Numerical simulations of a freely falling rigid sphere in bounded and unbounded water domains

Numerical studies were conducted on the hydrodynamics of a freely falling rigid sphere in bounded and unbounded water domains to investigate the drag coefficient, normalized velocity, pressure coefficient, and skin friction coefficient as a function of dimensionless time. The bounded domain was simulated by bringing the cylindrical water container's wall closer to the impacting rigid sphere and linking it to the blockage ratio (BR), defined as the ratio of the projection area of a freely falling sphere to that of the cross-section area of the cylindrical water container. Six cases of bounded domains (BR= 1%, 25%, 45%, 55%, 65%, and 75%) were studied. However, the unbounded domain was considered with a BR of 0.01%. In addition, the k–ω shear stress transport (SST) turbulence model was employed, and the computed results of the bounded domain were compared with those of other studies on unbounded domains. In the case of the bounded domain, which has a higher value of BR, a substantial reduction in normalized velocity and an increase in the drag coefficient were found. Moreover, the bounded domain yielded a significant increase in the pressure coefficient when the sphere was half-submerged; however, an insignificant effect was found on the skin friction coefficient. In the case of the unbounded domain, a significant reduction in the normalized velocity occurred with a decrease in the Reynold number (Re) whereas the drag coefficient increases with a decrease in Reynolds number.

Prototype-Scale Physical Model of Wave Attenuation Through a Mangrove Forest of Moderate Cross-Shore Thickness: LiDAR-Based Characterization and Reynolds Scaling for Engineering With Nature

This study investigates the potential of a Rhizophora mangrove forest of moderate cross-shore thickness to attenuate wave heights using an idealized prototype-scale physical model constructed in a 104 m long wave flume. An 18 m long cross-shore transect of an idealized red mangrove forest based on the trunk-prop root system was constructed in the flume. Two cases with forest densities of 0.75 and 0.375 stems/m2 and a third baseline case with no mangroves were considered. LiDAR was used to quantify the projected area per unit height and to estimate the effective diameter of the system. The methodology was accurate to within 2% of the known stem diameters and 10% of the known prop root diameters. Random and regular wave conditions seaward, throughout, and inland of the forest were measured to determine wave height decay rates and drag coefficients for relative water depths ranging 0.36 to 1.44. Wave height decay rates ranged 0.008–0.021 m–1 for the high-density cases and 0.004–0.010 m–1 for the low-density cases and were found to be a function of water depth. Doubling the forest density increased the decay rate by a factor two, consistent with previous studies for other types of emergent vegetation. Drag coefficients ranged 0.4–3.8, and were found to be dependent on the Reynolds number. Uncertainty in the estimates of the drag coefficient due to the measured projected area and measured wave attenuation was quantified and found to have average combined standard deviations of 0.58 and 0.56 for random and regular waves, respectively. Two previous reduced-scale studies of wave attenuation by mangroves compared well with the present study when their Reynolds numbers were re-scaled by λ3/2 where λ is the prototype-to-model geometric scale ratio. Using the combined data sets, an equation is proposed to estimate the drag coefficient for a Rhizophora mangrove forest: CD = 0.6 + 3e04/ReDBH with an uncertainty of 0.69 over the range 5e03 < ReDBH < 1.9e05, where ReDBH is based on the tree diameter at breast height. These results may improve engineering guidance for the use of mangroves and other emergent vegetation in coastal wave attenuation.

Aircraft Position Prediction during the Crosswind Approach

Testing the impact of the drag coefficient on an F16 aircraft model, depending on the angle of attack a was performed. First, a navigation model was introduced describing the preliminary and computational assumptions of the model. The final part of the present paper contains the relationships between the wind angle and the wind correction angle at the angle of attack a = 00, a = 110, a = 130 for a full-scale F-16 aircraft. The tables present results of all the calculations for individual angles of attack, taking into account variable wind angles relative to the longitudinal axis of the runway. The values show the corrections calculated for an 1/19 scale aircraft model and for a full-scale F16 aircraft. The "right" and "left" designations represent the direction from which the wind blows in relation to the aircraft.

Compressible Time-Dependent Steam Flow And Thermal Heat Analysis In Squared Cylinder: A Numerical Investigation

This paper investigates time-dependent compressible steam laminar flow coupled with heat transfer in fluids in a squared cylinder. The present problem has been designed in COMSOL-Multiphysics. The laminar flow is selected keeping the Mac number low. The flow possesses a no-slip condition with the wall of geometry. The pressure kept on flow is 0 Pas and the temperature of the flow regime is 305.13. The flow is initiated with a velocity of 0.5m/s. The effects of time on velocity distribution and pressure distribution are described with the help of graphs. Different results like drag coefficient, lift coefficient, heat distributions are also discussed. The technique used to solve modeled problem is BDF.

CFD Analysis of Flow Over Pickup Truck with And Without Covering Cargo Area Using OpenFOAM

Pickup truck serves purpose as car as well as small truck. Pickup truck is popularly used in USA and Saudi Arabia. Pickup truck consists of enclosed cab and an open cargo space. Here CFD analysis of full scale pickup truck is performed using free CFD software OpenFOAM for speed range from 40km/hr to 140km/hr. For turbulence modelling k-ω model is used. This work investigates effect of covering cargo area on aerodynamics drag. Covering cargo area decreases drag coefficient by 5.2% by horizontally covering cargo area whereas decreases by 13% by inclined surface covering cargo area. Thus, covering cargo area reduces drag coefficient as recirculation zone is reduced. Inclined cover case shows drastic rise in lift force, requiring attention for safety as traction will be affected.

A Study of Drag Reduction on Cylinders with Different V-Groove Depths on the Surface

In this study, the drag reduction effect is studied for a cylinder with different V-groove depths on its surface using a k-ω/SST (Shear Stress Transport) turbulence model of computational fluid dynamics (CFD), while a particle image velocimetry (PIV) system is employed to analyze the wake characteristics for a smooth cylinder and a cylinder with different V-groove depths on its surface at different Reynolds numbers. The study focuses on the characteristics of the different V-groove depths on lift coefficient, drag coefficient, the velocity distribution of flow field, pressure coefficient, vortex shedding, and vortex structure. In comparison with a smooth cylinder, the lift coefficient and drag coefficient can be reduced for a cylinder with different V-groove depths on its surface, and the maximum reduction rates of lift coefficient and drag coefficient are about 34.4% and 16%, respectively. Otherwise, the vortex structure presents a complete symmetry for the smooth cylinder, however, the symmetry of the vortex structure becomes insignificant for the V-shaped groove structure with different depths. This is also an important reason for the drag reduction effect of a cylinder with a V-groove surface.

Three-dimensional numerical simulation of a flat plate perpendicularly submitted to current with a blockage ratio of 0.214: URANS and DES

The uniform flow over a nominally two-dimensional normal thin flat plate with blockage ratio 0.214 was numerically investigated in three dimensions by three methods: unsteady Reynolds-averaged Navier–Stokes (URANS) based on the realizable k-epsilon (RKE) turbulence model, URANS based on the k–omega shear stress transport (SST) turbulence model and detached eddy simulation (DES). The Reynolds number based on the inlet flow velocity and the chord width of the plate was 117000. A comprehensive comparison against earlier experimental results showed that URANS-SST method only could give a correct Strouhal number but overestimated the mean base pressure distribution and mean drag coefficient, while URANS-RKE and DES methods succeeded in giving accurate prediction of all. Moreover, by comparing the instantaneous vorticity contours and 3D turbulent flow structures, it is found that DES is better suited for the present case because it can capture irregular small-scale structures and reproduce the three-dimensionality and low-frequency unsteadiness of the vortex shedding. Finally, through the volume-of-fluid (VOF) based simulation of the free surface, it is demonstrated that the free surface has no significant effect on mean drag coefficient and Strouhal number.

Air drag coefficient of textile-covered elastic cylinders – preliminary aerodynamic studies

This paper presents preliminary experimental results on the influence on the aerodynamic drag of a cylinder from the cylinder type (i.e., rigid or soft) and its textile surface. Both a rigid cylinder and a soft-body cylinder, with a gelatin layer, each with five different textile surfaces were measured in the wind tunnel using force measurement technology. The drag coefficient was determined for several Reynolds numbers. The study shows that the elasticity of a cylinder has a significant influence on the drag force and the airflow type. However, the influence of the soft-body cylinder depends on the respective fabric. With the given measurements, no exact statements can yet be made to quantify the influence. This influence must be studied independently and in conjunction with the textile surface in order to gain understanding of the overall system of airflow, textile and elastic body.