Rotational Flow Research Articles

Investigations on tip relieving of spur gears by non-contact process

ABSTRACT This paper describes tip relieving of spur gears by pulsed electrochemical flank modification (PECFM) process by a novel designed cathodic gear tool and apparatus. This work reports experimental findings on tip relieving and surface finish by varying the concentration, flow rate, and temperature of the electrolyte, modification duration, and cathodic gear rotational speed at four levels each and using predetermined values of voltage, pulse-on time, pulse-off time, and anodic gear reciprocating speed. The amount of tip relief is found to increase considerably with modification duration and electrolyte concentration. Identified optimum values of modification duration, cathode gear rotational speed, concentration, flow rate, and electrolyte temperature are 20 minutes, 45 rpm, 2 Molarity, 30 lpm, and 40°C, respectively. Scanning electron microscopy images of the tip-relieved spur gear revealed that PECFM effectively eliminates the hob cutter marks from its flank surfaces. This work will be helpful to gear manufacturers seeking productive tip relieving.

Optimization-Design and Atomization-Performance Study of Aerial Dual-Atomization Centrifugal Atomizer

The aerial atomizer is the most essential component of the plant protection UAV (unmanned aerial vehicle). However, the structural optimization of existing aerial atomizers lacks comprehensive consideration of spray parameters and structural parameters, and there is a shortage of available atomizer spray models, resulting in the unstable effect of UAV application. In our previous work, an aerial dual-atomization centrifugal atomizer was developed. In order to obtain an aerial atomizer with good atomization effect and its atomization model, structural optimization at different rotation speeds and flow rates of the atomizer, and its atomization performance, are studied in this paper. Firstly, with the droplet volume median diameter (VMD) and spectral width (SRW) as the evaluation index, through the single-factor, Plackett–Burman and Box–Behnken tests, the influence of rotation speed, flow rate, tooth number and tooth shape were studied. The regression models of the droplet VMD and SRW were established using multiple quadratic regression fitting of the test data. Secondly, in order to achieve the lowest droplet VMD and SRW, the response surface method and post-hoc multiple comparison method were used to obtain the optimized structure of the atomizer’s rotation ring at different rotation speeds (600–7000 r/min) and flow rates (500–1000 mL/min). Lastly, with the effective swath width (ESW) of the optimized atomizer as the evaluation index, through the Box–Behnken test, the influence of rotation speed, flow rate and spray height were studied. The multiple quadratic regression model of ESW was established with the test data. The test results indicated that rotation speed, flow rate and tooth number had a significant effect on droplet VMD and SRW; tooth shape had no significant effect on the droplet VMD and SRW, however, the square tooth shape had the best atomization effect; and rotation speed, flow rate and spray height had a significant effect on ESW. The optimized structural parameters were tooth shape: square, and tooth number: 20. The determination coefficient R2 of the regression model of VMD, SRW and ESW were 0.9976, 0.9770 and 0.9974, respectively, which indicates that the model was accurate, and can evaluate and predict the spray effect. This paper provides an optimized dual-atomization centrifugal atomizer, and its regression models of VMD, SRW and ESW for UAV applications can provide a reference for efficient UAV spraying.

Computational assessment of venous anastomosis angles and graft configurations in arteriovenous graft

Arterio-venous grafts are a viable option for hemodialysis as long-term vascular access. The leading cause of Arterio-venous Grafts (AVG) failure is the development of intimal hyperplasia (IH), primarily found in vessel areas with unfavorable hemodynamic conditions. Computational Fluid Dynamics (CFD) is utilized in this study to assess the effect of some geometrical designs at venous anastomosis on these conditions.At first, models with various anastomosis angles are designed. Results represent that the maximum Wall Shear Stress (WSS) in the model with the anastomosis angle of 15° has decreased from 34.07 Pa to 17.48 Pa (48.69%) compared to the conventional model. Moreover, vortices and regions with high WSS at vein anastomosis reduce remarkably.In the second part, to lessen the unfavorable hemodynamic conditions inspired by the rotational blood flow in the aorta, the graft is designed with several cross-sectional ridges to induce a swirl flow. Three essential hemodynamic parameters, including Oscillatory Shear Index (OSI), Time Averaged Wall Shear Stress (TAWSS), and Relative Residence Time (RRT) in pulsating blood flow models, are extracted, and the outcomes are compared to conventional AVG.Finally, according to the results of the previous sections, an optimized model is proposed. Comparing this model with the conventional one illustrates more than 90% decrement in regions related to high OSI values and a 22.84% reduction in RRT values as the main hemodynamic parameters to assess the areas with a high risk of IH development.

Helical-Ridge-Membranes from PVDF for enhanced gas–liquid mass transfer

New membrane geometries have the potential to increase mixing at the feed and permeate side to counteract concentration polarization and fouling. Such membrane geometries can be of very different architecture. Here, we address a new class of hollow fiber membranes having helical ridges. We focus on gas–liquid mass transfer, which is significantly slowed down by a liquid-side diffusion resistance. We present hydrophobic polyvinylidene fluoride (PVDF) helical ridge hollow fiber membranes produced by a rotating needle spinneret. Conceptually, the wet spinning methodology builds upon our Rotation-in-a-Spinneret platform technology, featuring customized microstructured rotating needles. The microstructured needle orifice includes two grooves to initiate ridge formation on the lumen side of the hollow fiber, while the ridges twist helically upon needle rotation. The new generation spinneret device produces hollow fiber membranes with reduced fiber diameter as compared to previous versions. It is specifically designed such that rotating spinning parameters enable an adjustable helical ridge pitch. Ridge formation and ridge shape strongly depend on rotational speed. The latter affects characteristic membrane properties such as membrane permeability and molecular selectivity. The helical ridges induce secondary flow in the lumen of the hollow fiber membranes, proven by pressure drop manipulation and experimental flow streamline visualization. In-depth analysis by flow simulation identifies rotational flow patterns as the governing flow phenomena. Ultimately, application in gas–liquid membrane contactors for oxygenation and CO2 capture revealed up to 10-fold improved transmembrane gas fluxes. Hence, the helical ridges cause turbulence promotion to introduce significant mass transfer enhancement.

Neurons in Primate Area MSTd Signal Eye Movement Direction Inferred from Dynamic Perspective Cues in Optic Flow.

Smooth eye movements are common during natural viewing; we frequently rotate our eyes to track moving objects or to maintain fixation on an object during self-movement. Reliable information about smooth eye movements is crucial to various neural computations, such as estimating heading from optic flow or judging depth from motion parallax. While it is well established that extraretinal signals (e.g., efference copies of motor commands) carry critical information about eye velocity, the rotational optic flow field produced by eye rotations also carries valuable information. Although previous work has shown that dynamic perspective cues in optic flow can be used in computations that require estimates of eye velocity, it has remained unclear where and how the brain processes these visual cues and how they are integrated with extraretinal signals regarding eye rotation. We examined how neurons in the dorsal region of the medial superior temporal area (MSTd) of two male rhesus monkeys represent the direction of smooth pursuit eye movements based on both visual cues (dynamic perspective) and extraretinal signals. We find that most MSTd neurons have matched preferences for the direction of eye rotation based on visual and extraretinal signals. Moreover, neural responses to combinations of these signals are well predicted by a weighted linear summation model. These findings demonstrate a neural substrate for representing the velocity of smooth eye movements based on rotational optic flow and establish area MSTd as a key node for integrating visual and extraretinal signals into a more generalized representation of smooth eye movements.SIGNIFICANCE STATEMENT We frequently rotate our eyes to smoothly track objects of interest during self-motion. Information about eye velocity is crucial for a variety of computations performed by the brain, including depth perception and heading perception. Traditionally, information about eye rotation has been thought to arise mainly from extraretinal signals, such as efference copies of motor commands. Previous work shows that eye velocity can also be inferred from rotational optic flow that accompanies smooth eye movements, but the neural origins of these visual signals about eye rotation have remained unknown. We demonstrate that macaque neurons signal the direction of smooth eye rotation based on visual signals, and that they integrate both visual and extraretinal signals regarding eye rotation in a congruent fashion.

Design space analysis for supercritical CO2 radial inflow turbine stators

Radial inflow turbines(RITs) play a vital role in power generation due to their small size, compact construction and large power density, especially when applying to supercritical CO2(sCO2) power cycles. Correct preliminary design of the RITs is important for enhancing the efficiency of cycles. Most preliminary design studies for RITs simply impose empirically developed angle constraints for the rotor inlet conditions instead of giving much attention to the stators. In addition, the previous design procedure can only calculate one geometry at a time, which does not allow the selection of the most suitable geometry that fits the cycle parameters and constraints. Hence, this paper presents a workflow to correctly size a stator for achieving a desired rotor inflow conditions. Then a stator design-space analysis with utilising an existing 500 kW sCO2 rotor is conducted. Based on a number of given stator radius ratio(r3/r4), blade number(Zs) and blade trailing edge thickness(t3), the obtained design map contains a total number of Nr3/r4×NZs×Nt3 preliminary design cases. New insights are discussed, including that the workflow is functional; the blade angles need to adjust between no-loss and loss cases; the rotor–stator interaction loss will increase the stator inlet/outlet operational parameter when guaranteeing the target rotor inlet conditions; and including of the stator losses in turbine design is significant.

Influence of magnetic dipole on ferrohydrodynamic thin film flow over an inclined spinning surface

This study investigates the three-dimensional problem of steady ferrofluid deposition on an inclined rotating surface in the presence of a magnetic dipole. A finite element procedure is used to solve normalized ordinary differential equations derived from momentum and energy equations. The current numerical model and its solution is compared and validated against previous numerical results. The velocity and temperature field variations are a representation of the effects of magnetic field-based viscosity, magnetic polarization force, Curie temperature, and Prandtl number. In addition, some common errors in the similarity transformation for inclined rotating disk flows are addressed in the present study. The results show that the magnetic field-dependent viscosity generated by the magnetic torque in the current flow reduces the velocity of the thin film liquid in all directions, including rotational flow (radial, tangential, and axial) and inclined flow (drainage and induced). Moreover, the local heat transfer between the fluid and the surface of the rotating disk increases with a rise in the ferromagnetic interaction number and Prandtl number. These findings imply that ferrofluids could be effective for cooling electronic devices in the presence of a magnetic dipole.

Monsoon Depression Amplification by Horizontal Shear and Humidity Gradients: A Shallow Water Perspective

Abstract Transient, synoptic-scale vortices produce a large fraction of total rainfall in most monsoon regions and are often associated with extreme precipitation. However, the mechanism of their amplification remains a topic of active research. For monsoon depressions, which are the most prominent synoptic-scale vortex in the Asian–Australian monsoon, recent work has suggested that meridional gradients in zonal wind in the vortex environment may produce growth through barotropic instability, while meridional gradients in environmental humidity have also been proposed to cause amplification through coupling with precipitating convection. Here, a two-dimensional shallow water model on a sphere with parameterized precipitation is used to examine the relative role played by these two environmental gradients. By systematically varying the meridional moisture gradient and meridional wind shear for both weak, quasi-linear waves and finite-amplitude isolated vortices, we show that rotational winds in the initial vortex are amplified most strongly by meridional shear of the environmental zonal wind, while vortex precipitation rates are most sensitive to environmental moisture gradients. The growth rate in the presence of both gradients is less than the sum of growth rates in the presence of isolated gradients, as the phase relation between moisture and vorticity anomalies becomes distorted with increasing shear. These results suggest that background meridional gradients in both zonal wind and environmental humidity can contribute to the amplification of vortices to monsoon depression strength, but with some degree of decoupling of the dry rotational flow and the moist convection.

CABARET on rotating meshes

The Compact Accurately Boundary-Adjusting high-REsolution Technique (CABARET) method for 3D gas dynamics equations is generalised to rotating hexahedral mesh zones using the sliding interface approach, which extends applications of the original algorithm to a wide range of unsteady rotor flow problems. Important properties of the suggested extension of the CABARET scheme include the preservation of good linear dispersion and dissipation properties of the original CABARET method on fixed grids. To strictly preserve flux conservation at the sliding interface, the so-called supermesh approach is implemented that uses the projection of the contact faces on both sides of the sliding interface onto an intermediate virtual surface. The implementation is based on applying the sub-cell and sub-face solution reconstruction on the sliding interface of hexahedral meshes rather than deforming unstructured meshes. The sub-faces are defined by constructing projection overlap polygons using the Sutherland-Hodgman clipping algorithm. A local characteristic flux splitting is applied at each overlap polygon face, while updating the local stencil connectivity table at each time step. To further improve the dispersion properties of the CABARET grid at small Courant–Friedrichs–Lewy numbers, the dispersion-improved version of the CABARET method previously developed on rectangular Cartesian meshes is extended to non-uniform curvilinear meshes typical of open-rotor applications. Numerical examples are provided for the analytical problem of normal acoustic wave propagation through a rotating cylindrical grid zone embedded in an outer stationary grid. The error decay rates are calculated and compared with the theoretical order of CABARET convergence. In addition, the same algorithm accelerated on Graphics Processing Units (GPUs) is applied for simulations the flow around a generic two-bladed rotor in hover in the Wall Model Large Eddy Simulation framework. For the latter case, flow solutions are analysed, and their numerical grid sensitivity is discussed.

Influence of the spanwise grooves on aerodynamic characteristics of the compressor cascade and rotor under different reynolds numbers

In order to study the influence of the suction surface spanwise grooves under different Reynolds numbers ( Re) on the loss characteristics of highly loaded compressor cascade and rotor. In the present study, numerical simulations were conducted to investigate the effects of the number and position of the suction surface spanwise groove on aerodynamic performance of the cascade with the final aim to extend the findings to a highly loaded transonic compressor rotor. Besides, the influence mechanism for the performance change of compressor cascade and rotor by spanwise groove at different Re was clarified. The combination 1-2-3-4-gro was selected as an optimal structure in accordance with the data weighting criterion. The investigation illustrates that, at high Re operating conditions, the spanwise grooves force the transition of boundary layer from laminar to turbulent, which causes a large turbulent boundary layer loss and increases the overall loss. But at low Re operating conditions, the laminar separation bubble is suppressed by spanwise grooves and the aerodynamic performance is improved. At Re = [Formula: see text], the total pressure loss can be reduced by 4.63% at the angle of attack of 0°. When this group scheme was applied to the highly loaded axial compressor transonic rotor, the stability margin of the rotor can be increased by 5.62% at Re = [Formula: see text] condition. Moreover, at 20 km height condition, with the increase of rotating speed, the influence of 1-2-3-4-gro groove group on rotor stability margin is not great, but its efficiency improvement effect is gradually enhanced, which shows that 1-2-3-4-gro can effectively reduce rotor flow loss and increase its aerodynamic performance within this Re range.

An Experimental Study on Rotor Aerodynamic Noise Control Based on Active Flap Control

Reducing rotor aerodynamic noise is an important challenge in helicopter design. Active flap control (AFC) on rotors is an effective noise reduction method. It changes the segment airfoil shape, aerodynamic load distribution, and the wake path of the rotor flow by adding trailing edge flaps (TEFs). Although AFC noise reduction control is easily simulated, the relevant experiments have not been widely conducted due to test technical problems and limited financial support. The acoustic characteristics of the AFC-equipped rotor, such as the placement of TEFs for noise reduction and whether multiple winglets can provide a better effect than single winglets, have not been verified in previous experiments. In this work, an AFC-equipped rotor with two TEFs was designed, and its acoustic properties were tested in the FL-17 acoustic wind tunnel with microphone arrays in the far field. The results showed that the noise reduction effect of AFC was closely related to the control frequency and phase. Increasing the control phase could move the reduction region toward the azimuth-decreasing region for far-field noise. The noise reduction in a single outboard TEF was better than that in a single inboard TEF, while the dual-TEF model performed better. In this experiment, the average noise reduction in the observation point at the lower front of the rotor could be more than 3 dB, and the maximum noise reduction could be 6.2 dB.

RETRACTED: Analysis of rotating-symmetric frame and MHD for peristaltic multiphase flow: An exact solution

The rotational mechanism forms the basis of various cosmic and geophysical transports. In medical science, rotational blood flows have been related to healthy cardiac function. This study consists of a mathematical model representing magnetohydrodynamic effects on the two-phase pumping flow of a Ree–Eyring–Powell stress model in a rotating frame. The model is controlled by switching the system into a wave frame of reference for better analysis of the wave phenomenon. Moreover, a lubrication theory is applied to the resulting set of relations in order to get a more comprehensive form of the reduced mathematical model. In the end, an exact solution is found to discuss the substantial contents of the study. The data on velocity and stream function are presented diagrammatically to examine the theoretical behavior of various quantities under the variation of considerable physical factors. It is concluded from the graphs that axial and secondary velocities are decreasing against rotation, magnetic field, and fluid’s factor, but the same rise in the case of wall stiffness and particle concentration. In both industrial and biomedical applications, this type of flow measurement gives tomographic information on the multiphase flow process, which entails acquiring signal changes at the edges of objects like fluid pipes or blood vessels to determine how the objects are distributed within. This work is extendable by considering nanoparticles of various types to enhance the thermal conductivity of the flow.

Numerical simulation and verification of rotor downwash flow field of plant protection UAV at different rotor speeds.

In aerial spraying of plant protection UAVs, the continuous reduction of pesticides is an objective process. Under the condition of constant flight state (speed and altitude), the change of pesticide loading will inevitably lead to the shift of lift force and rotor speed generated by UAV rotor rotation, which will change the distribution of the rotor flow field and affect the effect of aerial spraying operation of plant protection UAV. Therefore, the rotor speed of UAV is taken as the research object in this paper, and the adaptive refinement physical model based on the Lattice Boltzmann Method (LBM) is used to numerically simulate the rotor flow field of the quadrotor plant-protection UAV at different speeds. A high-speed particle image velocimeter (PIV) was used to obtain and verify the motion state of the droplets emitted from the fan nozzle in the rotor flow field at different speeds. The results show that, with the increase of rotor speed, the maximum velocity and vorticity of the wind field under the rotor increase gradually, the top wind speed can reach 13m/s, and the maximum vorticity can reach 589.64s -1. Moreover, the maximum velocity flow value is mainly concentrated within 1m below the rotor, and the maximum vorticity value is primarily concentrated within 0.5m. However, with the increase of time, the ultimate value of velocity and vorticity decreases due to the appearance of turbulence, and the distribution of velocity and vorticity are symmetrically distributed along the centre line of the fuselage, within the range of (-1m, 1m) in the X direction. It is consistent with the motion state of droplets under the action of the rotor downwash flow field obtained by PIV. The study results are expected to reveal and understand the change law of the rotor flow field of plant protection UAVs with the dynamic change of pesticide loading to provide a theoretical basis for the development of precise spraying operation mode of plant protection UAVs and improve the operation effect.

Rotational effects on the blade flow of a horizontal axis wind turbine under axial and yawed inflow conditions

Unsteady aerodynamic loads and fluctuating output power of wind turbines remain challenging to predict accurately due to the incomplete understanding of blade flow mechanisms. Rotational effects can significantly impact the wind turbine aerodynamic performance. Therefore, this paper presents a careful investigation into rotational flow characteristics of the NREL Phase VI blade under axial and yawed inflow conditions based on the DDES method. Rotational effects change the flow regime from the massive 2D trailing-edge separation into the moderate 3D leading-edge separation on the NREL Phase VI blade. Flow separation is found sufficient but not necessary for the radial flow. Under the axial inflow, rotational effects can effectively suppress the flow separation and increase the nonlinear aerodynamic loads. Under the yawed inflow, rotational effects also effectively suppress the unsteady separated flow and accelerate the flow reattachment, particularly on the downwind side. Sectional lift coefficient is therefore greatly increased at the high angles of attack due to the pronounced rotational effects. Increasing the yaw angle and wind speed may also strengthen the rotational effects and widen the difference between the 2D airfoil flow and 3D sectional flow. These findings imply that flow regime and aerodynamic hysteresis on the inboard blade can be substantially changed in comparison with the 2D airfoil flow due to strong rotational effects. This study might deepen the understanding of rotational effects on the near-wall flow of wind turbine blades and also improve the aerodynamic modelling.

Power characteristics and mass transfer of rotor injectors in a water physical model of an aluminum degassing ladle

A comparative experimental study of a physical model of a stirred ladle for a rotor-injector aluminum degassing system in the turbulent regime has been carried out. A quantitative analysis of the gaseous oxygen mass transfer to the water in a physical model is performed by evaluating the power consumption and mass transfer capacity employing the typical methods used in mechanically stirred tanks. Three rotor injector devices were compared, including two conventional designs and one new rotor design. The rotors were evaluated as a function of the rotational speed and gas flow rates. The conventional rotors exhibited similar performance, while the new design consumed more power when operating at high gassing flow rates and rotational speeds resulting in a higher breakup rate of bubbles and promoting a better formation of tiny bubbles, which are better distributed over the entire ladle. This behavior avoids bubbles rising freely to the free surface; so that the gas hold-up increases leading to an improved mass transfer capacity when using this rotor-injector. The results reported in this work agreed with previously reported works in the literature.

The Gas Sensing Drone with the Lowered and Lifted Measurement Platform.

A serious factor that limits the environmental applications of drones is the disturbance of the air pollution concentration field by the drone propulsion system. This work presents a gas-sensing drone offering measurements that are unaffected by this phenomenon. The novel development was based on the idea that, during measurements, the sensing device should be spatially separated from a zone influenced by the drone's rotors. To attain this goal, special equipment was designed that allows one to undock and lower the sensing device for measurement, lift it and dock for flight. The field experiments demonstrated the full functionality of the developed system and its superiority compared to a sensing platform mounted at the bottom of the drone. Higher measurement sensitivity and resolution were attained by lowering the sensing platform to the measurement point. This solution minimizes the rotor flow effect, ground effect, and pollution concentration field flattening. The test in real conditions confirmed that the designed construction assures drone stability. The presented technology may be an important step in developing effective mobile measurement tools that allow one to reach poorly accessible or dangerous places and perform measurements at a low cost and with high efficiency.

Multi-fidelity vortex simulations of rotor flows: Validation against detailed wake measurements

Two flow models with different fidelity of the DTU vortex solver MIRAS have been used to simulate the wake generated by a model wind turbine with various levels of asymmetry. Predictions are validated against experimental Particle Image Velocimetry measurements and dye visualizations. The experiments were conducted in a recirculating free-surface water channel with an immersed two-bladed rotor mounted on a shaft. The blades were designed to approximate a Joukowsky rotor. A detailed comparison between the measurements and the simulations is first performed for an unperturbed baseline case at different tip speed ratios. The analysis consists of a tip vortex characterization, including the vortex core profile, and a comparison of the instantaneous and mean velocity and vorticity fields, along with the mean wake profile at different downstream locations. Overall, good agreement is obtained between measurements and simulations, especially with the higher-fidelity particle-mesh model, which is capable of very closely predicting many of the flow features observed in the experiments. Rotor asymmetry triggers a vortex instability, commonly known as leapfrogging, which accelerates the breakdown of tip vortices, enhancing the mixing of wake structures and promoting a faster wake recovery. The prediction accuracy of this instability by the solvers is analyzed for different tip speed ratios and perturbation amplitudes. This work aims at setting the groundwork for future flow instability studies with the MIRAS solver.

Cloud-radiative impact on the dynamics and predictability of an idealized extratropical cyclone

Abstract. Extratropical cyclones drive midlatitude weather, including extreme events, and determine midlatitude climate. Their dynamics and predictability are strongly shaped by cloud diabatic processes. While the cloud impact due to latent heating is much studied, little is known about the impact of cloud radiative heating (CRH) on the dynamics and predictability of extratropical cyclones. Here, we address this question by means of baroclinic life cycle simulations performed at a convection-permitting resolution of 2.5 km with the ICON model. The simulations use a newly implemented channel setup with periodic boundary conditions in the zonal direction. Moreover, the simulations apply a new modeling technique for which only CRH interacts with the cyclone, which circumvents changes in the mean state due to clear-sky radiative cooling that has complicated the interpretation of previous work. We find that CRH increases the kinetic energy of the cyclone system. The impact is most prominent at upper levels. To understand the CRH impact on the upper-tropospheric circulation, we diagnose the evolution of differences in potential vorticity between a simulation with and without CRH, and we quantify through which processes these differences grow over the course of the cyclone's life cycle. According to this diagnostic, CRH affects the cyclone mostly via the intensification of latent heating from cloud microphysical processes. Near the tropopause, direct diabatic modification of potential vorticity by intensified latent heat release precedes further changes in the tropopause by the upper-tropospheric divergent flow, which represents an indirect impact of latent heat release. Subsequently, differences in the tropopause structure amplify with the rotational flow during the highly nonlinear stage of the baroclinic wave. Our results show that although CRH is comparably small in magnitude, it can affect extratropical cyclones by changing cloud microphysical heating and subsequently the large-scale flow. The CRH impact follows a previously identified mechanism of multi-stage upscale error growth. At the same time, simulations in which CRH is disabled after certain days show that the CRH impact operates throughout the entire intensification phase of the cyclone. This means that CRH does not merely provide an arbitrary initial perturbation to the cyclone, from which differences grow in a generic way. Instead, our results suggest that uncertainties associated with the representation of CRH in numerical models have a more systematic impact and may more fundamentally influence model predictions of extratropical cyclones.

A laboratory platform for studying rotational dust flows in a plasma crystal irradiated by a 10 keV electron beam

A novel laboratory platform has been designed and built for the irradiation of a plasma crystal (PC) with an electron beam (e-beam) having an energy around 10 keV and a current of tens of milliamperes. The pulsed e-beam collimated to a few millimeter-size spot is aimed at a crystal made of dust particles levitated in a radio-frequency (RF) plasma. The platform consists of three vacuum chambers connected in-line, each with different utility: one for generating free electrons in a pulsed hollow-anode Penning discharge, another for the extraction and acceleration of electrons at sim 10 kV and for focusing the e-beam in the magnetic field of a pair of circular coils, and the last one for producing PCs above a RF-driven electrode. The main challenge is to obtain both a stable e-beam and PC by insuring appropriate gas pressures, given that the e-beam is formed in high vacuum (lesssim 10^{-4} Torr), while the PC is produced at much higher pressures (gtrsim 10^{-1} Torr). The main diagnostics include a high speed camera, a Faraday cup and a Langmuir probe. Two applications concerned with the creation of a pair of dust flow vortices and the rotation of a PC by the drag force of the e-beam acting on the strongly coupled dust particles are presented. The dust flow can become turbulent as demonstrated by the energy spectrum, featuring vortices at different space scales.

Effect of Using a Passive Rotor on the Accuracy of Flow Measurements in Sewer Pipes Using a Slug Tracer-Dilution Method

Flow measurements in pipelines using slug tracer have proved highly accurate for turbulent flow. This study experimentally investigates the effectiveness of using a passive rotor on the accuracy of discharge measurements in sewer pipes based on a saline slug tracer technique. For this purpose, a saline injector stack was developed to help inject saline at selected injection points. A passive axial flow rotor was also proposed and encased in the injector stack to enhance the mixing of injected tracer with the transmitted downstream flow and to decrease the required minimum mixing length. It was found that adding the passive rotor significantly increased the accuracy of the flow measurements. Two tracer flow formulas were developed: one based on the dimensional analysis approach and the other based on a semi-empirical formula obtained from the mass conservation approach. The resultant formulas compared favourably with flow metering, especially when utilizing the passive fan unit.