Minimum Drag Force Research Articles

Magnetized hybrid nanofluid flow across a wedge: A computational three-dimensional study

The boundary layer fluid flow past a wedge surface occurs in various industrial processes, including wire drawing, metal foaming, polymer extraction, fiber processing, and in determining the dynamic properties (shear stress, drag) of working fluids. Theoretically, the boundary layer three-dimensional flow of a magnetized hybrid nanoliquid over a wedge surface is studied with viscous dissipation and radiation effects. The flow is due to moving wedge surface and power-law free-stream velocities. The current study unifies three different classical flow problems, namely, the Blasius flow, the Hiemenz flow, and the Falkner-Skan flow. Single-phase description of hybrid nanofluid is considered, and the problem is kept realistic by considering the experimental thermophysical properties of the nanomaterial. The governing system consists of conservation of mass, momentum, and the energy equations for hybrid nanofluids. Prandtl’s boundary layer approximations are applied to study the viscous dominant fluid regimes. The entropy equation and the Bejan number are also derived. Numerical computations of self-similar equations are obtained to explore the rheological and the heat transport features against the physical parameters. The Nusselt number and the drag on the wedge surface are computed and analyzed. Of the three classical flow problems, the maximum thickness of the momentum layer occurs for the Blasius flow problem. A minimum drag force on the wedge surface occurs for lower Hartmann number values. Furthermore, an increase in the volume fraction of the hybrid nanoparticles leads to an enhanced heat transport. The use of carbon nanotubes which has exceptional characteristics are taken into consideration in this study. This study also demonstrates the comparison on three-different classical flow problems (Blasius flow, Hiemenz flow, and Falkner-Skan flow).

A Fast and Efficient Method for Multiobjective Aerodynamic Optimization of a Civil Aircraft Fuselage

This study presents a new method for aerodynamic optimization of a civil aircraft fuselage. Typically, the fuselage is designed for minimum drag force at cruise conditions, which is essential for determining the flight cost. Evolutionary optimization methods, as a powerful tool, require the accurate computations of flows around several hundreds of candidate geometries, which in turn are too costly and time-consuming. One strategy is to use two-dimensional simulations that reduce the computational cost by at least one order of magnitude. This approach was applied in the current work, and the results were obtained with the aim of minimizing the drag coefficient and maximizing the lift coefficient. A genetic algorithm (GA) was used for shape optimization, and the objective function evaluation was carried out using computational fluid dynamics (CFD). A fuselage shape parameterization method is presented that accounts for important flow features. The 150-seat aircraft model designed in Amirkabir University of Technology was considered as a reference body. In the first step, the optimization is carried out for the single objective of minimizing the drag coefficient. Then, the multiobjective optimization is performed with the simultaneous drag coefficient minimization and lift coefficient maximization. Finally, the two-dimensional (2D) side view of the optimum fuselages is used for generation of the corresponding three-dimensional (3D) geometry. The results show that such 3D optimum fuselage reduced the drag coefficient by about 11% while increasing the lift coefficient by 29% in comparison with the original geometry.

Measurements of Aerodynamic Performance of the Fuselage of a Hybrid Multi-Rotor Aircraft with Autorotation Capability

The design and optimization of aircraft structures need to be accompanied by the analysis of their aerodynamics. This paper presents numerical calculations and wind tunnel tests to determine the aerodynamic characteristics of the designed unmanned aircraft. The aim of the study was to analyze the aerodynamic performance of the designed hybrid unmanned aerial vehicle and its longitudinal stability. This unique design, i.e. a hybrid aircraft which is a combination of a gyrocopter and a multi-rotor aircraft has not been the object of research yet. The research object is a 1:1 scale model created by the rapid prototyping method. The research was a computational and experimental study. The ANSYS Fluent software was used for the calculations, and the computational mesh of the developed model consisted of 3.5 million tetrahedral elements. The numerical investigations were carried out using the created CFD model with a k-ω turbulence submodel. In addition, the obtained results made it possible to numerically analyze the forces acting on the individual components of the research object, which is a valuable extension of the wind tunnel tests. The experimental studies were performed in a closed-loop subsonic wind tunnel. Aerodynamic forces and moments were measured using a six-component force balance. The obtained results were compared to validate the developed numerical model. The research values describe the performance of the research object in terms of minimum drag force coefficient, maximum lift to drag ratio, and properties related to stability.

Optimization of the Drag Forces of Shell Janus Micromotor: A Study Based on Hydrodynamical Analysis and Numerical Simulation

Micromotors are widely used in cell operation, drug delivery and environmental decontamination due to their small size, low energy consumption and large propelling power. Compared to traditional Janus micromotor, the shell Janus micromotor has better motion performance. However, the structural optimization of its motion performance is still unclear. The main factor restricting the motion performance of shell Janus micromotors is the drag forces. In the current work, theoretical analysis and numerical simulation were applied to analyze the drag forces of shell Janus micromotors. This study aims to design the optimum structure of shell Janus micromotors with minimum drag forces and obtain the magnitude of drag forces considering both the internal and external fluids of the shell Janus micromotors. Moreover, the influence of the motor geometry and Reynolds number on the drag coefficient was analyzed using numerical simulations. The results provide guidance for the optimum flow velocity, opening diameter and shell thickness to achieve minimum drag force.

Numerical investigations on the flow control over bumped surface circular cylinders

External flow-induced forces on bumped surface circular cylinders in laminar flow regimes are studied at a range of Reynolds numbers up to 200. This study examines three types of bumped surface cylinders, including square, triangular, and dimpled surfaces. The bumped surfaces are set at the top surface of the cylinder. The bumps are arranged between θ = 0° and 90° from the front stagnation point of the cylinder. It is shown that the presence of a bump on the leading edge of the cylinder manipulates the vortex dynamics and leads to significant changes in flow-induced forces. The results show that due to asymmetrical imposed pressure on the cylinder, the generated negative vorticity of the square bumped surface is approximately 28% stronger than those of triangular and dimpled surfaces once θ = 90°. Comparing to a smooth cylinder, significant reductions in drag and lift coefficients are obtained at Re = 150 once a bump is created on the surface of the cylinder apart from the type of geometry. It is found that the maximum time-mean lift coefficient is produced once the bump is located at θ≥ 45°. Furthermore, the minimum drag force is generated for the bumped surface cylinder with θ = 0° and Re = 150.

Modelling of Drag Force Reduction for a Waterjet Propulsion System

Abstract The paper provides simulation results for SUP (Stand Up Paddle) board appendage resistance. Additional propulsion is added to the SUP board. It is equipped with a waterjet. The waterjet is attached to the board rudder. This increases the drag coefficient for rudder five times. To reduce the drag variable, design options for the waterjet duct were proposed. The simulation tests were performed using SolidWorks Flow software using two types of simulations, namely, the pressure on the body and the flow around the body. The objective was to streamline the bluff duct of the waterjet and thus to create the appendage design with minimum drag force from fluid flow and possibly greater Inlet Velocity Ratio. Calculations showed that rounding-off the edges of waterjet duct resulted in 35 % of drag coefficient reduction, while further streamlining reduced it by additional 10 %.

Effect of Cutting Ratio and Catch on Drag Characteristics and Fluttering Motions of Midwater Trawl Codend

The codend of a trawl net is the rearmost and crucial part of the net for selective fish catch and juvenile escape. To ensure efficient and sustainable midwater trawl fisheries, it is essential to better understand the drag characteristics and fluttering motions of a midwater trawl codend. These are generally affected by catch, cutting ratio, mesh size, and twine diameter. In this study, six nylon codend models with different cutting ratios (no cutting, 6:1, 5:1, 4:1, 7:2, and 3:1) were designed and tested in a professional flume tank under two conditions (empty codends and codends with catch) and five current speeds to obtain the drag force, spatial geometry, and movement trend. As the cutting ratio of empty codends decreased, the drag force decreased, and the drag coefficient increased. The unfolding degree of codend netting and the height of empty codends were found to be directly proportional to the current speed and inversely proportional to the cutting ratio. The positional amplitude of codend with cutting ratio 4:1 was the smallest for catch. The drag force of codends with catch increased as the current speed increased, and first decreased and then increased as the cutting ratio decreased. To ensure the best stability and minimum drag force of the codend, it is recommended to use the 4:1 cutting ratio codend.

Numerical investigation of fluid-solid interaction for flow around three square cylinders

In this work, fluid-solid interactions are numerically investigated for flow around three equally/unequally spaced square cylinders using the lattice Boltzmann method. Two major trends of shear layers observed for equal gap spacings between cylinders: (i) without roll up (W), and (ii) with roll up (R). While for unequal gap spacings, four major trends of shear layers observed: (i) without roll up in both gaps (WW), (ii) without rollup in first gap and with roll up in second gap (WR), (iii) with roll up in first gap and without roll up in second gap (RW), and (iv) with roll up in both gaps (RR). g = 3 is found to be the critical equal spacing value. Also g = 1.5 is found to be suitable equal spacing in terms of minimum drag force. While the suitable unequal gap spacing combinations found in this study are (g1, g2) = (1.5, 0.5), (g1, g2) = (3, 0.5) and (g1, g2) = (5, 0.5). Results show that flow induced forces can be suppressed by suitable unequal gap spacing combinations.

A Nnumerical Study of Drag force for Optimist Dinghy on Flat Water

This study investigates numerically the drag force on the Optimal dinghy, which is one of the official classes of international sailing regatta. The drag force is affected by the forward and backward tilt angles and the heels angles. The results revealed that the minimum drag force on the dinghy occurred under the flat dinghy and zero tilt angle condition. The drag force decreases with increasing backward tilt angle. Meanwhile the minimum drag force occurred at the 10 degree of the heeling angle under low velocity condition, and it occurred at the 5 degree while the sailing velocity exceeded 2 m/s. The correlation of the drag force and the sailing velocity can be expressed as FD = 13.87V2 for flat dinghy sailing.

Genetic algorithm-based optimization design method of the Formula SAE racing car’s rear wing

The aerodynamic devices play an important role on the performance of the Formula SAE racing car. The rear wing is the most significant and popular element, which offers primary down force and optimizes the wake. In traditional rear wing optimization, the optimization variables are first selected, and separately enumerated according to the analyzing experience of the racing car’s external flow field, and thus the optimal design is chosen by comparison. This method is complicated, and even might lose some key sample points. In this paper, the attack angle of the rear wing and the relative position parameters are set as design variables; then the design variables’ combination is determined by the DOE experimental design method. The aerodynamic lift and drag of the racing car for these variables’ combinations are obtained by the computational fluid dynamics method. With these sample points, the approximation model is produced by the response surface method. For the sake of gaining the best lift to drag ( FL/ FD) ratio, i.e. maximum down force and the minimum drag force, the optimal solution is found by the genetic algorithm. The result shows that the established optimization procedure can optimize the rear wing’s aerodynamic characteristic on the racing car effectively and have application values in the practical engineering.

Experimental Study on the Effect of Reynolds Number Variation on Drag Force for Various Cut Angle on D-Type Cylinders

Experimental study on the effect of Reynolds number variation on drag force for various cut angles on D-type cylinders was performed. Five different cut angles on different cylinders were applied including: 35o, 45o, 53o, 60o, and 65o. The free stream velocity was varied so the Reynolds number also varied.The experiment was carried out at a subsonic wind tunnel. Drag force for a cut D-type cylinder (for example 35o) was measured using a force balance and wind speed was varied so that corresponding Reynolds number of 2.4×104÷5.3×104 were achieved. Wind turning angle was kept at 0o (without turning angle). This experiment repeated for other D-type cylinders.Experiment results show that, for all D-type cylinders, drag force decreased as the Reynolds number increased, then it was increased after attain minimum drag force. For all D-type cylinders and all variations of Reynolds number the drag minimum is attained at cut angle of 53o. This value is appropriate with previous experiment results.

Optimal shape determination of a body located in incompressible viscous fluid flow

The purpose of this study is to present a formulation and numerical results of a shape optimization of a body located in the incompressible viscous flow field. The formulation is based on an optimal control theory in which a performance function of fluid forces is introduced. The performance function should be minimized satisfying the state equation. Based on the adjoint equation, the gradient of the performance function can be derived. The weighted gradient method is successfully utilized as the minimization algorithm. The bubble function finite element method originated by authors’ group is used for the spatial discretization. For the control variables, the coordinate of the body is employed. The Delaunay triangulation is employed for the discretization with smoothing technique for the gradient. At the moderate Reynolds number flow, the drag minimization of a wing shape body located in the unsteady Navier–Stokes flow is carried out. Starting from a circular cylinder, the streamline shape has been obtained, which is similar to the NACA wing shape. However, the shape shows front-edged and rear-round type. It is clarified that the Reynolds number Re = 250 flow corresponds to the critical state at which the minimum drag force shape changes from the front-edge shape to the front-round shape.

Some vortex-shedding characteristics of the staggered configuration of circular cylinders

A pair of circular cylinders of equal diameter arranged in the staggered configuration was tested in the subcritical Reynolds number regime at centre-to-centre pitch ratios of P/ D=2.0 and 2.5. For each pitch ratio, the incidence angle was varied in small steps in the range α=0–90°. Vortex-shedding frequency measurements were made behind the upstream and downstream cylinders as the incidence angle, α, was varied. At small incidence angles, 2°< α<15°, the Strouhal number data were unreliable, since the peaks in the power spectra were either absent or broad banded. In this same range of incidence angle, the downstream cylinder experiences a maximum inward-directed lift force and a minimum drag force. The results indicate that the flow mechanisms responsible for the changes in the aerodynamic forces have an important influence on the vortex-shedding activity also.

Conceptual design of a hoop energy storage system

The hoop energy storage system (HESS) was conceptually designed for the diurnal load leveling of an electric power supply. It consists of an approximately 6 m diam carbon fiber composite hoop with permanent magnetic bearings and a linear motor/generator system with solid-state cycloconverter circuits for the energy conversion between kinetic energy and electric energy. With a vacuum chamber and strong tensile strength structure for nonresistive high-speed rotation, the HESS is expected to have a large capacity of energy storage. The optimization of magnet arrangement through the analysis of the magnet’s characteristics was suggested to reduce the power loss and instability. By the measurement of magnetic-field configuration and numerical calculations with a three-dimensional code (TOSCA), it is proved that NdFeB magnets have sufficient magnetic-field strength to support the levitation of the hoop. This analysis also led to minimum drag force and eddy–current loss to make use of the uniform field. As a result of analysis, construction of the HESS has begun in our laboratory and the fabrication procedure will be reported.

Interference between two circular cylinders; Series of unexpected discontinuities

When two cylinders face the flow one behind the other then they are in tandem arrangement. The systematic measurements of the front (gap) and base pressures of the downstream cylinder at various spacings showed a discontinuous ‘jump’ at some critical spacing. The drag force coefficients on the downstream cylinder showed a similar discontinuous change at the same critical spacing. This was attributed to two different flow patterns around the tandem cylinders. Following this, two cylinders arranged side-by-side to the approaching flow were considered. The inherently biased flow in the gap between the cylinders produced two different flow patterns around each cylinder. The biased flow was bistable causing a change over at irregular intervals of time. Thus each cylinder might be subjected to either of the two drag and lift forces. All the available data on measured forces were compiled together with the additional measurements in the range of spacings within which intermittent change-over of drag and lift took place. When two cylinders are neither in tandem nor in side-by-side arrangement then they are staggered. The systematic measurements of drag and lift forces on the downstream cylinder showed two unexpected features. Firstly, the position of the downstream cylinder at which the maximum lift force was exerted on it was plotted in transverse, ( T D ),-longitudinal, ( L D ), plane. Two different curves were obtained which overlapped one above the other within a range of staggered arrangments. This feature of the maximum lift force was considered as a sign that two entirely different flow patterns were the cause. The second feature found was that at some spacings the minimum drag force did not occur in the tandem arrangement but in adjacent staggered arrangements. A plausible explanation was offered for that peculiar C Lmax and C Dmin behaviour. Finally, a discontinuity in the lift force for some staggered arrangements was found and attributed to the bistable flow patterns in the gap.