Numerical Study on Reduction in Aerodynamic Drag and Noise of High-Speed Pantograph

Reducing the aerodynamic drag and noise levels of high-speed pantographs is important for promoting environmentally friendly,energy efficient and rapid advances in train technology.Using computational fluid dynamics theory and the K-FWH acoustic equation,a numerical simulation is conducted to investigate the aerodynamic characteristics of high-speed pantographs.A component optimization method is proposed as a possible solution to the problemof aerodynamic drag and noise in high-speed pantographs.The results of the study indicate that the panhead,base and insulator are the main contributors to aerodynamic drag and noise in high-speed pantographs.Therefore,a gradual optimization process is implemented to improve the most significant components that cause aerodynamic drag and noise.By optimizing the cross-sectional shape of the strips and insulators,the drag and noise caused by airflow separation and vortex shedding can be reduced.The aerodynamic drag of insulator with circular cross section and strips with rectangular cross section is the largest.Ellipsifying insulators and optimizing the chamfer angle and height of the windward surface of the strips can improve the aerodynamic performance of the pantograph.In addition,the streamlined fairing attached to the base can eliminate the complex flow and shield the radiated noise.In contrast to the original pantograph design,the improved pantograph shows a 21.1%reduction in aerodynamic drag and a 1.65 dBA reduction in aerodynamic noise.

Airfoil friction drag reduction based on grid-type and super-dense array plasma actuators

To improve the cruise flight performance of aircraft, two new configurations of plasma actuators(grid-type and super-dense array) were investigated to reduce the turbulent skin friction drag of a low-speed airfoil. The induced jet characteristics of the two actuators in quiescent air were diagnosed with high-speed particle image velocimetry(PIV), and their drag reduction efficiencies were examined under different operating conditions in a wind tunnel. The results showed that the grid-type plasma actuator was capable of producing a wall-normal jet array(peak magnitude: 1.07 m/s) similar to that generated in a micro-blowing technique, while the superdense array plasma actuator created a wavy wall-parallel jet(magnitude: 0.94 m/s) due to the discrete spanwise electrostatic forces. Under a comparable electrical power consumption level,the super-dense array plasma actuator array significantly outperformed the grid-type configuration,reducing the total airfoil friction drag by approximately 22% at a free-stream velocity of 20 m/s.The magnitude of drag reduction was proportional to the dimensionless jet velocity ratio(r), and a threshold r = 0.014 existed under which little impact on airfoil drag could be discerned.

Parametric Optimization of Wheel Spoke Structure for Drag Reduction of an Ahmed Body

The wheels have a considerable influence on the aerodynamic properties and can contribute up to 25%of the total drag on modern vehicles.In this study,the effect of the wheel spoke structure on the aerodynamic performance of the isolated wheel is investigated.Subsequently,the 35°Ahmed body with an optimized spoke structure is used to analyze the flow behavior and the mechanism of drag reduction.The Fluent software is employed for this investigation,with an inlet velocity of 40 m/s.The accuracy of the numerical study is validated by comparing it with experimental results obtained from the classical Ahmed model.To gain a clearer understanding of the effects of the wheel spoke parameters on the aerodynamics of both the wheel and Ahmedmodel,and five design variables are proposed:the fillet angleα,the inside arc radius R1,the outside radius R2,and the same length of the chord L1 and L2.These variables characterize the wheel spoke structure.The Optimal Latin Hypercube designmethod is utilized to conduct the experimental design.Based on the simulation results of various wheel spoke designs,the Kriging model and the adaptive simulated annealing algorithm is selected to optimize the design parameters.The objective is to achieve the best combination for maximum drag reduction.It is indicated that the optimized spoke structure resulted in amaximum drag reduction of 5.7%and 4.7%for the drag coefficient of the isolated wheel and Ahmed body,respectively.The drag reduction is primarily attributed to changes in the flow state around the wheel,which suppressed separation bubbles.Additionally,it influenced the boundary layer thickness around the car body and reduced the turbulent kinetic energy in the wake flow.These effects collectively contributed to the observed drag reduction.

Effects of Crosswise Appendage Plate Flexibility on the Drag Reduction Characteristics of Cylinder

In engineering applications (Like an ocean riser), fluid flow around bluff bodies generates substantial resistance, which can jeopardize structural integrity, lifespan, and escalate resource consumption. Therefore, employing drag reduction measures becomes particularly crucial. This paper employs the immersed boundary method to investigate the impact of transversely oriented appendage plate flexibility on the drag of cylinders under different Reynolds numbers and distances. The results indicate that flexible appendage plate exerts drag reduction effects on the downstream cylinder, with this effect gradually diminishing as Reynolds numbers increase. At identical Reynolds numbers, the drag reduction effect initially increases and then decreases with distance, with the optimal drag reduction distance observed at D = 2.5. Compared to cylinders without appendage plate, the maximum drag reduction achieved is 30.551%. Addressing the drag reduction issue in cylinders holds significant importance for ensuring engineering structural integrity, enhancing engineering efficiency, and developing novel underwater towing systems.

TRANSONIC DRAG REDUCTION ON SUPERCRITICAL WING SECTION USING SHOCK CONTROL BUMPS

Two-dimensional and three-dimensional shock control contour bumps are designed for a supercritical wing section with the aim of transonic wave drag reduction. The supercritical airfoil （NASA SC （02）-0714） is selected considering the fact that most modern jet transport aircrafts that operate in the transonic flow regime （cruise at transonic speeds） employ supercritical airfoil sections. Here it is to be noted that a decrease in the transonic wave drag without loss in lift would result in an increased lift to drag ratio, which is a key range parameter that can potentially increase both the range and endurance of the aircraft. The major geometric bump parameters such as length, height and span are altered for both the two-dimensional and three-dimensional bumps in order to obtain the optimum location and shape of the bump. Once an optimum standalone three-dimensional bump is acquired, an array of bumps is manually placed spanwise of an unswept supercritical wing and analyzed under fully turbulent flow conditions. Different configurations are tested with varying three-dimensional bump spacing in order to determine the contribution of bump spacing on overall performance. The results show a 14% drag reduction and a consequent 16% lift to drag ratio rise at the design Mach number for the optimum arrangement of bumps along the wing span.

Experimental demonstration of a new concept of drag reduction and thermal protection for hypersonic vehicles

A new idea of drag reduction and thermal protection for hypersonic vehicles is proposed based on the combination of a physical spike and lateral jets for shockreconstruction. The spike recasts the bow shock in front of a blunt body into a conical shock, and the lateral jets work to protect the spike tip from overheating and to push the conical shock away from the blunt body when a pitching angle exists during flight. Experiments are conducted in a hypersonic wind tunnel at a nominal Mach number of 6. It is demonstrated that the shock/shock interaction on the blunt body is avoided due to injection and the peak pressure at the reattachment point is reduced by 70% under a 4° attack angle.

Aerodynamic drag reduction of heavy vehicles using append devices by CFD analysis

Improving vehicle fuel consumption,performance and aerodynamic efficiency by drag reduction especially in heavy vehicles is one of the indispensable issues of automotive industry.In this work,the effects of adding append devices like deflector and cab vane corner on heavy commercial vehicle drag reduction were investigated.For this purpose,the vehicle body structure was modeled with various supplementary parts at the first stage.Then,computational fluid dynamic(CFD) analysis was utilized for each case to enhance the optimal aerodynamic structure at different longitudinal speeds for heavy commercial vehicles.The results show that the most effective supplementary part is deflector,and by adding this part,the drag coefficient is decreased considerably at an optimum angle.By adding two cab vane corners at both frontal edges of cab,a significant drag reduction is noticed.Back vanes and base flaps are simple plates which can be added at the top and side end of container and at the bottom with specific angle respectively to direct the flow and prevent the turbulence.Through the analysis of airflow and pressure distribution,the results reveal that the cab vane reduces fuel consumption and drag coefficient by up to 20 % receptively using proper deflector angle.Finally,by adding all supplementary parts at their optimized positions,41% drag reduction is obtained compared to the simple model.

The Mechanism of Drag Reduction around Bodies of Revolution Using Bionic Non-Smooth Surfaces

Bionic non-smooth surfaces （BNSS） can reduce drag. Much attention has been paid to the mechanism of shear stress reduction by riblets. The mechanism of pressure force reduction by bionic non-smooth surfaces on bodies of revolution has not been well investigated. In this work CFD simulation has revealed the mechanism of drag reduction by BNSS, which may work in three ways. First, BNSS on bodies of revolution may lower the surface velocity of the medium, which prevents the sudden speed up of air on the cross section. So the bottom pressure of the model would not be disturbed sharply, resulting in less energy loss and drag reduction. Second, the magnitude of vorticity induced by the bionic model becomes smaller because, due to the sculpturing, the growth of tiny air bubbles is avoided. Thus the large moment of inertia induced by large air bubble is reduced. The reduction of the vorticity could reduce the dissipation of the eddy. So the pressure force could also be reduced. Third, the thickness of the momentum layer on the model becomes less which, according to the relationship between the drag coefficient and the momentum thickness, reduces drag.

Drag reduction behavior of hydrolyzed polyacrylamide/xanthan gum mixed polymer solutions

Partially hydrolyzed polyacrylamide（HPAM）as the main component of slickwater fracturing fluid is a shear-sensitive polymer,which suffers from mechanical degradation at turbulent flow rates.Five different concentrations of HPAM as well as mixtures of polyacrylamide/xanthan gum were prepared to investigate the possibility of improving shear stability of HPAM.Drag reduction（DR）measurements were performed in a closed flow loop.For HPAM solutions,the extent of DR increased from 30%to67%with increasing HPAM concentration from 100 to1000 wppm.All the HPAM solutions suffered from mechanical degradation and loss of DR efficiency over the shearing period.Results indicated that the resistance to shear degradation increased with increasing polymer concentration.DR efficiency of 600 wppm xanthan gum（XG）was 38%,indicating that XG was not as good a drag reducer as HPAM.But with only 6%DR decline,XG solution exhibited a better shear stability compared to HPAM solutions.Mixed HPAM/XG solutions initially exhibited greater DR（40%and 55%）compared to XG,but due to shear degradation,DR%dropped for HPAM/XG solutions.Compared to 200 wppm HPAM solution,addition of XG did not improve the drag reduction efficiency of HPAM/XG mixed solutions though XG slightly improved the resistance against mechanical degradation in HPAM/XG mixed polymer solutions.

Formation mechanism of aerodynamic drag of high-speed train and some reduction measures

Aerodynamic drag is proportional to the square of speed. With the increase of the speed of train, aerodynamic drag plays an important role for high-speed train. Thus, the reduction of aerodynamic drag and energy consumption of high-speed train is one of the essential issues for the development of the desirable train system. Aerodynamic drag on the traveling train is divided into pressure drag and friction one. Pressure drag of train is the force caused by the pressure distribution on the train along the reverse running direction. Friction drag of train is the sum of shear stress, which is the reverse direction of train running direction. In order to reduce the aerodynamic drag, adopting streamline shape of train is the most effective measure. The velocity of the train is related to its length and shape. The outer wind shields can reduce train's air drag by about 15%. At the same time, the train with bottom cover can reduce the air drag by about 50%, compared with the train without bottom plate or skirt structure.

Comparison of Microbubble and Air Layer Injection with Porous Media for Drag Reduction on a Self-propelled Barge Ship Model

Ship resistance issues are related to fuel economy,speed,and cost efficiency.Air lubrication is a promising technique for lowering hull frictional resistance as it is supposed to modify the energy in the turbulent boundary layer and thereby reduce hull friction.In this paper,the objective is to identify the optimum type of air lubrication using microbubble drag reduction(MBDR)and air layer drag reduction(ALDR)techniques to reduce the resistance of a 56-m Indonesian self-propelled barge(SPB).A model with the following dimensions was constructed:length L=2000 mm,breadth B=521.60 mm,and draft T=52.50 mm.The ship model was towed using standard towing tank experimental parameters.The speed was varied over the Froude number range 0.11–0.31.The air layer flow rate was varied at 80,85,and 90 standard liters per minute(SLPM)and the microbubble injection coefficient over the range 0.20–0.60.The results show that the ship model using the air layer had the highest drag reduction up to a maximum of 90%.Based on the characteristics of the SPB,which operates at low speed,the optimum air lubrication type to reduce resistance in this instance is ALDR.

Characteristics and mechanism investigation on drag reduction of oblique riblets

This work primarily focuses on the drag reduction characteristics and mechanism investigation of oblique riblets. First, a calculation model of the oblique riblets surface is established, and Reynolds stress model(RSM) turbulence model is used for numerical simulation of the oblique riblets flow field. Subsequently, the influence of inclination angle between flow direction and arrangement direction of riblets on friction resistance and drag reduction rate is further analyzed. Through the investigation of the distribution of shear stress, pressure stress and velocity in oblique riblets boundary layer, the oblique riblets drag reduction mechanism is finally revealed. Results show that, with increase of velocity and inclination angle, the pressure resistance increases obviously, along with the decreasing of the viscous resistance distinctly. The maximum drag reduction rate of the oblique riblets is 7.33%. Moreover, when the inclination angle increases, the wall shear stress reduces on oblique riblets surface; while differential pressure increases at both sides of oblique riblets tips. In addition, when inclination angle is small, the secondary vortex at oblique riblets tips will disappear soon. New vortices will be formed inside the oblique riblets and cause the decrease of viscosity resistance. Thus, oblique riblets show a better drag reduction effect and have an effective control on boundary layer.

Experimental Study of Air Layer Drag Reduction with Bottom Cavity for A Bulk Carrier Ship Model

Air lubrication by means of a bottom cavity is a promising method for ship drag reduction. The characteristics of the bottom cavity are sensitive to the flow field around the ship hull and the effect of drag reduction, especially the depth of the bottom cavity. In this study, a ship model experiment of a bulk carrier is conducted in a towing tank using the method of air layer drag reduction (ALDR) with different bottom cavity depths. The shape of the air layer is observed, and the changes in resistance are measured. The model experiments produce results of approximately 20% for the total drag reduction at the ship design speed for a 25-mm cavity continuously supplied with air at Cq = 0.224 in calm water, and the air layer covers the whole cavity when the air flow rate is suitable. In a regular head wave, the air layer is easily broken and reduces the drag reduction rate in short waves, particularly when λ/Lw1 is close to one;however, it still has a good drag reduction effect in the long waves.

Experiment about Drag Reduction of Bionic Non-smooth Surface in Low Speed Wind Tunnel

The body surface of some organisms has non-smooth structure, which is related to drag reduction in moving fluid. To imitate these structures, models with a non-smooth surface were made. In order to find a relationship between drag reduction and the non-smooth surface, an orthogonal design test was employed in a low speed wind tunnel. Six factors likely to influence drag reduction were considered, and each factor tested at three levels. The six factors were the configuration, diameter/bottom width, height/depth, distribution, the arrangement of the rough structures on the experimental model and the wind speed. It was shown that the non-smooth surface causes drag reduction and the distribution of non-smooth structures on the model, and wind speed, are the predominant factors affecting drag reduction. Using analysis of variance, the optimal combination and levels were obtained, which were a wind speed of 44 m/s, distribution of the non-smooth structure on the tail of the experimental model, the configuration of riblets, diameter/bottom width of i mm, height/depth of 0.5 mm, arranged in a rhombic formation. At the optimal combination mentioned above, the 99% confidence interval for drag reduction was 11.13% to 22.30%.

The investigation and optimization of drag reduction in turbulent flow of Newtonian fluid passing through horizontal pipelines using functionalized magnetic nanophotocatalysts and lecithin

The nanophotocatalysts were synthesized in four stages and evaluated by FTIR, FESEM and VSM analysis. The influence of nanofluids containing functionalized magnetic Ti O2 nanophotocatalyst and dipalmitoylphosphatidylcholine lecithin in drag reduction of turbulent flow in four horizontal pipelines was studied. The effective parameters on drag reduction(nanoparticle concentration, surfactant concentration, p H and Re number) were investigated and optimized in each pipeline using response surface method. The drag reduction in 1/2 " galvanized, 3/4" galvanized, 1/2 "five-layer and 1/2" cuprous pipelines was found 99.1%, 92.5%, 87.6% and 85.2%, respectively. The model adequacy was measured using ANOVA. Based on the high determination coefficient, more than 95% of variance of experimental data in all pipelines was described by quadratic model.

COMPUTATIONAL FLUID DYNAMICS(CFD) SIMULATIONS OF DRAG REDUCTION WITH PERIODIC MICRO-STRUCTURED WALL

Computational fluid dynamics（CFD） simulations are adopted to investigate rectangular microchannel flows with various periodic micro-structured wall by introducing velocity slip boundary condition at low Reynolds number. The purpose of the current study is to numerically find out the effects of periodic micro-structured wall on the flow resistance in rectangular microchannel with the different spacings between microridges ranging from 15 to 60 pm. The simulative results indicate that pressure drop with different spacing between microridges increases linearly with flow velocity and decreases monotonically with slip velocity; Pressure drop reduction also increases with the spacing between microridges at the same condition of slip velocity and flow velocity. The results of numerical simulation are compared with theoretical predictions and experimental results in the literatures. It is found that there is qualitative agreement between them.

Active control of turbulence for drag reduction based on the detection of near-wall streamwise vortices by wall information

The spatial relations between the measurable wall quantities （streamwise shear stress τwx, spanwise shear stress τwz, and pressure fluctuations Pw） and the near-wall streamwise vortices （NWSV） are investigated via direct numerical simulation （DNS） databases of fully developed turbulent channel flow at a low Reynolds number. In the stan- dard turbulent channel flow, the results show that all the wall measurable variables are closely associated with the NWSV. But after applying a stochastic interference, the relation based on τwx breaks down while the correlations based on Pw and τwz are still robust. Hence, two wall flow quantities based on Pw and τwz are proposed to detect the NWSV. As an appli- cation, two new control schemes are developed to suppress the near-wall vortical structures using the actuation of wall blowing/suction and obtain 16 % and 11% drag reduction, respectively.

Role of on-board discharge in shock wave drag reduction and plasma cloaking

In the present paper, a physical model is proposed for reducing the problem of the drag reduction of an attached bow shock around the nose of a high-speed vehicle with on-board discharge, to the problem of a balance between the magnetic pressure and gas pressure of plane shock of a partially ionized gas consisting of the environmental gas around the nose of the vehicle and the on-board discharge-produced plasma. The relation between the shock strength and the discharge-induced magnetic pressure is studied by means of a set of one-fluid, hydromagnetic equations reformed for the present purpose, where the discharge-induced magnetic field consists of the electron current （produced by the discharge）-induced magnetic field and the partially ionized gas flow-induced one. A formula for the relation between the above parameters is derived. It shows that the discharge-induced magnetic pressure can minimize the shock strength, successfully explaining the two recent experimental observations on attached bow shock mitigation and elimination in a supersonic flow during on-board discharge [Phys. Plasmas 9 （2002） 721 and Phys. Plasmas 7 （2000） 1345]. In addition, the formula implies that the shock elimination leaves room for a layer of higher-density plasma rampart moving around the nose of the vehicle, being favourable to the plasma radar cloaking of the vehicle. The reason for it is expounded.

Drag reduction of turbulent channel flows over an anisotropic porous wall with reduced spanwise permeability

The direct numerical simulation (DNS) is carried out for the incompressible viscous turbulent flows over an anisotropic porous wall. Effects of the anisotropic porous wall on turbulence modifications as well as on the turbulent drag reduction are investigated. The simulation is carried out at a friction Reynolds number of 180, which is based on the averaged friction velocity at the interface between the porous medium and the clear fluid domain. The depth of the porous layer ranges from 0.9 to 54 viscous units. The permeability in the spanwise direction is set to be lower than the other directions in the present simulation. The maximum drag reduction obtained is about 15.3% which occurs for a depth of 9 viscous units. The increasing of drag is addressed when the depth of the porous layer is more than 25 wall units. The thinner porous layer restricts the spanwise extension of the streamwise vortices which suppresses the bursting events near the wall. However, for the thicker porous layer, the wall-normal fluctuations are enhanced due to the weakening of the wall-blocking effect which can trigger strong turbulent structures near the wall.

Drag reduction and shear resistance properties of ionomer and hydrogen bond systems based on lauryl methacrylate

Based on molecular dynamics simulation results, a lauryl methacrylate polymer with drag reduction and shear resistance properties was designed, and synthesized by emulsion polymerization using 2-vinyl pyridine and methyl methacrylate as the polar polymerization monomer. After ionization of lauryl methacrylate polymer, an ion-dipole interaction based drag reduction agent （DRA） was obtained. The existence of ion-dipole interaction was proven through characterization of the drag-reducing agent from its infrared （IR） spectrum. The pilot-scale reaction yield of the DRA under optimum conditions was investigated, and the drag reduction and shear resistance properties were measured. The results show that： l） The ion-dipole or hydrogen bonding interaction can form ladder-shaped chains, therefore the synthesized DRA has shear resistance properties; 2） The larger the molecular weight （MW） and more concentrated the distribution of MW, the better the drag reduction efficiency and the performance of the ionomer system was superior to that of the hydrogen bonding system; 3） With increasing shear frequency, the drag-reduction rates of both the DRAs decreased, and the drag reduction rate of the ionomer system decreased more slowly than of the corresponding hydrogen bonding system. From the point of view of drag reduction rate and shear resistance property, the ionomer system is more promising than the hydrogen bonding system