Multiple Reference Frames Research Articles

Numerical Investigation of The Effect of Impeller Blade Angle for Stirred Tank

In this study, the most widely used Rushton turbine in the industry was discussed, and the effect of different blade angles on the mixture was investigated numerically. As a standard model, 6 bladed propellers were used and 4 baffles were placed in the stirred tank. The selected tank model is in the form of a flat bottom cylindrical container. Flow characteristics were obtained by giving angles (10°, 20°, 30°, 40°, 50°, 60°) to the propeller blades used in the straight model. The obtained results were compared with each other. In addition, analyzes were repeated at different rotation speeds (600 rpm, 750 rpm, 1000 rpm) for each model at each angle. ANSYS Fluent 18 commercial software, which is the most preferred CFD program in the literature, was used for this numerical study. The analyzes were provided in the standard k-epsilon (ε) turbulence model. The Multiple Reference Frame (MRF) approach was used to simulate impeller rotation. The velocity profiles obtained from the simulations have been shown to be in consistent with the experimental estimates and the results of previous studies. As a result, it has been revealed that the best mixing balance is provided by the impeller blade at 40 and 50 degrees.

Progresses in Particle-Laden Flows Simulations in Multistage Turbomachinery With OpenFOAM

Abstract Numerical simulations of particle-laden flows have received growing attention in the last decade, due to the broad spectrum of industrial applications in which discrete phases prediction is of interest. Among these, ingestion of particles by turbomachinery is an area that is seeing vivid research and studies. The most common technique to tackle this kind of problem is the Eulerian–Lagrangian method, in which individual particles are tracked inside the domain. At the same time, in multistage turbomachinery simulation interfaces are needed to couple the flow solution in adjacent domains in relative motion. In this work, an open-source extension for Lagrangian simulations in multistage rotating machines is presented in the foam-extend environment. First, a thorough discussion of the implementation is presented, with particular emphasis on particle passage through general grid interfaces (GGI) and mixing planes. Moreover, a mass-conservative particle redistribution technique is described, as such a property is requested at interfaces between multiple reference frame (MRF). The peculiarities of the algorithm are then shown in a relevant test case. Eventually, three turbomachinery applications are presented, with growing complexity, to show the capabilities of the numerical code in real-life applications. Simulation results in terms of erosion and impacts on aerodynamic surfaces are also presented as examples of possible parameters of interest in particle-laden flow computations.

Noise prediction of a box fan by RANS simulation

Abstract The characteristics of aerodynamic performance and aerodynamic noise of a box fan were evaluated to investigate the industrial applicability of computational fluid dynamics (CFD) with Reynolds averaged numerical simulation (RANS) model for fan design. In the case of unsteady RANS, the characteristic of the static pressure rise for flow rates was in good agreement with the experimental results. Aerodynamic noise performance at the design flow rate and low flow rate is well predicted using acoustic/viscous splitting technique based on unsteady RANS with multiple reference frame (MRF). As a result, it was able to evaluate the overall sound characteristic of each fan design relatively. The results suggest that the acoustic/viscous splitting technique based on RANS with MRF simulation has potential as a useful design tool.

Effects of impeller designs and configurations on the flow field in multiple impeller system using Computational Fluid Dynamics (CFD)

The work presents the computational study of the flow field in multiple impellers stirred vessel with various impeller types and configurations at 300rpm, 450rpm and 600rpm. Three types of impellers are investigated, namely the pitched blade impeller (PB), flat blade impeller (FB) and sawtooth impeller (ST). In this study, the flow patterns, turbulent kinetic energy dissipation, and power consumption in dual impellers system have been studied using computational fluid dynamics (CFD) by employing the multiple reference frame (MRF) and realizable k-ɛ turbulence model. The results from PBFB and reversed FBPB indicate efficient and powerful mixing with the merging of flows from both impellers that circulates the entire vessel. Besides, the FB and ST configuration exhibits the mixing characteristics that enhance both dispersion and mixing homogeneity. It is proven in this study that the combination of axial and radial impellers improves the weak mixing zones in the stirred vessel by the complex flow patterns produced. On top of that, utilizing two different impellers could achieve two mixing objectives in a system with the exceptional features of each impeller. The results establish promising effects of the reverse rotation in axial impellers and the arrangement of two different impellers in a multiple impeller system. With the rapid growth of industrialization, understanding the fluid dynamics in a multiple impeller stirred vessel is fundamental to optimize and scale up industrial mixing operations. Hence, the empirical findings in this study will be beneficial in selecting the suitable combination of impellers and the orientations that will enhance industrial mixing operations. Apart from that, the present work also illustrates that the computational technique used can be extremely valuable in determining the fluid dynamics in complex multiple impeller system which is challenging to analyse experimentally.

Unravelling workplace educators’ judgment processes when assessing students’ performance at the workplace

ABSTRACT The assessment of workplace learning by educators at the workplace is a complex and inherently social process, as the workplace is a participatory learning environment. We therefore propose seeing assessment as a process of judgment embedded in a community of practice and to this purpose use the philosophy of inferentialism to unravel the judgment process of workplace educators by seeing it as an interrelated system of judgments, actions and reasons. Focussing on the unfolding of a process, we applied a longitudinal holistic case study design. Results show that educators are engaged in a constant judgment process during which they use multiple and adaptive frames of reference when forming their judgment about students. They construct an overarching image of students that develops throughout the placement, and their judgments about students go hand in hand with their actions relating to fostering independent practice.

Numerical investigation of full helicopter with and without the ground effect

In the present work, the aerodynamic performance of the full helicopter PSP in hover flight is investigated using a simplified concept of multiple reference frame (MRF) technique in the context of high-order Monotone Upstream Centred Scheme for Conservation Laws (MUSCL) cell-centred finite volume method. The predictions were obtained for two ground distances and several collective pitch angle at tip Mach number of 0.585. The calculations were made for both out-of-ground-effect (OGE) and in-ground-effect (IGE) cases and compared with experimental data in terms of pressure distribution and integrated thrust and torque and vortex system.

Parametric Analysis Using CFD to Study the Impact of Geometric and Numerical Modeling on the Performance of a Small Scale Horizontal Axis Wind Turbine

The reliance on Computational Fluid Dynamics (CFD) simulations has drastically increased over time to evaluate the aerodynamic performance of small-scale wind turbines. With the rapid variability in customer demand, industrial requirements, economic constraints, and time limitations associated with the design and development of small-scale wind turbines, the trade-off between computational resources and the simulation’s numerical accuracy may vary significantly. In the context of wind turbine design and analysis, high fidelity simulation under full geometric and numerical complexity is more accurate but pose significant demands from a computational standpoint. There is a need to understand and quantify performance deterioration of high fidelity simulations under reduced geometric or numerical approximation on a single small scale turbine model. In the present work, the flow past a small-scale Horizontal Axis Wind Turbine (HAWT) was simulated under various geometric and numerical configurations. The geometric complexity was varied based on stationary and rotating turbine conditions. In the stationary case, simple 2D airfoil, 2.5D blade, 3D blade sections are evaluated, while rotational effects are introduced for the configuration 3D blade, rotor only, and the full-scale wind turbine with and without the inclusion of a nacelle and tower. In terms of numerical complexity, the Single Reference Frame (SRF), Multiple Reference Frames (MRF), and the Sliding Meshing Interface (SMI) is analyzed over Tip Speed Ratios (TSR) of 3, 6, 10. The quantification of aerodynamic coefficients of the blade (Cl, Cd) and turbine (Cp, Ct) was conducted along with the discussion on wake patterns in comparison with experimental data.

Forward Flight Performance Analysis of Supercritical Airfoil in Helicopter Main Rotor

In this research, the aerodynamic performance and flow characteristics of NASA SC (2)-0714 airfoil and HH02 airfoil in the helicopter main rotor are evidently analyzed. The supercritical airfoil is used in the aircraft for attaining better transonic and high-speed flow characteristics. Moreover, a specialized helicopter airfoil called HH02 is used in the Apache helicopter rotor for increasing the operational speed. As most of the high-speed helicopters are using four-bladed main rotor configuration, it is analyzed with prior attention. The lift and thrust act in different directions for the forward phase of the flight whereas the lift and thrust act in the same direction for the other phases of flight, which is analyzed in this work. The computational analysis is done by using ANSYS Fluent whereas the rotational analysis is done by using the Multiple Reference Frame (MRF) method. An analysis is carried out for different RPM of 400,600 and 800 with the combination of 0.3, 0.4 and 0.5 Mach numbers with the assistance of grid independence test. The result shows that the NASA SC (2)-0714 rotor increases the thrust of the rotor around 5% to 10% under various rotor and forward speeds. Thus, the results proves that the supercritical airfoil is highly capable of producing higher thrust and good aerodynamic characteristics.

Numerical analysis and optimization of key parts in the stirred tank based on solid-liquid flow field

In order to further improve the mixing performance of the mixing device, the structure of the agitator was optimized, and the effects of the diameter and pitch of the agitator on the solid-liquid suspension characteristics were analyzed by single factor method. Multiple reference frame (MRF), computational fluid dynamics, Euler multiphase flow model and standard K- ε turbulence model were used to investigate the effect of the height from the bottom of the agitator on the suspension characteristics of particles in the agitator was studied. The results show that reducing the height from the bottom of the agitator can promote the suspension of particles at the bottom of the tank, but too low height from the bottom will easily produce mixing dead zone at the bottom of the tank, and cause the accumulation of particles. Reducing the height of the agitator from the bottom will enlarge the clear liquid area of the flow field, cause uneven particle distribution and increase the stirring torque. With the increase of agitator diameter, the critical suspension speed of the flow field decrease, but the stirring power required by the flow field increase. Increasing the blade spacing in a certain range can promote the suspension of particles and make the distribution of particles in the flow field more uniform. Therefore, the mixing power and the uniformity of particle concentration distribution need to be considered together in order to make the mixing device more efficient and energy-saving.

Numerical study on the cavitation noise of marine skew propellers

In this study, numerical simulations on the noise of the underwater marine propeller for different pressures, skew angles, and performance conditions are investigated. The study has been carried out for the prediction of cavity and noise cavitation characteristics of the propeller. The blade sheet cavitation created by an underwater propeller is then evaluated using numerical analysis. The cavitation and cavity around marine propellers were predicted using MRF (Multiple Reference Frame) techniques. The simulation uses the Reynolds Averaged Navier-Stokes (RANS) formulation with the turbulence model k-ω Shear Stress Transport and the Fast Fourier Transform. The FW-H equation is used to measure far-field radiation under various operating conditions. The simulation is carried out to present that the pressure and skew propeller angles have an effect on the form and area of the cavity, as well as cavitation noise. The noise characteristics at various positions of hydrophones and speeds of the marine propeller are presented. The 3D model of B-series marine propeller with D=250 mm, Z=4, P/D= 1.0, AE/AO=0.55, skew angles of 16, 35, 53, and 72 degrees at advance coefficient, J=0.221, is used for the simulation

Studi Numerik Centrifugal Fan Tipe Impeller Backward dengan Variasi Putaran Fan

The primary air fan functions as a primary air producer which is used as air to transport coal powder from the pulverizer to the burner to be burned in the boiler furnace. This study aims to obtain the effect of the rotation variation of fan to fluid flow characteristics such as the distribution of total pressure, the dynamic pressure, the pressure static contours, velocity distribution, and the fan optimal efficiency. This study was numerical study with simulated a backward impeller type centrifugal fan in a two-dimension model using Fluid Computational software with the multiple reference frame method with the variation of fan rotation. Based on the visualization of the pressure contour and velocity distribution, it could be concluded that there was a volute phenomenon, this was indicated that the greater the volume area in the volute is the greater the total pressure value too. Based on the visualization of the outlet velocity distribution at the position of -0,8531m to -1,01301m, it was found that the velocity is close to the value of 0 m/s2. It showed that the minimum velocity in the area due to the volute tongue radius occurs a flow collision and it impacted the velocity in the area decreased up to V=0. From the simulation results, it was found that the greater the fan rotation value was the greater the efficiency value too. It would be verified by the actual operating data of the centrifugal fan with a minimum rotation range value of 1194 rpm to a maximum of 1468 rpm

Mixing studies in an unbaffled bioreactor using a computational model corroborated with in-situ Raman and imaging analyses

• Designed a computational model of a non-standard 10 L bioreactor. • Single-phase mixing simulations validated against literature. • Tracer mixing experiments performed at various stirrer speeds & liquid viscosities. • Mixing times calculated from image analyses & inline Raman spectroscopy. • Simulated mixing times validated with experimental mixing data. A computational model of an unbaffled 10 L bioreactor fitted with a unique serpentine tubing structure and two standard six-blade Rushton impellers was developed using Reynolds Averaged Navier-Stokes (RANS) turbulence models (standard k-ε and k- ω SST) and multiple reference frame (MRF) CFD modeling. Flow and mixing time simulations were validated with literature findings for baffled stirred tanks ranging from laboratory to commercial scales, viz. 5 L, 38 L, 22 m 3 and 98 m 3 . Global quantities such as power number ( N p ), impeller flow number ( N Q ) and single-phase mixing times ( t 95 ) were verified with literature values. Flow and mixing simulations in the 10 L bioreactor were performed in full domain and a reduced 60° domain models. The reduced 60° domain model was selected for calculating mixing times at stirrer speeds from 50 to 500 rpm and fluid viscosities of 1 to 6 cP. This viscosity range corresponds to a typical high cell density E. coli fermentation run. For stirrer speeds more than 150 rpm in the 10 L bioreactor ( Re > 3000), the mixing pattern in such high-density cultures could be reliably simulated with the standard k-ε model. Mixing time simulations in the 10 L bioreactor were validated against tracer mixing experiments using an inert red dye with HD video recording and inline Raman spectroscopy. Analyses of video images, univariate calculations and multivariate chemometrics on Raman data yielded experimental mixing times to compare with simulation results at four distinct spatial positions in the unbaffled 10 L bioreactor.

Hydrodynamic Characteristics of an Internal Recycle Berty Catalytic Reactor in Batch/Continuous or Packed/Fluidized Bed Modes

Berty-type internal recycle reactors offer great opportunities for screening catalysts and reproducing catalytic reacting conditions in multiple processes, thus approaching industrial reactions while amplifying kinetic information. However, the rational design of these reactors requires a deeper understanding of their governing hydrodynamics and equations so that they can be better utilized in batch or continuous mode or as packed or fluidized beds. In this work, by adopting a slice model to represent a three-dimensional symmetric geometry with porous zone settings for catalyst beds, coupled with a species transport model, multiple reference frame, and SST k–ω turbulence model, we developed a computational fluid dynamic simulation strategy of a commercial Berty reactor manufactured by Integrated Lab Solutions (ILS). We conducted experiments to validate the proposed modeling approach under continuous packed bed operations, through which the hydrodynamic behaviors with packed/fluidized beds under the batch mode were also investigated by studying the influences of the transient injection, bed porosities, and rotation rates. As a result, we reported a set of equations to assess the bed velocity and contact time under different porosities, which simplified the performance improvements while replacing the need to perform complex simulations or conduct costly experiments. On the grounds of these hydrodynamic simulations and under various operating conditions, we discussed the pertinence of these instruments for intrinsic kinetic measurements in the batch/continuous or packed/fluidized bed operational modes.

Impact of impeller modelling approaches on SBES simulations of flow and residence time in a draft tube reactor

Predictions for flow and residence time in a draft tube reactor were investigated using momentum source, Multiple Reference Frame (MRF) and sliding mesh approaches together with the Stress Blended Eddy Simulation (SBES) turbulence model. Predictions of mean and fluctuating velocities in the annulus, and the exit residence time distribution, are found to be similar and in close agreement with experimental data with all impeller modelling approaches, confirming that the flow in the bulk of the vessel is dominated by the turbulence generated at the draft tube exit and is relatively insensitive to the small-scale turbulence generated by the impeller. On consideration of both accuracy and computational cost, momentum source and MRF approaches offer significant advantages for industrial simulation in this geometry. The SBES model is found to work well in a complex internal flow geometry with an impeller, negating the need for simplifications like zonal LES approaches.

Numerical investigation of a tidal stream turbine using two methods of the Multiple Reference Frame and the Actuator Disk Momentum

Numerical investigation of a tidal stream turbine using two methods of the Multiple Reference Frame and the Actuator Disk Momentum

Assessment of the methodology for the CFD simulation of the flight of a quadcopter UAV

The computational fluid dynamics (CFD) simulation is gaining attraction in the development of modern unmanned aerial vehicles (UAV), but few research has been made on quadcopters and the characterisation of the flows generated by the propellers, which determine the thrust capacity. Therefore, the purpose of this study is to assess the performance in the 3D flow simulation of the most promising methods: multiple reference frames (MRF) and sliding meshes. Additionally, the effect of the ground proximity has been included. The results for a sole propeller revealed both models as equivalent with respect to the evaluation of the ground effect, even though a noticeable deviation was observed in the thrust quantification. In the case of quadcopters, the relative position between blades and frame was proved as a key factor. Thus, similar rates of thrust change were obtained when minimising the superposition of the blade over the body arms in the MRF case. However, the thrust magnitude differed at least 11% at any simulated position. Assuming this deviation, the significantly lower computational cost of the MRF turns this model into a very interesting option. Finally, the influence of the relative blade-to-blade position in the sliding simulation was also assessed.

Analytical and Computational Fluid Dynamics Models of Wells Turbines for Oscillating Water Column Systems

AbstractThe sea is an important renewable energy resource for its extension and the power conveyed by waves, currents, tides, and thermal gradients. Amongst these physical phenomena, sea waves are the source with the highest energy density and may contribute to fulfilling the global increase of power demand. Despite the potential of sea waves, their harnessing is still a technological challenge. Oscillating water column systems operating with Wells turbines represent one of the most straightforward and reliable solutions for the optimal exploitation of this resource. An analytical model and computational fluid dynamics models were developed to evaluate the functioning of monoplane isolated Wells turbines. For the former modeling typology, a blade element momentum code relying on the actuator disk theory was applied, considering the rotor as a set of airfoils. For the latter modeling typology, a three-dimensional multi-block technique was implemented to create the computational domain with a fully mapped mesh composed of hexahedral elements. The employment of circumferential periodic boundary conditions allowed for the reduction of computational power and time. The models use Reynolds-averaged Navier-Stokes (RANS) or u-RANS schemes with a multiple reference frame approach or the u-RANS formulation with a sliding mesh approach. The achieved results were compared with analytical and experimental literature data for validation. All the developed models showed good agreement. The analytical model is suitable for a fast prediction of the turbine operation on a wide set of configurations during the first design stages, while the computational fluid dynamics (CFD) models are indicated for the further investigation of the selected configurations.

Vortex Pump as Turbine for Energy Recovery in Viscous Fluid Flows With Reynolds Number Effect

Abstract A vortex pump with a specific speed of 76 was studied in its turbine mode by using fluent 6.3 based on the steady, three-dimensional, incompressible, Reynolds time-averaged Navier–Stokes equations, standard k-ε turbulence model, and nonequilibrium wall function in multiple reference frame system. The performance and flow structure of six liquids with different densities and viscosities were characterized, and the hydraulic, volumetric, and mechanical losses were discomposed. The correction factors of flow rate, head, shaft-power, efficiency, and disk friction power in turbine mode were correlated with impeller Reynolds number at three operational points. The conversion factors of flow rate, head, efficiency from the pump mode to the turbine mode were expressed with Reynolds number and compared with the counterparts of centrifugal pumps in the literature. It was indicated that the vortex pump can produce power as a turbine but becomes inefficient with increasing viscosity or decreasing impeller Reynolds number, especially as the number is smaller than 104 due to increased hydraulic, volumetric, and mechanical power losses. A vortex structure with radial, axial, and meridian vortices occurs in the impeller at different flow rates and viscosities. The incidence at blade leading edge and deviation angle at the blade trailing edge depend largely on flow rate and viscosity. The impeller should be modified to improve its hydraulic performance under highly viscous fluid flow conditions. The entropy generation rate method cannot demonstrate the change in hydraulic loss with viscosity when the Reynolds number is below 104.

Conceptual Design and Multi-Disciplinary Computational Investigations of Multirotor Unmanned Aerial Vehicle for Environmental Applications

This study focuses on establishing a conceptual design for a multirotor unmanned aerial vehicle (UAV). The objectives of this octocopter are to reduce the number of flight cancelations and car accidents owing to low-visibility issues and to improve abnormal environmental conditions due to the presence of smoke. The proposed octocopter contains a convergent–divergent [CD] duct-based storage tank, which provides a platform to store saltwater and allows it to fly in foggy zones. Fine saltwater is sprayed from the octocopter and dispersed into the low clouds, thereby altering the vapor’s microphysical processes to break it up and improve visibility. The nature of the seawater and its enhanced fluid properties, due to the involvement of octocopter, creates the fluid flow mixing between atmospheric fluids and spraying particles, which increases the settling of foggy and smokey content groundward. For deployment, the conceptual design of the octocopter was initially constructed through analytical approaches. Additionally, three unique historical relationships were created. The standard engineering approaches involved in this work were stability analysis through MATLAB and fluid-property analysis through computational fluid dynamics (CFD) cum multiple reference frame (MRF) tools. The systematic model of this octocopter was developed by CATIA, and thereafter CFD and fluid–structure-interaction (FSI) analyses were computed, in ANSYS Workbench, on the octocopter for various environmental conditions. The aerodynamic forces on the drone, the enhancement of dynamic pressure by the presence of high amounts of rotors and nozzle sprayer, suitable material to resist aerodynamic loadings, and tests on the efficiency of the controller and its electronic components were investigated in detail. Finally, the proposed octocopter-based dynamic system was conceptually constructed.

Effect of baffle configuration on hydrodynamics and solid suspension in a continuous stirred vessel

Hydrodynamics of stirred vessel is difficult to predict due to complex flow conditions existing inside the reactor. Hence in this present work, hydrodynamics and solid suspension in a continuous stirred vessel are numerically investigated using Computational Fluid Dynamics (CFD). To predict the flow field, transient 3 D CFD simulations are performed using Multiple Reference Frame along with Sliding Mesh approach and realizable k-ε turbulence model. The flow field is quantified by spatial/temporal variation of liquid velocity magnitude and liquid circulation. To improve the performance of the stirred vessel, draft tube baffle configurations are proposed and these predictions are compared with the unbaffled system. Further, the suspension characteristics of solids are predicted using the Euler-Granular model and quantified by calculating cloud height in stirred vessel system. The solid concentration is found to be uniform in the baffled stirred vessel and it is concentrated at the bottom of the vessel in the unbaffled stirred vessel. Thus, the proposed draft tube configuration supports in achieving the uniform distribution of solids and overcomes sedimentation of solids in stirred vessel system.