Numerical Hydrodynamic Analysis Research Articles

Numerical-hydrodynamic analysis, vickers hardness, and tensile test of cast-brass alloy for boat propellers

Numerical-hydrodynamic analysis, vickers hardness, and tensile test of cast-brass alloy for boat propellers

Detailed experimental and numerical analysis of hydrodynamics in the outflow measurement channel of a sewage treatment plant

Abstract The ‘Bajo Grande’ Wastewater Treatment Plant has a design capacity of 2.78 m3/s, and discharges into the Suquia River (Córdoba, Argentina). The river has an average flow rate of 10 m3/s, with lower values during the summer. Currently, the treatment plant does not have an accurate discharge-measurement system prior to the discharge into the river, which makes it difficult to evaluate the dosing of the disinfection treatment. The outflow rate is measured in a straight flume. However, at the inlet section of the flume, a 180° sharp bend induces a complex turbulent flow with instabilities and low-frequency velocity fluctuations which are not appropriate for flow quantification. In this type of flow, most of the in situ flow discharge-measurement systems have great uncertainty. Therefore, in situ flow measurements with an Acoustic Doppler Current Profiler, Large-Scale Particle-Tracking Velocimetry techniques and a prototype-scale Detached Eddy Simulation model were combined to obtain a detailed characterization of the turbulent flow. The results provide flow rates, fields of mean flow velocity, temporal evolution, and characteristic parameters of the turbulence. This allowed a better understanding of the effects of turbulence and flow instabilities. The results provide a basis to validate numerical models used in the hydraulics design of contact chambers to improve the disinfection process.

An adaptive central‐upwind scheme on quadtree grids for variable density shallow water equations

AbstractMinimizing computational cost is one of the major challenges in the modeling and numerical analysis of hydrodynamics, and one of the ways to achieve this is by the use of quadtree grids. In this article, we present an adaptive scheme on quadtree grids for variable density shallow water equations. A scheme for the coupled system is developed based on the work of [M.A. Ghazizadeh, A. Mohammadian, and A. Kurganov,Computers & Fluids, 208 (2020)]. The scheme is capable of exactly preserving “lake‐at‐rest” steady states. A continuous piecewise bi‐linear interpolation of the bottom topography function is used to achieve higher‐order in space in order to preserve the positivity of water depth for the point values of each computational cell. Necessary conditions are checked to be able to preserve the positivity of water depth and density, and to ensure the achievement of a stable numerical scheme. At each timestep, local gradients are examined to find new seeding points to locally refine/coarsen the computational grid.

Numerical analysis of hydrodynamics influenced by a deformed bed due to a near-bank vegetation patch

Abstract This study uses a 2D hydro-morphological model to analyze hydrodynamics over flat and deformed beds with a near-bank vegetation patch. By varying the patch density, the generalized results show that the hydrodynamics over deformed beds differs a lot from those over flat beds. It is found that the deformed bed topography leads to an apparent decrease in longitudinal velocity and bed shear stress in the open region and longitudinal surface gradient for the entire vegetated reach. However, the transverse flow motion and transverse surface gradient in the region of the leading edge and trailing edge is enhanced or maintained, suggesting the strengthening of secondary flow motion. Interestingly, the deformed bed topography tends to alleviate the horizontal shear caused by the junction-interface horizontal coherent vortices, indicating that the turbulence-induced flow mixing is highly inhibited as the bed is deformed. The interior flow adjustment through the patch for the deformed bed requires a shorter distance, La, which is related to the vegetative drag length, (Cda)−1, with a logarithmic formula (La = 0.4ln[(Cda)−1] + b, with b = 3.83 and 4.03 for the deformed and flat beds). The sloping bed topographic effect in the open region accelerating the flow may account for the quick flow adjustment.

Hydrodynamic Analysis of a Multibody Wave Energy Converter in Regular Waves

A performance assessment of wave power absorption characteristics of isolated and multiple wave energy converter (WEC) rotors was presented in this study for various wave-heading angles and wave frequencies. Numerical hydrodynamic analysis of the WEC was carried out using the three-dimensional linear boundary element method (BEM) and nonlinear computational fluid dynamics (CFD). Experimental results were used to validate the adopted numerical models. Influence with and without power take-off (PTO) was estimated on both isolated and multiple WEC rotors. Furthermore, to investigate the interaction effect among WECs, a q-factor was used. Incorporation of viscous and PTO damping into the linear BEM solution shows the maximum reduction focused around peak frequency but demonstrated an insignificant effect elsewhere. The q-factor showed both constructive and destructive interactions with the increase of the wave-heading angle and wave frequencies. Further investigation based on the prototype WEC rotor was carried, and calculated results of the linear BEM and the nonlinear CFD were compared. The pitch response and q-factor of the chosen wave frequencies demonstrated satisfactory consistency between the linear BEM and nonlinear CFD results, except for some wave frequencies. Estimated optimal time-averaged power using linear BEM show that the maximum extracted power close to the zero wave-heading angle around the resonance frequency decreases as the wave-heading angle increases. Overall, the linear BEM on the extracted power is overestimated compared with the nonlinear CFD results.

Numerical analysis of hydrodynamics and thermochemical property of biomass gasification in a pilot-scale circulating fluidized bed

This study presents a three-dimensional reactive multiphase particle-in-cell (MP-PIC) model to simulate the hydrodynamics and thermochemical property of the biomass gasification process in a pilot-scale circulating fluidized bed gasifier. The bed hydrodynamics and thermochemical characteristics are investigated, together with discussing the effects of operating conditions on the species distribution, lower heating value (LHV), and combustible gas concentration (CGC). The results show that solid particles present oscillation behaviors for the time elapsed at the turbulent fluidization regime. Solid flux and rising velocity have peaks of about 249 kg/(m2·s) and 6.2 m/s in the core region of the bed, respectively. Increasing the gasification temperature reduces the CGC from 15.85% to 15.16%. However, only the concentration of H2 increases with the enlargement of the steam biomass ratio. Comparatively, the equivalence ratio (ER) has the most direct impact on gasification efficiency, and the increase of the ER adversely affects the LHV and CGC. The effect of particle diameter on the LHV, the magnitude of which can cover a range from 3.87% to 3.98%, is negligible compared with the other operational parameters, at least for the specific cases in the present investigation.

Derivation of cavitation characteristics of a 3MW prototype Francis turbine through numerical hydrodynamic analysis

Cavitation is one of the major causes for erosive wear in reaction hydraulic turbines. Evaluation of cavitation characteristics is one of the most important tasks while designing a water turbine. Aim of present work is to analyze the effects of cavitation phenomenon at different operating regimes of a 3 MW capacity prototype Francis turbine using CFD code ANSYS CFX. Detailed flow field analyses for part loads of 60% and 80%, full load and overload operation of 120% with and without cavitation are performed. A comparative study among different turbulent models is also carried out in order to select the most suitable and compatible model with cavitation model based on Rayleigh-Plesset equation. Different stages of profile cavitation in runner and development of cavitation in draft tube for different operating conditions are analyzed thoroughly. Estimation of suction head (turbine setting above the tail race) and turbine cavitation coefficient is one of the major objectives of the work. A critical study of variation of different flow parameters for with and without cavitation cases is one of the important highlights of the paper. Computationally obtained results are compared with experimental and literature results which are found in well accord with the former.

Hydrodynamic analysis of radial collector well ageing at Belgrade well field

The origin and effect of hydraulic resistances on the rate of ageing of radial collector wells are identified through numerical hydrodynamic analysis. The research includes hydrodynamic modeling of one such well with new laterals at Belgrade well field. The performance of the laterals is aggravated by rapid ageing. The change in the hydraulic parameters of the laterals during the first decade of operation is analyzed through simulations of the groundwater regime with realistically specified geometries and hydraulics of the laterals. Contrary to previous investigations, two genetically different types of clogging were identified. The initial hydraulic resistances are a result of colmation due to the gravel pack grain-sizes and screen slot sizes being mismatched with the sand and gravel sediments of the aquifer deposited at the depth of the laterals. Colmation affects the hydraulic performance of the laterals. Well ageing is aggravated by incrustation, caused by high iron concentrations in the captured groundwater. The research highlights a strong correlation between increasing resistances at the laterals, on account of iron precipitation, and groundwater entrance velocities at the laterals. It is possible to differentiate between colmation and incrustation and accurately define the increase in resistances at the laterals by specifying known thicknesses of the near-lateral screen zones and quantifying hydraulic conductivities of those zones. MODFLOW–USG code and Connected Linear Network Process package are recommended for simulating laterals and defining real rather than hydraulically equivalent characteristics of the laterals, as an approach to hydrodynamic investigations relating to radial collector wells.

Characterization of the local hydromechanical stress through experimental and numerical analysis of hydrodynamics under dark fermentation operating conditions

In mechanically stirred tanks, turbulent flow conditions have already been shown to impair biohydrogen production through dark fermentation even when the dimensionless Reynolds number (Re) is between 103 and 104. The aim was, therefore, to investigate the local hydrodynamic conditions encountered by bacterial aggregates in a fully baffled 2-L bioreactor equipped with a double stage Rusthton turbine in which dark fermentation had already been extensively studied. Both experimental and numerical tools (namely, Particle Image Velocimetry and Computational Fluid Dynamics) were applied to analyze the flow pattern and determine the main features of the turbulent flow. Experiments and simulations involved two levels of viscosity and three levels of agitation speed, corresponding to Re between 2.2·103 and 1.1·104 and power requirements P/V between 0.6 and 87 W/m3. A good agreement between simulated and experimental data was achieved, including velocity, turbulent kinetic energy and turbulent dissipation rate. Comparing the size of bacterial aggregates to Kolmogorov length scale, experimental and numerical results demonstrated that bacterial aggregates could be exposed to potentially damaging hydromechanical stress under turbulent flow in the vicinity of the impeller when Re = 2.2·103 and that this region rapidly expanded to the whole bioreactor when Re increased, which could explain the rapid fall of biohydrogen production vs.Re in the turbulent flow regime.

Analysis of enhanced heat transfer by magnetic nanofluids in a mini channel under hard/soft-magnetic elements

The heat transfer characteristic of magnetic nanofluid in a 2D channel, below which a current-carrying wire or hard-magnetic elements (HMEs)/soft-magnet elements (SMEs) are embedded, is analyzed using a two-phase mixture model. The magnetic field produced by the current-carrying wire, the HMEs or the magnetized SMEs permeates into the channel giving rise to an attractive Kelvin force on the magnetic nanofluids. An equivalent charge method is adopted to obtain a closed-form field analysis, which can be combined with numerical hydrodynamic analysis to predict the heat transfer process of the magnetic nanofluids. The heat transfer characteristics of the magnetic nanofluids in the presence of a current-carrying wire or an HME are compared, which denotes that one HME with a certain configuration can provide sufficient Kelvin force to control the behavior of the magnetic nanofluids without introducing additional heat. To further enhance the heat transfer, two HMEs are proposed. In addition, an SME is introduced to improve the heat transfer of the magnetic nanofluid, which can also implement the function of switching on/off by applying or removing the external magnetic field.

Numerical analysis of hydrodynamics in a mechanically agitated gas\u2013liquid pseudophase system

The paper presents the results of numerical simulations of hydrodynamics in a gas–liquid pseudophase system (sucrose solution with yeast suspension). The simulations were performed in a bioreactor with a working volume of 0.02 m3, equipped with a Rushton turbine or Smith turbine stirrers. The results of the study were developed in the form of vectors of liquid velocity and the contours of the analyzed magnitudes. Also, the local values of the gas hold-up φ in the gas–liquid pseudophase system were presented. The results of numerical simulations of the gas hold-up were compared to the results of my own experimental study.

Numerical Analysis of Hydrodynamics, Potential and Current Distribution, and Mass Transfer of Aluminum Ions in an Electrocoagulation Reactor Using CFD By Euler-Lagrange Approach

The reactor design for tannery wastewater treatment using computational fluid dynamics (CFD) techniques was carried out. The effluent contains different types of pollutants such as organic matter, salts, heavy metals, and dyes difficult to degrade. Due to the complexity of the effluent, a treatment based on an electrocoagulation process is proposed. In most of the references is mentioned that the characterization and design of this type of process is carried out empirically or semi-empirically, so in this work the influence of hydrodynamics, mass transfer of aluminum ions and secondary current distribution was studied. An electrochemical rotating cylinder electrode (RCE) reactor was used, with 6 working electrodes and an aluminum RCE as counter electrode. Besides, a decanter was incorporated in the reactor design. Current distribution and fluid velocity profiles as well as particle tracking animations were obtained. The most suitable geometry was designed from the theoretical results of the sedimentation process and aluminum ions generation. Finally, some operating parameters such as velocity inflow and velocity of the RCE were evaluated.

Boulder coastal deposits at Favignana Island rocky coast (Sicily, Italy): Litho-structural and hydrodynamic control

Boulders are frequently dislodged from rock platforms, transported and deposited along coastal zones by high-magnitude storm waves or tsunamis. Their size and shape are often controlled by the thickness of bedding planes as well as by high-angle to bedding fracture network. We investigate these processes along two coastal areas of Favignana Island by integrating geological data for 81 boulders, 49 rupture surfaces (called sockets) and fracture orientation and spacing with four radiocarbon dates, numerical hydrodynamic analysis, and hindcast numerical simulation data. Boulders are scattered along the carbonate platform as isolated blocks or in small groups, which form, as a whole, a discontinuous berm. Underwater surveys also highlight free boulders with sharp edges and sockets carved out in the rock platform. Boulders are composed of ruditic- to arenitic-size clastic carbonates. Their size ranges from 0.6 to 3.7m, 0.55 to 2.4m, and 0.2 to 1m on the major (A), medium (B), and minor (C) axes, respectively. The highest value of mass estimation is 12.5t. Almost all of boulders and sockets are characterized by a tabular or bladed shape. The comparisons between a) the fractures spacing and the length of A- and B-axes, and b) the frequency peaks of C-axis with the recurrent thickness of beds measured along the coastal zone demonstrate the litho-structural control in the size and shape of joint-bounded boulders. These comparisons, together with the similarity between the shapes of the boulders and those of the sockets as well as between the lithology of boulders and the areas surrounding the sockets, suggest that blocks originate by detachment from the platform edge. Thus, the most common pre-transport setting is the joint-bounded scenario. Hydrodynamic equations estimate that the storm wave heights necessary to initiate the transport of blocks diverge from ~2m to ~8m for joint-bounded boulders and from few tens of centimeters up to ~11m for submerged boulders. The comparison between the wave heights at the breaking point of the coastal zones with the results of hydrodynamic equations shows that waves approaching the coastline are able to transport all surveyed boulders. Our data suggest that boulders have been transported by several storm events, even in very recent times.

Experimental and numerical hydrodynamic analysis of a stepped planing hull

This work addresses the experimental and numerical study of a stepped planing hull and the related fluid dynamics phenomena typically occurring in the stepped hull in the unwetted aft body area behind the step. In the last few years, the interest in high-speed planing crafts, with low weight-to-power ratios, has been increasing significantly, and, in such context, naval architects have been orienting toward the stepped hull solution. Stepped planing hulls ensure good dynamic stability and seakeeping qualities at high speeds. This is mainly due to the reduction of the wetted area, which is caused by the flow separation occurring at the step. This paper presents the experimental results of towing tank tests in calm water on a single-step hull model, which is the first model of a new systematic series. The same flow conditions are analyzed via Reynolds Averaged Navier-Stokes (RANS) and Large Eddy Simulations (LES), with different moving mesh techniques (overset/chimera and morphing grid), performed at different model speeds. The numerical results are in accordance with experimental data, and overset/chimera grid is found to be the best approach between the analyzed ones. The flow patterns obtained numerically through LES on a refined grid appear similar to the ones observed in towing tank investigations through photographic acquisitions. These flow patterns are dominated by a rather complex 3D arrangement of vortices originating from air spillage at both sides of the step. The understanding of these phenomena is important for the effectiveness of stepped hull designs.

Numerical hydrodynamic analysis of an offshore stationary–floating oscillating water column–wave energy converter using CFD

Offshore oscillating water columns (OWC) represent one of the most promising forms of wave energy converters. The hydrodynamic performance of such converters heavily depends on their interactions with ocean waves; therefore, understanding these interactions is essential. In this paper, a fully nonlinear 2D computational fluid dynamics (CFD) model based on RANS equations and VOF surface capturing scheme is implemented to carry out wave energy balance analyses for an offshore OWC. The numerical model is well validated against published physical measurements including; chamber differential air pressure, chamber water level oscillation and vertical velocity, overall wave energy extraction efficiency, reflected and transmitted waves, velocity and vorticity fields (PIV measurements). Following the successful validation work, an extensive campaign of numerical tests is performed to quantify the relevance of three design parameters, namely incoming wavelength, wave height and turbine damping to the device hydrodynamic performance and wave energy conversion process. All of the three investigated parameters show important effects on the wave–pneumatic energy conversion chain. In addition, the flow field around the chamber's front wall indicates areas of energy losses by stronger vortices generation than the rear wall.

Numerical Analysis of Hydrodynamics for Bionic Oscillating Hydrofoil Based on Panel Method.

The kinematics model based on the Slender-Body theory is proposed from the bionic movement of real fish. The Panel method is applied to the hydrodynamic performance analysis innovatively, with the Gauss-Seidel method to solve the Navier-Stokes equations additionally, to evaluate the flexible deformation of fish in swimming accurately when satisfying the boundary conditions. A physical prototype to mimic the shape of tuna is developed with the revolutionized technology of rapid prototyping manufacturing. The hydrodynamic performance for rigid oscillating hydrofoil is analyzed with the proposed method, and it shows good coherence with the cases analyzed by the commercial software Fluent and the experimental data from robofish. Furthermore, the hydrodynamic performance of coupled hydrofoil, which consisted of flexible fish body and rigid caudal fin, is analyzed with the proposed method. It shows that the caudal fin has great influence on trailing vortex shedding and the phase angle is the key factor on hydrodynamic performance. It is verified that the shape of trailing vortex is similar to the image of the motion curve at the trailing edge as the assumption of linear vortex plane under the condition of small downwash velocity. The numerical analysis of hydrodynamics for bionic movement based on the Panel method has certain value to reveal the fish swimming mechanism.

Numerical analysis of hydrodynamics and crystal motion in a batch crystallizer

In this work, we investigate numerically the hydrodynamics and crystal motion in a draft tube batch crystallizer using Computational Fluid Dynamics (CFD) coupled with the Discrete Phase Model (DPM). The flow generated by the rotating impeller interacts with baffles and generates a complex, unsteady, three-dimensional turbulent flow with large-scale recirculations. To investigate this flow, a Multiple Reference Frame approach is first used as initial condition for a more accurate Sliding Mesh Model. Turbulence is modeled with the k–ε model considering the Unsteady Reynolds-Averaged Navier–Stokes formulation. The computational model is first used to analyze the impact of the liquid volume in the vessel on hydrodynamics. Coupling CFD with DPM, crystal motion is then investigated. For this purpose, crystals are introduced in the flow at eight different positions. Crystal motion has been investigated in a Lagrangian manner through one-way coupling considering drag and buoyancy forces. Deposition probabilities have been calculated for different crystal types and interpreted as an indicator for unfavorable crystallization conditions, allowing identifying suitable liquid volumes and seeding positions.

On the Shape Optimization of Semisubmersibles

The paper presents an automated shape optimisations system and illustrates its applications in two case studies. The system integrates a unique parametric design tool for offshore structure hulls with numerical hydrodynamic analysis of seakeeping characteristics. A library of optimisation algorithms is provided which allows the fine-tuning of already good designs to new constraints as well as performing larger scale studies for new concepts. The case studies provide examples of single and multi-objective optimisation of a semisubmersible with respect to seakeeping capability and payload capacity. Improvements in the applied design criteria have been achieved in all cases.

Computer modelling and numerical analysis of hydrodynamics and heat transfer in non-porous catalytic reactor for the decomposition of ammonia

Chemical reactors exhibit very complex behaviours such as multiple steady states, oscillations, etc. resulting from complex linkage between the transport processes and the non-linear chemical reaction kinetics. Ammonia is a potential hydrogen source for a number of fuel cell applications for small scale power generation useful for portable equipments. In the present work, we analyse the fluid dynamics and heat transfer in catalytic microreactor systems for the decomposition of ammonia over a monolayer Ni non-porous catalyst. The overall model for this convective–diffusive–reactive system consists of a flow model, a mass transport model, an energy conservation model and a reaction kinetics model for ammonia decomposition. The flow model is described by the Stokes equation for a creeping flow regime. The mass transport and energy conservation models are based on convective–diffusion equations. The rate of ammonia decomposition can be measured as a function of the catalyst activity and ammonia concentration. A standard Galerkin finite element technique has been applied for the solution of the flow equations. A slightly perturbed form of the mass continuity equation is used to satisfy the Ladyzhenskaya–Babuška–Brezzi stability criterion. For the solution of convection–diffusion equations, a streamline inconsistent upwind finite element scheme has been chosen to avoid any spurious oscillations. C 0 -continuous 9-noded Lagrangian biquadratic isoparametric finite elements are used for the approximation of the field variables. A second-order Taylor–Galerkin time-stepping scheme has been chosen for the temporal discretisation of the flow equations whilst an implicit theta method has been used for convection–diffusion equations. The results are presented in the form of velocity vectors and concentration, temperature contours and are examined for stability, convergence and theoretical consistency.

F02-5 CIP-セミラグランジュ法を用いた特性曲線法による流体方程式の数値解析(F02 変形を伴う複雑界面を含む流体力学)(フォーラム)

F02-5 CIP-セミラグランジュ法を用いた特性曲線法による流体方程式の数値解析(F02 変形を伴う複雑界面を含む流体力学)(フォーラム)