Vortex Circulation Research Articles

A numerical examination on the use of phase change materials to improve the sun-tracking photovoltaic panels' performance

The power generation of a photovoltaic (PV) panel is inherently affected by the amount of solar radiation striking the panel and the PV temperature. Tracking PV panels reach higher temperature than fixed panels due to more received radiation. Phase change materials (PCMs) are widely used as a passive method for cooling fixed PV panels. The melting dynamics of the PCM is very different during tracking compared to previous research carried out on fixed panels due to the changing orientation. A tracking PV-PCM system is numerically modeled in this research, and the temperature distribution and convection in the PCM are analyzed. The numerical results are presented as temperature-time curves for several different positions inside the PCM container, liquid fraction and streamlines in melted PCM, and isothermal curves. The temperature variation shows that the temperature of solid PCM increases rapidly in the initial time, reaching the melting temperature. The PCM changes from the solid phase to the liquid phase at a constant temperature. After complete melting, the PCM temperature increases over time. The PCM temperature changes were compared at two different distances from the photovoltaic panel. The streamlines show that the PCM starts to melt near the heated wall at the container's top corner. The melted PCM expands toward the down of the container due to vortex circulation created in the molten material. It is observed that the increase in PV panel temperature between 1.5 and 7 h is only 5.3 K, showing that using PCM is an effective method for absorbing heat from the PV panels during melting. Results show that the temperature of PV panel with PCM is on average 6.9 K lower than that without PCM.

Impacts of the Surface Potential Vorticity Circulation over the Tibetan Plateau on the East Asian Monsoon in July

Based on the definition of potential vorticity substance (W) and its equation, an index “iPV” representing the leading mode of the surface potential vorticity circulation (PVC) over the Tibetan Plateau is defined to characterize the orographic potential vorticity (PV) forcing on the atmospheric general circulation. The relationships between the iPV index and the East Asian monsoon in July, as well as the Silk Road pattern in Eurasia, are investigated on an interannual time scale. Results show that the iPV in July is closely related to the interannual variability of the East Asian monsoon. Corresponding to the positive phase of iPV with negative (positive) PVC over the north (south) of the plateau, strong positive PV anomalies and westerly flows develop in the troposphere over the plateau. Consequently, in the downstream region, the zonal PV advection increases with height just above the Jianghuai Meiyu front, which is conducive to the generation of upward movement. Over the East Asian area, the upper troposphere is controlled by the eastward shifted South Asian High. In the lower troposphere, the southwesterly flow anomaly on the northwestern side of the strengthened western Pacific subtropical high transports abundant water vapor to the north, forming a convergence in the Jianghuai area, leading to the formation of large-scale precipitation along the Meiyu front. Results from partial correlation analysis also demonstrate that the link between the variability of the East Asian monsoon in July and the plateau PV forcing is affected very little by the Silk Road pattern, whereas the plateau PV forcing plays a key “bridging” role in the influence of the Silk Road pattern on the East Asian monsoon.

Decomposition of airflow over topography and its application to a topographic blizzard event in central Asia

To better understand the triggering mechanisms of extreme precipitation events in Central Asia due to the complex terrain, a case study of a topographic blizzard that occurred in Xinjiang Province on 30 November 2018 is conducted. The near-surface wind field is decomposed into flow-around and flow-over components to analyze the dynamic and thermodynamic effects of the flow around and over the topography in the Ili River valley and the northern slope of the Tianshan Mountains. The results reveal that the flow around the topography is the dominant component of the flow field that transports water vapor and causes moisture convergence. The symmetric instability observed at the lower level of the snowfall area is attributed to the flow-around wind field, which leads to advective transport of generalized potential temperature and causes changes in potential vorticity, ultimately resulting in symmetric instability. The local variation of stratified instability in the snowfall area is caused by flow-over potential divergence, specifically, the advection of the flow-over wind vertical shear to equivalent potential temperature causes the change of flow-over potential divergence, thus promotes stratified instability. Moreover, the flow-over potential divergence is negatively correlated with the amount of topographic snowfall to a certain extent, which can provide reference for topographic snowfall forecast in the future. Additionally, the cyclonic vorticity in the snowfall area is mainly caused by the flow around topography and flow-around wind produces favorable vortical circulation conditions for snowfall, while the vertical movement near the ground at the snowfall triggering stage is mainly caused by the flow-over component. Furthermore, the flow-over kinetic energy in the snow area is stronger and the work done by the pressure gradient force caused by flow over terrain drives kinetic energy changes.

Rotation effects on turbulence features of viscoelastic spanwise-rotating plane Couette flows

Rotation effects on turbulence features have been examined in viscoelastic spanwise-rotating plane Couette flows (RPCF) at the Reynolds number Re = 1300 and the Weissenberg number Wi = 5, by using of direct numerical simulations for the rotation number Ro=0.02–0.9. Here, Re represents the ratio of inertial forces to viscous forces, and Wi and Ro quantify the strength of fluid elasticity and system rotation, respectively. Based on the detailed examinations of the turbulent kinetic energy and Reynolds stress budgets as well as vortical structures, the viscoelastic RPCF can be classified roughly into three regimes: weak rotation for Ro≤0.1, intermediate rotation for 0.1<Ro<0.4, and strong rotation for Ro≥0.4. Essentially, the comprehensive rotation effects are inherent to the rotation-driven vortical change characterized by an enhancement as Ro is changed from weak to intermediate rotation and a followed suppression at the elasto-inertial turbulence (EIT) state of strong rotation. Specifically, the turbulent kinetic energy and Reynolds stress at Ro = 0.9 are found less than 10% of those at Ro = 0.2. Of particular interest, at weak and intermediate rotation, intense polymer–turbulence interaction is found to occur primarily in the extensional flows between two neighboring roll cells, whereas for the high-Ro EIT state, it happens in the bulk region as the small-scale turbulent vortices serve to homogenize the polymer dynamics via their vortical circulations. The present finding has shed some new light onto the polymer–turbulence interaction under system rotation.

Asymmetric scattering behaviors of spin wave dependent on magnetic vortex chirality

We investigate asymmetric spin wave scattering behaviors caused by vortex chirality in a cross-shaped ferromagnetic system by using the micromagnetic simulations. In the system, four scattering behaviors are found: (i) asymmetric skew scattering, depending on the polarity of vortex core, (ii) back scattering (reflection), depending on the vortex core stiffness, (iii) side deflection scattering, depending on structural symmetry of the vortex circulation, and (iv) geometrical scattering, depending on waveguide structure. The first and second scattering behaviors are attributed to nonlinear topological magnon spin Hall effect related to magnon spin-transfer torque effect, which has value for magnonic exploration and application.

Numerical study on the scale effect of tip vortex cavitation induced by incoming velocities and scale ratios

Large eddy simulations of tip vortex cavitation (TVC) around an elliptical hydrofoil is performed to study its scale effect. A satisfying agreement is obtained between the numerical and experimental data. It indicates that the scale effect of TVC is remarkable. With the increase of scale ratio or incoming velocity, the intensity of TVC significantly increases. Based on our results, two mechanisms for the scale effect of TVC are proposed, i.e., the roll-up of boundary layer and the interaction between tip vortex (TV), secondary vortex and trailing vortex. As incoming velocity increases, the fusion of TV and secondary vortex enhances and the boundary layer thickness decreases, which lead to larger circulation and smaller vortex core radius, tending to intensify TV. As scale ratio increases, the fusion of TV and secondary vortex enhances and the boundary layer thickness increases slightly, which lead to much higher circulation and slight increase of vortex core radius, promoting the occurrence of TVC in general. In addition, with equal cavitation number and Reynolds number, TVC in the large scale is stronger than that in the small scale, indicating that it seems not so reasonable to equate the velocity-induced scale effect with the scale-ratio-induced one.

Fragmented Vortex in Heart Failure With Reduced Ejection Fraction: A Prospective Vector Flow Mapping Study.

Heart failure with reduced ejection fraction (HFrEF) is associated with structural and functional left ventricular changes. We compared intracardiac vortices between patients with HFrEF and normal participants using echocardiographic vector flow mapping, a novel intracardiac vortex analysis technology. Transthoracic echocardiography was performed on 20 patients with HFrEF (age: 61 ± 15 y, 15 men) and 20 normal participants (age: 59 ± 12 y, 12 men) age- and sex-balanced at the cohort level. Systolic and diastolic energy loss, area (indexed by left ventricular end-diastolic diameter), circulation (reflects vortex strength) and relative positions of the largest vortex during systole (S-vortex), early (E-vortex) and late (A-vortex) diastole and maximal number of vortices in a single frame (MNV) were assessed. Patients with HFrEF had disproportionately sized vortices with smaller indexed vortex areas (p < 0.0001), and more fragmented vortices with higher MNV during both systole (p=0.030) and diastole (p < 0.0001). These accompanied higher diastolic energy loss (p=0.001). Additionally, the E-vortex (p=0.002) and A-vortex (p < 0.0001) were more apically positioned, and the S-vortex was weaker (p=0.033) in patients with HFrEF. More severe fragmentation (higher MNV) correlated with worse energy efficiency (higher energy loss). Patients with HFrEF had more fragmented intracardiac vortices and lower energy efficiency predominantly during diastole.

The effect of dynamic twisting on the flow field and the unsteady forces of a heaving flat plate

Many marine animals can dynamically twist their pectoral fins while swimming. The effects of such dynamic twisting on the unsteady forces on the fin and its surrounding flow field are yet to be understood in detail. In this paper, a flat plate executing a heaving maneuver is subjected to a similar dynamic twisting. In particular, the effects of the direction of twist, non-dimensional heaving amplitude, and reduced frequency are studied using a force sensor and particle image velocimetry (PIV) measurements. Two reduced frequencies, , and , and two twisting modes are investigated. In the first twisting mode, the plate is twisted in the direction of the heave (forward-twist), and in the second mode, the plate is twisted opposite to the direction of the heave (backward-twist). Force sensor measurements show that the forward-twist recovers some of the lift that is usually lost during the upstroke of flapping locomotion. Additionally, the forward-twist maintains a near-constant lift coefficient during the transition between downstroke and upstroke, suggesting a more stable form of locomotion. PIV results show that forward-twist limits circulation and leading-edge vortex growth during the downstroke, keeping at the cost of the reduced lift. By contrast, backward-twist increases the circulation during the downstroke, resulting in large increases in both lift and drag coefficients. Force sensor data also showed that this effect on the lift is reversed during the upstroke, where the backward-twist causes a negative lift. The effects of each twisting mode are mainly caused by the changes in the shear layer velocity that occur as a result of twisting about the spanwise axis along the mid-chord. The twisting performed by forward-twist reduces the effective angle of attack through the upstroke and downstroke, resulting in a reduced shear layer velocity and lower circulation. The twisting performed by backward-twist does the exact opposite, increasing the effective angle of attack through the upstroke and downstroke and consequently increasing the shear layer velocity and circulation.

Characterization of the turbulent field behavior of an elevated jet-in crossflow investigated using direct numerical simulation

Direct numerical simulation (DNS) of a turbulent flow in an elevated jet in crossflow has been carried out at a Reynolds number (Re) of 3500 based on the outer width of the stack and crossflow velocity. The jet to crossflow velocity ratio is kept constant at VR=2. Second order spatial and temporal discretization have been used to solve the Navier–Stokes equations employing a high-resolution grid to determine the essential characteristics of the coherent and the incoherent flow fields accurately. The large-scale coherent and small-scale incoherent flow fields are extracted using a reference signal-based phase-averaged method that uses a reference signal against which the phases are identified in each cycle to minimize the phase jitter. The rate of decay of circulation of the stack-wake vortices is observed to be more than that of the jet-wake which has a lower circulation value. The contribution of the incoherent fluctuations to the total turbulent kinetic energy is more compared to its coherent counterpart in the wake as well as jet region, except for the near-wake of the stack. The normal and shear stresses of both coherent and incoherent fields reveal a relatively higher contribution in the near-wake of both stack-wake and jet-wake, while the far-wake shows the opposite trend. The anisotropy factor of both the large-scale coherent and the small-scale fluctuating fields provides the evidence of total anisotropy of the stack-wake. The characterization of both types of fluctuating fields is also carried out using the anisotropy-invariant-map which displays the one-component limit for the coherent fluctuating field in most of the regions, but the anisotropy state of the incoherent fluctuating field is found to switch among various limits, namely, the axisymmetric contraction, the axisymmetric expansion, and isotropic limits.

Tracking Point Vortices and Circulations via Advected Passive Particles: An Estimation Approach

We present a novel method for estimating the circulations and positions of point vortices in a two-dimensional (2D) environment using trajectory data of passive particles in the presence of Gaussian noise. The method comprises two algorithms: the first one calculates the vortex circulations, while the second one reconstructs the vortex trajectories. This reconstruction is done thanks to a hierarchy of optimization problems, involving the integration of systems of differential equations, over time sub-intervals all with the same amplitude defined by the autocorrelation function for the advected passive particles’ trajectories. Our findings indicate that accurately tracking the position of vortices and determining their circulations is achievable, even when passive particle trajectories are affected by noise.

Numerical Analysis of Heat Transfer Behaviours of Melting Process for Ice Thermal Storage Based on Various Heat Source Configurations

Ice thermal storage (ITS) performance for cooling systems is greatly influenced by the poor thermal conductivity of phase change material (PCM). The effect of natural convection on the melting process is significant for heat transfer enhancement. Thus, the melting performance of PCM in a shell-and-tube latent heat storage (STLHS) unit is numerically studied by considering natural convection in terms of various heat source positions and configurations, i.e., central position, eccentric position, and flat-tube type. Temperature distribution, melting time, and the overall heat transfer coefficient during the process are investigated. The results show that the circulation vortex formed by natural convection is a dominant factor that affects melting front evolution and the overall heat transfer coefficient. When input heat flux is relatively weak, PCM below the heat source is liquefied first. In contrast, PCM in the upper part melts earlier when the heat flux is excellent. The overall heat transfer coefficient decreases sharply with the increase in melting time in the early stage. Then, the heat transfer coefficient tends to be constant. PCM in an STLHS unit with a heat source in a lower position and a configuration of vertical flat-tube type has a desirable performance when compared with other cases, which could provide good support for ITS application.

Elliptical Bladed Savonius Rotor for Wind Energy: Efficacy of RANS Modeling for Flow Characteristics

Abstract Wind energy is a key contributor to renewable energy production. Vertical axis wind turbine (VAWT) of Savonius type is advantageous in places of small-scale power production and low wind speed regions. It is a VAWT of the drag-based type. The disadvantage of a Savonius rotor is its low efficiency due to the generation of negative torque on the returning blade. To reduce the negative torque, the performance parameters of a Savonius rotor need to be optimized. The shear-stress transport variant of k–ω turbulence model is used in the current study to compute 2D unsteady Reynolds-averaged Navier–Stokes calculations for an ellipse shape blade Savonius rotor to capture its aerodynamic behavior. The flow complexities, such as vortex generation and circulation, are analyzed for four different azimuthal angles 0deg, 45deg, 90deg, and 135deg for a tip speed ratio (TSR) of 0.8. A rise in CD to 1.0 at TSR equal to 0.9 indicates an adverse pressure gradient region on the forward-moving blade. The circulation studied in the present paper could be of practical importance in situations involving an array of Savonius rotors to find an optimum rotor position and rotational direction as in the case of horizontal axis wind turbine (HAWT).

Lift Enhancement by Trapped Vortex at Ultra-low Reynolds Numbers

A means of passively trapping a vortex to enhance the aerodynamic characteristics of an airfoil is explored in this paper. The flow over an airfoil with a cavity on the upper surface, an NACA 0004 airfoil, and a flat plate airfoil is studied computationally in the ultra-low Reynolds number regime. At low angles of attack a vortex is seen to be trapped in the cavity. With increasing angle of attack the trapped vortex grows in size and occupies the entire cavity and the effective geometry resembles a smooth airfoil. The vortex circulation also increases and enhances the lift characteristics of the airfoil. The drag coefficient of the cavity airfoil is comparable to the NACA 0004 airfoil. The lift-to-drag ratio of the cavity airfoil is found to be higher than the smooth airfoils in the entire range of angles of attack considered in the present study. The cavity airfoil, with a trapped vortex, offers an interesting prospect for engineering nano-air vehicles.

Impacts of heater-cooler position and Lorentz force on heat transfer and entropy generation of hybrid nanofluid convection in quarter-circular cavity

PurposeThe study aims to assess the heater and cooler positional impacts systematically using four different quadrantal cavities filled with hybrid nanofluid, keeping the curved surface adiabatic under the orientated magnetic fields. Both heat transfer and entropy generation analyses are performed for a hybrid nanofluid flow in a quarter circular cavity considering different orientations of magnetic fields. The investigation is focused to assess the heater and cooler positional impacts systematically using four different quadrantal cavities (first to fourth quadrantal cavities), keeping the curved surface always adiabatic. The impacts of pertinent variables like Rayleigh number, Hartmann number and volumetric concentration of hybrid nanofluid on heat transfer characteristics are in consideration with the second law of thermodynamics. The analysis includes the thermal, viscous and magnetic aspects of entropy generation.Design/methodology/approachAfter validating against the experimental results, the present work explores numerically following the Galerkin weighted finite element technique. The solution is obtained through an iterative process satisfying the convergence limit of 10−8 and 10−10 for the maximum residuals and the mass defect, respectively.FindingsIt revealed that the mutual exchange of heater-cooler positions on the adjacent straight edges of the quadrant cavity does not have any impact on the flow direction. Although the magnitude of flow velocity enhances, the sidewall plays a decision-making role in the formation of a single circulation vortex. It also shows that thermal entropy production is the main cause behind thermodynamic irreversibility. The second or third quadrantal arrangement could have been opted as the best configuration of the heater-cooler position for achieving superior heat transfer. The Lorentz force plays a great role to moderate the heat transfer process. The maximum entropy generation is located, as expected, at the heating-cooling junction point.Research limitations/implicationsThere are plenty of prospects for extension of the present research concept numerically or experimentally, adopting three-dimensional analysis, working fluids, boundary conditions, etc. In fact, the study could be carried out for unsteady or turbulent fluid flow.Practical implicationsAs the position of the heated source and cold sink on the enclosure geometry can significantly alter the thermo-fluid phenomena, this kind of analysis is of utmost relevance for the further development of efficient heating/cooling arrangements and proper management of the devices subjected to magnetic field applications. This original contribution could be a potentially valuable source for future research and exploration pertaining to a thermal system or device, like heat exchangers, solar collectors, thermal storage, electronic cooling, food and drying technologies and others.Originality/valueIn the literature, an inadequate number of works have focused on a quadrantal cavity, mostly considering the first quadrant of the circle. However, during practical applications, it is possible that the cavity can take the shape of the other three quadrants too, and the corresponding knowledge on relative performance is still missing. Furthermore, the present investigation includes the existence of magnetic fields at various orientations. The impact analysis of this field-induced Lorentz force on the nanofluid thermal performance is another major contribution from the present work that would enrich the domain knowledge and could be useful for thermal system engineers.

Suppression effect on TLV cavitation of overhanging grooves with different tab orientations: An experimental investigation

In this paper, a high speed camera and endoscopic particle image velocimetry system are utilized to investigate the influence of tab orientations of overhanging grooves on the suppression effect of tip-leakage vortex cavitation around a truncated NACA0012 hydrofoil. Four kinds of overhanging grooves (OHGs) with different tab orientations, namely OHGs_1–4, are tested, with the original hydrofoil as a comparison. The results suggest that compared with the baseline, all the overhanging grooves tested in our experiments show the suppression effect on TLV cavitation. However, the tab orientations of overhanging grooves leave significant influence on its effect. OHGs_2 with tabs extending beyond the pressure side surface shows the best suppression effect for all the measured gap sizes, followed by OHGs_1 with tabs extending beyond both the suction and pressure side surfaces. For OHGs_3 and OHGs_4, due to the lack of tabs extending beyond the pressure side surface, the suppression effect is not so good as OHGs_1 and OHGs_2. Further analysis indicates that the reason for the better suppression effect of OHGs_2 is the interference of tabs extending beyond the pressure side surface on the fusion of tip-leakage vortex and tip-separation vortex, which decreases the tip-leakage vortex circulation and increases its radius.

The Large and Strong Vortex Around the Trunk and Behind the Swimmer is Associated with Great Performance in Underwater Undulatory Swimming.

Swimmers can produce horizontal body velocity by generating and shedding vortices around their body during underwater undulatory swimming (UUS). It has been hypothesized that the horizontal shedding velocity, area and circulation of the vortex around the swimmer's body are associated with UUS performance. The purpose of this study was to investigate whether the shedding velocity, area and circulation of vortices around swimmers' bodies are correlated with the horizontal body velocity during UUS. Computational fluid dynamics (CFD) was conducted to obtain the vortex structure during UUS in nine male swimmers. Morphological and kinematic data of each subject were obtained and used to reconstruct the UUS movement on CFD. The horizontal velocity of the center of vorticity, the area and circulation of vortices around the ventral side of the trunk, dorsal side of shoulder and waist, and behind the swimmer were determined from the simulation results. Positive correlations were found between the vortex area and circulation around the ventral side of the trunk (area r = 0.938, p < 0.05; circulation r = 0.915, p < 0.05) and behind the swimmer (area r = 0.738, p < 0.05; circulation r = -0.680, p < 0.05), and the horizontal body velocity. The horizontal shedding velocity of the center of vorticity of the vortices around the swimmer's body was not significantly correlated with the horizontal body velocity. These results suggest that the generation of a large and strong vortex around the trunk and behind the swimmer is associated with great UUS performance.

A novel algorithm for visualizing and quantifying vortices in complex 3D flows based on marching and converging vortex atoms

Numerous investigations aiming to reveal the underlying physics behind complex flows highlighted the important roles of vortices. This article proposes an integrative algorithm for visualizing and quantifying the vortices in three-dimensional flows. The algorithm not only extracts the vortex centerlines but also returns the vortex radii and circulations varying along the centerlines. The novel aspect of this algorithm is to represent the vortex field as a collection of discrete vortex atoms. By iteratively updating the positions of these vortex atoms, the algorithm manipulates them into marching toward the underlying vortex centerlines. The radii and circulations varying along the centerlines are estimated based on the vortex atoms converged on the vortex centerlines. The accuracy and robustness of the algorithm are first accessed by numerical tests based on a synthetic vortex ring. Subsequently, the algorithm is employed to investigate the complex vortices in a turbulent boundary layer, validating the scaling law of the vortices reported in the literature. At last, the algorithm is applied to the three-dimensional experimental data of the wake flow behind a wall-mounted hemisphere. It concludes that the algorithm can be used as an effective tool for analyzing vortices in complex flows.

Exploring the Evolution of Typhoon Lekima (2019) Moving Offshore Northeast of Taiwan with a Multi-Resolution Global Model

Typhoon Lekima occurred in early August 2019 and moved northwestward toward Taiwan. During offshore passage, the typhoon underwent rapid intensification, with a northward deflected track, moving closer to northeastern Taiwan. A global model, MPAS, at a multi-resolution of 60-15-3 km, is utilized with ensemble forecasts to investigate the dynamic processes causing the track deflection and intensity change as well as identify the track uncertainty to initial perturbed conditions under the topographic effects of the Central Mountain Range (CMR). For spinning up the typhoon vortex in ensemble forecasts, dynamic vortex initialization has been enforced with a 3 km resolution targeted at the Taiwan area. As one specific member track is similar to the best track, the track deflection is significantly reduced in the absence of the Taiwan terrain, highlighting the role of the topographic effects of the CMR. For these tracks with similar deflection, the northward deflection is caused by the induced strong flow to the east of the typhoon center in response to the re-circulating flow around southern Taiwan, which produces the wavenumber-one gyre in the asymmetric flow difference to drive the vortex northward. The typhoon translation around the Taiwan terrain is dominated by the changing wavenumber-one horizontal potential vorticity (PV) advection during the track deflection in the ensemble forecasts. The formation of an intense PV tongue along the upper eyewall is a facilitation precondition of RI, while RI can be significantly enhanced in the presence of an intense lower-stratospheric PV core near the upper eye, which is produced by the radial inflow of the developed transverse vortex circulation over the upper-level outflow layer.

The shape shapes the interfacial liquid-liquid mass transfer: CFD simulations for single spherical and ellipsoidal drops

A CFD model is presented to understand internal circulation vortices induced in spherical and ellipsoidal drops by an external flowing immiscible liquid and the ensuing effect on interfacial mass transfer. The model is validated with experimental data reported in literature for spherical drops. Validated model is used for detailed parametric analysis to understand the effects of relative velocity, droplet diameter and physical properties on Sherwood number. Resulting data are regressed to propose a correlation to estimate Sherwood number for spherical drops. Simulations for symmetrical ellipsoidal drops reveal the presence of secondary circulation vortex in some cases. The secondary circulation vortex is found to enhance Sherwood number significantly. The correlation for estimating Sherwood number for spherical drops is modified to propose correlations for symmetrical ellipsoidal drop with and without secondary circulation vortex. Finally, asymmetric ellipsoidal drops are also studied to understand the effect of shape on internal circulation pattern and Sherwood number.

The Potential Value of Combining Assimilation of Water Vapor Radiances and Cloud Liquid/Ice Water Path From ABI on Analyses and Forecasts for Hurricane Irma (2017)

AbstractAll‐sky assimilation of infrared (IR), near‐IR, and visible band measurements are beneficial for forecasting cloud‐covered tropical cyclones, but numerous challenges remain. This study uses the combined assimilation of clear‐sky water vapor radiances and the cloud liquid/ice water path (CWP) retrieved from the Advanced Baseline Imager on the new generation geostationary environmental satellites. The two measurements are spatial complementary to one another. Microphysics schemes, cumulus parameterizations, and dynamic CWP observation errors are optimized using sensitivity tests. The cycling assimilations and subsequent forecasts of Hurricane Irma (2017) are investigated to assess the added value of the combined assimilation and its impacts on hurricane forecasts. Comparisons with ERA5 and dropsonde observations from the National Hurricane Operations Plan show that the combined assimilation can improve the prognostic variables of Hurricane Irma (2017) for both the large‐scale circumstances and the inner‐core area, resulting in a clear improvement in hurricane track and intensity predictions. The detailed diagnostics show that the improved track predictions can be attributed to the more precise steering flow produced by the combined assimilation. Moreover, the additional CWP assimilation allows for a more accurate initialization of water vapor in the hurricane's inner‐core area when the model produces dry simulated water vapor bias. Then the subsequent phase changes of water vapor improve the hurricane intensity forecasting by enhancing the feedback between heating and vortex circulation. The combined assimilation shows the potential value of better utilization of all‐sky satellite measurements to improve hurricane initialization and forecast.