Showing papers on "Drag coefficient published in 2021"

Comsolic solution of an elliptic cylindrical compressible fluid flow.

Abstract: In this article, the primary focus is to investigate the heat transfer effects with viscous compressible laminar flow in the permeable elliptic cylinder. The Reynolds number is kept 100 for flow to be laminar. The physics of heat transfer is selected to be coupled with the laminar flow. The results for particular step-size time for Velocity distribution, pressure profile, temperature profile, isothermal temperature contours, and drag coefficient have been analyzed. Mesh has been generated through COMSOL, mesh entities have been elaborated statistically. The maximum and minimum velocity profile is observed at the elliptical cylinder’s walls and upper, lower boundary respectively. The maximum velocity observed is 2.22 m/s. Pressure profile around elliptic corners is found maximum, distinct patterns are observed even under the influence of applied heat. Temperature is observed maximum at walls but it gradually increases as moving from the upper boundary towards the lower boundary. The isothermal contour patterns are observed maximum near the walls, drag coefficient of gradual decrease is observed. COMSOL multi-physics is utilized for mathematical modeling of problems and the Backward-Differentiation-Formula has been exploited to handle problems numerically. The results will help greatly to understand the characterizations of viscous fluids and in industries like air furnaces and automobile cooling systems.

Numerical investigation of the effect of surface roughness on flow and heat transfer characteristics of single sphere particle in supercritical water

Abstract: Supercritical water fluidized bed is a novel gasification reactor which can achieve efficient and clean utilization of coal. The rough surface of particle produced during grinding and thermochemical conversion processing will deeply affect supercritical water-particle two-phase flow and heat transfer characteristics. In this paper, fully resolved numerical simulation of supercritical water flow past single rough sphere particle with the Reynolds number ranging from 10 to 200 was carried out to investigate the effect of surface roughness. The simulation results show that as roughness increases, the separation bubbles generated in the dimple enhance the flow separation but has no significant effect on the drag coefficient. Particle surface-average Nusselt number decreases with an increase of roughness and surface enlargement coefficient due to the isolation effect at low Re and local separation bubbles in the dimple at high Re. Furthermore, the effect of surface enlargement coefficient on heat transfer efficiency factor for supercritical water near the critical point is greater than that under constant property condition and has a higher dependence on Re.

Supersonic and Hypersonic Drag Coefficients for a Sphere

Abstract: A comprehensive review of all relevant experimental data was completed, including recent data for the drag coefficient for a sphere in supersonic and hypersonic flows. The primary characterization ...

Hybrid (ND-Co 3 O 4 /EG) nanoliquid through a permeable cylinder under homogeneous-heterogeneous reactions and slip effects

Abstract: Modeling and computations are performed to study the ND-Co3O4/EG hybrid nanoliquid mixed convective flow past a vertical porous cylinder. The flow analysis and formulation are given accounting for slip effects and homogeneous-heterogeneous reaction impacts. The governing complex equations formed with prescribed boundary conditions are simplified into self-similar equations through the use of suitable transformations. The numerical solutions of the drag coefficient, Nusselt number, liquid velocity, liquid temperature, and the liquid concentration are explored through graphs with the setting of pertaining parameter values. From the results, it is noticed that an ND-Co3O4/EG nanofluid plays a more impressive role in the process of energy transfer than a Co3O4/EG nanofluid. Further, it is found that the heterogeneous reaction parameter decreases the concentration whereas multiple slips enhance the temperature.

An investigation of wake flows produced by asymmetrically structured porous coated cylinders

Abstract: The vortex shedding tone of a cylinder in uniform flow can be reduced by applying a porous coating yet this mechanism is not fully understood. An experimental investigation of asymmetric structured porous coated cylinders (SPCCs) was conducted in a small anechoic wind tunnel using a hot-wire anemometry probe placed in the boundary layer, separated shear layer and wake, in conjunction with a microphone in the far-field. Tests were conducted at Reynolds numbers 105, 1.53 × 10 5, and 1.66 × 10 5. Each SPCC revealed a widened and deeper wake and reduced turbulent kinetic energy levels in the separated shear layer than the bare baseline cylinder. Furthermore, each SPCC revealed two tones that were a multiple of two apart in both the velocity and acoustic power spectral densities. It was shown that the higher frequency tone is generated by localized flow behaviors in the separated shear layer, independent of the vortex shedding tone and its magnitude is inversely related to the SPCC windward surface porosity. Applying a more densely spaced porous region on the cylinder windward side resulted in higher frequency broadband contributions that were shown to be independent of the velocity fluctuations in the wake region. Time-averaged velocity profiles in the wake revealed that the leeward side porosity strongly influences the drag coefficient. Linear stability analysis revealed that the SPCCs develop absolute instabilities in the near wake.

Impact of activation energy on hyperbolic tangent nanofluid with mixed convection rheology and entropy optimization

Abstract: The present work numerically examines the entropy generation in the transport of hyperbolic tangent nanofluid over a stretchable surface with nonlinear Boussinesq approximation. Impacts of viscous dissipation, Joule heating, strength of uniform magnetic field along with modified Arrhenius expression is accounted. Under the significance of Buongiorno’s model, thermophoresis and Brownian effects are considered. The dimensionless form of mathematical system is obtained by adopting similarity variables. Consequence of flow parameters are explored through graphs. More, drag coefficient, heat transfer rate and Sherwood number are presented with tables and bar charts. Here, we noted that power law index parameter declines the fluid motion and entropy generation increases with diffusion variable.

Analysis of Cattaneo–Christov heat flux in Jeffery fluid flow with heat source over a stretching cylinder

Abstract: This analysis explores stagnation point in Jeffery liquid flow over a stretchable cylinder. Heat and mass transfer are investigated through Cattaneo–Christov model with double stratification, heat source and thermal relaxation. Moreover, the flow of liquid is caused by stretchable cylinder. Cylindrical coordinates are used for mathematical formulations. The acquired boundary layer problems for stretchable cylinder are dealt through homotopy analysis method. Results of variables appeared in governing equations are disclosed through graphs for flow, temperature, concentration and skin friction. The findings of the study show that higher values of ratio parameter and Deborah number in terms of relaxation time reduce magnitude of drag coefficient while reverse trend is noted for larger Deborah number in terms of retardation time and curvature parameter. Comparison of present work with previous published date is presented.

Industrial scale Large Eddy Simulations with adaptive octree meshes using immersogeometric analysis

Abstract: We present a variant of the immersed boundary method integrated with octree meshes for highly efficient and accurate Large Eddy Simulations (LES) of flows around complex geometries. We demonstrate the scalability of the proposed method up to O ( 32 K ) processors. This is achieved by (a) rapid in-out tests; (b) adaptive quadrature for an accurate evaluation of forces; (c) tensorized evaluation during matrix assembly. We showcase this method on two non-trivial applications: accurately computing the drag coefficient of a sphere across Reynolds numbers 1 − 10 6 encompassing the drag crisis regime; simulating flow features across a semi-truck for investigating the effect of platooning on efficiency.

Aerodynamic interaction of bristled wing pairs in fling

Abstract: Tiny flying insects of body lengths under 2 mm use the “clap-and-fling” mechanism with bristled wings for lift augmentation and drag reduction at a chord-based Reynolds number (Re) on O ( 10 ). We examine the wing–wing interaction of bristled wings in fling at Re = 10 as a function of initial inter-wing spacing (δ) and degree of overlap between rotation and linear translation. A dynamically scaled robotic platform was used to drive physical models of bristled wing pairs with the following kinematics (all angles relative to vertical): (1) rotation about the trailing edge to angle θr, (2) linear translation at a fixed angle (θt), and (3) combined rotation and linear translation. The results show that (1) the cycle-averaged drag coefficient decreased with increasing θr and θt and (2) decreasing δ increased the lift coefficient owing to increased asymmetry in the circulation of leading and trailing edge vortices. A new dimensionless index, reverse flow capacity (RFC), was used to quantify the maximum possible ability of a bristled wing to leak the fluid through the bristles. The drag coefficients were larger for smaller δ and θr despite larger RFC, likely due to the blockage of inter-bristle flow by shear layers around the bristles. Smaller δ during early rotation resulted in the formation of strong positive pressure distribution between the wings, resulting in an increased drag force. The positive pressure region weakened with increasing θr, which in turn reduced the drag force. Tiny insects have been previously reported to use large rotational angles in fling, and our findings suggest that a plausible reason is to reduce drag forces.

Drag on a spherical particle at the air-liquid interface : Interplay between compressibility, Marangoni flow, and surface viscosities

Abstract: We investigate the flow of viscous interfaces carrying an insoluble surface active material, using numerical methods to shed light on the complex interplay between Marangoni stresses, compressibility, and surface shear and dilatational viscosities. We find quantitative relations between the drag on a particle and interfacial properties as they are required in microrheology, i.e., going beyond the asymptotic limits. To this end, we move a spherical particle probe at constant tangential velocity, symmetrically immersed at either the incompressible or compressible interface, in the presence and absence of surfactants, for a wide range of system parameters. A full three-dimensional finite element calculation is used to reveal the intimate coupling between the bulk and interfacial flows and the subtle effects of the different physical effects on the mixed-type velocity field that affects the drag coefficient, both in the bulk and at the interface. For an inviscid interface, the directed motion of the particle leads to a gradient in the concentration of the surface active species, which in turn drives a Marangoni flow in the opposite direction, giving rise to a force exerted on the particle. We show that the drag coefficient at incompressible interfaces is independent of the origin of the incompressibility (dilatational viscosity, Marangoni effects or a combination of both) and that its higher value can not only be related to the Marangoni effects, as suggested earlier. In confined flows, we show how the interface shear viscosity suppresses the vortex at the interface, generates a uniform flow, and consequently increases the interface compressibility and the Marangoni force on the particle. We mention available experimental data and provide analytical approximations for the drag coefficient that can be used to extract surface viscosities.

Kinematics and dynamics of freely rising spheroids at high Reynolds numbers

Abstract: We experimentally investigate the effect of geometrical anisotropy for buoyant spheroidal particles rising in a still fluid. All other parameters, such as the Galileo number (the ratio of gravitational to viscous forces), the ratio of the particle to fluid density and the dimensionless moment of inertia (with being the moment of inertia of the particle and that of the fluid in an equivalent volume), are kept constant. The geometrical aspect ratio of the spheroids, is varied systematically from (oblate) to 5 (prolate). Based on tracking all degrees of particle motion, we identify six regimes characterised by distinct rise dynamics. Firstly, for, increased rotational dynamics are observed and the particle flips over semi-regularly in a 'tumbling'-like motion. Secondly, for oblate particles with, planar regular 'zig-zag' motion is observed, where the drag coefficient is independent of. Thirdly, for the most extreme oblate geometries (), a 'flutter'-like behaviour is found, characterised by precession of the oscillation plane and an increase in the drag coefficient. For prolate geometries, we observed two coexisting oscillation modes that contribute to complex trajectories: The first is related to oscillations of the pointing vector and the second corresponds to a motion perpendicular to the particle's symmetry axis. We identify a 'longitudinal' regime (), where both modes are active and a different one, the 'broadside'-regime (), where only the second mode is present. Remarkably, for the most prolate particles (), we observe an entirely different 'helical' rise with completely unique features.

Drag variations, tidal asymmetry and tidal range changes in a mangrove creek system

Abstract: Aboveground root structures enhance drag on tidal currents in intertidal mangrove forests whereas the creeks dissecting such forests provide low‐resistance conduits for tidal flows. Here, observations from an established mangrove forest in the Whitianga estuary, Aotearoa New Zealand, are used to investigate the variability of the drag experienced by tidal flows in a mangrove creek system and subsequent effects on tidal asymmetries and ranges. Tidal flow speed maxima in the creek occurred at overbank water levels during the sheet flow stage on rising tides, but at water levels below the creek bank (the creek flow stage) on falling tides. Inferred bulk drag coefficients for the creek were greater during the sheet flow than the creek flow stage, and were linearly correlated with the bulk drag coefficients at stations in the adjacent forest. Although falling tides, associated with larger bulk drag coefficients, had an increasingly longer duration than rising tides towards the back of the forest, we observed ebb‐dominant flow speed asymmetry that declined inland in the creek. Conversely, flow speeds within the forest were consistently flood‐dominant, in accordance with smaller bulk drag coefficients during rising tides. Along the full length of the mangrove system, high‐water levels were lowered by up to 12 cm/km within the creek and 36 cm/km within the mangrove forest. Creek bed roughness associated with bulk drag coefficients observed in deeper parts of the creek was much greater than the hydraulic roughness of the sediment. For accurate simulations of landscape‐scale feedbacks between the creek and mangrove forest, incorporating both direct and indirect contributions of the vegetated forest platform to creek bed roughness is essential. These findings show that the interaction between creek flow and sheet flow in a mangrove creek system is a key driver of tidal asymmetries as well as the attenuation of high‐water conditions.

Influence of the Drag Force on the Average Absorbed Power of Heaving Wave Energy Converters Using Smoothed Particle Hydrodynamics

Abstract: In this paper, we investigated how the added mass, the hydrodynamic damping and the drag coefficient of a Wave Energy Converter (WEC) can be calculated using DualSPHysics DualSPHysics is a software application that applies the Smoothed Particle Hydrodynamics (SPH) method, a Lagrangian meshless method used in a growing range of applications within the field of Computational Fluid Dynamics (CFD) Furthermore, the effect of the drag force on the WEC’s motion and average absorbed power is analyzed Particularly under controlled conditions and in the resonance region, the drag force becomes significant and can greatly reduce the average absorbed power of a heaving point absorber Once the drag coefficient has been determined, it is used in a modified equation of motion in the frequency domain, taking into account the effect of the drag force Three different methods were compared for the calculation of the average absorbed power: linear potential flow theory, linear potential flow theory modified to take the drag force into account and DualSPHysics This comparison showed the considerable effect of the drag force in the resonance region Calculations of the drag coefficient were carried out for three point absorber WECs: one spherical WEC and two cylindrical WECs Simulations in regular waves were performed for one cylindrical WEC with two different power take-off (PTO) systems: a linear damping and a Coulomb damping PTO system The Coulomb damping PTO system was added in the numerical coupling between DualSPHysics and Project Chrono Furthermore, we considered the optimal PTO system damping coefficient taking the effect of the drag force into account

Topography generation by melting and freezing in a turbulent shear flow

Abstract: We report an idealized numerical study of a melting and freezing solid adjacent to a turbulent, buoyancy-affected shear flow, in order to improve our understanding of topography generation by phase changes in the environment. We use the phase-field method to dynamically couple the heat equation for the solid with the Navier–Stokes equations for the fluid. We investigate the evolution of an initially flat and horizontal solid boundary overlying a pressure-driven turbulent flow. We assume a linear equation of state for the fluid and change the sign of the thermal expansion coefficient, such that the background density stratification is either stable, neutral or unstable. We find that channels aligned with the direction of the mean flow are generated spontaneously by phase changes at the fluid–solid interface. Streamwise vortices in the fluid, the interface topography and the temperature field in the solid influence each other and adjust until a statistical steady state is obtained. The crest-to-trough amplitude of the channels is larger than approximately 10 the viscous length scale, but is much larger and more persistent for an unstable stratification than for a neutral or stable stratification. This happens because a stable stratification makes the cool melt fluid buoyant such that it shields the channel from further melting, whereas an unstable stratification makes the cool melt fluid sink, inducing further melting by rising hot plumes. The statistics of flow velocities and melt rates are investigated, and we find that channels and keels emerging in our simulations do not significantly change the mean drag coefficient.