the $$k-\upomega $$ SST Turbulence Model for Base Flow Analysis

Optimized Ristorcelli’s Compressibility Correction to the $$k-\upomega $$ SST Turbulence Model for Base Flow Analysis

Application of hydrogen mechanisms in combustion simulation of DLR scramjet combustor and their effect on combustion performance

In view of the promising application of hydrogen in scramjet combustor and the rapid development of hydrogen kinetic mechanisms, present work applies representative mechanisms with good kinetic performance to the combustion simulation of DLR scramjet combustor with a customized solver based on OpenFOAM platform. Different Reynolds-Averaged Navier Stokes (RANS) turbulence models including standard k-ε, SST k-ω and their corresponding modified versions for turbulent round jets, are utilized to simulate the non-reactive and reactive flow fields. Compared with the detailed experimental measurements of schlieren image, streamwise velocity, pressure etc., the modified k-ω SST turbulence model shows good performance and improves the simulation results near hydrogen jet. In combination with partially stirred reactor (PaSR) combustion model, three representative detailed hydrogen mechanisms (marked with Ó Conaire-2004, Varga-2015 and Konnov-2019) are adopted to evaluate their effect on combustion performance under scramjet combustion condition. And their effects on the combustion performance are quantified based on combustion efficiency, net thrust, total pressure loss, etc. All of them can well characterize the thermal combustion characteristics of hydrogen in the combustor. Among them, Ó Conaire-2004 slightly overestimates flame temperature, combustion efficiency and net thrust, and underestimates total pressure loss. Whereas Varga-2015 and Konnov-2019 provide nearly identical results on these performance parameters and give temperature profiles coinciding well with experimental data. Although the newly added excited states in Varga-2015 and Konnov-2019 deepen the understanding of hydrogen combustion processes and can served for optical combustion diagnostics, their effects on thermal combustion characteristics are negligible under present combustion condition, judging from their low content and the analysis on the performance parameters. Present work is conducive to the selection of hydrogen mechanisms for the combustion simulation of hydrogen-fueled scramjet combustor, and facilitates to obtain reliable simulation results for scramjet with turbulent round jets by employing the modified SST k-ω turbulence model.

A near-wake survey of an Ahmed body comparing low- & high-fidelity numerical models with experiments

A full-scale square-back Ahmed body is analysed experimentally and numerically for a free-stream flow velocity of 45m/s corresponding to a Reynolds number ReH=7.7×105. Numerical simulations are performed for matching inflow conditions and different turbulence models. The main goal of this study is to examine the effectiveness of the Delayed Detached Eddy Simulations and the Reynolds Averaged Navier–Stokes k−ω SST turbulence model to capture the mean flow physics. Local and global aerodynamic parameters are compared with experimental results, including boundary-layer parameters evolving over the roof, the wake characteristics, the shear layer, and the mass entrained into the wake. A particularly good agreement is found between the experiment and the DDES. An in-depth analysis of the shear-layer growth, mass-entrainment and momentum budget analyses along the recirculation region interface, allow for identifying and quantifying the differences in predicting drag and the mechanisms at stake between the different approaches. The momentum budget, performed on the experimental data shows that pressure can be accurately obtained from experiments and closely follows that computed from high-fidelity numerical simulations. These results confirm the effectiveness of DDES in studying flows at high Reynolds numbers. The mass/momentum budget along the recirculation-region interface is also found as a possible mean to quantify road vehicle’s aerodynamic performances, naturally extending to more complex geometries.

Flow-Induced Forces for a Group of One Large and Several Small Structures in the Sheared Turbulent Flow

Evaluating the hydrodynamic force fluctuations acting on each structure in a group of subsea objects of different cross-section shapes, sizes and relative positions represents a challenge due to the sensitivity of the vortex shedding process, especially for a variety of sheared flows. The present study uses the numerical 2D computational fluid dynamics model to estimate the flow-induced forces on a group of small circular and D-shaped cylinders in the linear and parabolic sheared flow, which are placed in proximity to a larger structure of the squared cross-section. This allows us to evaluate loads, which are affected by the presence of subsea equipment located on the seabed. The average Reynolds number of the considered linear flow profile is 3900, while the parabolic flow profile has the maximum Reynolds number of 3900. The k-ω SST turbulence model is used for simulations. The work demonstrates the effect of the cross-sectional shape of smaller cylinders on hydrodynamic coefficients, explores the effect from the spacing in between the structures and highlights differences between loads in the linearly sheared and parabolic flow. The results obtained show that the presence of the squared cylinder notably influences the mean drag coefficient on the first cylinder, for both circular and D-shaped cylinders. The parabolic sheared flow profile in this series leads to the highest mean drag and the highest amplitudes of the fluctuating drag and lift coefficients.

Transient Numerical Study to Determine the Effect of Inlet Angle Variation on Flow Conditions inside a Circular Aquaculture Tank

Seeing how great the contribution and potential of the aquaculture sector to the fulfillment of food for the people of Indonesia, the development of aquaculture including the Recirculating Aquaculture System (RAS) is very important to be carried out intensively. An important aspect that should be considered for the development of RAS is maintaining water quality as the main medium of cultivation. Optimization of the aquaculture tank is an effort that can be conducted to achieve this goal. A transient numerical study to determine the effect of inlet angle variation on flow conditions inside a circular aquaculture tank was conducted to assess the optimum geometry for the application. Single-phase CFD simulations using the k-ω SST turbulent model were carried out to evaluate the effect of inlet nozzle angle variations. Three angle variations 0°, 45°, and 90° were selected and the resultant fluid flow conditions were analyzed. From the CFD results, it can be known that the optimum condition for the circular aquaculture tank is achieved for the angle 0° among the tested angle in this present study.

Effects of splitter geometry as a passive control method on sound pressure level, a mathematical modeling

This study investigates the aeroacoustics of flow around a square cylinder using an in-house OpenFoam solver with Ffowcs Williams’ Hawking methodology and the [Formula: see text] SST turbulence model. First, the numerical results were validated against experimental data. Then, the effects of a 1[Formula: see text]mm thick splitter with different lengths, 2.5 ([Formula: see text]), 5 ([Formula: see text]), 7.5 ([Formula: see text]) and 10 ([Formula: see text]), were studied as a passive control method. The findings indicate that the splitter suppresses the vortex shedding, a dipole source of aeroacoustic emission, resulting in a reduction of the noise level by up to 7% for [Formula: see text] for [Formula: see text] for [Formula: see text] and 17.5% for [Formula: see text].

Advanced turbulence modeling improves thermal gradient prediction during compressed hydrogen tank filling

In order to use gaseous hydrogen for mobility of light and heavy duty vehicles, the standard J2601 from the Society of Automotive Engineers (SAE) recommends that the temperature in the tank must not exceed 85 °C for safety reasons. Prior experiments reported that a vertical thermal stratification can occur during the filling of horizontal tanks under specific conditions. Thermodynamic modeling of hydrogen tank filling can predict the average gas temperature but not the onset of stratification. In a previous study, the computational fluid dynamics (CFD) software OpenFOAM was used to carry out simulations of hydrogen filling for a type IV 37 L tank. The CFD results, by comparison with experimental results, were capable to predict the rise of the thermal stratification with however an underestimation of thermal gradient magnitudes. The maximal temperature predicted at the end of the filling was 15.05 °C bellow the experimental measurements. In this work, the k − ω SST turbulence model is replaced by the k − ω SST SAS turbulence model to limit the prediction of high levels of eddy-viscosity in stagnation areas which over-diffuses the temperature. By using the same mesh as in the above mentioned study, (651 482 cells in the fluid region and 449 126 cells in solid regions), the k − ω SST SAS turbulence model is found to be more appropriate for CFD simulation of tank filling as it predicts a thermal gradient magnitude in the gas in better agreement with experimental measurements than the k − ω SST turbulence model for a similar time of simulation. The maximal temperature predicted at the end of the filling is 2.17 °C bellow the experimental measurements.

Resistance on Catamaran Decommissioning Unit: A Comparison of Numerical Analysis (Two Turbulence Models) to Model Test Result

A new concept design Catamaran Decommissioning Unit has been developed by Research Center for Hydrodynamics Technology Indonesia. The catamaran has a unique shape, however in order to achieve resilient and sustainable the decommissioning unit as it has a unique shape, resistance analysis both model testing and numerical calculation must be conducted. The resistance value from the numerical analysis needs to be validated with the results from model testing in the towing tank. A model of a catamaran unit with a scaling factor λ=36 was taken as the object of study. The model test was conducted in a towing tank with service speed varies from 7-15 knots. As a comparison, a numerical analysis using the CFD method was being performed under two different turbulence models (k-ε and k-ω SST) with the same speed regarding the experimental speed parameter. Iin a conclusion, numerical analysis with k-ω SST turbulence model gives a better performance with smaller relative deviation compared to the k-ε turbulence model.

Examination of thermo-hydraulic performance and exergy efficiency in a heat exchanger equipped with spiral tube using a two-phase approach for climatic conditions of Kuwait

This study examines the effect of twisting the inner tube and using DWCNT-Cu/water hybrid nanofluid (HNF) on the hydrodynamic performance and exergy efficiency of a heat exchanger (HE) in the turbulent flow regime for the climatic conditions of Kuwait. The impacts of pitch ratio (PR) and concentration of nanoparticles (NPs) on the results are evaluated. Using the two-phase mixture model, the DWCNT-Cu/water HNF flow is simulated. To model the turbulent flow, the k-ω SST turbulence model is utilized. The effect of solar radiation in Kuwait is assessed on the inlet temperature of the nanofluid (NF). The results demonstrate that heat transfer (HT) and pressure drop (ΔP) are enhanced with Reynolds number (Re) and volume fraction of NPs (φ). In addition, the maximum average Nusselt number (Nuave) (Nuave)and heat exchanger (ΔP) correspond to Re = 32,000 and φ = 7%. By enhancing the PR of the internal spiral tube (ST), the average Nuave and (ΔP) are enhanced by 39.21% and 44.14%, respectively, when Re = 32,000 and φ = 7%. Also, it is revealed that the exergy efficiency is intensified by 32.37% as Re is enhanced from 10,000 to 32,000 when the PR is 4 and φ = 7%.

Study on conjugate heat transfer characteristics of flexible structure of solid motor nozzle based on multiple working conditions

In order to study the influence of the deformations of the nozzle’s flexible sections on its inner wall’s heat transfer, this research uses the two-dimensional axisymmetric model and the k − ω SST turbulence model to numerically analyze the tail flow field of the flexible-extendible nozzle under multiple working conditions. The flow field and the inner wall’s heat transfer of the flexible sections with and without deformations are simulated and analyzed. The simulation results show that when the flexible sections are deformed, new shock waves will be generated in the tail flow field of the nozzle; the temperature and the heat flux of the first half of each flexible section decrease, while those at the end of each flexible section increase, and the deformations’ effect on temperature and heat flux diminishes over time. The research shows that the deformations of the flexible sections will make the inner wall’s heat transfer of the flexible sections uneven, and the inner wall’s ablation at the end of each flexible section may be aggravated, while that of the front half may be alleviated.

Systematic investigation of power enhancement of Vertical Axis Wind Turbines using bio-inspired leading edge tubercles

Wind energy is employed as an effective source for catering to the increasing energy demands and depleting fossil fuels, while also counteracting their adverse environmental effects. VAWTs have numerous advantages over HAWTs. But, the relatively low power coefficient of VAWTs in comparison to HAWTs restricts their utilization. Bio-inspired leading-edge tubercles appear to be one of the potential design changes for enhancing the power performance of VAWTs. This study systematically investigated the relative influence of tubercle design variables and their geometrical trend subjected to power performance by employing a hybrid Design of Experiments (DoE) approach and Response Surface Methodology (RSM) rather than choosing random values of tubercle variables. Furthermore, the conflict existing in the literature about the improved or degraded power performance of VAWTS with tubercles is resolved by evaluating the power performance of VAWT at on-design and off-design conditions. For the computation of aerodynamic forces, unsteady Computational Fluid Dynamics (CFD) was utilized with a 4-equation transition SST turbulence model. Tubercle amplitude influences the aerodynamic efficiency of VAWTs relatively more than its wavelength. It is evident from the results that energy is harnessed efficiently at on-design conditions considering lower tubercle amplitude and higher wavelength. However, the reverse trend of variables is observed under off-design conditions. At on-design conditions, tubercles degraded the VAWTs performance in comparison to baseline VAWT configuration by a minimum of 13.55% among the 14 hybrid DoE generated cases, while the performance was enhanced by a maximum of 55% at off-design conditions of VAWT.

NUMERICAL INVESTIGATION OF PLATE COOLING USING MULTIPLE IMPINGING JETS IN DIFFERENT ALIGNMENTS

In this study, convective heat transfer by multiple impinging jet arrays in different arrangements is numerically investigated using Computational Fluid Dynamics (CFD). Computational domain consists of multiple jet array either in inline or staggered alignment and a target plate to be cooled by impinging jets. Distance between the jet array and the target plate is kept constant at H=28 mm. Diameter of circular jet nozzles is fixed at D=5 mm for all configurations. Effects of jet Reynolds number (Rej), spacing between circular jets and the alignment of the jet nozzles on aerothermal performance are parametrically investigated in the scope of this study. For staggered and inline alignments of the jet nozzles, Rej ranges from 5000 to 20000 and the ratio of the spacing to the jet diameter (s/D) changes between 2 and 6. CFD calculations are performed using finite volume based ANSYS-Fluent flow solver. Simulations are conducted for incompressible, steady and turbulent flow using k-ω SST turbulence model with ideal gas assumption for density and Sutherland law for viscosity. After intensive mesh convergence and validation tests, appropriate mesh resolution is determined and parametric investigations are performed. The study reveals that most dominant parameter for plate cooling is Rej followed by spacing between jets and finally jet alignment. For all Rej, inline jet nozzle alignment provides 15% higher average heat transfer rate than staggered alignment when s/D is close to the lower limit. However, it is shown that jet alignment does not affect thermal performance when s/D is higher.

CFD Investigation of a Hybrid Wells Turbine with Passive Flow Control

In the past decade, there has been renewed interest in wave energy harvesting utilizing oscillating water columns (OWC), one of the most well-studied wave energy harnessing technologies. In the OWC, pneumatic power from ocean waves is converted to mechanical energy by Wells turbines. It should be noted, however, that such turbines tend to perform poorly, have a limited operating range, and have low efficiency. In the present study, we incorporate a rectangular Gurney flap (GF) at the trailing edge (TE) of a Wells turbine consisting of hybrid airfoil (NACA 0015 and NACA 0025) blades with variable chord distribution along the span. This passive flow control mechanism was adopted to achieve increased power production by the Wells turbine. This study aimed to determine the aerodynamic performance of the variable chord turbine with GF compared to a turbine with a constant chord. By using ANSYS™ CFX, the three-dimensional, steady-state, incompressible Reynolds averaged Navier–Stokes (RANS) equations coupled with the k-ω SST turbulence model are solved. The performance was evaluated through the use of non-dimensional coefficients of torque, pressure drop, and efficiency. In addition, the numerical accuracy was achieved through a grid independence study. There was a good agreement between the computed results and the available experimental and numerical data. The GF increased the torque coefficient by 18.6% and 47.3% but with the expense of peak efficiency of 8.5% and 7.4% for the baseline and the hybrid turbine, respectively. Additionally, the hybrid turbine with GF delayed the onset of the stall by ~3° angle of attack (AOA).