SST Model Research Articles

Gas turbine combustor CFD study and single-objective DoE optimization

A fast RANS method for methane-air non-premixed combustion is proposed, using a k-ω SST model for turbulence, a transport species model for chemistry and eddy dissipation model for turbulence-chemistry interaction. The method is validated with experimental data from Sydney Swirl Flow and Flame Database. The same method is then used to simulate a two-dimensional axisymmetric combustor liner geometry, and finally a Design Exploration is proposed to optimize the Pattern Factor at the combustor outlet, obtaining the response surface for the entry variables, namely the Swirl Number and mass flows for each row of holes. An optimal combustor configuration is chosen. The results are then discussed and compared to similar works, showing the viability of the simplified CFD simulation and DoE optimization methodology.

Numerical simulation of the airflow in a mine axial fan in reverse mode

The article considers the numerical calculations of the air flow flow in an asian fan operating in reverse mode. The calculation was carried out in the ANSYS CFX. Fan of the TsAGI OV-103 aerodynamic scheme was considered, for which experimental aerodynamic characteristics are known. K-ε and SST turbulence models were used in the calculation. The dependences of the total fan pressure on the flow rate are obtained. For a single-stage Rotor+OGV scheme, the closest to experimental results were calculated using the SST model. For a two-stage Rotor+OGV+Rotor+OGV dependence of the total pressure is determined using the k-ε model. For such a scheme, axial velocity distributions in the outlet are calculated for different performance values.

A Modified Turbulent Model for the Supercritical Water Flows in the Vertical Upward Channels

The supercritical water undergoes drastic changes in the thermal physical properties near the pseudo-critical point. It is necessary to evaluate whether the conventional turbulent models could successfully capture the wall temperature variations. In this study, the heat transfer of the supercritical water in the vertical tube and multiple fuel rods channel is numerically investigated using different turbulent models. The numerical results are compared with the experimental data. The comparisons indicate that the realisable k - ɛ model, k – ω SST model, and the Reynolds stress model generally give a better agreement with the experimental data on the predictions of the wall temperatures. A new variable turbulent Prandtl model is proposed. Selected better performance turbulent models coupled with the proposed turbulent Prandtl model are assessed. The modified turbulent model shows a great improvement in the prediction of the wall temperatures, especially for the condition in a multiple fuel rods channel.

Research on the thermal performance of a heat exchanger with meso-scale twisted helical tube bundles

Heat exchangers with helical tubes are applied widely in various industrial fields and cryogenic applications. Currently, the most common ones are the spiral wound heat exchangers, which consists of many layers of spiral tubes with different coil diameters in a closed shell. Most of the fluid in the shell-side passes directly through the gap between two adjacent layers, which weakens the turbulence and the associated heat transfer coefficient. A novel twisted helical bundle geometry is proposed in this paper of which the thermal performance is explored using CFD simulation. The heat exchanger uses helium gas as the working fluid and operates between 300 K and 30 K. The curve of each tube in the bundle is generated by different 3D sinusoidal equations, and the tubes at adjacent layers are twisted together thereby producing the same end-to-end length for each tube. By simulating a spiral wound heat exchanger using different turbulent equations and comparing the results with experimental data from literature, the k-omega SST model is found to be the most suitable one to simulate this kind of geometry. Nusselt numbers and friction factors are obtained under different Re values and compared with those of standard spiral wound heat exchangers. The creative twisted geometry can improve the Nu number although also increasing the friction factor. Geometry parameters such as pitch length are being further explored to obtain an optimal thermal performance.

Studi performa aerodinamis turbin hidrokinetik Savonius dengan 2 semicircular blade-sharp leading edge

This current investigation was conducted to study the aerodynamic characteristics of Savonius hydrokinetics turbine with semicircular blade-sharp leading edge. The influences of blade thickness and freestream velocity were simulated using ANSYS FLUENT with k-w SST model. The results show that the flow structure changes with increasing turbine rotation in which the flow complexity is formed at a larger rotation angle. The coefficient of torque and power for thin blades is higher than for thicker turbine blades and its values increase with the increase in the freestream velocity.

Numerical analysis of a pre-chamber vortex burner with a steam blast atomizer

The combustion of diesel fuel in a pre-chamber vortex burner with a steam blast atomizer has been studied numerically. The well-proven k-w SST (URANS) model was chosen for calculations. Combustion was simulated using the Eddy Dissipation Concept (EDC) model, taking into account detailed chemical mechanisms in turbulent reacting flows. The results of testing the selected mathematical model showed good agreement of calculations with the known experimental data, a high agreement of the results was achieved: temperature, CO, NOx, O2, and CO2. The influence of steam and fuel flow rates on the flow structure and physicochemical processes in the burner and at the nozzle outlet has been studied. The structure of the flow inside the burner was shown. A high-velocity jet of steam ejects fuel, oxidizer flow and hot combustion products, forming a large zone of circulation and intense mixing. The influence of burner operating regimes on fuel underburning and environmental performance has been investigated. It was found that in the selected range an increase in the relative steam flow rate leads to almost complete combustion of fuel inside the burner. In the combustion chamber with a natural air supply, the excess air ratio was (0.96–1.23). For the considered fuel flow rate of (0.8–1.2 kg/h), the concentration of toxic emissions meets the environmental standard EN:267 – CO < 40 ppm, NOx < 50 ppm. The minimum emissions of CO = 5 ppm and NOx = 27 ppm are achieved at mass steam concentration of 44–50%.

Numerical Study of Different Models for Turbulent Flow in 90° Pipe Bend

The investigation of the turbulence statistics for single-phase turbulent flow around pipe bends have mainly been experimental. Considering the cost-effectiveness of the numerical computational fluid dynamics (CFD) compared to experimental measurement, this work aims to study the accuracies of different CFD models, and establish their functionality and limitations. This paper investigates the capabilities of different numerical turbulence models and spatial discretization schemes for CFD analysis of a pipe bend. The pipe has a curvature radius which is seven times the inside diameter and a Reynolds number of 34132. The numerical modelling was developed on the commercial CFD software, ANSYS Fluent, evaluating the following viscous models:,, Spalart-Allmaras and Reynolds Stress Models. The streamwise velocities of the flow at cross-stream planes along the bend at 45º and 75º were computed for each of the turbulence models under different discretization schemes. The numerical results were compared against the existing experimental data for streamwise velocity, in order to investigate the accuracies of the different models. The results showed that the realizable K-E and Spalart-Allmaras models exhibited the best agreements with the experimental measurements, with respective average errors of 3.83% and 3.27% under the first-order spatial discretization scheme. It was also observed that the velocity profiles obtained through the K-W models (Standard and BSL), Transition SST and Reynolds Stress models exhibited better correlation with the experimental velocity profiles within the velocity transition region.

Numerical and Experimental Investigation of the Effect of Micro Restriction Geometry on Gas Flows through a Micro Orifice

This study experimentally and numerically investigates the effects of the nozzle/needle distance (clearance) and supply pressure on single phase compressible gas flow in a micro orifice with needle restriction, which play important roles in many engineering applications such as cryogenic cooling and MEMS (microelectromechanical systems) device cooling. Nitrogen was used as the working fluid at supply pressures ranging from 10 to 50 bars, while the conical needle draft angle was 15°. The nozzle/needle distance (clearance) was changed from 100 µm to 500 µm. From the experimental point of view, the load provided by the working fluid over the needle was measured by a load sensor. For the numerical analysis, six turbulence models and three wall treatments were considered in numerical simulations. The effect of micro restriction on high-pressure micro-gas flows was further assessed by numerical modeling. It is evident from the results that the utilized turbulence model has a considerable effect on the computed results. The k–ε standard and Spalart–Allmaras models were found to be not suitable for modeling micro-scale gas flows with restriction. On the other hand, the k–ε realizable and k–ω SST models exhibit the best performance in predicting the results.

Conjugate heat transfer investigation of impingement cooling for ribbed internal passage of a turbine vane

In this study, the effect of internal cooling configuration on overall cooling effectiveness of gas turbine vane is investigated using conjugate heat transfer approach. The C3X turbine vane with internal cooling and a turbine vane leading edge model with combined impingement and film cooling scheme are used as primary cases. An impingement cooling configuration is designed in order to enhance cooling effectiveness on the leading edge of the internally cooled C3X vane. In an attempt to further improvement, two rows of ribs are added on regions where impingement jets do not cover. In the leading edge model, the effect of modification for internal cooling channel and within film cooling holes are investigated by adding different rib configurations in those regions. The SST model is adopted for turbulence modeling in fluid zones. In the C3X vane, overall cooling effectiveness is generally enhanced using impingement cooling configuration. Furthermore, span wise distribution of overall cooling effectiveness becomes uniform in the leading edge of the vane. In the leading edge model, it is found that overall cooling effectiveness is varied due to the change in distribution of coolant flow in internal cooling channel and on external surface of the vane by adding ribs in internal cooling channel. The case with ribs perpendicular to the internal channel cross flow provides higher overall effectiveness. The results also indicate that cooling performance of the film cooled vane is sensitive to the location of ribs installed within film holes. The interaction between coolant flow and hot gas flow and its contribution in cooling performance of the vane are elaborately discussed for the leading edge model.

Local heat/mass transfer distributions on the bottom surface of a cavity exposed to an approaching turbulent boundary layer: Aspect ratio effects

We investigate convective transport from the bottom surface of rectangular cavities of depth d exposed to an oncoming boundary layer flow, using experimental and numerical techniques. The effects of cavity width W are explored for cavities with different lengths L in the downstream direction. Depending on the value of L/d (0.52≤L/d≤10), the approaching boundary layer separates and reattach on the bottom surface and establish a new boundary layer, or skims past the open face of the cavity. This results in significantly different convective transport coefficient distributions on the bottom surface. As cavity width is reduced, three-dimensional effects arise, with interaction of vortex systems on the cavity floor. Detailed spatial distributions of the transport coefficient are captured using a mass transfer technique based on naphthalene sublimation. Further insight into the flow structure responsible for the observed distributions is gained through numerical simulations using a k−ω SST model that is first validated using the experimental results by using a heat/mass transfer analogy factor. Flow streamlines from the computations are used to explain how the time averaged streamlines affect the heat transfer at the bottom surface.

발사체 기저 유동 해석을 위한 2-방정식 난류 모델의 압축성 보정

Explicit compressibility correction methods have been applied to two-equation RANS turbulence models for analyzing the base flow and the entire flow field of a projectile. First, supersonic base flow at a specific Mach number has been analyzed to compare performances of the various compressibility corrections. Base flows at various Mach numbers and Reynolds numbers with Ristorcelli’s compressibility correction applied to κ-ω SST model have been computed, and compared with the experimental results. Lastly, transonic flow analyses of a secant-ogive-cylinder projectile have been performed with Ristorcelli’s compressibility correction. It is found that Ristorcelli’s compressibility correction gives considerable improvement in predicting the base pressure and drag at various flow conditions.

Study of the airflow and vortex distributions in a long-narrow enclosed space

In an aircraft cabin, there is a great influence of indoor air quality on the physiological and mental health of passengers. To promote indoor air quality, this research performed experiments and CFD to analyze the flow field characteristics in an aircraft cabin. This study investigated the airflow characteristics of a full-scale cabin using a scaled model. The experimental results indicated that the supply air jet easily formed vortex structures around the chest and head zones of the occupants. The airflow was unstable at the cross-section and longitudinal scales. The Transition SST (4eqn) model could accurately simulate the flow field, and the supply air jet alternatively controlled the cross-section flow field, induced the unstable phenomena spatially and temporally. The vortex structures around the occupants produced and disappeared in both time and space. It showed the instability of the airflow in the aircraft cabin. And this instability of the airflow could induce the dissipation of vortex structures in the time series. This enhanced the unstable distribution of vortex structures. This study further clarifies the distribution of the velocity field and provides references for the futural design of airflow in aircraft cabins.

Numerical simulation of sodium mist behavior in turbulent Rayleigh-Bénard convection using new developed mist models

In order to evaluate the mist behavior in the cover gas region of Sodium-cooled Fast Reactors (SFRs) in good accuracy, turbulent model for Rayleigh-Bénard convection (RBC) was selected, and the Reynolds-averaged number density and momentum equations for mist behavior were developed and incorporated into the OpenFOAM code. In the first stage, the RBC in a simple parallel channel was calculated using Favre-averaged k-ω SST model. The average temperature and flow characteristics agreed well with results from DNS, LES, and experiments. Then the basic heat transfer experiment simulating the cover gas region of SFRs was calculated using this turbulent model and new mist models. The calculated average temperature distribution in the height direction and the mist mass concentration agreed well with the experimental results. We developed a method that could simulate the mist behavior in turbulent RBC environments and the cover gas region of SFRs with high accuracy.

Evaluation of Different Turbulence Models at Low Reynolds Number for the Flow over Symmetric and Cambered Airfoils

This paper presents an evaluation of five different turbulence models by comparing the numerical data derived from these models using ANSYS Fluent with experimental data at a Reynolds number and a Mach number of 0.05 × 106 and 0.015 respectively based on the centerline chord of the airfoil for the flow over NACA 0012 and NACA 2412 airfoils. Moreover, the aim of the present study is to demonstrate the difference in aerodynamic characteristics of the airfoils in order to find aerodynamically more advantageous airfoil. It is concluded that Spalart-Allmaras model and k-ω SST model are capable of providing the most accurate prediction for lift coefficient at a low angle of attack for both airfoils. Standard k - ε model gives a slightly low value of lift coefficient at low angle of attack and slightly high value of lift coefficient at high angle of attack for both airfoils. k-ω SST model, Spalart-Allmaras model, Transition k-kL - ω model, and γ-Rⅇθ Transition SST model can predict drag coefficient reasonably at low angle of attack. At a high angle of attack, however, no turbulence model is able to give a satisfactory prediction for lift coefficient as well as drag coefficient, which implies that these models are unable to predict post-stall characteristics. NACA 2412 airfoil produces more lift coefficient than that of the NACA 0012 airfoil at all angles of attack. Moreover, the drag coefficient of NACA 2412 airfoil is less than that of the NACA 0012 airfoil, which implies that NACA 2412 airfoil exhibits better aerodynamic performance. The lift to drag coefficient ratio of NACA 2412 airfoil is also higher than that of the NACA 0012 airfoil indicating NACA 2412 airfoil to be more fuel economic.

MODELING OF THE FLOW AROUND A SQUARE CYLINDER WITH HYBRID TURBULENCE MODELS

The development of computing resources has played an exceptional role in the development of turbulence modeling. However, simulation of a real flow is still a significant problem if high accuracy of simulation results with low computational resources is required. Therefore, the use of hybrid models is a promising direction for solving this problem of computational fluid dynamics. When using hybrid models, modeling of near-wall flows is carried out using RANS models, while far from the wall, LES models are used. In this work, we used the k - ω SST and DDES models. The aim of the work is to identify a suitable turbulence model that could give accurate and reliable results for practical engineering applications. To evaluate the model used in this work, the problem of modeling the air flow around a square cylinder is considered. Comparison of the results of numerical calculations with the corresponding experimental data shows that the use of the hybrid k - ω SST()-DDES model is promising.

The Effects of a Morphed Trailing-Edge Flap on the Aeroacoustic and Aerodynamic Performance of a 30P30N Aerofoil

This paper presents initial results on the aeroacoustic and aerodynamic effects of morphing the trailing-edge flap of the 30P30N aerofoil, over five flap deflections (5–25°), at an 8° angle of attack and a Reynolds number of Re=9.2×105. The Ffowcs-Williams–Hawkings acoustic analogy estimates the far-field noise, whilst the flow field is solved using URANS with the four-equation Transition SST model. Aerodynamic and aeroacoustic simulation data for the 30P30N’s full configuration compare well with experimental results. A Courant number (C) ≤ 1 should be used for resolving tonal noise, whilst a C of up to 4 is sufficient for broadband noise. Sound pressure level results show an average 11% reduction in broadband noise across all flap deflections and frequencies for the morphed configuration compared with the conventional, single-slotted flap. The morphed flap eliminates the multiple tonal peaks observed in the conventional design. Beyond 15° flap deflection, the morphing flap achieves higher stall angles, but with increased drag, leading to a maximum reduction of 17% in Cl/Cd ratio compared with the conventional flap. The methodology reported here for the 30P30N is a quick tool for initial estimates of the far-field noise and aerodynamic performance of a morphing flap at the design stage.

Numerical Investigations of Aerodynamic Characteristics Prediction of High-lift Low Reynolds Number Airfoil

The Micro Aerial Vehicles (MAVs) operate at a critical range of low Reynolds number (Re). The implementation of the low (Re) aerodynamics for MAVs has brought interest into the study of high-lift low Re airfoils. Such investigations may bring new insight into the aerodynamic performance of MAVs flights. The aim of the current investigation is to exam different numerical methods in the aerodynamics prediction of high-lift low Reynolds number S1223 airfoil. For that purpose, the Spallart Allmaras (S-A), two equations SST K-ω and the four equations transition γ-Reθ SST turbulence models were used. Results revealed that the SA turbulence model can predict the pre-stall low angles of attack and provides a good agreement with experimental data and XFOIL results. Whereas the two-equation model SST-enhanced K-ɷ and the transition SST models predict better the unsteadiness of the stall behaviour. XFoil accurately predicts the highest lift coefficient, even if it occurs at a lower angle of attack. These results showed the promising ability of the transition SST selection in predicting the stall behaviour.

An eddy-viscosity model for turbulent flows of Herschel–Bulkley fluids

This article presents a new turbulence closure based on the k-ω SST model for predicting turbulent flows of Herschel–Bulkley fluids, including Bingham and power-law fluids. The model has been calibrated with direct numerical simulations (DNS) data for fully-developed pipe flow of shear-thinning and viscoplastic fluids. The new model shows good agreement in the mean velocity, average viscosity, mean shear stress budget and friction factor. The latter compares well also against correlations from the literature for a wide range of Reynolds numbers. With the new model, improvements are also observed in the iterative convergence, which is often difficult for calculations with yield-stress fluids. Additionally, three eddy-viscosity models for Newtonian fluids, namely the k-ω SST, k-kL and Spalart–Allmaras model, have been tested on turbulent Herschel–Bulkley flows. Results show that (i) the new model produces the best prediction; (ii) the standard SST model may be considered for simulations of weakly shear-thinning/viscoplastic fluids at high Reynolds numbers; (iii) the k-kL and the Spalart–Allmaras models appear to be unsuitable for turbulent Herschel–Bulkley flows. The new model is simple and appealing for engineering applications concerned with turbulent wall-bounded flows and is presented in a formulation that can be easily adapted to other generalised Newtonian fluids.

OpenFOAM을 이용한 평판 팬 형상 막냉각 홀 하류에서의 막냉각 특성 연구

In this study, a numerical analysis was performed for a 7-7-7 fan-shaped film cooling hole on a flat plate using OpenFOAM, a well-known open source CFD code. To assess the availability of compressible flow solver in the OpenFOAM, a numerical analysis using Ansys CFX under the same conditions was also performed. The OpenFOAM results using RANS with κ-ω SST model confirmed the influence of the spatial discretization schemes, such as Upwind, linearUpwind and LUST, and compared with the CFX result. A comparative analysis using OpenFOAM with linearUpwind scheme according to the blowing ratio ranged between 0.5 and 2.0 was performed and the OpenFOAM results were compared with the CFX results under the same conditions. In addition, the numerical analysis results were compared with the experimental results. The distribution of film cooling effectiveness in the OpenFOAM result becomes thinner than that of the CFX result as the blowing ratio increases. It shows that the coolant flow is lifted off from the adiabatic wall at the high blowing ratio and the OpenFOAM results have more interaction between mainstream and coolant flow than the CFX results due to difference between spatial discretization schemes. In overall, the distribution patterns of film cooling effectiveness are different between the numerical results and experimental results and the results of the laterally averaged film cooling effectiveness both from OpenFOAM and Ansys CFX are higher than those of the experiments. In term of calculating the averaged effectiveness for the lateral direction and the specific area, the result of the OpenFOAM shows closer to the experimental result as the blowing ratio increased. Current numerical study using the OpenFOAM shows the feasibility for resolving the film cooling flow behavior over the flat plate and demonstrates possibility of replacing commercial codes.

A study of the heat transfer of an atomizer gas jet impinging perpendicular on a circular cylinder

This contribution presents the methodology and results from an experimental and numerical study of the heat transfer behavior of the gas-only jet flow from a close-coupled atomizer (CCA) configuration impinging on a heated cylindrical surface. A set of experiments are conducted under different operating conditions (gas pressures 0.6, 0.8 and 1.0 MPa) to measure the local heat transfer coefficient (HTC) on the surface of the cylinder by recording the cooling curve at specific locations along circumferential and axial directions. The numerical study of the heat transfer is executed by employing computational fluid dynamics (CFD) under the same conditions as in the experiments. The Transition SST model is selected for turbulence closure as it obtained results most close to the experimental ones. Predictions of HTC on the cylindrical surface are derived from this model with variable parameters, i.e., nozzle-to-substrate distance (110, 130 and 150 mm), diameter of the cylinder (80, 100, 120 mm) and the temperature difference between the cylinder and ambient temperature (20–730 K). In addition, the gas flows from a circular nozzle and the atomizer configuration with same exit area are compared by the CFD simulation, which shows that the gas jet flow becomes self-similar when the distance to the nozzle is > 80 mm. The experimental and numerical results both show that at each measured position the heat flux q˙ obtains a linear relationship with the temperature difference. The fitted line in the stagnation region has a small negative intercept while that at other positions is close to 0. The local HTC variation in the circumferential and axial directions on the cylinder surface and the parameters affecting the distribution of the HTC are outlined and discussed.