K-omega SST Turbulence Model Research Articles

Determination of Optimum Outlet Slit Thickness and Outlet Angle for the Bladeless Fan Using the CFD Approach

Bladeless fans are more energy efficient, safer due to the hidden blades, easier to clean, and more adjustable than conventional fans. This paper investigates the influence of the airfoil’s outlet slit thickness on the discharge ratio by varying the outlet slit thickness of an Eppler 473 airfoil from 1.2 mm to 2 mm in intervals of 0.2 mm by using a k-omega SST turbulence model with an all y+ wall treatment used to numerically simulate in CFD. The computational results indicated that smaller slits showed higher discharge ratios. The airfoil with a 1.2 mm slit thickness showed a discharge ratio of 18.78, a 24% increase from the discharge ratio of the 2 mm slit. The effect of outlet angle on the pressure drop across the airfoil was also studied. Outlet angles were varied from 16° to 26° by an interval of 2°. The airfoil profile with a 24° outlet angle showed a maximum pressure difference of 965 Pa between the slit and leading edge. In contrast, the 16° outlet angle showed the least pressure difference of 355 Pa. Parameters such as average velocity (U), turbulent kinetic energy, the standard deviation of velocity, and outlet velocity magnitude are used to assess the performance of airfoil profiles used in bladeless fan.

A wide-speed-range aerodynamic configuration by adopting wave-riding-strake wing

The wide-speed-range characteristics of aerodynamic configuration are critical to the design of the horizontal take-off and landing aircraft. To address this problem, the work proposes a wide-speed-range aerodynamic configuration by assembling a waverider to the aircraft with arrow-shaped wing. To enhance the aerodynamic performance of this configuration, surrogate optimization method is applied to the airfoil of the arrow-shaped wing. Thus, the optimized airfoil with double “S” cambers on the lower surface, and a small leading-edge radius is obtained. The aerodynamic performance of the whole aircraft in the wide-speed range has been investigated numerically by means of the three-dimensional Reynolds-averaged Navier-Stokes (RANS) equations coupled with the SST k-omega turbulence model. At subsonic conditions, the waverider can act as a strake-wing to induce vortex from the leading edge of the upper surface. With the large sweep arrow-wing, the subsonic aerodynamic performance is improved by utilizing the vortex lift. At supersonic conditions, wave-riding characteristics as well as the small leading-edge radius wing can effectively reduce the wave-drag. Overall, the lift-to-drag ratio of this configuration is not less than 5.4 at 4-degree angle of attack within Mach number 0.5–7, indicating that this configuration provides outstanding hypersonic aerodynamic performance as well as fairly acceptable subsonic aerodynamic characteristics.

Performance investigation for CRMC and CPM ejectors applied in refrigeration under equivalent ejector geometry by CFD simulation

In this paper, one of the remaining questions for ejector design, “Does the constant rate of momentum change (CRMC) ejector provide better performance than the constant pressure mixing (CPM) ejector under identical ejector area ratio, ejector length, and operating conditions?”, has been answered. Two steam ejector designs operating with the various boiler and evaporator temperatures were simulated by the SST k-omega turbulence model. The present computational fluid dynamics (CFD) model produced a reasonable agreement with our previous published experimental data. The upstream operating conditions were simultaneously considered to assess the better performance ejector design with the help of the primary expansion coefficient. The predicted results revealed that the CRMC ejector showed an advantage in entrainment ratio and a disadvantage in critical condenser pressure. However, the ejector efficiency comparison confirmed that the CRMC ejector design provided better performance than the CPM ejector design for a primary expansion coefficient greater than unity. The maximum percentage improvement of ejector efficiency was 32.418%.

AERODYNAMIC ANALYSIS IN THE DESIGN OF AN ELECTRIC VEHICLE MODEL TOBACCO STYLE M-164 WITH COMPUTATIONAL FLUID DYNAMIC (CFD) METHOD

The aerodynamic aspect is one of the most important things in the automotive sector which is used to find information on the performance of an aerofoil model design. The performance of an aerofoil through streamflow associated with fuel consumption which means the higher the air speed, the greater the resistance received, so that the fuel consumption will be greater. At this case, fuel consumption can be reduced by creating an aerofoil model design that maintain great aerodynamic to minimize drag forces. The affects of streamflow around the vehicle are discussed in this papper. This research simulated 3D electric vehicle Tobacco Style M-164 in steady condition with various velocities, i.e. 50 km/h, 60 km/h, 70 km/h, and 80 km/h. This simulation use the Tethahedron mesh model and run in SST k-omega turbulence model. The affects can be observed with the quantitative and qualitative data. The quantitative data used as measurable data were Maximum Fluid Pressure, Drag Force, and Coefficient of Drag (CD). The quantitative data is shown to provide a better visual explanation of the streamflow affects. The qualitative data shown in this paper are velocity contours, vectors, and pathlines. The value of the maximum fluid pressure and drag force is directly proportional to the increase in velocity stream. The coefficient of drag decreased as the free stream increased with a percentage decrease of 2.48%. The average value of the coefficient of drag (CD) from this research was 0.318.

Numerical Study of Oil-water Separation in Inline Axial Hydrocyclone

The fluid mixture hydrocyclone is an excellent tool for downhole oil/water separation (DOWS) for high water cut. In the present work the flow through inline axial inlet hydrocyclone is investigated computationally using ANSYS-FLUENT-19 software. The three dimensional continuity and momentum equations with SST k-omega turbulence model are used to simulate the strongly swirling, turbulent flow. Oil/water two phase mixture treated as the working fluid, water is considered as the primary phase and oil is the secondary phase. The considered oil volume fraction this work is 0.25 and flow split is 0.3 for three different flow rates of (14, 28, 56) m3/hr corresponding to Reynold's number range of (1.6 to 6.6)*104. The pressure and velocity fields were analyzed in the whole hydrocyclone with core recirculation. The results are helpful to predict the flow motion inside the cyclone to estimate the oil/water separation process. The present work indicates that the water purity at cyclone exit was 90%, while the obtained oil purity was 38%.

Computational Fluid Dynamics Study of Wing in Air Flow and Air–Solid Flow Using Three Different Meshing Techniques and Comparison with Experimental Results in Wind Tunnel

The main purpose of this work is to simulate the flow of air and solid particles over a wildfire and to investigate the single and multiphase flow over the surface of a custom-designed wing with an Eppler-420 airfoil including an appendant custom-designed blended winglet. The wing is the result of a conceptual and preliminary design of a small-scale unmanned aerial vehicle (UAV) designed to assist in firefighting. The fire embers will be simulated in the Ansys Fluent commercial code as solid particles injected in the continuous phase, in an Euler–Lagrange approach. Primarily studied were the response of the model in air and air–solid flows, as well as the impact on aerodynamic efficiency due to the existence of the second phase. Moreover, the effects of unstructured, structured and mosaic poly-hexcore meshes are investigated and compared. The computational fluid dynamics (CFD) simulations, were implemented using a pressure-based solver, spatial discretization was conducted with a second-order upwind scheme, and the k-omega SST (k-ω SST) turbulence model was applied. Meanwhile, the two-phase flow was simulated using the Discrete Phase Model with reflect boundary condition on the surface of the wing and two-way coupling between continuous and discrete phase. To validate the results, experiments were conducted in a subsonic wind tunnel using a 3D printed model of the wing. The results show good agreement between simulations and experiments, with the structured mesh coming closer to reality, followed by the mosaic and unstructured meshes, respectively. Finally, a reduction in the aerodynamic efficiency of the wing section is observed, due to the presence of solid particles.

Computational Analysis of 2D Transition Inlets for Supersonic Capture

Scramjets are the futuristic propulsion technology for supersonic and hypersonic flights. Transition inlets form one of the major technologies to make the Scramjets more utilizable in reality. This paper deals with the 2-dimensional computational analysis of the supersonic capture of the transition inlets using the finite volume approach of ANSYS. The main objective of this paper is to demonstrate the advantage of the transition inlets over the conventional ramp inlets. This study involves sharp-edged ramp, smooth-edged ramp and transition ramp. Simulation of the inlet at supersonic capture has been done using the SST k-omega turbulence model along with a density-based solver with Roe flux. The performance of the inlet is calculated in terms of the total pressure recovery. Along with this the static pressure, Mach number variation through the inlet and the internal reflected shocks at the isolation chamber are studied. The 2D study of the transition inlet is highly important because the effects of the notch can be studied in depth using the 2D models with minimal number of errors. The comparative study of the 2D transition model helps to validate the advantage of the transition ramps over the conventional ramps. Supersonic capture analysis is inevitable as it determines the starting condition of the inlet. In this paper, the analysis is done for the Mach numbers of 2, 3, and 4.

Vibration Analysis of Cylindrical with Splitter Plates under Different Deflection Angles at High Reynolds Number

In order to study the influence of the splitter plate in the elastic support system, the SST k-omega turbulence model is used to solve the problem, and the cylindrical system with splitter plate is numerically simulated by overset mesh. This paper studies the effect of the splitter plate on the vibration system at different deflection angles. The results show that the splitter plate has little effect on the system when the deflection angle is low. When the deflection angle is about 10 degrees, the system vibration characteristics will have a sudden change, the amplitude will decrease, and the vortex frequency will increase. Between the deflection angle of 10 degrees and 45 degrees, as the deflection angle increases, the amplitude increases and the vortex frequency decreases. It can be seen from the motion trajectory that the deflection angle changes suddenly after 10 degrees, and the system has a very small amplitude between 10 degrees and 25 degrees. In this declination interval, the splitter plate controls the vibration of the cylindrical system better.

CFD modelling of the flow in zero-secondary flow ejectors: a sensitivity analysis to numerical parameters

This paper presents a sensitivity study of various CFD simulation parameters conducted in the case of a 2D axisymmetric ejector operating without induced flow. The influence of numerical parameters (solver, discretisation scheme, mesh and turbulence model) is investigated by comparing the various CFD results obtained (pressure, velocity, Mach number, and mass flow rate) with each other. The influence of the turbulence model is closely examined by comparing CFD results with the velocity measurements obtained by particle image velocimetry. The rules to be respected to achieve correct CFD simulation of the flow in supersonic ejectors are proposed. The use of the pressure-based coupled solver associated with the SST k-omega turbulence model is recommended. The terms of energy and pressure can be solved using first-order discretisation while the other equations (momentum, turbulent quantities) require second-order discretisation to correctly predict the supersonic flow with shocks.

Influence of input methods on jet mixing in a four-vortex chamber

In this work, a numerical study of aerodynamics and interaction of vortex structures is carried out depending on the organization of the injection of jets in the chamber. For unsteady calculation of aerodynamics, the URANS approach based on the k-omega SST turbulence model was used. The calculation results show the conditions for the formation of a stable four-vortex structure. The options are also identified in which a significant restructuring of the flow structure occurs.

Oscillating Water Column Wave Energy Converter for Low Wave Height Conditions

For continuous and uninterrupted extraction of energy from marine wave motion, majority of wave energy extraction systems employ bi-directional turbines. The aerodynamic loss due to symmetrical placement of guide vanes causes a major loss in power output of the system. To optimize this problem, researchers have developed and tested a variety of oscillating water column air turbines. Most commonly used are the axial turbines because of their simplicity and operational ease. The present work focuses upon design of an oscillating water column energy extraction system based on uni-directional axial impulse turbine with a novel rectifying system arrangement which primarily focuses to minimize the losses due to downstream guide vanes and in turn shoot up the power output for low wave height conditions. A numerical model was developed and investigated using RANS equations and k-omega SST turbulence model. The results obtained portrays that the proposed flap based bi-directional impulse system is operationally viable and produces substantially greater power output in comparison to conventional bi-directional and uni-directional turbine systems under low wave height conditions. A hybrid choking scheme was followed which resulted in additional power output. Results show that full choking of the idle turbine is ensured during the inhalation cycle, which was not possible in existing models. During the exhalation cycle, additional power output was also obtained from the secondary turbine i.e., front end turbine during exhalation cycle. The proposed system generates maximum total power output at around flow coefficient of 1.

Aerodynamics Analysis on Wings with Winglets and Vortex Generators

This project was based on the principle of designing, simulating and developing an inexpensive, aerodynamically efficient and regular class electric powered RC aircraft. This prototype was designed to have the maximum strength to weight ratio with minimum drag coefficient (and highest lift coefficient). Moreover, all constraints provided by SAE International competition were followed. The investigation was conducted for the complete airplane and for wing optimization. The model was numerically investigated with ANSYS Fluent 16.1 through the SST K-Omega turbulence model at Reynolds number of 360,000. Once the results were obtained, model and result verification were done by wind tunnel test to validate the data. It was concluded that the airplane with 45° winglet has the highest lift force with minimal drag and 45° winglet was further modified with rectangular and triangular vortex generators in order to further enhance its aerodynamic efficiency for a range of Angle of Attacks (AOA).

Effect of aspect ratio on the recirculation region of 35° Ahmed body

ABSTRACT This paper reports a numerical investigation of the effect of aspect ratio (AR) on the flow structure around the 35° Ahmed body. The AR is defined as the ratio of length to the height of the model. A total of five ARs are considered at a Reynolds number based on the height of the Ahmed body of 7.8 105. The flow governing equations are solved in the FLUENT solver using the SST K-Omega turbulence model. It is found that the drag coefficient (Cd) slightly increases at the AR1 4.2%. As the aspect ratio increases, the drag coefficient decreases. The analysis reveals that early flow separation in the AR1 causes a reattachment at the rear slant end, which leads to an increase in drag. It also highlights that there exists a minimum aspect ratio beyond which the drag increases. and there is a limit in the increasing order beyond which the drag will begin to reduce. Further, it demonstrates that there is no change in the recirculation region and consequently drag coefficient is not a function of the recirculation region. Thence, a clear understanding of the effect of the length-based aspect ratio can help to optimize the length during design.

Investigations of HAWT Airfoil Shape Characteristics and 3D Rotational Augmentation Sensitivity Toward the Aerodynamic Performance Improvement

This study investigates the impacts of dierent airfoil shapes on the 3D augmentationand power production of horizontal axis wind turbines (HAWTs). The aerodynamic eect fromchanging the leading and trailing edge of the airfoil is the emphasis of the research. Varied powerproduced from modifying sensitivity on 3D augmentations, caused by revamping airfoil shapes, areshown. The 3D correction law, considering the chord to radius ratio and the blades’ pitch angle inthe rotation, is applied to the airfoil lift coecients. The blade element method (BEM) embeddedin the software Qblade with modified lift coecients simulates the power productions of threewind turbines from these airfoils. The comparisons of the boundary layer characteristics, sectionalforces, and inflow angle of the blade sections are calculated. The k-omega SST turbulence model inOpenFoam visualizes the stall and separation of the blades’ 2D section. The airfoils with a roundedleading edge show a reduced stall and separated flow region. The power production is 2.3 timeshigher for the airfoil constructed with a more rounded leading edge S809r and two times higher forthe airfoil S809gx of the symmetric structure.

Numerical investigation of the pressure and friction resistance of a high-speed subway train based on an overset mesh method

The aerodynamic resistance induced by a high-speed metro train entering and operating in a tunnel with a speed of 120 km/h is simulated using a three-dimensional, compressible turbulence model. An overset mesh method is adopted to solve the moving boundary problem, and the flow field around the train is simulated with a k-omega SST turbulence model to obtain accurate stress values at the walls. The selected model is verified with experimental and numerical data from the literature. Then, numerical simulations are performed to analyse the formation mechanisms of the pressure and friction drags. The aerodynamic drag basically stabilizes after the expansion wave passes the train head. The results reveal that the variations in friction resistance are related to the direction of the Mach wave, and this trend differs from that observed for pressure resistance. Mach wave influences the velocity where it passes, and further influences the friction drag. Result shows that friction drag of the train increases when encounter with compression wave propagated from the front or expansion wave propagated from the back, and decreases otherwise. The effects of the blockage ratio on the maximum and average pressure and friction resistance values of each train section are evaluated based on fitting functions. The predicted aerodynamic drag varies with the blockage ratio and for each train section, and the results are summarized and compared with predictions and experimental data from the literature. The variations in tunnel resistance and the overall trend are in good agreement with the previous results. Therefore, the findings presented in this study may provide a reference for the design of high-speed subway tunnels.

Conjugate heat transfer of impingement cooling using conical nozzles with different schemes in a film-cooled blade leading-edge

In this paper, the effect of utilizing different schemes of conical nozzles for impingement cooling is studied in the conjugate heat transfer in a film cooled blade leading-edge. Three conjugate cooling schemes (tangential, inline normal, staggered normal) are analyzed and compared at different nozzle Reynolds numbers from 5000 to 25,000 and different temperature ratios from 0.5 to 0.85. The SST k-Omega turbulence model and a very fine unstructured mesh are validated and applied for all simulations. Based on the design, the staggered normal scheme can protect the most critical zone of a blade subjected to the highest temperature (stagnation area) better than the other cooling schemes. The internal cooling performance increases with the nozzle Reynolds number under a fixed temperature ratio. At identical nozzle Reynolds number, the internal heat transfer increases with the temperature ratios from 0.5 to 0.675 while it decreases over 0.675 up to 0.85. The staggered normal scheme achieves an increase in overall Nusselt number by 5.26–9% and by 9.78–21.27% compared to the tangential scheme and inline normal scheme, respectively over the applied range of nozzle Reynolds number. The staggered normal scheme achieves the highest cooling performance internally and externally among the other cooling schemes.

Aerodynamic Optimization of Unmanned Aerial Vehicle through Propeller Improvements

This paper aimed at presenting a number of suggested improvements that can enhance the performance of a multi-rotor Unmanned Aerial Vehicle. Evaluating each suggestion in terms of the added benefits and feasibility concluded a final choice, which is incorporating a sinusoidal leading-edge profile to the propeller. This choice was numerically investigated with ANSYS Fluent 16.1 through the SST K-Omega turbulence model. The performance of the modified propeller was assessed by comparing the lift and drag results to the same propeller with a straight leading-edge under the same conditions. Both models were studied at pre-stall and post-stall conditions to see the performance effect with respect to the angle of attack. The findings of this research showed 7% increase in the lift force and coefficient that were associated with the addition of the sinusoidal leading-edge including improved recovery from stall spanning from angle of attack that extends between 10° to 25°. This research also provides more insights into how the delayed stall and improved lift help the multirotor to extend flight time and carry heavier payloads. It allows for the exploration of the inner working of the sinusoidal leading-edge and its relationship with the flow field over the propeller.

Computational modeling of non-equilibrium condensing steam flows in low-pressure steam turbines

Abstract Condensation occurring in low pressure stages of steam turbines contributes to many losses in efficiency and damage to the stator blades such as corrosion and pitting. This problem has been observed profusely in power generation industries. The purpose of this study is to properly simulate the condensation and shock wave phenomenon at the last stage of the steam turbine and accordingly understand this phenomenon. Numerical simulation was conducted by using ANSYS Fluent and applying k-omega SST turbulence model. The results agreed with the experimental values.

Numerical Simulation and Modal Analysis of External Flow Field of Large Wind Turbine

Aiming at the problems of complex and slow optimization process of large-scale wind turbine blade design and the influence of wind turbine flutter, etc. The numerical simulation analysis and modal analysis of the external flow field of the wind turbine under the rated wind speed are carried out by the hybrid method. A fluid simulation model based on CFD was established. The method of rotating reference frame and SST k-omega turbulence model are used to simulate the external flow of fan wind turbine in FLUENT. The first 6 natural modes of the wind wheel are calculated in Hypermesh/Optistruct. The results show that the hybrid simulation method can quickly obtain the impeller flow field information, and the flow of the tip portion is extremely unstable. In each natural mode, the blade deformation position is basically from the maximum chord length to the tip position. The closer to the tip, the more obvious the blade vibration deformation is. At the same time, the first-order natural frequency of the wind wheel is 0.919Hz, which is greater than 0.382Hz when the rated speed is 12m/s, thus effectively avoiding resonance phenomenon.

Engineering of a backpack ventilation technology for cycling using CFD analysis

Thermoregulation of an athlete during physical activities plays an important role especially in endurance sports such as cycling. Depending on the kind and intensity level of the activity thermoregulation can affect performance and/or thermal comfort. During cycling, especially within the MTB categories, athletes often wear a backpack. The overall goal of the study was to engineer a new backpack ventilation technology utilizing the relative headwind generated during cycling for convective heat transfer between backpack and first clothing layer. Exploration and evaluation of new rear panel designs were done applying a CFD analysis. CFD Analyses were done at AirShaper TM using a steady-state RANS (Reynols Averaged Navier Stokes) method with k-omega SST turbulence model. The CFD analysis of the newly developed rear panel designs exhibit the potential to influence the convective heat transfer especially around the spine region in a positive way during cycling.