Dimensional Numerical Simulations Research Articles

Numerical simulations over a three body launch vehicle for incompressible flows

In the present work, three dimensional numerical simulations over a launch vehicle at 70 m/s are performed for 3 scale models. The vehicle has a cylindrical core body and two strap on boosters. The scaled models chosen so that they represent a wind tunnel blockage ratio of 3%, 4% and 5% respectively. Simulations are performed using commercial CFD software Ansys Fluent. Three dimensional structured mesh is generated using ICEMCFD software. The solver depends on finite volume technique, and SIMPLE calculation is utilized to address the couple continuity and energy conditions. K-w SST model is utilized for disturbance demonstration. The computed flow field is analyzed in terms of velocity, pressure and turbulent kinetic energy contours. Surface pressure acquired from the three simulation (relating to every blockage ratio) arrangements in balance plane is compared to understand the impact of blockage ratio on the stream field and drag coefficients. As the blockage is increased, it was observed that maximum velocity is increasing. Lowest blockage found to give highest drag coefficient.

Three- dimensional numerical simulation analysis of the influence of structural parameters on the performance of air ejector

Nowadays, CFD technology has become the third tool to study hydrodynamics problems after theoretical analysis and experimental research, especially in dealing with and solving complex engineering problems such as supersonic. In this paper, using the method of control variables, the system studied a type air ejector structure parameters within a certain range changes affect the performance of the work by means of FLUENT, at the same time, the optimal combination of the structural parameters are given, then three dimensional numerical simulation of the optimal combination model, and the simulation value and experiment value has carried on the contrast and analysis, Compared with the two-dimensional and axisymmetric model, Three-dimensional calculation model is more reliable and reasonable.

Performance evaluation of a seawater exchange breakwater with Helmholtz resonator using OpenFOAM

In this study, the three dimensional numerical simulation of a seawater exchange breakwater using the Helmholtz resonator has been carried out in OpenFOAM. When the frequency of the incident wave coincides with one of the natural frequencies of a closed semi-circular resonator, resonance occurs in the resonator. The amplified water elevation in a resonator pushes the seawater periodically into the ocean/port side through the water channel and consequently improves the water quality of the port. The numerical model is based on Reynolds Averaged Navier Stokes equations with SST turbulence model. The VOF (Volume of Fluid) method is used to capture the free surface behavior. The numerical model is validated with model experiments conducted by Cho (2001) in a two-dimensional wave tank for regular waves. Numerical simulations for the prototype model in irregular waves based on the JONSWAP spectrum are also conducted to show whether the proposed seawater exchange breakwater can be feasible to the real seas. It is found that the seawater exchanging rate is greatly enhanced in the low-frequency wave region where the frequency of the Helmholtz resonance situates. If designing the Helmholtz resonator properly, it can supply the clean seawater sustainedly into the port side without additional electric power.

Dimensionless Charts for Predicting the Range of Goaf Roof Caving

In engineering, the method of charts can provide a convenient query for specific engineering problems. To provide the basis for the potential hazard evaluation and rational governance of the goaf, it is necessary to study the quantitative evaluation for the range of goaf roof caving. Undoubtedly, the charts used to visually query the caving range can simplify the workload of the quantitative evaluation. Therefore, the methods of dimensional analysis, numerical simulation, and linear interpolation are introduced to study the dimensionless charts for predicting the caving range. The dimensionless analysis is used to establish the fuzzy function relationship among the influence factors of the goaf roof caving, and the numerical simulation is used to calculate the dimensionless groups in the fuzzy function. Using the linear interpolation, the dimensionless charts in this work can predict the range of goaf roof caving under more working conditions. The results show that the characteristics of the goaf roof caving corresponding to the dimensionless curves are consistent with the actual situation. With the continuous increase of the goaf span l, the dimensionless curves of the caving range experience zero growth, rapid growth, and steady growth. The growth degree varies with the fracture spacing S. Especially in the zero growth phase, the duration of the relatively stable state in the overlying strata of the goaf increases with the increase of fracture spacing S. Moreover, based on the case study of Shirengou Iron Mine, the dimensionless charts obtained in this work can predict the range of goaf roof caving under different working conditions, which indicates the findings of this study have certain guiding significance to the treatment of the goaf.

Hydrodynamics and heat transfer of multiple droplets successively impacting on cylindrical surface

Based on the sparseness of research on the multi-droplet impact coupled with the anisotropy induced by cylindrical surface, in this paper, the hydrodynamics and heat transfer of multiple droplets successively impacting on cylindrical surface are deeply studied with three dimensional numerical simulation method. The comparison of single, two and even three droplets impacting on the heated cylindrical surface is carried out, and the effect of vertical space between successive droplets is discussed. Moreover, the influence of cylinder diameter on the hydrodynamics and heat transfer of multi-droplet impact is analyzed in detail. The results show that, the combination of multi-droplet interaction and anisotropy induced by cylindrical surface greatly affects the global heat flow, heat transfer coefficient, temperature distribution of liquid-vapor interface. By decreasing the vertical space between successive droplets impacting on the heated cylindrical surface, the heat transfer performance is obviously improved. Increasing the cylinder diameter boosts the heat transfer performance, but once the cylinder diameter augments to a certain value, the change of cylinder diameter no longer has an effect on the heat transfer performance, which is very close to the flat surface situation.

A three-dimensional thermal model of the human cochlea for magnetic cochlear implant surgery

In traditional cochlear implant surgery, physical trauma may occur during electrode array insertion. Magnetic guidance of the electrode array has been proposed to mitigate this medical complication. After insertion, the guiding magnet attached to the tip of the electrode array must be detached via a heating process and removed. This heating process may, however, cause thermal trauma within the cochlea. In this study, a validated three-dimensional finite element heat transfer model of the human cochlea is applied to perform an intracochlear thermal analysis necessary to ensure the safety of the magnet removal phase. Specifically, the maximum safe input power density to detach the magnet is determined as a function of the boundary conditions, heating duration, cochlea size, implant electrode array radius and insertion depth, magnet size, and cochlear fluid. A dimensional analysis and numerical simulations reveal that the maximum safe input power density increases with increasing cochlea size and the radius of the electrode array, whereas it decreases with increasing electrode array insertion depth and magnet size. The best cochlear fluids from the thermal perspective are perilymph and a soap solution. Even for the worst case scenario in which the cochlear walls are assumed to be adiabatic except at the round window, the maximum safe input power density is larger than that required to melt 1 mm3 of paraffin bonding the magnet to the implant electrode array. By combining the outcome of this work with other aspects of the design of the magnetic insertion process, namely the magnetic guidance procedure and medical requirements, it will be possible to implement a thermally safe patient-specific surgical procedure.

Evolution of a wall-attached buoyant plume in confined boxes: Direct numerical simulations, entrainment coefficient and an integral model

The evolution of a wall-attached plume in a confined box is studied here with the aid of three dimensional direct numerical simulations (DNS). The plume originates from a local line heat source of length, L, placed at the bottom left corner of the box. The Reynolds number of the wall plume, based on box height and buoyant velocity scale, is ReH=14530 and boxes of two different aspect ratios (ratio of box width to height) for a particular value of L are simulated. We observe that the plume develops along the vertical sidewall while remaining attached to it before spreading across the top wall to form a buoyant fluid layer and eventually moving downwards and filling the whole box. The original filling box model of Baines and Turner (1969) is modified to incorporate the wall shear stress, and the results from the DNS are compared against the new model. In modelling plumes, we find that the entrainment coefficient (α) for wall-attached plumes is reduced to approximately half of that in the free plume, and the main reason is a diminished contribution of turbulence production to α resulting from a restricted ability of the large-scale eddies to transport momentum. Also, unlike the free plume where away from the source inertial forces balances buoyancy forces, here in our simulations of wall-attached plumes this balance is marginally off, likely due to wall friction. A reasonable agreement is observed between our model and DNS data for the volume and momentum fluxes in the quiescent uniform environment and also for the time-dependent buoyancy profile calculated far away from the plume.

Overbank Floods of Lower Yellow River Based on Two - dimensional Numerical Simulation and Analysis

When the flow of the Yellow River is large, a large range of floodplains will be formed around the main channel, and the crisis will greatly improve safety. Analysis of the changes of flood peak shape, flood peak propagation speed and flood level at large flow rate plays an important role in the protection and flood prevention of the Yellow River levee. Based on the established two-dimensional mathematical model of Luokou to the Yellow River estuary, the data of peak flow, velocity and water level are obtained by simulation calculation. By drawing the flood peak evolution process map from Luokou to Yellow River estuary, the change of flood peak type and flood peak propagation speed are analyzed to provide technical support for flood defense.

Correction and laboratory investigation for energy loss coefficient of square-edged orifice plate.

A lot of studies have shown that the hydraulic characteristics of orifice plate are mainly controlled by its contraction ratio, but the thickness of square-edged orifice plate also has many impacts on energy loss characteristics. The primary objective of this study was to investigated the effects of square-edged orifice plate thickness on energy loss characteristics. In this paper, the effects of square-edged orifice plate thickness on energy loss characteristics are investigated by numerical simulation using CFD. Orifice plate discharge tunnel is axial symmetric, two dimensional numerical simulations of orifice plate discharge tunnel flow was used. The equation (9) for calculating energy loss coefficient of square-edged orifice plate energy dissipater considering the influence of thickness is proposed. The results of the present research demonstrate that energy loss coefficient decreases with increase of the orifice plate thickness. The results of model experiment are consistence with the results calculated by using rectified equation in present paper. The CFD simulations and Model experiment for the flow through an orifice plate are carried out. For square-edged orifice plate energy dissipater, the relative orifice plate thickness T/D has remarkable impacts on its energy loss coefficient ξ. The Traditional equation (8) is corrected by numerical results. The equation (9) for calculating energy loss coefficient of square-edged orifice plate energy dissipater considering the influence of thickness is proposed and this equation is available in the condition of d/D = 0.4-0.8, T/D = 0.05-0.25, and Re > 105(Re is Reynolds number). Comparing with the physical model experimental data, the relative errors of equation (9) is smaller than 15%.

Numerical study on hydraulic characteristics of improved X-shaped FGP

The three dimensional numerical simulation was carried out for flood discharge and energy dissipation process of five improved X-shaped FGPs in hydropower project by using coupled Level set and VOF model and RNG k-ε turbulent model. The change laws of flow pattern, water surface profile and velocity distribution of X-shaped FGP and lock chamber were gained. The results of numerical simulation were compared with the model test data and good agreement was found. It validated the numerical simulation method is reliable, It can provide strong references for the design of energy dissipation and shape optimization of practical project, the results from computation can be supplement for experiment.

Overstable rotating convection in the presence of a vertical magnetic field

Recently, Banerjee et al. [Phys. Rev. E 102, 013107 (2020)] investigated overstable rotating convection in the presence of an external horizontal magnetic field and reported a rich bifurcation structure near the onset. However, the bifurcation structure near the onset of overstable rotating convection in the presence of a vertical magnetic field has not been explored yet. We address the issue here by performing three dimensional direct numerical simulations and low-dimensional modeling of the system using a Rayleigh–Bénard convection model. The control parameters, namely, the Taylor number (Ta), the Chandrasekhar number (Q), and the Prandtl number (Pr) are varied in the ranges 750≤Ta≤106, 0<Q≤103, and 0<Pr≤0.5. Our investigation reveals two qualitatively different onset scenarios including bistability (coexistence of subcritical and supercritical convections). Analysis of the low-dimensional model shows that a supercritical Hopf bifurcation is responsible for the supercritical onset and a subcritical pitchfork bifurcation is responsible for the subcritical onset. It is also observed that the appearance of a subcritical convection at the onset has strong dependence on all three control parameters: Ta, Q, and Pr. The scenario of a subcritical convection is found to disappear as Pr is increased for fixed Ta and Q. However, most striking findings of the investigation are that the increment in Ta for fixed Q and Pr opposes the subcritical convection, whereas the increment in Q for fixed Ta and Pr favors it. This is in sharp contrast with the earlier results reported in rotating magnetoconvection.

MHD effects of partition plates on thermofluid performance of Indian variant LLCB TBM for ITER

Abstract Liquid metal Lead-Lithium (PbLi) flow channels in Indian LLCB (lead lithium cooled ceramic breeder) Test Blanket Module consist of a sequence of parallel channels which are fed from a common inlet header. Thin radial-toroidal vertical plates known as partition plates at the central plane perpendicular to the applied magnetic field are primarily envisaged to enhance the mechanical strength of high aspect ratio electrically coupled parallel poloidal channels. In that case the partition plates are acting as an internal Hartmann wall and they have significant effects on velocity profile, pressure drop and heat transfer characteristics at ITER relevant applied magnetic field (B0 = 4 T). Three dimensional numerical simulation is performed in a model of full scale LLCB variant to study the effects of these partition plates on various flow field variables. Axial velocity near the thin partition wall and side wall jet structures are found to get significantly. Magneto-hydraulic pressure drop and redistribution of flow rates due to the presence of partition plates are assessed by comparing the results with no partition wall. Thermofluid simulation is carried out to obtain the temperature distribution of various structures for a given heat load profile based on neutronic estimation. The effects of buoyancy force on thermofluid flow profile in channels with high temperature gradient are also presented.

Model code and input files in "Three Dimensional Numerical Simulations of Internal Tides in the Angolan Upwelling Region"

Model code and input files in "Three Dimensional Numerical Simulations of Internal Tides in the Angolan Upwelling Region"

Model code and input files in "Three Dimensional Numerical Simulations of Internal Tides in the Angolan Upwelling Region"

Model code and input files in "Three Dimensional Numerical Simulations of Internal Tides in the Angolan Upwelling Region"

Two Dimensional Direct Numerical Simulation of N-Heptane/Air Autoignition with Temperature Fluctuation

Two Dimensional Direct Numerical Simulation of N-Heptane/Air Autoignition with Temperature Fluctuation

Measurement of the interconnected turgor pressure and envelope elasticity of live bacterial cells.

Turgor pressure and envelope elasticity of bacterial cells are two mechanical parameters that play a dominant role in cellular deformation, division, and motility. However, a clear understanding of these two properties is lacking because of their strongly interconnected mechanisms. This study established a nanoindentation method to precisely measure the turgor pressure and envelope elasticity of live bacteria. The indentation force-depth curves of Klebsiella pneumoniae bacteria were recorded with atomic force microscopy. Through combination of dimensional analysis and numerical simulations, an explicit expression was derived to decouple the two properties of individual bacteria from the nanoindentation curves. We show that the Young's modulus of bacterial envelope is sensitive to the external osmotic environment, and the turgor pressure is significantly dependent on the external osmotic stress. This method can not only quantify the turgor pressure and envelope elasticity of bacteria, but also help resolve the mechanical behaviors of bacteria in different environments.

Numerical simulation of in-cylinder combustion characteristics of LNG-diesel dual-fuel engine

Three - dimensional numerical simulation of diesel engine cylinder combustion process was carried out by using computational fluid Dynamics (CFD) software AVL-FIRE. The combustion characteristics of LNG under different ignition diesel ratio, cylinder pressure were studied. Through the simulation calculation of pilot diesel ratio, cylinder pressure, combustion heat release rate, the analysis results showed that the minimum value of pilot diesel ratio was not less than 0.5. During a cycle, there was no cliff-like change in cylinder pressure. CFD simulation has guiding significance for optimizing combustion chamber structure parameters and improving diesel engine performance. CFD simulation is instructive for the optimization of diesel engine performance.

Analysis of application of cement paste grouting curtain in coastal environment

Zhejiang Datang Wushashan power plant is composed of farmland and aquaculture ponds in the Xizhou seawall, which are backfilled with artificial riprap. In order to block the seepage path in the rock fill layer, the vertical curtain cement paste grouting anti-seepage reinforcement measures are adopted to block the connection between the underground water and the surrounding surface water in the plant area, so as to achieve the purpose of gas closure. This paper mainly analyzes and evaluates the technical indexes, such as grout diffusion range and impermeability, of the cement paste grouting curtain, via field tests and two dimensional numerical simulation based on the platform of PFC2D or Geostudio.

Rapid deployment and continuous shape maintenance of tethered-space net robot based on single-pulse action

The tethered-space net robot is one of new technologies for capturing space debris. Rapid deployment and continuous shape maintenance of the tethered-space net robot system are essential in capturing space debris. A single-pulse rotation deployment strategy of the tethered-net robot system is proposed in this paper. The rapid deployment and continuous shape maintenance of the tethered-net are investigated through dimensional analysis, numerical simulation, and regression analysis. Results reveal that the single-pulse rotation deployment strategy can fully deploy the net and maintain the net-shape without any closed-loop controller, and it dramatically increases the effective deployment distance of the net. The parameter sensitivity analyses provide a reference for the rapid deployment and continuous shape maintenance of the tethered-space net robot system.

High Pressure in-Situ X-Ray CT Measurement of Sulfide Solid Electrolyte for All-Solid-State Lithium Ion Battery

The sulfide solid electrolyte has a high ionic conductivity and is a candidate for use as the solid electrolyte in lithium ion batteries used for electrical vehicles [1]. A previous study showed that high ionic conductivity is achieved with compression of solid electrolyte powder by suppressing the void between the solid electrolyte particles as the structure of the solid electrolyte has a strong correlation with the ionic conductivity. However, this correlation has not been discussed directly.In this study, the solid electrolyte three dimensional structure is measured with high pressure in-situ X-ray CT measurement and its ionic conductivity measured by EIS to elucidate the correlation between the structure and ionic conductivity. Moreover, three dimensional electromagnetic field numerical simulations based on the Maxwell and Nernst-Prank equations are conducted with the X-ray CT images to build a numerical model of the ionic conduction in a compressed sulfide solid electrolyte. The solid electrolyte used in this experiment is Li6PS5Cl [2].Figure 1 illustrates the X-ray CT images of the sulfide solid electrolyte with various applied pressures. With a low applied pressure of 10.5 MPa (Fig.1 (a)), solid electrolyte particles exist independently, and there are many voids between them. The ionic conductivity with this structure is 0.35 mS/cm. With the increase in applied pressure to 95.0 MPa, the voids between the solid electrolyte particles disappear as shown in Fig.1 (b). This disappearance is owing to the room temperature sintering with creeping of solid electrolyte with high pressure [3]. The ionic conductivity with this structure is 1.15 mS/cm. The three dimensional electromagnetic numerical results for each X-ray CT image is 0.21 mS/cm and 1.16 mS/cm and these numerical results almost agree with the experimental results. In the numerical simulation, contact resistance, inhomogeneity of the ionic conductivity, and anisotropy of the ionic conductivity are not considered and only the distribution of the solid electrolyte and voids are inputted. Therefore, this numerical result suggests that the contact resistance between solid electrolyte particles can be neglected for numerical simulation of sulfide solid electrolytes.AcknowledgementThis study is partially supported by the Japan Keirin Autorace Foundation (JKA).