scholarly journals Numerical Investigation on Flapping Aerodynamic Performance of Dragonfly Wings in Crosswind

2020 ◽  
Vol 2020 ◽  
pp. 1-14
Author(s):  
Chao Wang ◽  
Rui Zhang ◽  
Chaoying Zhou ◽  
Zhenzhong Sun
Keyword(s):  
Stokes Equations ◽  
Three Dimensional ◽  
Lateral Force ◽  
Aerodynamic Characteristics ◽  
Navier Stokes ◽  
Aerodynamic Forces ◽  
Sideslip Angle ◽  
Flight Direction ◽  
Time Average ◽  
Dragonfly Wings

Numerical simulations are performed to investigate the influence of crosswind on the aerodynamic characteristics of rigid dragonfly-like flapping wings through the solution of the three-dimensional unsteady Navier-Stokes equations. The aerodynamic forces, the moments, and the flow structures of four dragonfly wings are examined when the sideslip angle ϑ between the crosswind and the flight direction varied from 0o to 90o. The stability of the dragonfly model in crosswind is analyzed. The results show that the sideslip angle ϑ has a little effect on the total time-average lift force but significant influence on the total time-average thrust force, lateral force, and three-direction torques. An increase in the sideslip angle gives rise to a larger total time-average lateral force and yaw moment. These may accelerate the lateral skewing of the dragonfly, and the increased rolling and pitching moments will further aggravate the instability of the dragonfly model. The vorticities and reattached flow on the wings move laterally to one side due to the crosswind, and the pressure on wing surfaces is no longer symmetrical and hence, the balance between the aerodynamic forces of the wings on two sides is broken. The effects of the sideslip angle ϑ on each dragonfly wing are different, e.g., ϑ has a greater effect on the aerodynamic forces of the hind wings than those of the fore wings. When sensing a crosswind, it is optimal to control the two hind wings of the bionic dragonfly-like micro aerial vehicles.

A Computational Analysis of Flow Field in Twin-Track Subway Tunnel to Improve Air Quality

2013 ◽  
Vol 319 ◽  
pp. 599-604
Author(s):  
Makhsuda Juraeva ◽  
Kyung Jin Ryu ◽  
Sang Hyun Jeong ◽  
Dong Joo Song
Keyword(s):  
Air Quality ◽  
Computational Model ◽  
Stokes Equations ◽  
Ventilation System ◽  
Three Dimensional ◽  
Aerodynamic Characteristics ◽  
Navier Stokes ◽  
Subway Tunnel ◽  
Air Supply ◽  
And Performance

A computational model of existing Seoul subway tunnelwas analyzed in this research. The computational model was comprised of one natural ventilationshaft, two mechanical ventilationshafts, one mechanical airsupply, a twin-track tunnel, and a train. Understanding the flow pattern of the train-induced airflow in the tunnel was necessary to improve ventilation performance. The research objective wasto improve the air quality in the tunnel by investigating train-induced airflow in the twin-track subway tunnel numerically. The numerical analysis characterized the aerodynamic behavior and performance of the ventilation system by solving three-dimensional turbulent Reynolds-averaged Navier-Stokes equations. ANSYS CFX software was used for the computations. The ventilation and aerodynamic characteristics in the tunnel were investigated by analyzing the mass flowrateat the exits of the ventilation mechanicalshafts. As the train passed the mechanical ventilation shafts, the amount of discharged-air in the ventilationshafts decreased rapidly. The air at the exits of the ventilation shafts was gradually recovered with time, after the train passed the ventilation shafts. The developed mechanical air-supply for discharging dusty air and supplying clean airwas investigated.The computational results showed that the developed mechanical air-supplycould improve the air quality in the tunnel.

Large Eddy Simulation of Aerodynamic Forces on a Bridge Pylon

2011 ◽  
Vol 243-249 ◽  
pp. 1578-1582
Author(s):  
Xu Yong Ying ◽  
Fu You Xu ◽  
Zhe Zhang ◽  
Yong Gang Tan
Keyword(s):  
Large Eddy Simulation ◽  
Bluff Body ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Wind Tunnel Test ◽  
Navier Stokes ◽  
Aerodynamic Forces ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Les Model

In this study, aerodynamic forces on a bridge pylon are investigated by three-dimensional computational fluid dynamics using Large eddy simulation (LES) technology. The main objective is to identify the wind load parameters of the pylon and examine the accuracy of LES model applied to the bluff-body flows. The numerical results were compared with the available wind tunnel test results. Also, a comparison between using LES and Reynolds averaged Navier-Stokes equations with the RNG model have been made. It is found that the LES model competes the RNG model in accuracy for predictions of aerodynamic forces on the pylon.

Unsteady Aerodynamic Characteristics of a High Speed Train with Crosswind

2011 ◽  
Vol 66-68 ◽  
pp. 1878-1882
Author(s):  
Ming Lu Zhang ◽  
Yi Ren Yang ◽  
Chen Guang Fan ◽  
Li Lu
Keyword(s):  
Wind Tunnel ◽  
Flow Field ◽  
High Speed ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Aerodynamic Characteristics ◽  
Navier Stokes ◽  
Vehicle Speed ◽  
High Speed Train ◽  
Mesh Method

The aerodynamic performances of a high speed train will significant change under the action of the crosswind. Large eddy simulation (LES) was made to solve the flow around a simplified CRH2 high speed train with 250km/h and 350km/h under the influence of a crosswind with 28.4m/s base on the finite volume method and dynamic layering mesh method and three dimensional incompressible Navier-Stokes equations. Wind tunnel experimental method of static train with relative flowing air and dynamic mesh method of moving train were compared. The results of numerical simulation show that the flow field around train is completely different between Wind tunnel experiment and factual running. Many vortices will be produced on the leeside of the train with alternately vehicle bottom and back under the influence of a crosswind. The flow field around train is similar with different vehicle speed.

scholarly journals Inertial migration of a rigid sphere in three-dimensional Poiseuille flow

2015 ◽  
Vol 765 ◽  
pp. 452-479 ◽  
Author(s):  
Kaitlyn Hood ◽  
Sungyon Lee ◽  
Marcus Roper
Keyword(s):  
Particle Size ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Lateral Force ◽  
Navier Stokes ◽  
Rigid Sphere ◽  
Asymptotic Model ◽  
Navier Stokes Equations ◽  
Inertial Migration

AbstractInertial lift forces are exploited within inertial microfluidic devices to position, segregate and sort particles or droplets. However, the forces and their focusing positions can currently only be predicted by numerical simulations, making rational device design very difficult. Here we develop theory for the forces on particles in microchannel geometries. We use numerical experiments to dissect the dominant balances within the Navier–Stokes equations and derive an asymptotic model to predict the lateral force on the particle as a function of particle size. Our asymptotic model is valid for a wide array of particle sizes and Reynolds numbers, and allows us to predict how focusing position depends on particle size.

Computational Analysis of Aerodynamics and Thermodynamics for the X-51 High-Velocity Aircraft

2020 ◽  
pp. 41-57
Author(s):  
P.V. Silvestrov ◽  
S.T. Surzhikov
Keyword(s):  
High Velocity ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Distribution Patterns ◽  
Aerodynamic Characteristics ◽  
Convergence Time ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Thermally Conductive ◽  
Spatial System

The paper presents a numerical investigation of aero-dynamic coefficients for a model of an X-51-type high-velocity aircraft moving at Mach 6. The simulation made use of the original and modified versions of our custom hydrocodes (UST3D and UST3D-AUSMPW) designed for numerical simulation of aerodynamics and thermodynamics in high-velocity aircraft of arbitrary shapes. Such hydrocodes implement a model of viscous compressible thermally conductive gas described by a non-steady-state spatial system of Navier --- Stokes equations solved over unstructured three-dimensional tetrahedral meshes. The paper considers the theoretical aspects of simulating the aerodynamics and thermodynamics of high-velocity aircraft numerically. We describe the method for computing mass flow through mesh cell boundaries implemented in the modified custom hydrocode version. We performed cross-validation of the results obtained using our custom hydrocodes and compared our hydrocodes in terms of result convergence time. We show that these custom hydrocodes ensure adequately accurate distribution patterns concerning the fields of the values sought, and provide high-precision computation of aerodynamic characteristics as compared to each other

Design Optimization of a Centrifugal Fan with Splitter Blades

2015 ◽  
Vol 32 (2) ◽  
Author(s):  
Man-Woong Heo ◽  
Jin-Hyuk Kim ◽  
Kwang-Yong Kim
Keyword(s):  
Stokes Equations ◽  
Reference Model ◽  
Three Dimensional ◽  
Pressure Rise ◽  
Latin Hypercube Sampling ◽  
Aerodynamic Characteristics ◽  
Navier Stokes ◽  
Centrifugal Fan ◽  
Multi Objective ◽  
Design Variables

AbstractMulti-objective optimization of a centrifugal fan with additionally installed splitter blades was performed to simultaneously maximize the efficiency and pressure rise using three-dimensional Reynolds-averaged Navier-Stokes equations and hybrid multi-objective evolutionary algorithm. Two design variables defining the location of splitter, and the height ratio between inlet and outlet of impeller were selected for the optimization. In addition, the aerodynamic characteristics of the centrifugal fan were investigated with the variation of design variables in the design space. Latin hypercube sampling was used to select the training points, and response surface approximation models were constructed as surrogate models of the objective functions. With the optimization, both the efficiency and pressure rise of the centrifugal fan with splitter blades were improved considerably compared to the reference model.

Aerodynamic Performance Analysis of a Bobsleigh Body Shape

2015 ◽  
Author(s):  
Hyeon-Seok Shim ◽  
Hyo-Yeon Jung ◽  
Kwang-Yong Kim
Keyword(s):  
Drag Coefficient ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Major Axis ◽  
Aerodynamic Characteristics ◽  
Aerodynamic Performance ◽  
Optimal Number ◽  
Navier Stokes ◽  
Computational Domain ◽  
Axis Length

Aerodynamic performance of a bobsleigh is one of the most important factors in reducing the race time. In this study, an investigation on the aerodynamic characteristics of a bobsleigh has been performed using three-dimensional Reynolds-averaged Navier-Stokes equations with the k-ε turbulence model. An unstructured tetrahedral grid system was constructed in the computational domain, and the optimal number of grids was selected through a grid-dependency test. The major axis length and thickness of ellipse-shaped front bumper, and the radii of the cowling on side and front views, were selected as four geometric parameters to be tested, and the drag coefficient was considered as an aerodynamic performance parameter. It was found that the drag coefficient was more sensitive to the thickness of the front bumper and the radius of the cowling on side view of the bobsleigh than on the other parameters.

Aerodynamic characteristics of a dual-spin projectile with canards

2019 ◽  
Vol 233 (12) ◽  
pp. 4541-4553
Author(s):  
Xiaodong Liu ◽  
Xiaosheng Wu ◽  
Jintao Yin
Keyword(s):  
Mach Number ◽  
Normal Force ◽  
Angle Of Attack ◽  
Three Dimensional ◽  
Lateral Force ◽  
Aerodynamic Characteristics ◽  
Navier Stokes ◽  
Force Coefficient ◽  
Sliding Mesh ◽  
Flow Mechanisms

Based on the three-dimensional Navier–Stokes (N–S) equations, using unsteady numerical technology, flow over a dual-spin projectile was simulated to investigate its aerodynamic characteristics during flight. Spin was achieved via the sliding mesh method. The influence laws of the aftbody spin rate, Mach number, and angle of attack on the aerodynamic characteristics of the projectile are presented, and the flow mechanisms for the laws are revealed. The results demonstrate that the influence of the aftbody spin rate on the normal force coefficient is very small, whereas, on the lateral force coefficient, it is larger. With the increase in the Mach number, the time-averaged normal force coefficient and lateral force coefficient increase, while the fluctuation quantities of the normal force coefficient and the lateral force coefficient decrease. The variation of angle of attack will influence the size, distribution, and interference effect of the shedding vortices.

scholarly journals Kolmogorov's dissipation number and the number of degrees of freedom for the 3D Navier–Stokes equations

2019 ◽  
Vol 149 (2) ◽  
pp. 429-446
Author(s):  
Alexey Cheskidov ◽  
Mimi Dai
Keyword(s):  
Fluid Flow ◽  
Degrees Of Freedom ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Critical Value ◽  
Time Dependent ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
All Solutions ◽  
Time Average

AbstractKolmogorov's theory of turbulence predicts that only wavenumbers below some critical value, called Kolmogorov's dissipation number, are essential to describe the evolution of a three-dimensional (3D) fluid flow. A determining wavenumber, first introduced by Foias and Prodi for the 2D Navier–Stokes equations, is a mathematical analogue of Kolmogorov's number. The purpose of this paper is to prove the existence of a time-dependent determining wavenumber for the 3D Navier–Stokes equations whose time average is bounded by Kolmogorov's dissipation wavenumber for all solutions on the global attractor whose intermittency is not extreme.

Numerical Simulation and Experiment Research on Aerodynamic Characteristics of a Multi-Blade Centrifugal Fan

2011 ◽  
Vol 317-319 ◽  
pp. 2157-2161
Author(s):  
Yong Chao Zhang ◽  
Qing Guang Chen ◽  
Yong Jian Zhang ◽  
Xiang Xing Jia
Keyword(s):  
Numerical Simulation ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Simple Algorithm ◽  
Internal Flow ◽  
Aerodynamic Characteristics ◽  
Navier Stokes ◽  
Computational Domain ◽  
Centrifugal Fan ◽  
Cfd Method

The full flow field model of a widely used multi-blade centrifugal fan was built, and unstructured grids were used to discrete the computational domain. The moving reference frame is adopted to transfer data between the interfaces of the rotating field and the stationary field. Pressure boundary conditions are specified to the inlet and the outlet. The SIMPLE algorithm in conjunction with the RNG k-ε turbulent model was used to solve the three-dimensional Navier-Stokes equations. The steady and unsteady numerical simulations of the inner flow in the fan at different working conditions were presented using the CFD method. The numerical simulation results were validated by contrasting to the experiment results. The results displayed the characteristics of the velocity field, pressure field, pressure fluctuation at two monitoring points in the centrifugal fan. The results can provide basis for optimizing the fan design and the internal flow, and have important value of engineering applications in the increase of the overall performance in operation.

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