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result(s) for
"drag coefficient correction"
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Numerical Simulation of Bubble Flow in Continuous Casting Mold with Bubble Swarm Correction of Drag Coefficient
This study employs a numerical simulation approach to investigate argon bubble flow behavior within a steel continuous casting mold, with a focus on the impact of bubble swarm correction models. Three scenarios are compared: one without any correction and two incorporating drag coefficient corrections, specifically designed for bubble swarm effects. The results demonstrate that incorporating these correction models significantly improves the predictive accuracy of simulations. In particular, the inclusion of a bubble swarm correction model reduces the error in predicted bubble trajectories by 51.7% and 23.0%, respectively, when measured by Hausdorff distances against experimental trajectory data, compared to the scenario without corrections. These findings underline the importance of selecting an appropriate drag correction model for accurate simulations of bubble dynamics and their interaction with the liquid steel in continuous casting molds. This study highlights that drag correction models tailored to the specific conditions of the continuous casting process are essential for achieving realistic predictions.
Journal Article
A New Solution of Drag for Newtonian Fluid Droplets in a Power-Law Fluid
Understanding flow behaviors of multiple droplets in complex non-Newtonian fluids is crucial in many science and engineering applications. In this study, a new and improved analytical solution is developed based on the free surface cell model for the flow drag of swamp of Newtonian fluid drops through a power-law fluid. The developed solution is accurate and compares well to the numerical solutions. The improvement involves a new quantification of shear stress boundary condition at the interface and a more consistent approximation in linearizing the power-law fluid flow governing equation. The Newtonian fluid solutions can be reasonably used to linearize the flow governing equation. The approximation of the boundary conditions at the interface, however, has a major impact on the model prediction. The main improvement in the new solution is observed under the condition of comparable viscosities of the Newtonian drops and the outside power-law fluid when the results are sensitive to the interface boundary condition. Under the two extreme conditions of high viscosity ratio (approaching particles) and low ratio (approaching bubbles), the present and existing solutions converge.
Journal Article
Surface waves and currents in aquatic vegetation
A multiscale asymptotic theory is formulated for surface gravity waves and currents in finite-depth water with a vegetation canopy that provides a drag force on both flows with known drag coefficients. It assumes that the density is uniform and the depth is uniform pro tem and that the wave frequency is fast compared to the current advective rate. It is a quasi-linear theory in which the wave dynamics is independent of current and drag to leading order but provides perturbative corrections, and in which wave nonlinear interactions are neglected while quadratic wave-averaged wave fluxes and quadratic wave-drag effects are retained. The primary surface wave is modified by drag and current interactions, and the wave-averaged current momentum balance includes a wave-augmented drag force and several vortex forces due to Earth's rotation, current vorticity, Stokes drift and drag-induced wave vorticity. The wave-averaged current equations derived here are a suitable basis for future large-eddy simulation and submesoscale circulation computational models.
Journal Article
Estimates of Surface Wind Stress and Drag Coefficients in Typhoon Megi
Estimates of drag coefficients beneath Typhoon Megi (2010) are calculated from roughly hourly velocity profiles of three EM-APEX floats, air launched ahead of the storm, and from air-deployed dropsondes measurements and microwave estimates of the 10-m wind field. The profiles are corrected to minimize contributions from tides and low-frequency motions and thus isolate the current induced by Typhoon Megi. Surface wind stress is computed from the linear momentum budget in the upper 150 m. Three-dimensional numerical simulations of the oceanic response to Typhoon Megi indicate that with small corrections, the linear momentum budget is accurate to 15% before the passage of the eye but cannot be applied reliably thereafter. Monte Carlo error estimates indicate that stress estimates can be made for wind speeds greater than 25 m s −1 ; the error decreases with greater wind speeds. Downwind and crosswind drag coefficients are computed from the computed stress and the mapped wind data. Downwind drag coefficients increase to 3.5 ± 0.7 × 10 −3 at 31 m s −1 , a value greater than most previous estimates, but decrease to 2.0 ± 0.4 × 10 −3 for wind speeds > 45 m s −1 , in agreement with previous estimates. The crosswind drag coefficient of 1.6 ± 0.5 × 10 −3 at wind speeds 30–45 m s −1 implies that the wind stress is about 20° clockwise from the 10-m wind vector and thus not directly downwind, as is often assumed.
Journal Article
A Study on Enhancing the Accuracy of Wave Prediction Models Through SWAN (Simulating WAves Nearshore) Model Sensitivity Experiments: Focusing on Wind Input and Whitecapping Dissipation
Accurate wave prediction in coastal waters is essential for marine safety and engineering, yet it is significantly influenced by uncertainties in wind forcing and dissipation parameterization. This study evaluates the sensitivity of the SWAN model around the Korean Peninsula using 2021 data from 138 observation stations. To address structural biases in wind fields, the Drag Coefficient Scaling Factor (CDFAC) was implemented alongside the Komen and ST6 physics packages. While the Komen scheme provided stable performance under normal conditions, the ST6 + CDFAC configuration exhibited superior physical consistency during extreme events. Notably, applying CDFAC to the ST6 package reduced the high-wave (Hs > 3 m) RMSE by approximately 32.7%, decreasing from 0.52 m to 0.35 m. Bathymetric stratified analysis further confirmed that the ST6 scheme maintains robust performance in offshore and deep-water regions (depth > 50 m), achieving a correlation of 0.94 and an RMSE of 0.20 m. This is attributed to ST6’s frequency-dependent saturation approach, which effectively decouples wind-sea and swell components in environments where whitecapping dissipation is the governing energy sink. In contrast, improvements in coastal waters (depth < 50 m) were moderated by topographical dissipation mechanisms such as bottom friction and depth-induced breaking. These findings demonstrate that integrating wind input bias correction with frequency-dependent dissipation physics is vital for reliable wave forecasting and coastal disaster mitigation.
Journal Article
Dynamics of Three-Dimensional Turbulent Wall Plumes and Implications for Estimates of Submarine Glacier Melting
Subglacial discharges have been observed to generate buoyant plumes along the ice face of Greenland tidewater glaciers. These plumes have been traditionally modeled using classical plume theory, and their characteristic parameters (e.g., velocity) are employed in the widely used three-equation melt parameterization. However, the applicability of plume theory for three-dimensional turbulent wall plumes is questionable because of the complex near-wall plume dynamics. In this study, corrections to the classical plume theory are introduced to account for the presence of a wall. In particular, the drag and entrainment coefficients are quantified for a three-dimensional turbulent wall plume using data from direct numerical simulations. The drag coefficient is found to be an order of magnitude larger than that for a boundary layer flow over a flat plate at a similar Reynolds number. This result suggests a significant increase in the melting estimates by the current parameterization. However, the volume flux in a wall plume is found to be one-half that of a conical plume that has 2 times the buoyancy flux. This finding suggests that the total entrainment (per unit area) of ambient water is the same and that the plume scalar characteristics (i.e., temperature and salinity) can be predicted reasonably well using classical plume theory.
Journal Article
Drag of a heated sphere at low Reynolds numbers in the absence of buoyancy
Fully resolved simulations are used to quantify the effects of heat transfer in the absence of buoyancy on the drag of a spatially fixed heated spherical particle at low Reynolds numbers (
$Re$
) in the range
$10^{-3}\\leqslant Re\\leqslant 10$
in a variable-property fluid. The case where buoyancy is present is analysed in a subsequent paper. This analysis is carried out without making any assumptions on the amount of heat addition from the sphere and thus encompasses both the heating regime where the Boussinesq approximation holds and the regime where it breaks down. The particle is assumed to have a low Biot number, which means that the particle is uniformly at the same temperature and has no internal temperature gradients. Large deviations in the value of the drag coefficient as the temperature of the sphere increases are observed. When
$Re
Journal Article
Analysis of the Impact of Curvature Correction Factor fc on the Flow Past a Two-Dimensional Bluff Body
This paper presents an improved k-ω SST turbulence model to enhance the simulation accuracy of Bluff Body Bypassing Problems (BBBPs) within the Reynolds-Averaged Navier–Stokes (RANS) framework. Although RANS methods are computationally efficient, they are limited in resolving instantaneous turbulent fluctuations, which often results in significant errors when predicting turbulent kinetic energy variations in complex flows. To address this, a curvature correction factor (fc) is introduced into the production term (Pk) of the turbulent kinetic energy equation. This factor is derived from the local fluid rotational rate, enabling the model to better account for streamline curvature effects and unsteady vortex dynamics. The modified model, along with the baseline k-ω SST formulation, is applied to two-dimensional (2D) square column flow cases. Numerical results show that the corrected model significantly improves predictive accuracy, reducing the error in the time-averaged drag coefficient (CD) from 24% to 8.3%, thereby demonstrating its effectiveness in capturing key flow characteristics around bluff bodies.
Journal Article
3D trajectories and velocities of rainfall drops in a multifractal turbulent wind field
Weather radars measure rainfall in altitude, whereas hydro-meteorologists are mainly interested in rainfall at ground level. During their fall, drops are advected by the wind, which affects the location of the measured field. The governing equation of a rain drop's motion relates the acceleration to the forces of gravity and buoyancy along with the drag force. It depends non-linearly on the instantaneous relative velocity between the drop and the local wind, which yields complex behaviour. Here, the drag force is expressed in a standard way with the help of a drag coefficient expressed as a function of the Reynolds number. Corrections accounting for the oblateness of drops greater than 1–2 mm are suggested and validated through a comparison of the retrieved “terminal fall velocity” (i.e. without wind) with commonly used relationships in the literature. An explicit numerical scheme is then implemented to solve this equation for a 3+1D turbulent wind field, and hence analyse the temporal evolution of the velocities and trajectories of rain drops during their fall. It appears that multifractal features of the input wind are simply transferred to the drop velocity with an additional fractional integration whose level depends on the drop size, and a slight time shift. Using an actual high-resolution 3D sonic anemometer and a scale invariant approach to simulate realistic fluctuations of wind in space, trajectories of drops of various sizes falling form 1500 m are studied. For a strong wind event, drops located within a radar gate in altitude during 5 min are spread on the ground over an area of the size of a few kilometres. The spread for drops of a given diameter is found to cover a few radar pixels. Consequences on measurements of hydro-meteorological extremes that are needed to improve the resilience of urban areas are discussed.
Journal Article
Experimental investigation into flow resistance of large benthic crab burrows in the Yellow River Delta, China
The current study investigates the impact of burrowing activities by crab species in the tidal flats of the Yellow River Delta in China on the hydraulic resistance characteristics of water flow, particularly the regulatory effect of biological activity on hydraulic parameters. Although there are many models that attempt to describe the resistance to water flow, these models tend to ignore the influence of such things as biological structures, geomorphological features, and artificial constructs in complex natural water bodies, resulting in insufficient predictive accuracy of the resistance coefficients and Manning's roughness coefficients. In this paper, a new theoretical model is developed to achieve the construction of a model for predicting the hydrodynamic resistance characteristics of crab-hole regions affected by water flow by introducing a cross-sectional area correction coefficient to improve the accuracy of the calculation. The experimental results show that there is a significant positive correlation between the drag coefficient, and the hydraulic radius, and cave density, and a negative correlation with the Reynolds number, and the modification for the sidewall and bed effect greatly improves the representativeness of the measured data. In addition, a new theoretical model is proposed to improve the prediction of drag and Manning's roughness coefficient, and the prediction results are in good agreement with the measured data. The improved drag coefficient calculation model proposed in this paper improves the applicability to the research object and helps to establish a more accurate hydrodynamic model.
Journal Article