Sliding Mesh Technique Research Articles

Investigation on Resistance, Squat and Ship-Generated Waves of Inland Convoy Passing Bridge Piers in a Confined Waterway

The average and unsteady hydrodynamics of an inland convoy passing bridge piers in a confined waterway were investigated using both numerical and experimental approaches. The numerical simulations are realized by solving the RANS (Reynolds-averaged Navier–Stokes) equations accounting for the solid body motion using the sliding mesh technique, while the experiments were carried out in the towing tank. The advancing resistance, trim, sinkage and ship-generated waves were analyzed as functions of the water depth, distance between bridge piers, draught and velocity. The existence of the piers is found to only influence the transient hydrodynamics of the convoy, but not the averaged properties. The ship-generated waves, especially the wave profiles at a specific lateral position, were characterized. Two wave crests exist at the pier position because of the additional reflections, creating a very complex wave pattern in the confined waterway.

A better insight on physics involved in the self-starting of a straight-blade Darrieus wind turbine by means of two-dimensional Computational Fluid Dynamics

Computational Fluid Dynamics (CFD) has recently provided the needed improvements in simulation capabilities that allowed enhancing the design of Darrieus wind turbines. While the performance in operating conditions has increased, poor self-starting is still one of the major drawbacks of these machines. In this study, the aerodynamics of Darrieus-turbines during start-up were investigated using a two-dimensional CFD approach. A fluid-structure interaction simulation was carried out using the ANSYS® FLUENT® solver incorporating the sliding mesh technique and enabling the rotational degree of freedom of the Six Degrees of Freedom (6DOF) solver. The issue of translating a fully-resolved flow field into lumped parameters of use to characterize the instantaneous kinematic properties of the airfoils is tackled by means of two velocity sampling methods recently proposed in the literature, i.e. the 2-PointsAverage and LineAverage methods. The results provide a clear estimation of how much the blade local absolute velocity (V∞, L) is dependent on the instantaneous tip speed ratio during the first revolutions of the starting rotor. At λ < 1, the blockage of the slow-moving blades causes sudden acceleration/deceleration in V∞, L. At 1 < λ < 1.5, a significant increase in V∞, L takes place between 90° < θ < 180° where the blade is moving in the direction of the wind. At λ > 1.5, V∞, L decreases significantly during the azimuth positions of 210° < θ < 340°, where it falls in the other blades’ wake zone. It is also confirmed that the drag force significantly contributes to the Darrieus turbine start-up during the initial cycles, up to λ ≤ 1.5; this in turn corroborates the importance of having reliable data not only for lift coefficient of the airfoil but also of drag coefficient, especially at high angles of attack. Overall, the present study is thought to provide a deeper understanding of the aerodynamics of the Darrieus turbine behaviour during starting that will hopefully enable optimization of these machines.

Effect of pitch angle in the performance of wind turbine using numerical techniques

The study of performance on the Darrieus turbine is an emerging topic using many techniques to make it improve the performance up to the industrial standard. The angle of air received at the leading edge of the aerodynamic wind blade influencing the performance of the turbine. Every instant of the angle of air varying each blade due to the rotating motion of the turbine. The objective of this paper is to determine the optimum pitch angle using the Computational Fluid Dynamics simulation technique in Ansys 18.1, where the sliding mesh technique is used. The geometry of the blade is taken from the previous literature which is used to verify the results. The various pitch angles are chosen from -6° to +6°. The coefficient of the moment is calculated using K-epsilon SST 2 equation model. The graph is plotted between TSR and the coefficient of performance of various pitch angle for optimization purpose.

Numerical prediction of cavitation erosion to investigate the effect of wake on marine propellers

This paper presents validation studies to simulate performance, cavitation and cavitation erosion properties of the King's College (KCD) KCD-193 model propeller. The simulations are performed to investigate the effect of wake on the cavitation formation and the cavitation erosion intensity. The numerical (CFD) study is achieved by using unsteady Reynolds Averaged Navier-Stokes (RANS) and Detached Eddy Simulation (DES) techniques with SST (Menter) k-ω turbulence model. The Schnerr-Sauer cavitation model and Eulerian approach with the Volume of Fluid (VOF) multiphase model are used to model a two-phase cavitation flow. The sliding mesh technique is applied to simulate the rotation of the propeller, and particular mesh refinement is performed on the regions where cavitation development is observed. Erosion intensity values on the propeller surface are obtained by Erosive Power Method (EPM) approach, and erosion formation on the blades is illustrated by utilizing the erosion intensity dataset. Numerical comparison for the erosion intensity values using RANS and DES models is carried out to evaluate the effect of wake in behind condition. Numerical results are evaluated against cavitation tunnel measurements at the Emerson Cavitation Tunnel (ECT) of Newcastle University. The main objectives of the study are to obtain the cavitation and cavitation erosion formation on the propeller in good agreement with experimental data obtained in ECT and to investigate the characteristics of the erosion intensity subject to cavitation conditions. In view of the flow conditions investigated, the RANS model is also found appropriate and required less computing efforts to predict the erosion intensity than the DES model. The results confirm the EPM method is to be compatible in predicting the erosion intensity. The results of the simulations indicate that a decrease in cavitation number does not necessarily cause an increase in the erosion intensity, requiring further investigation.

O-008. Influence of Hypertension in Pregnancy on Hematological Phenotypes of Preterm Infants with Gestational Age Inferior to 32 Weeks

This paper presents validation studies to simulate performance, cavitation and cavitation erosion properties of the King's College (KCD) KCD-193 model propeller. The simulations are performed to investigate the effect of wake on the cavitation formation and the cavitation erosion intensity. The numerical (CFD) study is achieved by using unsteady Reynolds Averaged Navier-Stokes (RANS) and Detached Eddy Simulation (DES) techniques with SST (Menter) k-ω turbulence model. The Schnerr-Sauer cavitation model and Eulerian approach with the Volume of Fluid (VOF) multiphase model are used to model a two-phase cavitation flow. The sliding mesh technique is applied to simulate the rotation of the propeller, and particular mesh refinement is performed on the regions where cavitation development is observed. Erosion intensity values on the propeller surface are obtained by Erosive Power Method (EPM) approach, and erosion formation on the blades is illustrated by utilizing the erosion intensity dataset. Numerical comparison for the erosion intensity values using RANS and DES models is carried out to evaluate the effect of wake in behind condition. Numerical results are evaluated against cavitation tunnel measurements at the Emerson Cavitation Tunnel (ECT) of Newcastle University. The main objectives of the study are to obtain the cavitation and cavitation erosion formation on the propeller in good agreement with experimental data obtained in ECT and to investigate the characteristics of the erosion intensity subject to cavitation conditions. In view of the flow conditions investigated, the RANS model is also found appropriate and required less computing efforts to predict the erosion intensity than the DES model. The results confirm the EPM method is to be compatible in predicting the erosion intensity. The results of the simulations indicate that a decrease in cavitation number does not necessarily cause an increase in the erosion intensity, requiring further investigation.

A numerical investigation into the influence of bio-inspired leading-edge tubercles on the hydrodynamic performance of a benchmark ducted propeller

Marine ducted thrusters are widely used to provide propulsive thrust for a range of marine vessels due to their high thrust capability in heavy loaded conditions. This paper presents a novel and optimised bio-inspired marine ducted thruster, where leading-edge tubercles are applied to the duct of a ducted propulsor to explore the impact on hydrodynamic performance. Nine different geometrical configurations of tubercle were investigated with varying amplitude and wavelength within the optimisation study. The hydrodynamic performance of the marine ducted thruster is evaluated using a commercially available computational fluid dynamics (CFD) code, STAR-CCM+, with an incompressible implicit unsteady Reynolds-Averaged Navier Stokes (RANS) solver combined with the Body Force Propeller (BFP) method for the duct optimisation study. Then, the selected optimal duct was chosen for further analysis using the propeller resolved Rigid Body Motion (RBM) method, more commonly known as the sliding mesh technique. Through the numerical optimisation study, the leading-edge modification is predicted to have the capability to enhance the duct thrust in the heavy-loaded conditions, although this is dependent on the wavelength and amplitude of the tubercle. Furthermore, during the investigation the traditional tubercle behaviour was observed, namely the high-low pressure patterns and streamwise counter-rotating vortices. Interestingly, flow separation was observed to be compartmentalised on the outer side of the duct cross-section in conditions where flow separation occurred such as at the maximum efficiency operating point.

Numerical method to predict ice accretion shapes and performance penalties for rotating vertical axis wind turbines under icing conditions

This paper proposes a numerical method to predict the ice accretion shapes and aerodynamic performance of rotating vertical axis wind turbine (VAWTs) under icing conditions. A multiple reference frame (MRF) and sliding mesh technique (SMT) are combined to efficiently reflect the unsteady icing effects on rotating wind turbines. The SMT calculates the flow field considering the rotational and unsteady effects of the VAWTs. The MRF can efficiently clarify the rotational effects of the droplet field and ice accretion. Using the MRF technique, a series of icing simulations is implemented in which the ice shapes are updated at azimuth angle intervals of 36°. Using the proposed method, ice shapes in agreement with those obtained in icing wind tunnel tests can be obtained. Moreover, ice that is evenly distributed over the blade surface under glaze ice conditions can be examined instead of only the forms concentrated on the leading-edge, such as ice horns. The overall output power of an ice-covered VAWT is noted to be significantly reduced. Massive flow separation is induced owing to the increased airfoil thickness at azimuthal angles between 0° and 180°. Nevertheless, the performance of the thickened airfoil is enhanced owing to the delayed flow separation via dynamic stall in azimuthal angles between 180° and 270°.

Computational Investigation on Effect of Impeller Dimension on Fluid Flow and Interface Behavior for Kanbara Reactor Hot Metal Treatment

Kanbara Reactor (KR) is widely used for hot metal desulfurization pretreatment in the steelmaking industry. The configuration of its impeller plays a crucial role in the reactor performance, but its function is not fully understood. Herein, a 3D volume of fluid (VOF) model coupled with the sliding mesh technique is developed, and the performance of five impellers with different dimensions is investigated. After the test of grid dependency, the calibration of turbulent models, and the validation via experiments, the numerical model is applied to study the typical developing phenomena and the effect of impeller dimension on the fluid flow characteristics, mixing time, interface profile, and vortex core depth. The results show that the centrifugal discharging flow extruded by the rotating impeller creates a double‐recirculation flow pattern in the axial direction. When the aspect ratio χ of the impeller increases, the upper recirculating region is successively strengthened and enlarged. Furthermore, the mixing time as a function of impeller configuration exists a minimum value. Impeller III is the optimal configuration in the current study. In addition, the relationship between vortex core depth and χ is obtained, and the velocity of the gas–liquid interface increases with the increase in χ.

Interactions of wakes and shock waves with two-phase air/mist cooling in a transonic gas turbine stage

A 2-D two-phase numerical simulation was conducted to investigate the effect of interactions of moving wakes and shock waves on mist cooling performance over airfoils in a transonic gas turbine stage. The two-phase flow consists of a continuous phase (i.e., air) and a dispersed phase (i.e., mist). The tracking and evaporation of the mist are simulated by using the discrete phase model (DPM). The interactions between the droplets themselves with respect to collision and breakup were simulated by using the breakup and coalescence sub-models. The motion of the rotor domain was simulated by using the linear sliding mesh technique to study the transient stator-rotor interaction. The results show that the passing unsteady wakes caused by the blade rotation press the mist toward the blade surface, providing more enhanced film cooling effectiveness. The oblique shock wave was observed downstream of the vanes passage. The lambda shock wave was observed downstream of the blades passage. Both shock waves did not exert noticeable effect on the air/mist cooling performance. Injecting a 10% mist ratio noticeably improved the cooling enhancement by obtaining a maximum temperature reduction of 200 K and an average temperature reduction of 51 K on the vane, and a maximum of 350 K reduction and an average of 24 K reduction on the blade surface under the influence of wakes and shocks. Injecting the tiny water droplets increased the total pressure losses by 0.1% on the vane and 4% on the blade compared to the air cooling case. Injecting mist has negligible effect on the formations of shocks/wakes and their corresponding behaviors.

Influence of blockage ratio on slipstreams in a high-speed railway tunnel

The train-induced airflow in a railway tunnel is of great significance for tunnel ventilation, fire rescue, and ancillary facilities overall. Previous research mainly focused on piston wind in metro tunnels, while the slipstream in high-speed railway tunnels is more drastic and complicated owing to the faster vehicle speed and diverse blockage ratios. In this research, a computational fluid dynamics (CFD) study was carried out to explore the three-dimensional transient airflow induced by a commercial high-speed train circulating through tunnels at 350 km/h under different blockage ratios (β = 0.175, 0.160, 0.140, 0.122, and 0.112). First, the train-tunnel model was established based on the unsteady Reynolds-Averaged Navier–Stokes (URANS) method merged with the sliding mesh technique, altogether validated with experimental evidence. Then, the resultant slipstream and the individual components were investigated, and it was concluded that the longitudinal component was dominant. The variation behaviors of the slipstream and local pressure with the different blockage ratios were comparatively obtained. Finally, the relationships between the slipstream and the spatial distance in longitudinal, lateral, and vertical directions were analyzed. This study provides a guideline for the determination of the tunnel clearance, and wind load evaluation in a high-speed railway tunnel.

Hydrodynamics and wake flow analysis of a Π-type vertical axis twin-rotor tidal current turbine in surge motion

For a floating tidal current turbine power station, the motion response of the floating carrier would affect the hydrodynamic performance of the tidal current turbine. To study the turbine loads and power output characteristics of the proposed twin-rotor turbine in moving condition, the hydrodynamic performance of a vertical axis twin-rotor turbine in surge motion is thoroughly discussed in this manuscript. Based on the moving mesh and sliding mesh technique, the rotary motion and surge motion of the turbine are combined to simulate the turbine operation conditions in waves and currents. The twin-rotor turbine working at different surge frequencies, surge amplitudes, and tip speed ratios is simulated and the simulation results are compared with the fixed turbine in an uniform flow. The change characteristics of thrust force, lateral force, and flow field are analyzed. The results show that the twin-rotor can improve the power output efficiency better than a stand-alone turbine. Surge frequency and surge amplitude have very little influence on the average power output of the turbine. The fluctuation amplitude of the thrust and lateral forces of a twin-rotor turbine is larger than the stand-alone turbine, while the fluctuation amplitude of thrust and lateral forces increase with surge amplitude and frequency. Spectra of turbine loads and power output show that surge and rotation frequencies have different impacts on the dynamics and performances of the turbine. The research results can provide a reference for the development of floating tidal current power stations in the future.

Performance enhancement of Savonius wind turbine by blade shape and twisted angle modifications

Three-dimensional CFD simulations are carried out to study the increase of power generated from Savonius vertical axis wind turbines by modifying the blade shape and blade angel of twist. Twisting angle of the classical blade are varied and several proposed novel blade shapes are introduced to enhance the performance of the wind turbine. CFD simulations have been performed using sliding mesh technique of ANSYS software. Four turbulence models; realizable k -[Formula: see text], standard k - [Formula: see text], SST transition and SST k -[Formula: see text] are utilized in the simulations. The blade twisting angle has been modified for the proposed dimensions and wind speed. The introduced novel blade increased the power generated compared to the classical shapes. The two proposed novel blades achieved better power coefficients. One of the proposed models achieved an increase of 31% and the other one achieved 32.2% when compared to the classical rotor shape. The optimum twist angel for the two proposed models achieved 5.66% and 5.69% when compared with zero angle of twist.

Cycloidal rotor coupled with DBD plasma actuators for performance improvement

This study analyzes the effect of DBD plasma actuators on the unsteady flow of a cycloidal rotor with six blades of NACA 0016 type using computational fluid dynamics (CFD). The flow field modeling is performed through a sliding mesh technique that was used with k-ω SST turbulence model. The plasma body force generated by a dielectric barrier discharge DBD actuator is modeled with the phenomenological Shyy's model. The impact of plasma actuators on the flow is studied using two actuators located on the upper and bottom surfaces of the airfoil in each of the cyclorotor blades. Three cases are studied: actuation off; actuation over the upper surface of the blades; actuation over the bottom surface of the blades. The vorticity field and the evolution of the lift, thrust and power consumption are analyzed for when a control law is designed that combines both actuations based on the two last cases. The results show that the use of the proposed control law for plasma actuation improves the cyclorotor lift peak value per blade in 11% and the overall thrust by 1.5%. It is also demonstrated that the plasma actuator mitigates the virtual camber on the cyclorotor, this effect is named counter-virtual camber. We show that DBD actuators produce a reduction on the recirculation bubble at the blades suction surface. This effect is important to reduce the thickness of the blades, bringing improvements in terms of mitigating unsteady periodic mass acceleration in cyclorotors.

Numerical investigation of conventional and tapered Savonius hydrokinetic turbines for low-velocity hydropower application in an irrigation channel

In the present work, computational fluid dynamics simulation was carried out using ANSYS Fluent to study the performance of conventional and tapered turbine blades for hydrokinetic power generation. The sliding mesh technique is used to study the influence of taper on conventional Savonius turbine using the SST k-ω turbulence model and performance parameters were determined. The geometric parameters used in the present simulation for conventional and tapered turbine blades are aspect ratio and overlap ratio of 1.0 and 0.0. The inlet velocity and depth of water used for present simulation are 0.5 m/s and 103.6 mm for both conventional and tapered turbine blades. The results show that a 5% increase in the performance of a conventional turbine as compare to tapered turbine blade with a taper angle of 5°. The value of maximum coefficient of power for conventional Savonius turbine blade is 0.21 with a tip speed ratio 0.9. The flow field around the conventional and tapered turbine blades at different angular positions are analysed. It was found that there is a loss of energy at the exit side of the advancing blade for the case of tapered turbine, that leads to 5% reduction of performance as compared to the conventional turbine.

Investigation on optimization of self-adaptive closure law for load rejection to a reversible pump turbine based on CFD

Pumped storage plants (PSP) are operated under transient processes frequently in the case of the intermittent and unpredictable renewable energy. When PSPs are working in the load rejection process, the serious accident may be caused by the significant fluctuations of rotating speed and pressure. Seeking an appropriate law of guide vane movement in load rejection process is an approach to improve operating stability of PSP. This paper focuses on the optimization of self-adaptive closure law of pump turbine model for one Chinese PSP, based on sliding mesh technique and current closure law. Variations of speed and pressure are regarded as judgment functions. Meanwhile, detached eddy simulation(DES) is adopted to characterize internal flow field of pump turbine(PT) with adaptation of the optimized closure law. Not only the distribution of pressure and the turbulence kinetic energy in flow domains is analyzed details, but also the fluid evolution in passage is investigated. As a result, the optimized closure law is beneficial to impair the fluctuating rates of speed and pressure in transient process. It is illustrated that both the rotor-rotor and rotor-stator interaction in vaneless spaces are the sources of increased fluid instability in pump turbine. Note that the unstable flow regime emerges at the same moment in the inlet and outlet conduits, whereas their locations are opposite to the unit.

An Introductory CFD Analysis Study of Novel Cavity Vane Driven Wind Turbine Blade Design

Climate in Malaysia is heavily influenced by monsoon seasons, where the wind speed pattern is inconsistent and highly unsteady. Existing commercial wind turbines are only designed to accommodate high wind speed regions. In order to harvest energy in Malaysia, design modification is required on conventional wind turbine blade. This paper presents an introductory computational investigation of proposed drag driven vertical axis wind turbine. The objective of this research is to investigate the factors that governs the aerodynamics attributes of the proposed design. The design is simulated in 2D using sliding mesh technique via FLUENT based on URANS model. Previous mesh dependency study shows that fine and medium grid topology indicated a good agreement. In this numerical study, the proposed wind turbine is simulated based on SST k-ω turbulent transport model under fine grid spatial discretization. The design is analyzed under the influence of constant freestream velocity of 25 m/s in order to study the behavior of the turbine at high speed and low RPM. Result shows that high static pressure of 64.8 kPa exerts on the returning blade 1 which overwhelms the motion of advancing blade. Blade 1-3 indicated stable numerical values after 216°. Hence, the governing factors in terms of flow properties that affected the wind turbine is studied for future improvement. It is found that the cavity vane of the proposed design requires modification in order to improve moment.

Ground Test and Numerical Simulation on Ground Effect of Ducted Propeller System

The aerodynamic performances of a ducted propeller system applied in a manned vertical takeoff and landing aircraft considering the ground effect are investigated. Based on the ground test and CFD simulation combined with sliding mesh technique, the thrust and power characteristics of the ducted propeller under different heights between the duct and ground are compared and analyzed, and the influence mechanism of the ground effect on the aerodynamic performance of the ducted propeller is detailed analyzed based on the CFD simulation results. The test and simulation results show that, the ground near the ducted propeller leads to a high-pressure zone to block the jet flow through the outlet of the duct, while an upward rebounded flow with the vortex rings is also generated to affect the aerodynamic forces and powers of both the duct and propeller. As the influence of the high-pressure zone, the thrust of the propeller increases. However, the thrust of the duct decreases when the rebounded flow is inhaled again into the duct. With the increase of the heights between the ground and the ducted propeller, the ground effect is weakened, and the power of the system recovers more quickly than the thrust. In general, the ground effect seriously affect the aerodynamic efficiency of the ducted propeller in near ground hover state, which should be mainly considered in the process of aerodynamic and conceptual design.

Numerical simulation on the hydrodynamic performance of an azimuthing pushing podded propulsor in reverse flow and rotation

In this study, the hydrodynamic performance of a reverse podded propulsor under azimuthing conditions is evaluated. The shear stress transfer (SST) k-omega turbulence model and sliding mesh technique are adopted for this evaluation, and the commercially available software, STAR-CCM+ is used for the numerical simulation. An extensive convergence study was performed with respect to time step and grid size to verify the numerical simulation. The hydrodynamic performance is analyzed under different advance velocities as the propulsor sinusoidally azimuths from 130° to 230°. The forces and moments generated by the propulsor in steady oblique flow are compared with those under azimuthing condition. It is found that the forces and axial moments of the propulsor in oblique flow generally varies in between the envelopes of the transient ones under an azimuthing state, while the vertical and horizontal moments are observed too strongly deviate from one another.

Ballasted track aerodynamic optimization by wind tunnel test and CFD simulation

Ballast flight problem sets back high-speed railway development, which causing damages to train and rail. The present paper puts forward wind tunnel tests and CFD simulation to study ballast flight mechanisms and ballasted track aerodynamics. A 1:1 scale ballasted track model was set up to analyze ballast flight phenomena, where aerodynamics influencing factors and impacts on ballast bed were investigated. A numerical model of CRH3 train-ballast bed was built by combining the Realizable k- ϵ viscous model and sliding mesh technique. CFD model with the above method was used to investigate aerodynamic effects as well as the mechanism of ballast flight, thus providing the theoretical basis for optimizing ballast bed profile and preventing ballast flight. Results show that pressure distribution exhibits large value at the center of the ballasted track and decreases at track edge. The head, tail and bogie area of the train result in large fluctuation of wind pressure, which has a great probability of ballast flight. Appropriate countermeasures should be taken, such as reduce shoulder ballast height and crib ballast could be effective methods to decrease the probability of ballast flight.

Design, Simulation and Test of Thermal Control System of Centrifuge for Space Utilization

Taking centrifuge system for space utilization as the research object, an active air-cooling thermal control system is put forward. Physical models of the centrifuge thermal control system are built on the basis of simplifying assumptions under actual conditions. A numerical calculation model of centrifuge system is established by using the sliding mesh technique and flow resistance model of heat exchanger is introduced based on the porous medium theory. A numerical analysis of the dynamic heat exchange performance of the centrifuge is carried out and the results show the flow and heat exchange characteristics of each part of the system in the dynamic equilibrium state. Also, the centrifuge system and its heat exchange performance test platform are designed and built, and the monitoring probes are placed at the key position. The curves of the whole equilibrium process of key points are obtained and the test condition is consistent with numerical simulation condition. The equilibrium temperatures of the test are in agreement with that of the numerical analysis, which proves that the numerical model and calculation method are accurate. Meanwhile, the test and numerical analysis results can also improve each other to provide data and supporting techniques for in-orbit engineering utilization of manned space station in future.