Numerical Analysis of Aerodynamic Characteristics of Hyperloop System

The aerodynamic resistance induced by a high-speed metro train entering and operating in a tunnel with a speed of 120 km/h is simulated using a three-dimensional, compressible turbulence model. An overset mesh method is adopted to solve the moving boundary problem, and the flow field around the train is simulated with a k-omega SST turbulence model to obtain accurate stress values at the walls. The selected model is verified with experimental and numerical data from the literature. Then, numerical simulations are performed to analyse the formation mechanisms of the pressure and friction drags. The aerodynamic drag basically stabilizes after the expansion wave passes the train head. The results reveal that the variations in friction resistance are related to the direction of the Mach wave, and this trend differs from that observed for pressure resistance. Mach wave influences the velocity where it passes, and further influences the friction drag. Result shows that friction drag of the train increases when encounter with compression wave propagated from the front or expansion wave propagated from the back, and decreases otherwise. The effects of the blockage ratio on the maximum and average pressure and friction resistance values of each train section are evaluated based on fitting functions. The predicted aerodynamic drag varies with the blockage ratio and for each train section, and the results are summarized and compared with predictions and experimental data from the literature. The variations in tunnel resistance and the overall trend are in good agreement with the previous results. Therefore, the findings presented in this study may provide a reference for the design of high-speed subway tunnels.

This work involves numerical simulations based on finite volume method to study the effects of different factors on the aerodynamic drag on a vacuum tube train running at subsonic and transonic speeds in a partially vacuum tunnel. Investigation includes the study of the effects of the shapes of head, tail, vacuum pressure and also blockage ratio of the tunnel on aerodynamic drag on a high speed train. The simulation is performed by using fluent software. Two dimensional, axisymmetric, compressible Navier-Stokes equations were solved by using k-ε turbulent modeling. Five different blockage ratios at five different speeds of the train have been considered. The simulated results show that, the blockage ratio and different working vacuum pressure significantly affects the aerodynamic drag of the train in a tunnel. Investigations with respect to different shapes of the head as well as that of the tail indicate the optimum shape for minimum drag.

Numerical analysis of the aerothermodynamic behavior of a Hyperloop in choked flow

Effective control of frictional drag on a model surface is crucial for achieving total drag reduction at high Reynolds number conditions. This study presents wind tunnel tests at high Reynolds numbers, employing two sets of flat plate models with identical external dimensions. The tests cover incoming Mach numbers ranging from 0.3 to 0.85, corresponding to Reynolds numbers from 2.52 × 106 to 6.35 × 106. The velocity distributions and statistical properties within the turbulent boundary layer were measured using a combination of hot-wire probes and total pressure probes. Total model drag was assessed using a high-precision balance. The results demonstrate that the application of porous media significantly reduces frictional drag, with the cavity arrangement yielding superior drag reduction compared to the non-cavity arrangement. As the Reynolds number increases, the effectiveness of friction drag control diminishes. Moreover, the arrangement of porous media with appropriately chosen parameters can effectively reduce the total drag of the model. Flow field analysis reveals that porous media alter the vortex structure distribution within the boundary layer, increasing small-scale vortex structures and mitigating the impact of large-scale streamwise vortices on the wall, thereby reducing frictional drag. These findings provide important technical support and experimental evidence for the application of porous media in drag reduction at high Reynolds number conditions.

This study investigates the impact of tube shape on the aerodynamic forces experienced by an evacuated tube transportation (ETT) system. Using CFD simulations, the study explores various tube geometries to discern their influence on aerodynamic forces, particularly drag, critical for high-speed travel. The investigation centers on a standard tube shape derived from maglev design, considering parameters like tube radius, guideway height, and eccentricity between the tube and pod, with pod speeds ranging from 50 to 350 m/s. The study also examines the influence of the levitation air gap. The findings reveal that aerodynamic drag is mainly dictated by the blockage ratio (BR), especially within the range of 0.5 < BR < 0.68. An empirical formula is proposed to estimate aerodynamic drag based on BR and pod speed, validated against CFD results with a maximum error of 6.26%. These insights guide the aerodynamic design of vacuum-based ETT systems.

The aerodynamic drag of high speed trains

Numerical simulations of incompressible laminar flow past a circular cylinder using wavy wall confinement are performed in order to study drag reduction and vortex shedding suppression for Reynolds numbers (50 ≤ Re ≤ 280) and blockage ratios (0.5 ≤ D/H ≤ 0.9), where D is the cylinder diameter and H is the channel height. The optimum configuration of wavy wall confinement is identified to have an amplitude of 0.2D and wavelength of 4D which manifests the minimum drag coefficient and complete vortex shedding suppression (zero lift coefficient). The flow over the cylinder with optimized wavy wall confinement produces a stable vortex pair in the wake of the cylinder. The length of vortex pair in the wake increases by increasing the Reynolds number and decreasing the blockage ratio. The drag on the cylinder reduces when the length of vortex pair increases due to early flow separation and reduction in pressure drag. The drag coefficient decreases by 36% in comparison to the plane wall confinement at D/H = 0.5. The drag coefficient decreases for wavy wall configuration by about 67% for D/H = 0.7 and 94% for D/H = 0.9. The lift coefficient remains zero at all Reynolds numbers and blockage ratios which indicates complete suppression of vortex shedding.

This paper presents the results of experimental and computational investigations on the effect of slot cavities on a supersonic projectile. Experimental work was carried out to show the effects of the slots on the drag at Mach numbers M = 1·36, 1·65, 1·83. The computational analysis was done at M = 1·36. A single configuration of the slot pattern was used with two different slot widths (0·5mm and 2·0mm). Flow features were investigated in the slotted area and at the base. The analysis presented includes the pressure distribution, the supersonic cavity flow and the effect of the slots on the overall aerodynamic drag. Unlike the case of slots at transonic speeds, the suction and blowing mechanism is not found at supersonic Mach numbers. Streamwise cavity slots cause a small base drag reduction. The reduction in total drag is modest when the width is 0·5mm. However, the experiments showed that with the wider slots (2mm) the drag actually increases at Mach numbers from 1·36 to 1·83.

Evaporation of a moving liquid droplet: Solutions for intermediate Reynolds numbers

The aerodynamics of sailing apparel

Aerodynamic drag is still one of the main challenges facing the automotive industry. The design engineers are trying to develop novel techniques that could help to control the flow and optimize the shape of a vehicle to make it able to increase the base pressure drag at the wake region. The pressure drag is one of the main contributors to the aerodynamic drag. In our investigation, we have dealt with a benchmark car model (Windsor geometry) and visualized its effect on the characteristic parameters of the flow. In order to maximize the reduction of aerodynamic drag of vehicles, a numerical study has been undertaken based upon the CFD analysis with an active flow control technique including tapering of the rear lower and upper body along the length and height of the Windsor geometry. Taper angles from 12° to 20° in 4° steps have been implemented on the upper and lower part of the body while a taper length has been implemented along with the height of the body sides for the two cases. In comparison to other studies, we have come to sufficient results that gave us a significant reduction of aerodynamic drag for all the cases that we have tested. Thus, our study showed that the aerodynamic drag reductions are maximized, which indicates the efficiency of the technique we have applied.

In order to further reduce the aerodynamic drag of High-speed Electric Multiple Units (EMU), an active flow control drag reduction method combining air suction and blowing is proposed at the rear of the EMU train. A numerical calculation method based on realizable k-ε is used to investigate the aerodynamic drag characteristics of a three-car EMU with a speed of 400 km/h. The influence of different suction-blowing mass flow rates, the position and number of suction and blowing ports on the aerodynamic drag and surface pressure of the EMU tail are analyzed. The results demonstrate that suction and blowing at the tail reduce the pressure drag of EMU. And with the growth of air suction-blowing mass flow rate, the aerodynamic drag reduction rate of the tail car gradually increases, but the increment of drag reduction rate gradually decreases. Under the same mass flow rate of the suction and blowing, the closer the ports are to the upper and lower edges of the windscreen, the lower the pressure drag of the tail car is. At the same flow flux of air suction and blowing, the more the number of ports, the better the pressure drag reduction effect of the tail car. This study provides a reference for the next generation of EMU aerodynamic drag reduction and is of great significance for breaking through the limitations of traditional aerodynamic drag reduction.

Aerodynamic aspects of train shapes suitable for Vacuum Tube Train System are investigated in this paper. Three feasible geometries for the vacuum tube train system have been considered and modelled in three dimensions and have been computationally studied using the commercial software Ansys Fluent. Aerodynamic drag loads on these geometries have been calculated under different tube pressures and speeds of the train, which provide insight on various operating parameters that need to be considered while designing the vacuum tube train system. The present computational research shows that, the suitable vacuum pressure, and different shapes of head and tail of the train have significantly effects the drag force of the vacuum train in the tunnel. Overall, the elliptical train shape with a height to base ratio of 2:1 is more efficient for aerodynamic drag reduction of the vacuum tube train at the vacuum tube pressure of 1013.25 Pa.

A two-dimensional computational study of gas flow regimes past of square cylinder confined in a long microchannel

Experimental thermal hydraulics study of the blockage ratio effect during the cooling of a vertical tube with an internal steam-droplets flow