Reynolds-averaged Navier-Stokes Method Research Articles

Exploration on Nonaxisymmetric Flow Phenomenon in a Slinger Injector

The slinger is an important configuration of an aeroengine combustion chamber. It is well matched to smaller gas turbines that are more sensitive to cost than larger and more sophisticated models. The slinger combustor is inherently low cost itself, by eliminating fuel injectors and much of the fuel tubing and manifolding and also reducing costs in the requirements of the main fuel pump by operating at fuel delta pressures significantly lower than conventional fuel systems. The slinger's inherent drawbacks of increased combustion liner surface area and less atomization are less of a concern in a lower temperature, lower cost small turbines. The slinger's internal flow is of great significance to fuel atomization. This paper conducts experiments and numerical simulations on the slinger fuel injector. Numerical analysis and high-speed photography of the fuel slinger were applied to investigate the film flow pattern inside the slinger and the liquid phase distribution inside the combustion chamber to predict the flow field in an aeroengine combustion chamber. The transient Reynolds-averaged Navier–Stokes method, the volume of fluid method, and the discrete phase method were adopted in the simulation, and a high-speed camera and the rotational rig were used to perform the experiments. The nonaxisymmetric flow was present in the slinger and the combustor space. In the simulation results, the total mass-flow rate varies with time. Each hole's mass-flow rate value in the slinger is also different at the same time. The Sauter mean diameter (SMD) difference for each injection orifice is relatively small compared with the SMD difference caused by a rotation rate. The spatial distribution of the spray is also uneven as shown in the result of different single discharge channels' mass-flow rates. The experimental photos confirmed the simulation outcomes. The general theoretical analysis was made that these nonaxisymmetric phenomena were driven by the combined action of centrifugal force, surface tension, and instability phenomenon.

Performance Improvement of the Regional Jet CRJ700 Aircraft Equipped with Adaptive Winglets

This research follows a previous study that consisted in analyzing the aerodynamic performance of an aircraft equipped with adaptive winglets compared to an aircraft equipped with fixed winglets. Based on Reynolds-averaged Navier–Stokes methods, it was observed that adaptive winglets help the CRJ700 to reduce its drag by up to 2.90%. Using these aerodynamic results, this research now involves analyzing the climb and cruise performance benefits achieved by an aircraft equipped with adaptive winglets. The methodology presented in this paper details the aerodynamic and performance models used to obtain these new results. A new methodology for calculating the downwash deflection angle from OpenFoam simulations was also developed. The results show that an adaptive winglet can reduce the fuel flow of an aircraft by up to 1.99% in cruise with respect to an aircraft equipped with a fixed winglet. Interesting benefits were also found for climb segments, such as a climb time reduction of up to 128.11 s.

Effects of blade lean on internal swirl cooling at turbine blade leading edges

The blade lean technique has been extensively employed in the design of modern gas turbine blades. Since swirl cooling is a promising alternative for internal cooling techniques at the blade leading edge due to its strongly-enhanced heat transfer, it is thereby vital to completely understand the fundamental flow and heat transfer behavior of swirling flows in a leaned tube to provide guidance for improved swirl cooling design in today's advanced turbine blades. In this study, to model a realistic internal swirl passage, the flow and heat transfer patterns of swirl cooling were numerically investigated within leaned, convergent tubes. To examine the effects of blade lean levels, two leaned tubes with moderate and extra angles were considered. The simulations were carried out using the unsteady Reynolds-averaged Navier-Stokes (URANS) method for a strong geometrical swirl number of 5.3. Furthermore, to demonstrate the necessity of using the unsteady simulation in modeling swirling flows, steady and unsteady RANS simulations were compared against experimental data for a straight tube with constant cross section. Results reveal that the steady RANS method fails to capture the reverse flow in the downstream section of the tube where vortex breakdown occurs, leading to over-predicted axial velocity and under-predicted circumferential velocity. However, the unsteady RANS method provides satisfactory results for both flow and heat transfer, achieving a good compromise between computational efforts and numerical accuracy. In comparison with the straight tube, Dean vortices in the leaned tube decelerate the decay of the swirl in the upstream section, and vice versa in the downstream part by changing the axial velocity profile. In addition to the double helical vortex typically observed in the swirling flow, the inner vortex induced by strong shear in a transition layer between core and ring zones also contributes to enhanced turbulence mixing and thus improves heat transfer. The stronger swirl in the inlet regions of the leaned tubes decreases the turbulence production in the core zone, resulting in a lower flow loss relative to the straight tube. Globally, the extra-leaned tube has an increase of heat transfer coefficients by 5.3% and a reduction of pressure loss by 24.90%, while the moderate-leaned tube has a decrease of heat transfer coefficients by 6.1% and a reduction of pressure loss by 12.89%, relative to the straight tube.

Leading-edge-vortex tailoring on unsteady airfoils using an inverse aerodynamic approach

In this paper, we present an approach to obtain a desired leading-edge vortex (LEV) shedding pattern from unsteady airfoils through the execution of suitable motion kinematics. Previous research revealed that LEV shedding is associated with the leading-edge suction parameter (LESP) exceeding a maximum threshold. A low-order method called LESP-modulated discrete vortex method (LDVM) was also developed to predict the onset and termination of LEV shedding from an airfoil undergoing prescribed motion kinematics. In the current work, we present an inverse-aerodynamic formulation based on the LDVM to generate the appropriate motion kinematics to achieve a prescribed LESP variation, and thus, the desired LEV shedding characteristics from the airfoil. The algorithm identifies the kinematic state of the airfoil required to attain the target LESP value through an iterative procedure performed inside the LDVM simulation at each time step. Several case studies are presented to demonstrate design scenarios such as tailoring the duration and intensity of LEV shedding, inducing LEV shedding from the chosen surface of the airfoil, promoting or suppressing LEV shedding during an unsteady motion on demand, and achieving similar LEV shedding patterns using different maneuvers. The kinematic profiles generated by the low-order formulation are also simulated using a high-fidelity unsteady Reynolds-averaged Navier–Stokes method to confirm the accuracy of the low-order model.

Transition-based constrained large-eddy simulation method with application to an ultrahigh-lift low-pressure turbine cascade flow

A transition-predictive Reynolds-averaged Navier–Stokes (RANS) model is introduced as the Reynolds controlling condition to constrained large-eddy simulation (TrCLES) to improve the ability of this method to predict wall-bounded laminar–turbulent transition flows. In the TrCLES method, the constraint conditions for total Reynolds stress and heat flux are only imposed to the near-wall region in transitional and turbulent boundary layer. The newly proposed method recovers direct numerical simulation in the laminar boundary region, and retrieves the traditional large-eddy simulation method in the far-wall regions. The TrCLES method is validated in simulations of external flow around the Eppler 387 (E387) airfoil and internal flow past the ultrahigh-lift low-pressure turbine T106C cascade. The improved delayed detached-eddy simulation (IDDES) method, CLES method based on full-turbulence shear stress transport model and RANS method with a three-equation transition model are also evaluated in comparison with the available experimental and numerical data. As expected, the TrCLES method can predict laminar separation bubble and separation-induced transition process in both the E387 and T106C flows pretty well. In contrast, neither IDDES nor the original CLES can provide reasonable prediction for the laminar separation-induced transition phenomenon. The validity and fidelity of the TrCLES method are further verified by simulations of the T106C cascade flows in a wider range of exit Reynolds and Mach numbers. It is shown that the TrCLES method can not only predict the time-averaged aerodynamic quantities such as isentropic Mach number and exit kinetic energy loss very well, but also capture the laminar separation bubble and unsteady flow structures with satisfactory accuracy.

Simulation and experimental research on aerodynamic noise of gas turbine 1.5-stage axial compressor

The aerodynamic noise of the axial compressor is one of the significant noise sources of gas turbines, and it has gradually attracted the attention of the majority of researchers. In this paper, the aerodynamic noise characteristics of a 1.5-stage axial compressor were studied through simulations and experiments. A full-channel calculation of a three-dimensional unsteady flow field was computed using the Reynolds-averaged Navier Stokes (RANS) method. Spectral analysis of the static pressure in the tip clearance area was in good agreement with experimental data, which verifies the accuracy of the calculations. The volume and surface sound sources were extracted from computational fluid dynamics calculations to estimate the far-field acoustic characteristics of the compressor. The simulated results of the sound field were verified by a comparison with experimental data. The results show that the sound source intensity of the compressor’s guide vanes is much lower than that originating in the rotor and stator, which indicates that the interaction between the rotor and stator is much stronger than that of the guide vane and rotor. This conclusion is consistent with the unsteady flow field analysis. To investigate the influence of complex geometric structures on sound propagation, three sets of finite element grids were employed for noise prediction. The calculations considering all structures are in the best agreement with the experimental data, which shows that complex structures cannot be ignored when calculating aeroacoustic predictions.

Numerical investigations of a membrane morphing wind turbine blade under gust conditions

Flexibility during flight using elasto-flexible membrane-material systems is an attractive solution regarding loads reduction under unsteady flow conditions. Based on this idea, a wind turbine blade with flexible surfaces is designed from the NASA-Ames Phase VI configuration and investigated under gust conditions. Two concepts are modelled, a flexible as well as a rigid blade geometry. While the rigid concept is only simulated using Unsteady Reynoldsaveraged Navier Stokes (URANS) method, the flexible blade is computed with Fluid-Structure Interaction simulations coupling URANS and Finite Element Method. In both cases, the fluid is modelled with a rigid-body rotation method. The latest enables to take into account the rotation of the blade and, for the flexible case, to simultaneously capture the strong relationship between the flow and the membrane's deformation. The resulting axial force, pressure distribution, vorticity, and flow field velocity are analyzed for both geometries. While the rigid geometry serves as a baseline, the flexible case is investigated, focusing on the difference between rigid and flexible configurations.

Investigation on shock-induced separation loss mitigation method considering radial equilibrium in a transonic compressor rotor

AbstractA shock-induced separation loss reduction method, using local blade suction surface shape modification (smooth ramp structure) with constant adverse pressure gradient with the consideration of radial equilibrium effect to split a single shock foot into multiple weaker shock wave configuration, is investigated on the NASA Rotor 37 for promoting aerodynamic performance of a transonic compressor rotor. Numerical investigation on baseline blade and improved one with blade modification on suction side has been conducted employing the Reynolds-averaged Navier–Stokes method to reveal flow physics of ramp structure. The results indicate that the passage shock foot of baseline is replaced with a family of compression waves and a weaker shock foot generating moderate adverse pressure gradient on ramp profile, which is beneficial for mitigating the shock foot and shrinking flow separation region as well. In addition, the radial secondary flow of low-momentum fluids within boundary layer is decreased significantly in the region of passage shock-wave/boundary-layer interaction on blade suction side, which mitigates the mass flow and mixing intensity of tip leakage flow. With the reduction of flow separation loss induced by passage shock, the adiabatic efficiency and total pressure ratio of improved rotor are superior to baseline model. This study herein implies a potential application of ramp profile in design method of transonic and supersonic compressors.

A study on the flow physics of a supersonic partial admission impulse turbine for different tip clearances

Compared to traditional turbines, supersonic partial admission impulse (SPAI) turbines have significantly different flow physics owing to partial admission configuration and high supersonic flow at the rotor entrance. The objective of the present study is to reveal the intrinsic flow physics of an SPAI turbine for different rotor tip clearance dimensions. Numerical simulations were carried out based on the unsteady Reynolds-averaged Navier-Stokes (URANS) method in an SPAI turbine whose time-averaged relative Mach number at the rotor inlet was up to 2.1. The partial admission configuration led to a severer blockage in the hub region of the rotor entrance than that in the mid-span and tip regions. As a consequence, corner separation occurred near the leading edge of the rotor hub. The tip leakage flow was divided into two vortices. Due to the strong shock/tip leakage vortex interaction, the first vortex broke down and disappeared immediately. The second vortex originated from the leading edge shock foot, migrated downstream toward the mid-span (near the rotor trailing edge). It subsequently interacted with the trailing edge shock and exhibited an expansion process without experiencing a breakdown. Under the unsteady conditions, slight variations were observed in the shock train at the nozzle as the rotor passed. In contrast, due to the partial admission, the blade loading and the rotor leading edge shock experienced significant periodic variations. The rotor blade exhibited the maximum loading when the bulk flow originated from the nozzle flowed toward the rotor blade, whereas the minimum loading was achieved when the nozzle induced wake streamed toward the rotor blade. The leading edge shock/tip leakage vortex interaction occurred periodically, resulting in a periodic vortex breakdown. For the lowest efficiency condition, the highest total to static pressure ratio was achieved and the maximum intensity was exhibited for the leading edge shock of the rotor blade. This generated a significant loss due to the shock and the shock-induced flow separation.

Experimental Techniques against RANS Method in a Fully Developed Turbulent Pipe Flow: Evolution of Experimental and Computational Methods for the Study of Turbulence

Fully developed turbulent flow in a pipe was studied by considering experimental and computational methods. The aim of this work was to build on the legacy of the University of Manchester, which is widely regarded as the birthplace of turbulence due to the pioneering work of the prominent academic Professor Osborne Reynolds (1842–1912), by capturing the evolution of fluid turbulence analysis tools over the last 100 years. A classical experimental apparatus was used to measure the mean velocity field and wall shear stress through four historical techniques: static pressure drop; mean square signals measured from a hot-wire; Preston tube; and Clauser plot. Computational Fluid Dynamics (CFD) was used to simulate the pipe flow, utilizing the Reynolds-averaged Navier–Stokes (RANS) method with different two-equation turbulence models. The performance of each approach was assessed to compare the experimental and computational methods. This comparison revealed that the numerical results produced a close agreement with the experiments. The finding shows that, in some cases, CFD simulations could be used as alternative or complementary methods to experimental techniques for analyzing fully developed turbulent pipe flow.

Multi-objective optimization of a bow thruster based on URANS numerical simulations

In this study, a multi-objective design optimization of a bow thruster, which involved both experimental and numerical analyses, was performed. By changing the chamfer form at the tunnel opening of the bow thruster and the position of the anti-suction tunnel, the optimization procedure aimed to improve the propulsion efficiency, reduce the amplitude of the fluctuating pressure on the tunnel wall, and balance the pressure difference on the hull caused by the speed. First, model tests were conducted to measure the thrust and torque of the bow thruster as well as the fluctuating pressure acting on the tunnel. Numerical simulations were also performed under the same conditions based on the unsteady Reynolds-averaged Navier-Stokes (URANS) method. The accuracy of the numerical results was verified by comparison with the experimental data. Second, the chamfer depth and angle of the tunnel opening and the distance between the anti-suction tunnel and the propeller axis in the length and height directions were taken as the design variables. A sample set that contained 30 sampling points was selected using the optimal Latin hypercube sampling (opt-LHS) method. A surrogate model was built based on the Support Vector Regression (SVR) algorithm, and the multi-island genetic algorithm was utilized during the tuning process of the surrogate model parameters. On this basis, the non-dominated sorting genetic algorithm II (NSGAII) was used for the three-objective optimization and the Pareto solution set was obtained. Due to the inverse relationship between the propulsion efficiency and the fluctuating pressure amplitude, four optimal solutions were selected from the Pareto optimal solution set, and direct numerical computations were conducted to verify the optimization results. The results showed that, compared with the original shape, the fluctuating pressure amplitudes for the four optimal solutions were reduced significantly after the optimization, with a maximum reduction of 18.56%, but their propeller propulsion efficiencies were slightly lower than the original hull. Increasing the chamfer angle and depth significantly reduced the flow-separation area around the tunnel entrance, but it correspondingly increased the flow velocity in the tunnel, which caused the propeller to not work at its highest efficiency point; thus, the propulsion efficiency was reduced to a certain extent. Moreover, the position of the anti-suction tunnel could be determined using the SBD method, but with an increase in the chamfer angle, the location where the jet of the bow thruster re-attached to the hull after mixing with the external flow moved towards the stern. This led to an expansion of the low-pressure area near the rear of the tunnel that correspondingly increased the pressure difference on the hull. If the chamfer angle was large enough, although the pressure difference could be reduced to a fairly low value through the anti-suction tunnel, it could not be balanced completely.

Aerodynamic Characteristics of Morphing Supercritical Airfoils for Aircraft with All-Stage High Performance

Morphing airfoil is a promising technology for future aircraft to realize all-stage high performance. In the present paper, a conceptual aircraft with morphing airfoil is proposed and the aerodynamic characteristics of three types of morphing airfoils (variable-camber airfoil, variable-chord airfoil, and the combination of both morphing styles) are numerically investigated. The baseline airfoil is RAE 2822 supercritical airfoil; the Reynolds-averaged Navier–Stokes method is adopted for numerical simulation of flow around airfoils, and the accuracy of the numerical simulation method is validated by comparing with experimental data. It is found that the variable-camber and -chord airfoil can not only improve the high lift characteristics at take-off stage, but also increase the lift-to-drag ratio at transonic cruise and low-speed task stages during which the required lift is continuously decreasing due to the consumption of fuel. These findings imply that aircraft with proper morphing airfoil can achieve all-stage high aerodynamic performance.

Optimization of Rib Shape and Inclination in a Square Duct With Response Surface Methodology

Abstract This article conducts numerical investigation coupled with Reynolds-averaged Navier–Stokes method on detailed flow field and heat transfer characteristics of ribbed channel with symmetric ribs mounted on two walls. The physical domain is modeled by reference to a practical turbine blade internal cooling channel. The effects of three selected geometric factors of ribs, i.e., rib inclination angle, dimensionless rib height, and dimensionless rib pitch, on the flow and heat transfer are investigated by variable-controlled simulations with the Reynolds number ranges from 5000 to 90,000. The parameter ranges are 30 deg ≤ α ≤ 90 deg, 0.5 ≤ e/w ≤ 1.5, and 5 ≤ P/w ≤ 15 with the rib width w fixed at 1 mm. It is newly found that the friction factor does not follow a monotonical trend with respect to the Reynolds number under certain rib configurations. In addition, three-level numerical calculations about three geometric factors as well as the Reynolds number are conducted with the response surface method (RSM). Quadratic regression model for the targeted response, thermal performance factor (TPF), is obtained. The optimal rib shape for the goal of maximizing the channel overall thermal performance turns out to be e/w = 0.5, P/w = 15, and α = 30 deg as Re is fixed at 30,000.

Hydrodynamic Performance of Open-frame Deep Sea Remotely Operated Vehicles Based on Computational Fluid Dynamics Method

The resistance performance and motion stability of deep sea remotely operated vehicles (ROVs) subjected to underwater motion conditions are studied on the basis of the unsteady Reynolds-averaged Navier-Stokes method combined with the six-degree-of-freedom equation of motion to quickly and accurately predict them. In the modeling process, we consider the complexity of ROV geometry and thus reduce the model to a series of regular geometries to maximize the position and weight of the original components. The grid and value slots of an ROV are divided, and the surface is reconstructed. The forward, backward, transverse, floating, and submerged resistance of ROVs are simulated and compared with existing experimental forces to determine the accuracy of the calculation method. Then, the oblique navigation of the ROV on the horizontal and vertical planes is studied. Furthermore, the motion response of the ROV to direct horizontal motion, heave, pitch, and yaw are studied. The force, moment, and motion time curves are obtained. The stability of ROV motion is analyzed to provide technical support for the safety of ROVs.

NUMERICAL STUDY ON PROPULSIVE FACTORS IN REGULAR HEAD AND OBLIQUE WAVES

This paper applies Reynolds-averaged Navier-Stokes (RANS) method to study propulsion performance in head and oblique waves. Finite volume method (FVM) is employed to discretize the governing equations and SST k-ω model is used for modeling the turbulent flow. The free surface is solved by volume of fluid (VOF) method. Sliding mesh technique is used to enable rotation of propeller. Propeller open water curves are determined by propeller open water simulations. Calm water resistance and wave added resistances are obtained from towing computations without propeller. Self-propulsion simulations in calm water and waves with varying loads are performed to obtain self-propulsion point and thrust identify method is use to predict propulsive factors. Regular head waves with wavelengths varying from 0.6 to 1.4 times the length of ship and oblique waves with incident directions varying from 0° to 360° are considered. The influence of waves on propulsive factors, including thrust deduction and wake fraction, open water, relative rotative, hull and propulsive efficiencies are discussed.

Transient numerical simulations of a cold-flow bidirectional vortex chamber

Bidirectional chambers are well-studied in terms of the flow structure and influence of their input parameters. However, most of the available studies are based on steady-state or time-averaged research methods and do not allow to obtain data on bidirectional flow dynamics over time. The present paper reports on detailed numerical studies based on detached eddy simulations (DESs) and unsteady Reynolds-averaged Navier–Stokes methods applied for two vortex chambers with different aspect ratios. A comparison of the numerical results with the available experimental data shows that the DES method gives the most accurate results on bidirectional flow structure, turbulent fluctuations, and precessing vortex core (PVC) motion. A notable feature of the studied bidirectional flow is the central recirculation zone (CRZ) formation, which is correctly predicted by the DES method only. The presence of a CRZ in a bidirectional flow has a significant effect on turbulent velocity fluctuations and PVC behavior. It is found that CRZ formation leads to a significant decrease in radial and circumferential velocity fluctuations whereas the axial velocity fluctuations are slightly increased. Additionally, the paper reports new findings on CRZ and PVC interaction in bidirectional flows. PVC motion is almost completely nullified by the presence of a CRZ. This can prove useful in many industrial applications of bidirectional chambers, e.g., vortex thrusters and gas turbine combustors. The bidirectional swirling flow transient properties studied in this paper could assist in determining the most efficient operational modes and geometric configuration of industrial chambers as well as enabling control of turbulent fluctuations, which would allow for reliable ignition and stable combustion.

Comparative Study of Coaxial Main Rotor Aerodynamics at Forward Flight Based on Free Wake Model and Unsteady ReynoldsAveraged Navier–Stokes Method

This paper is dedicated to the numerical modeling of the aerodynamic characteristics of the full-scale coaxial main rotor. The modes of forward flight in the range of values V = 30-60 m∙s –1 (108-216 km∙h –1) have been under consideration. The simulation has been performed with the usage of two computational fluid dynamics (CFD) approaches: the free wake model (FWM) developed by the authors and the unsteady Reynolds-averaged Navier –Stokes (URANS) equations method based on the Ansys Fluent software. The coefficients of rotor thrust and torque, vortex wake shapes and induced velocity fields have been obtained and analyzed. The FWM and the URANS modeling data match satisfactorily. The FWM demonstrates a significant advantage in computing time and resources costs with sufficient accuracy in resulting rotor’s basic aerodynamic characteristics. That’s why it seems appropriate to use the FWM for preliminary simulations, taking into account before using the high time and resource intensive the URANS method for comprehensive investigation of coaxial rotor aerodynamics at forward flight modes.

A CFD based Kriging model for predicting the impact force on the sphere bottom during the early-water entry

To efficiently achieve an accurate trajectory of the ocean observation device with a spherical bottom when it is thrown into the sea in the airdrop deployment, a computational fluid dynamics (CFD) based Kriging model is established for predicting the impact force on the sphere bottom during the early-water entry stage which is considered as the beginning of a full immersion process. The early-water entry of a sphere is simulated using the Reynolds-Averaged Navier-Stokes (RANS) method and k–ϵ turbulent model and the validity of the CFD model is verified by the comparison with experimental data. A Kriging surrogate model is then established based on the results of CFD simulation and extensive sample points where a proper range for the correlation parameter of the Kriging model is achieved through a study on the effect of the correlation parameter on the results from the Kriging model. The comparison with the CFD simulation results shows that the established Kriging model significantly improves the computational efficiency while maintaining high numerical accuracy.

High Resolution 3-D Simulations of Venting in 18650 Lithium-Ion Cells

High temperature gases released through the safety vent of a lithium-ion cell during a thermal runaway event contain flammable components that, if ignited, can increase the risk of thermal runaway propagation to other cells in a multi-cell pack configuration. Computational fluid dynamics (CFD) simulations of flow through detailed geometric models of four vent-activated commercial 18650 lithium-ion cell caps were conducted using two turbulence modeling approaches: Reynolds-averaged Navier-Stokes (RANS) and scale-resolving simulations (SRS). The RANS method was compared with independent experiments of discharge coefficient through the cap across a range of pressure ratios and then used to investigate the ensemble-averaged flow field for the four caps. At high pressure ratios, choked flow occurs either at the current collector plate when flow through the current collector plate is more restrictive or the positive terminal vent holes when flow through the current collector plate is less restrictive. Turbulent mixing occurred within the vent cap assembly, in the jets emerging from the vent holes, and in recirculating zones directly above the vent cap assembly. The global maximum turbulent viscosity ratio (μT/μ) of the MTI, LG MJ1, K2, and LG M36 caps at pressure ratio ofP1/P2= 7 were 4,575, 3,360, 3,855, and 2,993, respectively. SRS and RANS simulations showed that both velocity magnitude and fluctuating velocity magnitude were lower for vent holes which are obstructed by the burst disk. SRS showed high levels of fluctuating velocity in the jets, up to 48.5% of the global maximum velocity. The present CFD models and the resulting insights provide the groundwork for future studies to investigate how jet structure and turbulence levels influence combustion and heat transfer in propagating thermal runaway scenarios.

Investigation of fine viscous flow fields in ship planar motion mechanism tests by DDES and RANS methods

The fine large separated flow is a focus in the naval architecture and ocean engineering. In the present study, the CFD solver, naoe-FOAM-SJTU, coupled with delayed detached-eddy simulation (DDES) and Reynolds Averaged Navier-Stokes (RANS) is adopted to simulate the fine viscous flow field in the ship planar motion mechanism (PMM) tests for the benchmark model Yupeng Ship. This paper compares the time histories of forces/moment acting on the hull and their oscillation frequency obtained by Fast Fourier Transform. The predicted results are in good agreement with the experimental data. By comparing the turbulent kinetic energy (TKE) and eddy viscosity coefficient calculated by both numerical methods, the results show that the TKE and eddy viscosity coefficient obtained by DDES method are much less than that achieved by RANS approach. The capacity of four vortex identification methods to capture vortex structures is analyzed in this paper, indicating that the third generation of vortex identification methods (ΩR and Liutex methods) are more suitable for analyzing the flow mechanism in the viscous large separated flow field. The axial Liutex and streamlines on the cutting planes are used to depict the flow around the hull.