Surface Drag Coefficient Research Articles

Thermal analysis of magnetized pseudoplastic nano fluid flow over 3D radiating non-linear surface with passive mass flux control and chemically responsive species

The process of fluid flow over three-dimensional (3D) domains has valuable and promising applications in multiple disciplines like in aerodynamics, computer graphics, environmental science, material synthesis technology, geographic information system, polymer industry and so forth. So, in view of such admirable utilization of fluid flowing processes over 3D surfaces current effort is presented to examine the flow behavior of non-Newtonian fluid past a bidirectional non-linearly stretched sheet. In this regards, Williamson model is considered which represent speculative features of shear thinning materials which are obliged in biomechanics, lubricants formation, polymer solution, suspension etc. Momentum transport with in flow field is envisioned by the appliance of transversally directed magnetic. The novelty of analysis is strengthened by Fourier heat flux and Buongiorno mass conservation models. Mathematical modelling of conventional energy equation is modified by incorporation of nanofluid Brownian and thermophoresis effects. The condition of zero normal flux of nanoparticles at the stretching surface is defined to impulse the particles away from the surface in combination with nonzero normal flux condition. Mathematical modelling of Williamson fluid including the impact of chemical reaction, radiative heat flux and heat source is manifested in the form of partial differential equations. Similarity variables are capitalized to transmute governing modelled conservation laws in to ordinary non-dimensionalzed expressions. Assessment of flow attributing profiles is disclosed by implementing Runge-Kutta-Fehlberg procedure (RKF-45) in collaboration with shooting method. Behavior of momentum, temperature and concentration distributions against miscellaneous arising parameters is visualized through graphical structures. Graphical visualization and numerical data about surface drag coefficients and heat and mass transfer rates are also presented. The computed solution is in excellent agreement with existing data in a limiting sense which assures the credulity of this work.

RETRACTED: Numerical Treatment for 3D Squeezed Flow in a Rotating Channel With Soret and Dufour Effects

This article examines magnetohydrodynamic three-dimensional (3D) squeezed flow by a rotating permeable channel subject to Dufour and Soret impacts. Impact of viscous dissipation is also considered. An applied magnetic field is considered subject to electrically conducting viscous fluid. The change from the non-linear partial differential framework to the non-linear ordinary differential framework is assumed into position by utilizing appropriate variables. Governing differential frameworks are computed numerically by shooting method. Numerical results have been achieved by considering numerous values of emerging flow parameters. Contributions of influential parameters on physical quantities are studied thoroughly. Surface drag coefficients and mass and heat transport rates are also processed and examined. Furthermore, the concentration and temperature distributions are reduced for larger values of Soret number. The prime interest of presented study is to model and examine the Dufour and Soret aspects in concentration and energy expressions. To our knowledge, no such analysis has been addressed in the literature yet.

Revised Estimates of Ocean Surface Drag in Strong Winds

AbstractAir‐sea drag governs the momentum transfer between the atmosphere and the ocean and remains largely unknown in hurricane winds. We revisit the momentum budget and eddy covariance methods to estimate the surface drag coefficient in the laboratory. Our drag estimates agree with field measurements in low‐to‐moderate winds and previous laboratory measurements in hurricane‐force winds. The drag coefficient saturates at 2.6×10−3 and U10≈25 m s−1, in agreement with previous laboratory results by Takagaki et al. (2012,). During our analysis, we discovered an error in the original source code used by Donelan et al. (2004,). We present the corrected data and describe the correction procedure. Although the correction to the data does not change the key finding of drag saturation in strong winds, its magnitude and wind speed threshold are significantly changed. Our findings emphasize the need for an updated and unified drag parameterization based on field and laboratory data.

Thermal buoyancy effects on the flow field and heat transfer of a rotating cylinder: A numerical study

The present paper numerically investigates the laminar, two-dimensional and horizontal flow around a horizontal isothermal rotating cylinder under the buoyancy effect. To study the buoyancy effect, a range of Grashof numbers from 0 to 12 × 104 is used, and to check the effect of the cylinder rotation, the ratio of the rotational speed to the free-stream velocity between −4.5 and 4.5 is applied. The simulation is carried out at the Reynolds number of 200 and the Prandtl number of 0.7. To simulate the fluid flow, the Navier-Stokes equations are numerically solved using a finite-volume scheme. Results show that the interaction of the main stream with the rotation and buoyancy can alter the flow field and heat transfer characteristics such as flow pattern, surface pressure distribution, lift and drag coefficients, and Nusselt number. The clockwise (cw) rotation decreases the amplitude of oscillations in the flow compared to the counterclockwise (ccw) rotation. In ccw rotation, as the Grashof number increases, the mean lift coefficient increases; while in cw rotation, increase in the Grashof number reduces the mean lift coefficient. Moreover, in terms of Grashof numbers ranging between 8 × 104 and 12 × 104, the Nusselt number is almost unchanged.

The Effect of Surface Drag Strength on Mesocyclone Intensification and Tornadogenesis in Idealized Supercell Simulations

AbstractA suite of six idealized supercell simulations is performed in which the surface drag coefficient Cd is varied over a range of values from 0 to 0.05 to represent a variety of water and land surfaces. The experiments employ a new technique for enforcing a three-force balance among the pressure gradient, Coriolis, and frictional forces so that the environmental wind profile can remain unchanged throughout the simulation. The initial low-level mesocyclone lowers toward the ground, intensifies, and produces a tornado in all experiments with Cd ≥ 0.002, with the intensification occurring earlier for larger Cd. In the experiment with Cd = 0, the low-level mesocyclone remains comparatively weak throughout the simulation and does not produce a tornado. Vertical cross sections through the simulated tornadoes reveal an axial downdraft that reaches the ground only in experiments with smaller Cd, as well as stronger corner flow in experiments with larger Cd. Material circuits are initialized enclosing the low-level mesocyclone in each experiment and traced backward in time. Circulation budgets for these circuits implicate surface drag acting in the inflow sector of the supercell as having generated important positive circulation, and its relative contribution increases with Cd. However, the circulation generation is similar in magnitude for the experiments with Cd = 0.02 and 0.05, and the tornado in the latter experiment is weaker. This suggests the possible existence of an optimal range of Cd values for promoting intense tornadoes within our experimental configuration.

Mathematical and Engineering Aspects of Chemically Reactive Tangent Hyperbolic Nanofluid over a Cone and Plate with Mixed Convection

Current disquisition is expressed to elucidate the mathematical and engineering aspects of tangent hyperbolic liquid over a cone and plate which has valuable applications in industrial technological instruments such as cone and plate viscometer, spinning column technology, and biomass pyrolysis processing. The role of mixed convection and chemical reaction on physical features of fluid is considered. The attained coupled system is scrutinized by the aid of self-coded shooting method. In order to produce accuracy and refinement in the consequences, the coefficients of Runge–Kutta scheme are obliged. To get complete intellect about the current pagination, the impact of flow controlling variables on pertinent profiles are evaluated in quantitative and qualitative manner. The computations of wall drag force and heat and mass fluxes are presented pictorially and tabularly. From the thorough analysis, it is deduced that surface drag and convective thermal coefficient for cone is more in magnitude compared with those of plate. Similarly, dominance in thermal field is noted for cone compare with that in plate. Increment of velocity profile is revealed with enhancement in mixed convection parameter, whereas contrasting behavior is observed by varying Williamson and magnetic field parameters. Declining aptitude in thermal profile is exhibited against Prandtl number, whereas temperature of fluid mounts by changing the Brownian movement and thermophoresis parameters.

Response of Air–Sea Fluxes and Oceanic Features to the Coupling of Ocean–Atmosphere–Wave During the Passage of a Tropical Cyclone

A coupled ocean–atmosphere–wave model was used to assess the impact of model coupling on the simulations of air–sea fluxes, surface currents, waves, and temperature profile during the passage of a tropical cyclone (TC) Phailin in the Bay of Bengal. Four numerical experiments with different coupling configurations among the atmosphere, ocean, and wave models were carried out to identify differences in simulated atmospheric and oceanic parameters. The simulated track and intensity of Phailin agree well with the observations. The inter-comparison of model experiments with different coupling options highlights the importance of better air–sea fluxes in the coupled model as compared to the uncoupled model towards an improvement in the simulation of TC Phailin. The coupled model configurations overcome the cold bias (up to − 2 °C) in sea surface temperature simulated by the uncoupled ocean model. A higher magnitude of the surface drag coefficient in the uncoupled atmosphere model enhanced the bottom stress (> 2 N m−2). As a result of excess momentum transfer to the sea surface, the uncoupled ocean model produced stronger surface currents as compared to the coupled model. The inclusion of the wave model increases the sea surface roughness and, thereby, improves the wind speed and momentum flux at the air–sea interface. The maximum significant wave height in the coupled model was about 2 m lower than the uncoupled wave model. The model experiments demonstrate that the periodic feedback among the atmosphere, ocean, and wave models leads to a better representation of momentum and heat fluxes that improves the prediction of a tropical cyclone.

Numerical Simulations of Unsteady 3D MHD Micropolar Fluid Flow over a Slendering Sheet

The purpose of the present analysis is to explore the numerical investigation on the time-dependent 3D magnetohydrodynamic flow of micropolar fluid over a slendering stretchable sheet. The prevailing PDEs are rehabilitated into coupled non-linear ODEs with the aid of appropriate similarity variables and then numerically calculated by applying the 4th RKM incorporate with shooting scheme. The contributions of various interesting variables are shown graphically. Emerging physical parameters on velocity, microrotation, and the surface drag coefficient are portrayed graphically. It is noticed that the microrotation profiles highly influenced by the vortex viscosity parameter and the micro-inertia density parameter. It is also concluded that the microrotation profiles (h2) are promoted by increasing the spin gradient viscosity parameter. Excellent accuracy of the present results is observed with the formerly published as a result of a special case.

A discussion on influences of turbulent diffusivity and surface drag parameterizations using a linear model of the tropical cyclone boundary layer wind field

Abstract In order to investigate and predict dynamics and developments of the tropical cyclone boundary layer (TCBL), theoretical and engineering models depicting the TCBL wind field are of great academic and practical interest. In the present study, a linear height-resolving model, where the vertically varying turbulent diffusivity (K) and speed dependent surface drag coefficient (Cd) parameterizations are incorporated, is proposed based on the original model proposed by Kepert (2001) . The proposed model is validated through comparisons with the estimates made based on the observational data gathered by dropsondes. As the more realistic and sophisticated parameterizations are integrated, the proposed model produces predictions in better agreements with observations in the lower part of the TCBL. It is noted that the value of the proposed model is not only the improvements over the original model by Kepert (2001) , but also the room for more sophisticated K and Cd parameterizations. With the help of the proposed model, it is feasible to discern the fundamental relationships between K and Cd parameterizations and the TCBL wind field in a parametric study. As the first step, a few K and Cd parameterizations are implemented in the proposed model, and their influences on the prediction of the TCBL wind field are systematically discussed. It is concluded that, whereas the prediction of the TCBL wind field is sensitive to the parameterization of K, Cd has limited effects on the prediction. Moreover, assuming K and Cd as constants could lead to erroneous estimates of the wind profile and strength of surface winds in the TCBL.

Impact on Sea-Surface Electromagnetic Scattering and Emission Modeling of Recent Progress on the Parameterization of Ocean Surface Roughness, Drag Coefficient, and Whitecap Coverage in High Wind Conditions

Ocean surface wind stress is the force generating ocean surface roughness and whitecaps. The surface wind stress is related to the surface wind speed by the drag coefficient. Consequently, the magnitude of roughness and whitecaps calculated from wind speed input depends on the applied drag coefficient formula, which remains uncertain especially for high wind conditions. Because roughness and whitecaps are two major components of the ocean surface response in microwave remote sensing, a clear understanding of the drag coefficient, ocean surface roughness, and whitecap coverage is critical to interpreting the microwave signals emitted or scattered from the ocean surface. In reverse, the microwave signals represent precious data sources of these ocean surface properties [surface wind stress (or equivalently the drag coefficient), surface roughness, and whitecaps] that are difficult to measure with traditional oceanographic instruments, especially in severe weather conditions. This article describes the improvement of ocean surface properties achieved by incorporating microwave remote sensing measurements. In essence, the global data of microwave monostatic and bistatic radar cross sections contribute to the revision of ocean surface roughness spectrum model, and microwave radiometer measurements in tropical cyclones provide clarification regarding the dependence on wind speed of the drag coefficient and whitecap coverage. In return, the calculated excess emissivities and scattering radar cross sections are improved from implementing the updated results of drag coefficient, whitecap coverage, and surface roughness in microwave emission and scattering models.

Toward the GMF for Wind Speed and Surface Stress Retrieval in Hurricanes Based on the Collocated GPS-Dropsonde and Remote Sensing Data

This article describes the first step toward the development of the geophysical model function (GMF) for the retrieval of wind speed and wind stress in hurricanes, based on developing a relation between the cross-polarized satellite SAR data from Sentinel-1 and winds/stress observed from collocated NOAA GPS-dropsondes data. Field measurements and remote sensing data for tropical cyclones in the Atlantic Ocean were analyzed. Using the data measured by GPS-dropsondes, average wind velocity profiles were obtained, while the parameters of the wind boundary layer (drag coefficient and friction velocity) were restored from the “wake” part of the velocity profiles using the self-similarity property. The self-similarity of the velocity profile “defect” in the boundary layer, known from the fluid dynamics, was used to retrieve the parameters of the atmospheric boundary layer (the surface wind velocity, drag coefficient, and friction velocity) from the dropsonde wind velocity profiles in ten major hurricanes. Based on the processing of the measurements in the hurricanes Irma 2017/09/07 and Maria 2017/09/21 and 2017/09/23 at a time close to the time of acquisition of the Sentinel-1 images, the dependencies of the cross-polarized normalized radar cross section on the wind speed and wind friction velocity were obtained and used for constructing the GMFs.

Dissipative effects on a chemically and thermally radiative heat fluid flow past a shrinking porous sheet

The present study analyses the dissipative influence into an unsteady electrically conducting fluid flow embedded in a pervious medium over a shrinkable sheet. The behavior of thermal radiation and chemical reactions are also contemplated. The governing partial differential equations are reformed to ordinary differential equations by operating similarity transformations. The numerical outcomes for the arising non-linear boundary value problem are determined by implementing the Successive linearization method (SLM) via Matlab software. The velocity, temperature, and concentration magnitudes for distant values of the governing parametric quantities are conferred, and their conduct is debated via graphical curves. The surface drag coefficient increases, whereas the local Nusselt number and Sherwood number decreases for enhancing unsteadiness parameter across suction parameter. Moreover, the magnetic and suction parameters accelerate velocity magnitudes while by raising porosity parameter, velocity decelerates. Larger numeric of thermal radiation parameter and Eckert number accelerates the temperature profile while by enhancing Prandtl number it decelerates. Schmidt number and chemical reaction parameters slowdowns the concentration distribution, and the chemical reaction parameter influences on the point of chemical reaction that benefits the interface mass transfer. It is expected that the current achieved results will furnish fruitful knowledge in industrious utilities.

A numerical study on viscoelastic boundary layer on flat plate

In this study, the effects of viscoelastic properties of non-Newtonian fluids on the flat plate boundary layer are investigated numerically. The numerical solution is obtained using a second-order parallelized finite volume method based on pressure implicit with splitting of operators’ algorithm. Here, the nonlinear Giesekus model is used as the constitutive equation for numerical simulations. The effects of elasticity number, mobility factor and nonlinear normal stress differences on thickness of boundary layer, displacement thickness, momentum thickness, wall shear stress and drag coefficient are studied in detail. Interestingly, a finite thickness is observed at the leading edge of the flat plate. It is also observed that the boundary layer thickness, surface shear stress and drag coefficient of viscoelastic fluids are less than Newtonian fluids.

Significance of heat generation/absorption in three-dimensional flow of Prandtl nanofluid with convectively heated surface

In this article, the hydromagnetic three-dimensional flow of Prandtl nanoliquid subject to convectively heated extendable surface and heat generation/absorption has been discussed. A linear extendable surface makes the flow. Thermophoresis and Brownian motion impacts are explored. Heat transfer via convective procedure is considered. Condition associated with zero nanoparticles mass flux at the surface is used. Prandtl liquid is taken electrically conducted through constant applied magnetic field. Suitable non-dimensional variables lead to strong nonlinear ordinary differential system. The obtained nonlinear differential system is solved through optimal homotopy analysis method. Graphical results have been provided for temperature and concentration fields. Physical quantities like surface drag coefficients and local Nusselt number are sketched and analyzed. Our results depict that the temperature field has a direct relationship with Hartman parameter and Biot number.

Numerical Study for Darcy–Forchheimer Flow of Nanofluid due to a Rotating Disk with Binary Chemical Reaction and Arrhenius Activation Energy

The present article investigates Darcy–Forchheimer 3D nanoliquid flow because of a rotating disk with Arrhenius activation energy. Flow is created by rotating disk. Impacts of thermophoresis and Brownian dispersion are accounted for. Convective states of thermal and mass transport at surface of a rotating disk are imposed. The nonlinear systems have been deduced by transformation technique. Shooting method is employed to construct the numerical arrangement of subsequent problem. Plots are organized just to investigate how velocities, concentration, and temperature are influenced by distinct emerging flow variables. Surface drag coefficients and local Sherwood and Nusselt numbers are also plotted and discussed. Our results indicate that the temperature and concentration are enhanced for larger values of porosity parameter and Forchheimer number.

Practical Uncertainties in the Limited Predictability of the Record-Breaking Intensification of Hurricane Patricia (2015)

AbstractHurricane Patricia (2015) was a record-breaking tropical cyclone that was difficult to forecast in real time by both operational numerical weather prediction models and operational forecasters. The current study examines the potential for improving intensity prediction for extreme cases like Hurricane Patricia. We find that Patricia’s intensity predictability is potentially limited by both initial conditions, related to the data assimilation, and model errors. First, convection-permitting assimilation of airborne Doppler radar radial velocity observations with an ensemble Kalman filter (EnKF) demonstrates notable intensity forecast improvements over assimilation of conventional observations alone. Second, decreasing the model horizontal grid spacing to 1 km and reducing the surface drag coefficient at high wind speed in the parameterization of the sea surface–atmosphere exchanges is also shown to notably improve intensity forecasts. The practical predictability of Patricia, its peak intensity, rapid intensification, and the underlying dynamics are further investigated through a high-resolution 60-member ensemble initialized with realistic initial condition uncertainties represented by the EnKF posterior analysis perturbations. Most of the ensemble members are able to predict the peak intensity of Patricia, but with greater uncertainty in the timing and rate of intensification; some members fail to reach the ultimate peak intensity before making landfall. Ensemble sensitivity analysis shows that initial differences in the region beyond the radius of maximum wind contributes the most to the differences between ensemble members in Patricia’s intensification. Ensemble members with stronger initial primary and secondary circulations beyond the radius of maximum wind intensify earlier, are able to maintain the intensification process for longer, and thus reach a greater and earlier peak intensity.

Analysis of entropy generation for MHD flow of third grade nanofluid over a nonlinear stretching surface embedded in a porous medium

The main focus of present research work is to elaborate magnetohydrodynamic flow of third grade nanofluid with activation energy and binary chemical reaction. Fluid flow is generated by a nonlinearly stretched surface. Temperature and nano-concentration distributions are analyzed in the presence of Brownian motion and thermophoresis effects. The effects of Joule heating, thermal radiation and porous medium are further investigated for current analysis. Thermodynamic second mechanism is utilized to explore entropy generation rate of the system. Newly developed condition having zero mass flux of nanoparticles at the boundary is also incorporated. Partial differential equations governing the flow problem has been converted into ordinary ones using appropriate similarity variables. Builtin Shooting technique via NDsolve has been used to construct the numerical solution of the resulting problem. Impacts of various physical flow parameters are presented graphically for temperature, nano-concentration, surface drag coefficient and rates of heat trasnfer and entropy generation. It is found that impacts of third grade parameters on the thermal and nano-concentration fields are quite similar. Temperature, concentration and associated layer thicknesses are reduced via higher third grade parameters. It is established that the magnetic field restricts the flow strongly and serves as a potent control mechanism. It can be concluded that an applied magnetic field will play a major role in applications like micropumps, actuators and biomedical sensors. The activation energy aspect reduces the concentration boundary layer thickness. Total entropy of the entire system increases against higher values temperature difference variable, Brinkman number, porosity parameter, radiation parameter and magnetic parameter.

Active and passive controls of 3D nanofluid flow by a convectively heated nonlinear stretching surface

This article presents magnetohydrodynamic three-dimensional flow of nanoliquid by a nonlinear stretchable surface with active and passive controls of nanoparticles. A bidirectional nonlinear stretching surface generates the flow. The convective condition of heat transfer is taken into consideration. Impacts of thermophoresis and Brownian diffusion are present. Fluid is electrically conducted subject to a uniform applied magnetic field. Zero normal flux condition is defined to impulse the particles away from the surface in combination with nonzero normal flux condition. Convergent series solutions for the nonlinear governing system are established. Graphs have been sketched in order to analyze how the temperature and concentration distributions are affected by distinct physical flow parameters. Surface drag coefficients and heat and mass transfer rates are also computed.

Numerical simulation for Darcy-Forchheimer 3D rotating flow subject to binary chemical reaction and Arrhenius activation energy

Three-dimensional Darcy-Forchheimer nanoliquid flow in the presence of rotating frame and activation energy is inspected. Flow is developed through linearly stretching of the surface. Convection of heat and mass exchange is given due consideration. The novel characteristics in regards to Brownian dispersion and thermophoresis are retained. The variation in partial differential framework (PDEs) to nonlinear ordinary differential framework (ODEs) is done through reasonable transformations. Governing differential frameworks have been computed in edge of NDSolve. Discussion regarding thermal field and concentration distribution for several involved parameters is pivotal part. Physical amounts like surface drag coefficients, transfer of heat and mass rates are portrayed by numeric esteems. It is noticed that impacts of porosity parameter and Forchheimer number on the thermal and concentration fields are quite similar. Both temperature and associated thermal layer thickness are enhanced for larger porosity parameter and Forchheimer number. Temperature and concentration fields exhibit similar trend for the higher values of rotational parameter. Effects of thermal and concentration Biot numbers on the temperature and concentration fields are qualitatively similar. Higher Prandtl and Schmidt numbers correspond to stronger temperature and concentration fields. Larger nondimensional activation energy, temperature difference parameter and fitted rate constant yield weaker concentration field. Brownian motion parameter for temperature and concentration has reverse effects while similar trend is observed via thermophoresis parameter.

Experimental Investigation of the Aerodynamic Roughness Length for Flexible Plants

The aerodynamic roughness length z0 is modelled as a function of the zero-plane displacement d, plant drag coefficient CdR, the ratio β of the drag coefficient for an isolated roughness element and the surface drag coefficient, and the lateral cover λ. The model is investigated using wind-tunnel experiments on a ground surface covered by artificial plastic flexible plants of very small basal-to-frontal area ratios (0.001–0.007). The plant drag coefficient at different plant densities is inferred from measurements of the total shear stress and the average surface shear stress for five plant heights at four plant densities. The aerodynamic roughness length and zero-plane displacement are estimated by logarithmic regression of the measured velocity profile with a predetermined friction velocity. With the increase of lateral cover λ, the plant drag coefficient can be considered as a constant for λ 0.01. With an increase in the friction velocity, the roughness length z0 generally decreases because of plant flexibility, while with increases in plant density and plant height, the value of z0 increases because the surface becomes physically rougher. Our model for the roughness length z0 is verified using experimental data for flow over flexible plants. Compared with rigid roughness elements, such as cylinders, cubes and blocks, the normalized roughness z0/h (where h is the plant height) for the flexible plants is smaller because of the porosity and the larger value of the ratio d/h.