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Numerical investigation of the aerodynamic noise mechanism in high-speed trains operating at 400 km/h
(2025-08-01)
Huang, Junhui
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Lu, Weishuang
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Sun, Zhenxu
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Prapamonthon, Prasert
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Guo, Dilong
In this study, an improved delayed detached eddy simulation in conjunction with the Ffowcs Williams-Hawkings acoustic analogy is used to numerically compare the aerodynamic noise characteristics of the CR400BF and CR450 high-speed trains operating at 350 and 400 km/h, respectively. The results show that although there are noticeable changes in the distribution of acoustic energy, increasing the operating speed to 400 km/h has no discernible effect on the locations of the main noise sources. The airflow characteristics are optimized by using streamlined front designs, bogie web plates, and fully enclosed skirts, resulting in reduced turbulent kinetic energy and pressure fluctuations. As a result, the noise amplitude in the front car region is effectively reduced, while the formation of small-scale vortices, which can cause noise at high frequencies, is inhibited. However, because of the smoothing of the underbody and the lack of bogie web plates in the middle sections, higher airflow velocities are introduced, intensifying the interaction with the third and fourth bogies. This leads to the increase in noise amplitudes in these regions.
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Hydrodynamic performance of a penguin wing: Effect of feathering and flapping
(2023-06-01)
Hao, Zhanzhou
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Yin, Bo
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Prapamonthon, Prasert
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Yang, Guowei
The penguin is the fastest underwater swimmer among the wing-propelled diving birds. To figure out the mechanism for its excellent swimming, the hydrodynamic performance of a penguin wing is numerically investigated using an immersed boundary method with the incompressible flow solver. This study examines the effects of feathering, flapping, and Strouhal number (St) under preset motion. Results indicate that feathering is the primary contributor to thrust generation. The change in angle of attack (AoA) can qualitatively reflect the change in lift but not thrust. Therefore, a new variable, angle of thrust (AoT, α<inf>T</inf>), is introduced to effectively reflect the change of thrust across different kinematic parameters. Optimal feathering amplitude balances the decrease in AoA and the increase in feathering angle to achieve the highest AoT and thrust. Excessive feathering amplitude degrades the leading-edge vortex to shear layers, transforms the pressure side to the suction side, and ultimately causes negative thrust (drag). Spatial analysis of the thrust shows that the outer three-fifths of the wing are the primary source of thrust, contributing 85.4% of thrust generation at optimal feathering amplitude. Flapping amplitude has little impact on the optimal feathering amplitude. The optimal feathering amplitude increases linearly with the St number in the scope of examination, leading to larger thrust but lower swimming efficiency. Thus, a dimensionless number, St<inf>m</inf>, is introduced to describe the optimal wing motion. This work provides new insights into the propulsion mechanism of aquatic swimmers with flapping-feathering wings and helps design novel bio-inspired aquatic vehicles.
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Aerodynamic optimization using passive control devices near the bogie cabin of high-speed trains
(2022-09-01)
Yao, Yongfang
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Sun, Zhenxu
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Li, Guibo
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Yang, Guowei
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Prapamonthon, Prasert
Bogies are responsible for a significant amount of aerodynamic resistance and noise, both of which negatively affect high-speed train performance and passenger comfort. In the present study, the passive control method is applied in designing the bogie cabins of a high-speed train to improve its aerodynamic characteristics. Two passive control measures are introduced, namely, adding a spoiler and creating diversion grooves near the bogie cabins. Furthermore, the aerodynamic and aeroacoustic characteristics of a high-speed train operating at 350 km/h under different control strategies are numerically investigated using the improved-delayed-detached-eddy simulation (IDDES) and the acoustic finite element method (FEM). The impacts of passive control devices on drag reduction, slipstream, and aerodynamic noise are presented and discussed. Numerical results reveal that the passive control devices have a major effect on the slipstream around the train. The amplitude of the fluctuating pressure is higher in the first half of the train than in the second half. The first bogie has the maximum amplitude of the acoustic pressure for both the train with and without passive devices. In the far field, the spoiler installation and placement of the diversion grooves in the front of the bogie cabin can significantly reduce aerodynamic drag and noise. Hence, as shown in this study, using passive control methods to improve the aerodynamic and aeroacoustic properties of high-speed trains can be a viable option. [Figure not available: see fulltext.].
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Recent progress in flexibility effects on wing aerodynamics and acoustics
(2021-01-01)
Prapamonthon, Prasert
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Yin, Bo
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Yang, Guowei
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Zhang, Mohan
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Lu, Panpan
Since the theoretical aeroelasticity for flapping-wing aerodynamics was introduced in the 1920s, the effects of flexibility on aeroelasticity have been paid more attention to aerodynamic design. In recent years, the trait of the wing flexibility is applied for small-scale wings of biomimetic flyers including micro air vehicles and mini unmanned aerial vehicles. Until now, the aerodynamic performance and great agility of these flyers, which are beneficially used for military missions and other civilian applications, have been improved through surrogate flapping wings with the favorable effects of the flexibility. As per the aeroelasticity principle for the forward flying, the chordwise flexibility of an elastic flapping wing can generate thrust and lift redistributions, whereas the spanwise flexibility can result in variations of the angle of attack and the shift of phase along the wingspan direction. Consequently, all vortices generated by the flapping wing i.e. (1) leading-edge vortices, (2) tip vortices, and (3) trailing-edge vortices are blended supportively, thereby improving the aerodynamic performance and agility. Hence, the growth of research and development of the aerodynamic performance and agility for these flyers under the influence of flexible wings increases through experimental and computational studies dynamically and rapidly. This review aims to highlight the important role of the flexibility in the recent progress in wing aerodynamics of these flyers through several wing models done by famous groups of experts in this field. In addition, this review includes the acoustics of the wings under the flexibility effects which is considered as a new key for better flyer design and improvement. A comprehensive understanding of the integrated aerodynamics and acoustics under the wing flexibility is, therefore, needed.
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Parametric study on wing-lambda-shock formation
(2021-01-01)
Chainok, Sirikorn
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Rungroch, Thanapol
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Chairach, Pattarasuda
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Prapamonthon, Prasert
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Yooyen, Soemsak
It is well-known that a wing is one of the most important parts of an aircraft as it is used to generate lift force. According to a wing moving at sufficiently high subsonic speeds, the flow speed on the wing's upper surface can be supersonic due to acceleration through the curvature-created suction, thereby forming a shock wave in a lambda shape. Additionally, the lambda shock can interact with the boundary layer flow. These phenomena relate to disturbances in the flow field, including flow separation, thus causing undesirable effects on lift production. Hence, a better understanding of the phenomenon of wing-lambda-shock formation and its nature is essential. This study presents a numerical investigation of the lambda-shock formation on an ONERA M6 wing, which is known as a swept, semi-span wing with no twist, under parametric effects of angleof-attack, and free-stream Mach number, which is increased up to the supersonic regime. The pressure coefficients obtained by simulations are validated by open data. Then, numerical results in terms of the local pressure coefficient, local Mach number, averaged lift and drag coefficients, and?-shape characteristics based on Mach number and pressure coefficients are discussed under an investigated range of the parameters. Results show that the angle-of-attack and free-stream Mach number can affect the lambda shock formation on the wing upper surface physically. Specifically, an iso-sonic surface with lambda shock waves is disturbed when the angle-of-attack and free-stream Mach number vary in an investigated range. This also affects lift and drag coefficients of the wing.
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Multi-objective design optimization of the combinational configuration of the upstream energy deposition and opposing jet for drag reduction in supersonic flows
(2020-10-01)
Ju, Shengjun
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Sun, Zhenxu
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Yang, Guowei
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Prapamonthon, Prasert
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Zhang, Junyuan
Optimization design has been widely used in the supersonic vehicle design process and the drag reduction characteristic is an important objective of the optimization. The drag reduction mechanism applied to the blunt body with the combinational configuration of the upstream energy deposition and opposing jet for drag reduction has been conducted numerically. In the current study, the three-dimensional coupled implicit compressible Reynolds Averaged Navier-Stokes equations and Menter's shear stress transport turbulence model are employed to simulate the flow fields around the blunt body with the combined method. The results show that in the jet-to-freestream total-pressure ratio of 0.2 and 0.4, the drag is reduced by 47.44% and 45.96%, respectively. Further, the Latin hypercube method is used for the generation of initial samples for optimization and the multi-objective design optimization algorithm coupled with the Kriging model surrogate model is applied to determine optimal flow control parameters. The drag reduction factor R<inf>d</inf> and drag reduction effectiveness E<inf>eff</inf> are selected as optimization objectives. The Pareto-optimal front for the multi-objective design optimization results is acquired and there exists a challenging tradeoff between the two optimization objectives. The drag reduction factor R<inf>d</inf> and drag reduction effectiveness E<inf>eff</inf> further increase as much as 28.16% and 116.47%, respectively. The jet has a stronger penetration in the optimum design condition, and the findings suggest that the strategy of adding energy spot to the upstream flow field of the opposing jet can be an effective way for drag reduction.
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Parametric study on drag reduction with the combination of the upstream energy deposition and the opposing jet configuration in supersonic flows
(2020-06-01)
Ju, Shengjun
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Sun, Zhenxu
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Yang, Guowei
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Prapamonthon, Prasert
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Zhang, Junyuan
The drag reduction characteristics play an important role in the supersonic vehicle design phase. According to two drag reduction schemes, the opposing jet and the upstream energy deposition have aroused the widespread interest of researchers. In the current study, the drag reduction effectiveness of a blunt body with the combination of the upstream energy deposition and the opposing jet configuration in supersonic flows is investigated numerically. The three-dimensional coupled implicit compressible Reynolds Averaged Navier-Stokes (RANS) equations coupled with the Menter's shear stress transport (SST) turbulence model are applied to numerically predict flow fields of the blunt body, the variance analysis method is introduced to a parametric study on the drag reduction. Results indicate that a larger overall drag is decreased by the combinational configuration than the single strategies of the opposing jet and the energy deposition. The proposal of the combination of the upstream energy deposition and the opposing jet configuration can be used as an effective method of drag reduction. Meanwhile, due to the existence of the upstream energy deposition, the stability and penetrability of the opposing jet substantially increase, especially for the long penetration mode. Further, some recommendations are provided for the drag reduction factor and drag reduction effectiveness.
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Understanding of temperature and cooling effectiveness sensitivity of a film-cooled vane under coolant inlet temperature effect: A case study
(2019-09-01)
Prapamonthon, Prasert
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Yin, Bo
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Yang, Guowei
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Zhang, Mohan
This work presents a case study of the relationship between temperature and cooling effectiveness of a film-cooled vane under effect of coolant inlet temperature in two aspects based on the actual and base coolant inlet temperatures. Results are conducted in terms of temperature, cooling effectiveness, and heat transfer coefficient based on surface and volume analyses using CFD/CHT approach. Sensitivity of the vane temperature and cooling effectiveness under this effect is discussed also. The results show that for the surface basis, although the cooling effectiveness obtained from the actual coolant inlet temperature is quite straightforward and follows the definition of the cooling effectiveness directly, the cooling effectiveness obtained from the base coolant inlet temperature is more understandable because it corresponds to the variation of the surface temperature. Based on the volume basis and the base coolant inlet temperature, the 8% increase in the coolant inlet temperature causes the reduction of the average and maximum cooling effectiveness, which corresponds to 18 K and 25 K increments in the average and minimum temperatures, respectively. However, when the actual coolant inlet temperature is used, the variation of the cooling effectiveness is rather insensitive due to the reduction of heat flux on the hot-side wall.
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Analysis of aerodynamic noise characteristics of high-speed train pantograph with different installation bases
(2019-06-01)
Yao, Yongfang
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Sun, Zhenxu
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Yang, Guowei
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Liu, Wen
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Prapamonthon, Prasert
The high-speed-train pantograph is a complex structure that consists of different rod-shaped and rectangular surfaces. Flow phenomena around the pantograph are complicated and can cause a large proportion of aerodynamic noise, which is one of the main aerodynamic noise sources of a high-speed train. Therefore, better understanding of aerodynamic noise characteristics is needed. In this study, the large eddy simulation (LES) coupled with the acoustic finite element method (FEM) is applied to analyze aerodynamic noise characteristics of a high-speed train with a pantograph installed on different configurations of the roof base, i.e. flush and sunken surfaces. Numerical results are presented in terms of acoustic pressure spectra and distributions of aerodynamic noise in near-field and far-field regions under up- and down-pantograph as well as flushed and sunken pantograph base conditions. The results show that the pantograph with the sunken base configuration provides better aerodynamic noise performances when compared to that with the flush base configuration. The noise induced by the down-pantograph is higher than that by the up-pantograph under the same condition under the pantograph shape and opening direction selected in this paper. The results also indicate that, in general, the directivity of the noise induced by the down-pantograph with sunken base configuration is slighter than that with the flush configuration. However, for the up-pantograph, the directivity is close to each other in Y-Z or X-Z plane whether it is under flush or sunken roof base condition. However, the sunken installation is still conducive to the noise environment on both sides of the track.
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Extra-low Reynolds number vane separation using immersed boundary method
(2019-01-01)
Prapamonthon, Prasert
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Yin, Bo
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Yang, Guowei
Nowadays, mini unmanned aerial vehicles (MUAVs) and micro air vehicles (MAVs) are not only beneficially used as aviation models but also as modern drones for military missions and other civilian applications. Hence, research and development of propulsion sources for MUAVs and MAVs dynamically increase with a future trend of high performance, but low energy consumption. Certainly, using micro and ultra-small-size gas turbine is a good option for the propulsion source. To achieve ideal flight of MUAVs and MAVs powered by micro and ultra-small-size gas turbines under this trend, understanding of flow phenomena at wide ranges of Reynolds number is essential. This research presents a 2D numerical study of characteristics of laminar flow separation and the trailing-edge vortex on a turbine vane at extra-low Reynolds numbers (Res) i.e. Re = 1800 and 3600, and three rotational angles (a) i.e. a = 0º, 15º and 30º using immersed boundary method (IBM). With this method, the problem of incompressible flow is addressed by a sharp interface IBM. Numerical results indicate that IBM can characterize phenomena of laminar separation flow, which usually happens on the turbine airfoil when laminar boundary layer cannot overcome adverse pressure gradients and viscous effects. To our current knowledge, this may be the first research to study flow behavior at such low Res for gas turbine vanes using IBM. Even though it is now not common to operate micro and ultra-small-size gas turbines under these conditions, it is important to know how aerodynamic performance may be if micro and ultra-small-size gas turbines need to run under such conditions in the near future.

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