Detailed Velocity Distributions Research Articles

Wind tunnel experiment on cross-ventilation of generic isolated building with various roof shapes: Impact of roof pitch and eaves

This study examined the effects of roof shape, specifically roof pitch and eaves, on cross-ventilation performance through wind tunnel experiments that measure static pressure on walls and the detailed wind velocity distribution for isolated building models with basic roof geometries. A flat roof, a gable roof, and two types of shed roof with different orientations were compared. The buildings with a flat or shallow roof pitch (15°) showed no significant change in the pressure difference between windward and leeward facades. However, a steeper roof pitch (30°) caused a significant increase in pressure difference, especially for the shed roof that ascends in the wind direction (shed-A roof). This was caused by larger projected building areas creating stronger recirculation zones behind the building, leading to lower pressure on the leeward facade. The shed-A roof with a pitch of 30° had the best ventilation performance among the tested cases. Eaves generally reduced pressure differences, except for the shed-A roof. The effect of eaves was weaker than reported in previous studies. The experimental results obtained in this study can serve as a validation database for a more detailed study of this problem using computational fluid dynamics.

Evaluation of aneurysm flow divertor (stent) treatment using multi-angled 1000 fps High-Speed Angiography (HSA) and Optical Flow (OF).

Understanding detailed hemodynamics is critical in the treatment of aneurysms and other vascular diseases; however, traditional digital subtraction angiography (DSA) does not provide detailed quantitative flow information. Instead, 1000 fps High-Speed Angiography (HSA) can be used for high-temporal visualization and evaluation of detailed blood flow patterns and velocity distributions. In the treatment of aneurysms, flow diverter expansion and positioning play a critical role in affecting the hemodynamics and optimal patient outcomes. Patient-specific aneurysm phantom imaging was done with a CdTe photon-counting detector (Aries, Varex). Treatment was done with a Pipeline Flex Embolization Device on a 3D-printed fusiform aneurysm phantom. The untreated aneurysm and two treatment stent expansions and positions were imaged, and velocity calculations were generated using Optical Flow (OF). Pre- and post-treatment images were then compared between different HSA image sequences and evaluated using OF with different stent positions. Differences in flow patterns due to changes in stent placement characteristics were identified and quantified with OF velocimetry. The velocity results within the aneurysm post-treatment showed significant flow reduction. Differences in stent placement result in substantial changes in velocities. The peak velocities found in the aneurysm dome show a reduction with the widened stent placement compared to the narrowed placement and both are reduced compared to the untreated aneurysm. The stent placements were compared quantitatively with the adjusted widened stent clearly better diverting the flow away from the aneurysm with decreased velocity in the aneurysm dome compared to both the narrowed stent placement and the untreated aneurysm. Providing this information in-clinic can help improve treatment and patient outcomes.

Temperature and velocity characteristics of rotating turbulent boundary layers under non-isothermal conditions

This paper describes an experimental investigation, by means of hot-wire anemometry, of the characteristics of velocity and temperature in a rotating turbulent boundary layer under isothermal and non-isothermal conditions. The ranges of experimental parameters are as follows: Reynolds number from 10 000 to 25 000, rotational speed from 0 to 150 rpm, and y+ from 1.8 to 100. The relative temperature difference is held constant at 0.1. Detailed velocity and temperature distributions in the boundary layer are measured in the rotating state, and a new criterion for boundary layer segmentation under rotation is proposed. The applicability of boundary layer theory under the rotating state is extended. The influence of Coriolis force and buoyancy on the velocity and temperature distributions in the turbulent boundary layers are analyzed. Coriolis force is found to play an important role in the behavior of the boundary layer under rotation, as it shifts the velocity and temperature boundary layers. Under isothermal conditions, such effects can be classified according to the dominant force: viscous, Coriolis, or inertial. Under non-isothermal conditions, buoyancy occurs. The buoyancy induced by the Coriolis force suppresses the effect of the Coriolis force, and the suppression effect increases with temperature difference. The variation of turbulent Prandtl number Prt under rotation is also obtained.

Validation of the Porous Medium Approximation for Hydrodynamics Analysis in Compact Heat Exchangers

AbstractCompact heat exchangers (HXs) have gained attention in recent years in various fields such as solar and nuclear power generation, oil and gas, and refrigeration due to their low cost, high power density, and robustness in high-pressure and/or high-temperature environments. However, the large difference between a compact HX's overall dimensions (∼m) and the much smaller scale of its channels (∼mm) makes it challenging to model the entire HX at once, due to computational limitations. In this work, we treat the channeled region of a compact HX as a porous medium (PM) to circumvent the need to model/mesh each individual channel. This allows us to simulate the entire HX, including both the header and channeled regions while maintaining the computational cost at a practical level. Although the porous medium approach has been used to model heat exchangers, its validity is still questionable because (1) the resistance coefficients are heavily data-based and thus difficult to be applied to new heat exchangers and (2) the validation has been focused on matching the overall pressure drop in the channel region, which does not address whether such model can predict detailed pressure and velocity field. For the first time, this work addresses under what circumstances and with what uncertainty does the PM approach work for hydrodynamics modeling in compact HXs. By answering these questions, we introduce the PM approach as a powerful tool for HX hydrodynamics modeling that can predict not only the overall pressure drop but also the detailed pressure and velocity distributions.

Modeling of supply airflow from slot line diffuser on ceiling for CFD of thermal environment in perimeter zone

The slot line diffuser is widely used in Japan near the perimeter windows because of its blocking effect on convective heat transfer. However, research on this diffuser has mainly focused on the effects of the turbulence model on CFD simulations and longitudinal airflow distribution, while studies on its detailed outlet characteristics in three-dimensional have been limited. In order to obtain and summarize this diffuser's outlet characteristics more accurately, this paper set a slot line diffuser with an adjustable outlet area in free space. The detailed velocity and turbulence statistics distribution on the diffuser's outlet surface were obtained by a hot-wire anemometer, and the diffuser's airflow distribution in the free space was measured by an ultrasonic anemometer. Then the outlet characteristics of this diffuser were summarized using these measured data in order to make a detailed supply airflow model. At the same time, the difference of the airflow of full-size supply and that of half-size supply is characterized. Moreover, a detailed CFD simulation of the diffuser's outlet airflow was performed using the characteristics model to define the boundary conditions. The detailed CFD result with outlet characteristics model were validated by comparing with experimental data. Additionally, the prescribed velocity (P.V.) method and simple boundary simulation were also attempted to reproduce the diffuser's outlet airflow, and compared with the experiment and detailed CFD results. This study clarified this diffuser's outlet characteristics in three-dimensional, and it is considered that the outlet characteristics model can help improve the simulation accuracy of the kind of diffuser.

Estimating outflow masses and velocities in merger simulations: Impact of r -process heating and neutrino cooling

The determination of the mass, composition, and geometry of matter outflows in black hole-neutron star and neutron star-neutron star binaries is crucial to current efforts to model kilonovae, and to understand the role of neutron star merger in r-process nucleosynthesis. In this manuscript, we review the simple criteria currently used in merger simulations to determine whether matter is unbound and what the asymptotic velocity of ejected material will be. We then show that properly accounting for both heating and cooling during r-process nucleosynthesis is important to accurately predict the mass and kinetic energy of the outflows. These processes are also likely to be crucial to predict the fallback timescale of any bound ejecta. We derive a model for the asymptotic veloicity of unbound matter and binding energy of bound matter that accounts for both of these effects and that can easily be implemented in merger simulations. We show, however, that the detailed velocity distribution and geometry of the outflows can currently only be captured by full 3D fluid simulations of the outflows, as non-local effect ignored by the simple criteria used in merger simulations cannot be safely neglected when modeling these effects. Finally, we propose the introduction of simple source terms in the fluid equations to approximately account for heating/cooling from r-process nucleosynthesis in future seconds-long 3D simulations of merger remnants, without the explicit inclusion of out-of-nuclear statistical equilibrium reactions in the simulations.

Measurements of exhaled airflow velocity through human coughs using particle image velocimetry

The sudden outbreak of coronavirus (COVID-19) has infected over 100 million people and led to over two million deaths (data in January 2021), posing a significant threat to global human health. As a potential carrier of the novel coronavirus, the exhaled airflow of infected individuals through coughs is significant in virus transmission. The research of detailed airflow characteristics and velocity distributions is insufficient because most previous studies utilize particle image velocimetry (PIV) with low frequency. This study measured the airflow velocity of human coughs in a chamber using PIV with high frequency (interval: 1/2986 s) to provide a detailed validation database for droplet propagation CFD simulation. Sixty cough cases for ten young healthy nonsmoking volunteers (five males and five females) were analyzed. Ensemble-average operations were conducted to eliminate individual variations. Vertical and horizontal velocity distributions were measured around the mouth area. Overall cough characteristics such as cough duration time (CDT), peak velocity time (PVT), maximum velocities, and cough spread angle were obtained. The CDT of the cough airflow was 520–560 m s, while PVT was 20 m s. The male/female averaged maximum velocities were 15.2/13.1 m/s. The average vertical/horizontal cough spread angle was 15.3°/13.3° for males and 15.6°/14.2° for females. In addition, the spatial and temporal distributions of ensemble-averaged velocity profiles were obtained in the vertical and horizontal directions. The experimental data can provide a detailed validation database the basis for further study on the influence of cough airflow on virus transmission using computational fluid dynamic simulations.

Numerical analysis of the flows around fishing plane nets using the lattice Boltzmann method

Flow through and around fishing net cages is an important issue in aquaculture. A three-dimensional multi-relaxation time (MRT) lattice Boltzmann model was used to simulate the flow field around a plane net in a constant current. The model was validated with experimental data. The results show that this numerical model is applicable to and reliable for the investigation of the flow field around a fishing net and can provide the detailed velocity distribution in the net aperture. Based on this model, a series of simulations were carried out to analyze the influences of the net solidity and the current velocity on hydrodynamic characteristics and flow-velocity attenuation. The results indicate that the flow-velocity attenuation is mainly related to the net solidity of the plane net, with a higher velocity drop response related to a higher net solidity. These results provide fundamental information for further studies on the flow field around the fishing net cage, which has potential application in analyzing the impacts of biofouling on fishing nets.

Capturing the Swirling Vortex and the Impact of Ventilation Conditions on Small-Scale Fire Whirls

The fundamental flow structure and temperature distribution of small-scale fire whirls, including tangential and axial velocities, temperature variation, and air entrainment in the lower boundary layer, were successfully captured using a generic fire field model with large eddy simulation (LES) turbulence closure. Numerical predictions were validated thoroughly against two small-scale experimental measurements, where detailed temperature and velocity distributions were recorded. Good agreement between numerical and experimental results was achieved. Normalization was also performed to compare the numerical predictions with the empirical correlations by Lei et al. (2015) developed from medium-scale fire whirl measurements. The transient development stages of small-scale fire whirls and the impact of air entrainment on the stability of the fire whirls were also investigated based on the validated numerical results. The numerical validations showed the potential of the current LES fire field model in capturing the dynamic behaviour of the fire whirl plume and performing a quantitative analysis on its onset criteria and combustion dynamics in future.

Effect of Vaneless Diffuser Shape on Performance of Centrifugal Compressor

The influence of four different vaneless diffuser shapes on the performance of centrifugal compressors is numerically studied in this paper. One of the studied shapes was a parallel wall diffuser. Two others had the width reduced only from hub and shroud and the rest had the width reduced from hub and shroud divided evenly. Then the numerical simulation was employed and the overall compressor aerodynamic performance was studied. The detailed velocity and pressure distribution and energy loss within the centrifugal compressor with different diffuser geometries and different operating conditions were analyzed. The results revealed that shroud pinch significantly improved the overall compressor aerodynamic performance more than any other pinch types, and the best performance can be achieved by pinched diffusers under the design condition compared with pinched diffusers under the near surge condition or choking condition. The range of energy loss, namely the static entropy area in the compressor, become reduced with the above three pinches diffusers.

Numerical investigation of velocity distribution of turbulent flow through vertically double-layered vegetation

The velocity structures of flow through vertically double-layered vegetation (VDLV) as well as single-layered rigid vegetation (SLV) were investigated computationally with a three-dimensional (3D) Reynolds stress turbulence model, using the computational fluid dynamics (CFD) code FLUENT. The detailed velocity distribution was explored with a varying initial Froude number (Fr), with consideration of the steady subcritical flow conditions of an inland tsunami. In VDLV flows, the numerical model successfully captured the inflection point in the profiles of mean streamwise velocities in the mixing-layer region around the top of short submerged vegetation. An upward and downward movement of flow occurred at the positions located just behind the tall and short vegetation, respectively. Overall, higher streamwise velocities were observed in the upper vegetation layer due to high porosity, with Pr = 98% (sparse vegetation, where Pr is the porosity), as compared to those in the lower vegetation layer, which had comparatively low porosity, with Pr = 91% (dense vegetation). A rising trend of velocities was found as the flow passed through the vegetation region, followed by a clear sawtooth distribution, as compared to the regions just upstream and downstream of vegetation where the flow was almost uniform. In VDLV flows, a rising trend in the flow resistance was observed with the increase in the initial Froude number, i.e., Fr = 0.67, 0.70, and 0.73. However, the flow resistance in the case of SLV was relatively very low. The numerical results also show the flow structures within the vicinity of short and tall vegetation, which are difficult to attain through experimental measurements.

Effect of taper, pressure and temperature on cavitation extent and dynamics in micro-channels

The prevention of erosion caused by hydrodynamic cavitation plays an important role in the design of hydraulic components, such as fuel injection systems. A high pressure level and the corresponding flow speeds at a very small scale of several micrometers limit the optical accessibility in real fuel injectors. For this reason, flat micro-channels of different geometry, covered by sapphire windows at the front and the back side are used in this paper. Calibration fluid ISO 4113 and dodecane serve as flow media. The aim is to investigate the influence of pressure, temperature and the geometry of the micro-channels on the cavitation extent and to resolve the cavitation dynamics such as cloud shedding. Detached clouds will collapse if the static pressure exceeds the vapor pressure and may damage channel walls of hydraulic components. Shadowgraph images visualize the cavitation extent and flow instabilities, Computational Fluid Dynamics (CFD) results reveal detailed pressure and velocity distributions. Particle Image Velocimetry (PIV) measurements show the motion of the cavitating structures. With high-speed (HS) visualization, cloud detachment is investigated.It was found that the normalized cavitation length can be described as an S-shaped curve depending on the normalized cavitation number. The cavitation length significantly increases in the parallel and diverging channels when reaching the cavitation transition point. The optical setup reveals a deeper insight into the cavitation inception in the shear layer near the throttle inlet. Kelvin–Helmholtz vortices downstream the shear layers could be observed. The calculated pressure and velocity distributions help to validate the plausibility of the cavitation inception for different tapers.For a deeper understanding of the overall flow conditions, basic velocity measurements of the phase boundary in the diverging part of a converging-diverging flow channel were carried out. No seeding particles are used as cavitation structures serve as tracers for the image evaluation. It was found that the velocity of phase boundary between liquid and vapor is lower than the mean fluid velocity derived from the measured mass flow because of the unstable behavior of cloud shedding. A recirculation flow and eddy formation at the cavitation tip is visible.With the help of high-speed visualization, the re-entrant motion which occurs in connection with cloud shedding could be observed. The investigation of the shedding frequency reveals its dependency of pressure, temperature and geometry.

Numerical Study of Creeping Flow Through Sinusoidally Periodic Tube

There has been renewed interest in the flow behaviour within tubes with periodically varying cross-section with the recognition that they can be used as particle separation devices. In this paper, we present a numerical study of the effect of tube geometry on creeping flow of viscous incompressible fluid through sinusoidally constricted periodic tube which is axisymmetric but longitudinally asymmetric. The boundary element method is used to solve for the flow in the tube by specifying the pressure drop across the ends of the tube. The boundary element equations have been formulated for ­an infinite periodic tube by writing the velocity in terms of the integrals over the tube boundary and is used to calculate the force on the tube boundary, to obtain the detailed velocity distribution within the tube and to determine the effect of amplitude and wavelength of corrugation on the structure of the flow. We have found that the highest axial velocity is at throat region and lowest axial velocity is at expansion region. Also, we have discovered that the maximum radial velocity occurs at diverging cross-section and minimum radial velocity occurs at converging cross-section. The tangential force on the tube wall is examined for different amplitudes and wavelengths of corrugation and observed that the tangential force is greater in the constricted region than in the expansion region. The physical quantities (such as velocity and force) increase with increasing amplitude and decrease with increasing wavelength. Finally, we have compared our results with the work of Hemmat and Borhan [3] and have found good agreement with them.

Effects of non-submerged boulder on flow characteristics – A field investigation

The effect of fully submerged boulders on the flow structure in channels has been studied by some researchers. However, many natural streams have bed material with boulders that are not fully submerged under water. In many natural streams, boulders cover between 1% and 10% of the area of the stream reach. The effect of non-submerged boulders on the velocity profile and flow characteristics is very important for assessing riverbed deformation. The objectives of this paper are to find the pattern of velocity distribution around a non-submerged boulder and to compare it with the classical studies on flow resistance and Reynolds stress distribution in open channels. Also, by considering the variation in the Reynolds stress distribution at different locations around a non-submerged boulder, the effect of a non-submerged boulder on the estimation of shear velocity and resistance to flow has been investigated. Results indicates that inside the scour hole caused by a non-submerged boulder in a river velocity distributions are irregular. However, velocity distributions are regular outside the scour hole. The presence of the boulder causes a considerable deviation of the Reynolds shear stress from the classic distribution, showing a non-specific distribution with negative values. The classical methods for calculating shear velocity are not suitable because these methods do not give detailed velocity and Reynolds stress distributions in natural rivers with a lot of boulders. Thus, the effect of a non-submerged boulder on the estimation of the resistance to flow by considering the variations in velocity and Reynolds stress distributions at different locations around a non-submerged boulder is important and needs to be studied in a natural river instead of just in laboratory flumes. The negative values in Reynolds stress distribution around a boulder indicate that the classical methods are unable to predict resistance to flow, and also show strong turbulence inside the scour hole where the complex flow conditions present ambiguous Reynolds stress distributions. In the current study, to obtain a reasonable estimation of parameters in natural rivers, the classical method has been modified by considering velocity and Reynolds stress distributions through the boundary layer method.

Development of Hybrid Airlift-Jet Pump with Its Performance Analysis

A new pump, called the hybrid airlift-jet pump, is developed by reinforcing the advantages and minimizing the demerits of airlift and jet pumps. First, a basic design of the hybrid airlift-jet pump is schematically presented. Subsequently, its performance characteristics are numerically investigated by varying the operating conditions of the airlift and jet parts in the hybrid pump. The compressible unsteady Reynolds-averaged Navier-Stokes equations, combined with the homogeneous mixture model for multiphase flow, are used as the governing equations for the two-phase flow in the hybrid pump. The pressure-based methods combined with the Pressure-Implicit with Splitting of Operators (PISO) algorithm are used as the computational fluid dynamics techniques. The validity of the present numerical methods is confirmed by comparing the predicted mass flow rate with the measured ones. In total, 18 simulation cases that are designed to represent the various operating conditions of the hybrid pump are investigated: eight of these cases belong to the operating conditions of only the jet part with different air and water inlet boundary conditions, and the remaining ten cases belong to the operating conditions of both the airlift and jet parts with different air and water inlet boundary conditions. The mass flow rate and the efficiency are compared for each case. For further investigation into the detailed flow characteristics, the pressure and velocity distributions of the mixture in a primary pipe are compared. Furthermore, a periodic fluctuation of the water flow in the mass flow rate is found and analyzed. Our results show that the performance of the jet or airlift pump can be enhanced by combining the operating principles of two pumps into the hybrid airlift-jet pump, newly proposed in the present study.

Computational study of flow and heat transfer in fixed beds with cylindrical particles for low tube to particle diameter ratios

A three dimensional CFD model was developed for studying flow and heat transfer in fixed beds with cylindrical particles for low tube to particle diameter ratios. The packing structures were generated by means of the discrete element method (DEM), in which the rigorous cylindrical particle was adopted. The detailed packing structure features were obtained, including the particle position, orientation, porosity distribution and the effect on the flow and heat transfer process was analyzed. The wall effect was found to be obvious for fixed beds with low tube to particle diameter ratios. The cylindrical particles tend to be organized in circles, which is even more visible in the vicinity of walls. The radial porosity distribution showed that the obvious oscillation existed in near wall region. The detailed velocity and temperature distribution were investigated. The average axial velocity showed similar tendency with radial porosity distribution. Large porosity caused large velocity and temperature gradients in the wall region. The radial temperature distribution was also calculated by the improved two dimensional quasi-homogeneous model, in which the local porosity and axial average velocity distributions from CFD simulations were adopted and good consistencies for temperature distribution were achieved for different tube to particle diameter ratios.

Feedback of atomic jets from embedded protostars in NGC 1333

Star-formation feedback onto the parent cloud is conventionally examined through the study of molecular outflows. Little is however known on the effect that atomic ejecta, tracing fast shocks, can have on the global cloud properties. In this study we employ Herschel/PACS [OI] and [CII] spectral line maps of the NGC 1333 star-forming region to assess the relative influence of atomic jets onto the star-formation process. Atomic line maps are compared against molecular outflow tracers and atomic ejecta are associated to individual driving sources. We study the detailed morphology and velocity distribution of [OI] line using channel and line-centroid maps and derive the momentum, energy, and mass flux for all the bipolar jets traced by [OI] line emission. We find that the line-centroid maps can trace velocity structures down to 5 km s$^{-1}$ which is a factor of $\sim$20 beyond the nominal velocity resolution reached by Herschel/PACS. These maps reveal an unprecedented degree of details that assist significantly in the association and characterization of jets and outflows. Comparisons of the dynamical and kinematical properties shows that [OI] momentum accounts for only $\sim$1% of the momentum carried by the large scale CO outflows but the energy released through the jets corresponds to 50 - 100% of the energy released in outflows. The estimated ratios of the jet to the outflow momenta and energies are consistent with the results of two-component, nested jet/outflow simulations, where jets are associated to episodic accretion events. Under this scenario, the energy from atomic jets to the cloud is as important as the energy output from outflows in maintaining turbulence and dissipating the cloud gas.

Experimental and numerical studies on the gas velocity deviation in a 600 MWe tangentially fired boiler

In this paper, a comprehensive method containing cold-state modeling experiment, cold-state numerical simulation, and hot-state numerical simulation is employed to analyze the aerodynamic field in a 600MWe tangentially fired pulverized boiler. To investigate the non-uniformity characteristics of flow field distribution in the horizontal flue under deep air-staged condition by this method, a major attention is paid to the gas velocity deviation in front of the final super-heater. Experiments at the cases of various yaw angles of separate over-fire air (SOFA) are carried out under a cold model of the large utility boiler with a roughly 1:28 scale. And the cold model is equipped with 3D-printed nozzles arranged in the four corners. Moreover, the corresponding cases are conducted by cold-state numerical simulation in the cold model furnace, and hot-state numerical simulation in the original furnace. The results show that the experimental data are in general agreement with simulated results in the cold modeling furnace. And through comparison of velocity profile at the same dimensionless furnace height, the results of cold-state model show the similar characteristics of gas velocity distribution that presented in the hot-state situation of the original furnace. Thus, through reasonable cold-state modeling, a detailed velocity distribution can be obtained to give a good insight into the gas velocity deviation characteristics in the horizontal flue.

Particle velocity distribution in a flow of gas-solid mixture through a horizontal channel

Detailed velocity distribution as well as the profiles of the mean velocities and volume fraction of the particles in a flow of gas-solid mixture through horizontal channel, are determined using the high speed particle tracking velocimetry, for various combinations of solid mass loading ratios and superficial gas velocities. Spherical glass particles of two different sauter mean diameters are used in the experiment. The smaller particles are better dispersed in the channel than the larger ones. Also, the lower mass loading ratio and higher gas velocity result in more homogeneity in the flow. Particles are observed to accumulate at the bottom of the channel as the mass loading ratio is increased for reduced gas velocities. The distribution of the stream-wise velocity is negatively skewed whereas that of the cross-stream component of the velocity is symmetric. The tail of the distribution is non-Gaussian in nature.

Study of the effects of translation and roughness on tornado-like vortices by large-eddy simulations

The numerical simulation by LES turbulent model for translating tornadoes and those over roughness was carried out in a Ward type simulator. The tornado translation was modeled by providing a relative motion on the ground and the roughness was simulated through adding a momentum source in the Navier–Stokes equation. The effects of translation and roughness on the flow fields of three typical tornado-like vortices, i.e., vortex breakdown, vortex touching down and multi-vortex, were investigated and the detailed velocity distributions, Reynolds stresses and the pressure on the ground were examined. The similarity of the flow fields after the introduction of translation and ground roughness was also studied. It was found that, at the high elevation, Vc and rc shows the same trend versus the external swirl ratio for stationary and translating tornadoes. However, if the ground is rough, the core radius at high elevation changes greatly. The ground roughness will expand the size of the core. But for the very small swirl ratio cases, the ground roughness shows the effect reducing the core size. The explanation for the evolution of the flow fields due to translation and ground roughness is provided.