实验流体力学

2023, 37(1): 1-2.

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2023, 37(1): 1-2.

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Abstract:

Aerodynamic design of the 600 km/h high-speed maglev transportation system

DING Sansan, LIU Jiali, CHEN Dawei

2023, 37(1): 1-8. doi: 10.11729/syltlx20220131

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Abstract:
After several generations of technological innovation and development, China's rail transit has made remarkable achievements. The adhesion of the wheel rail system limits the further high-speed development of rail transit, and the application of the maglev technology in rail transit arises at the historic moment. During the 13th Five-Year Plan period, China began to develop the high-speed maglev transportation system with a speed of 600 km/h. The operational speed of the high-speed maglev train is 600 km/h and the Mach number reaches 0.49, and the aerodynamic performance of the train deteriorates sharply. Due to the change of the operational environment (train-rail gap, throttling on both sides) of the high-speed maglev train, the aerodynamic characteristics of the high-speed maglev train are different from that of the high-speed wheel-rail train. The aerodynamic problem has become one of the key issues in the design and development of the high-speed maglev train. In the present paper, the technical challenges faced by the aerodynamic design of the high-speed maglev train are discussed, and the solutions of the aerodynamic design of the high-speed maglev train are proposed. Then the aerodynamic design schemes of the China’s 600 km/h high-speed maglev train are introduced, and the future research fields of aerodynamics of the high-speed maglev train are prospected.

Distribution and unsteady characteristics of the temperature and pressure loads acting on the car-body in evacuated tube maglev transport

HU Xiao, MA Tianhao, WANG Xiaofei, DENG Zigang, ZHANG Jiwang, ZHANG Weihua

2023, 37(1): 9-28. doi: 10.11729/syltlx20220084

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Based on the SST $k-\omega$ turbulence model and the IDDES method, a three-dimensional numerical model was used to simulate the transient state of an evacuated tube maglev transport system at 800 km/h in the choked (blockage ratio of 0.3 and 0.2) and unchoked (blockage ratio of 0.1) states. The accuracy of the numerical method was verified using transonic wind tunnel bump test data. Additionally, the significant coherent structure of the flow field was extracted based on the proper orthogonal decomposition, the region with the strong unsteady load on the train surface was identified, and its space-time evolution law was revealed. The results show that the load distribution on the upper surface of the train is similar to that of the Laval nozzle, and the difference in load distribution between the chocked/unchoked conditions is mainly in the divergent section. The load distribution on the lower surface of the train becomes complex due to the abrupt change in the cross-section of the bogie cavity. The difference in the interaction between the upwash and downwash flow leads to different locations of the temperature peaks under the choked/unchoked conditions. The strong unsteady pressure region on the train surface is mainly located at the bottom bogie and has a characteristic frequency of 14 Hz. The tail car shock wave is also an unsteady source under choked conditions. The first-order modes of the middle and tail car temperature loads reflect the heat accumulation process.

The aerodynamic characteristics of roof-wing combination of a high-speed train

GAO Jianyong, ZHANG Jun, NI Zhangsong, ZHOU Peng, ZHU Yan, WANG Chengqiang, GAO Guangjun

2023, 37(1): 29-35. doi: 10.11729/syltlx20220053

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Adding the aeronautic wing to the high-speed train equivalently reduces its weight through the lift force provided by the wing. Hopefully, the energy consumption of the high-speed train can be reduced. This provides a new concept for the high speed train design. The aerodynamic characteristics of the wing directly affect the weight reduction effects. Therefore, it is important to analyze the aerodynamic characteristics of the wing under different conditions for the design of the train lift wing. The k–ε model was used in this study for numerical simulation. Firstly, the influence of the connection rod between the wing and the train roof on the aerodynamic characteristics of the lift wing was analyzed. On this basis, the effects of design parameters such as the wing-roof height, the incoming flow velocity and the angle of attack on the aerodynamic characteristics of the wing were studied. The results shows that: the influence of the connection rod on the lift and drag of the wing is less than 3.7%. Due to the high-speed airflow induced by the leading edge of the train roof model, the air velocity impacting on the lift wing decreases with the increase of the flying height of the lift wing, and the lift force tends to decrease. Within 3 times of the chord length height, the maximum lift difference of different lift wings does will not exceed 3%. When the velocity of the incoming flow is up to 90 m/s and larger, the lift coefficient and the drag coefficient of the lift wing were close to near 1.62 and 0.61, respectively. As the angle of attack varies within 0° to 22°, the lift coefficients of the wing increase continuously. However, the lift coefficients decrease when the attack angle is above 22°.

Experimental investigation on tunnel pressure wave of high-speed train

YANG Wenzhe, LIU Feng, WEI Mengjie, YAO Shuanbao, CHEN Dawei

2023, 37(1): 36-43. doi: 10.11729/syltlx20220096

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Abstract:
When a high-speed train enters a tunnel, an initial compression wave occurs and radiates to the outside of the tunnel to form a micro pressure wave when it propagates longitudinally along the tunnel to the exit. An experimental device for generating the initial compression wave by the instantaneous release of high-pressure air was built, and the experimental research on the compression wave generated by it was carried out. Firstly, the composition of the experimental device was introduced, and the pressure time history curve and formation mechanism in the tunnel were analyzed. Secondly, the influence of the parameters of the experimental device on the initial compression wave was drawn out. The subsequent attenuation process of the compression wave was studied at last. The experimental results show that the pressure fluctuation in the tunnel is mainly affected by the reflected wave at the tunnel portal. The amplitude, gradient and positive peak value of the initial compression wave can be adjusted by changing the relevant parameters of the experimental device. The attenuation period of the compression wave is the same under different initial pressures of the high-pressure chamber, but the larger the initial amplitude is, the faster the pressure decays in the same time period.

Study on the critical tunnel length distribution characteristics of high-speed maglev railway single-track tunnel based on pressure comfort

DU Yingchun, MEI Yuangui

2023, 37(1): 44-52. doi: 10.11729/syltlx20220120

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Abstract:
The different pressure fluctuation caused by a high-speed train passing through tunnels of various length can cause different degrees of pressure comfort problems for passengers. The one-dimensional compressible unsteady non-isentropic flow model characteristic line method and the time constant method pressure tightness index model were used to study the pressure wave outside the train and the pressure change characteristics inside the train under two pressure tightness indexes when a single high-speed maglev train passes through the tunnel. The concept of the critical tunnel length of the high-speed maglev single line based on the pressure comfort standard was improved, and the influence of the train speed and train dynamic pressure tightness index on the critical tunnel length was studied. It is found that: under the condition of critical tunnel length based on the maximum negative pressure value of the external pressure, the maximum negative pressure value of the internal pressure is smaller. The maximum value of the maximum pressure change in each 1, 3, 10 and 60 s in the train increases first and then decreases with the increase of the tunnel length, and there is the critical tunnel length under pressure comfort constraints. The critical tunnel length at different train speeds is different. Except for per 10 s limit conditions, the critical tunnel length under different train dynamic pressure tightness indexes is approximately the same. When a 600 km/h single-train maglev train with a dynamic pressure tightness index of 83 s passes through a 100 m² tunnel, the critical tunnel length based on the UIC660 comfort standard is 10–12 km. The research results of this paper have good reference value for the study of tunnel clearance area and train pressure tightness based on comfort standard, and for further improvement of the theoretical system of the critical tunnel length of the rail transit based on the tunnel pressure wave effect.

Slipstream at the tunnel exit induced by a high-speed maglev train passing through a tunnel

CHENG Jionghao, GUO Yi, GUO Dilong, JI Zhanling, MAO Jun, LIU Wen

2023, 37(1): 53-63. doi: 10.11729/syltlx20220110

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Abstract:
When the high-speed maglev train enters a tunnel, a compression wave generated by it will induce the air flow at the exit of the tunnel to form an adjoint velocity. The three-dimensional, compressible, unsteady calculation method is used to simulate the process of the high-speed maglev train passing through a tunnel with different blocking ratios under different speeds. The features of the slipstream around the tunnel exit induced by the compression wave are analyzed, and the influence of the train speed and blocking ratio on the slipstream is ascertained. The results show that at the tunnel exit, the trend and the peak speeds of the slipstream induced by the compression wave have no apparent change in the direction of the train’s movement; the peak wind speed of the measuring point outside the tunnel exit gradually decreases in the longitudinal range of 25 m, and basically remains unchanged in the transverse range of 5 m. With the vehicle speed and blocking ratio increasing, the peak wind speeds inside and outside the outlet are raised obviously. When the train speed is 600 km/h and the blocking ratio is 17.04%, the maximum wind speed at 5 m outside the tunnel is up to 56 m/s. This conclusion is helpful to strengthen people's understanding about the harm of the slipstream induced by a train passing through a tunnel, and to provide references for protection against the slipstream in the railway tunnel and the safe operation of maglev train in the future.

Research on aerodynamic characteristics of evacuated tube train in dynamic operation

SONG Jiayuan, LI Tian, ZHANG Jiye

2023, 37(1): 64-71. doi: 10.11729/syltlx20220121

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The research on aerodynamic characteristics of the evacuated tube train provides a reference for the construction of ETT(Evacuated Tube Train) test platform. A 3-dimensional model was established, and the SST k–ω model was used to solve the flow field. The aerodynamic resistance, pressure distribution and flow field characteristics under constant speed and acceleration conditions were compared, and the influence mechanism of acceleration on the aerodynamic resistance was revealed. The results show that the aerodynamic drag of the head car and the tail car is mainly affected by the choked flow and the detach of the tail shock. In no-choked state, the drag of the tail car increases slowly while that of the head car is unchanged. Compared with the acceleration condition, the reflection of the oblique shock caused by the large starting speed leads to the pressure fluctuation on the train surface, and the amplitude of the fluctuation gradually decreaseswith time. As the head car compresses the front air slowly and the precursor shock wave is weak under the acceleration condition, the changes of the aerodynamic resistance and surrounding pressure of the head car lags behind that of the running speed, and the smaller the acceleration is, the more obvious the lagging effect is. In the stage of uniform speed, the length of the choked section and the tail shock is proportional to the operation time.

Study on the influence of atmospheric environment change on the temperature field of vacuum tube

GAO Chao, YAN Rihua, WU Bin, ZHOU Tingbo

2023, 37(1): 72-81. doi: 10.11729/syltlx20220116

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The temperature distribution in the vacuum tube directly affects the aerodynamic performance and operation safety of the maglev train. It is of great significance to study the influence of the atmospheric environment effect for the construction of the vacuum tube train transportation system in the future. The parameters of the atmospheric environment such as the solar radiation intensity, air humidity, temperature and wind speed in each season are obtained by collecting meteorological data of Chengdu in recent five years. The numerical calculation method of the radiation heat transfer from the vacuum tube is established. The DO (Discrete Ordinate) radiation model was used to study the influence of solar radiation on the air flow in the vacuum tube, and the temperature distribution and variation rule of the air flow in the tube under conditions of different seasons and different vacuum degrees were obtained. The results show that the air in the tube has a stable temperature rise under the influence of solar radiation. With the same vacuum degree, the temperature in the vacuum tube is the highest in summer and the lowest in winter. With the gradual decrease of the vacuum degree, the temperature of the air flow in the tube increases gradually in each season. When the vacuum degree is 0.1 atm (～10.1 kPa), the air temperature in the vacuum tube increases by 56.60 K in summer.

Characteristics of car body pressure load of 600 km/h maglev trains crossing in tunnel

WEI Kang, LAI Jiwei, MEI Yuangui

2023, 37(1): 82-90. doi: 10.11729/syltlx20220117

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Abstract:
With the rapid increase of the train speed, aerodynamic effect has a more serious impact on the pressure load of the car body, and the trains crossing in the tunnel is more violent than that of a single train passing through the tunnel. In order to research the aerodynamic load of maglev train crossing in the tunnel, the one-dimensional unsteady compressible non-homentropic flow model method was adopted. The distribution characteristics of the maximum positive pressure, negative pressure and maximum pressure (maximum positive and negative pressure and maximum peak pressure) of the car body were analyzed and the influence characteristics of the tunnel length, speed and blocking ratio on the external pressure were researched. The results show that the maximum negative pressure value of the car body is much greater than the maximum positive pressure value during the train crossing in the tunnel; only when the tunnel length exceeds a certain value, would the maximum positive and negative pressure value of the car body appear in the head and tail train, respectively; the maximum pressure values of the head and tail cars remain constant after the tunnel length exceeds 2 km, and the maximum positive pressure values of the head and tail cars at different speeds basically coincide, which are close to “zero”; when the tunnel length is within a certain range, the maximum pressure is proportional to the square of the speed; and the maximum pressure increases linearly with the increase of the blocking ratio. The findings of this research can provide support for the car body aerodynamic fatigue strength design.

Effect of deflector devices on the aerodynamic characteristics of high-speed maglev trains

LI Yifan, LI Tian, ZHANG Jiye, ZHANG Weihua

2023, 37(1): 91-99. doi: 10.11729/syltlx20220109

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Due to the existence of suspension gap, the flow field around the suspension frame of high-speed maglev trains is turbulent and aerodynamically complex, which in turn affects the suspension and guidance performance of the trains. Based on Computational Fluid Dynamics (CFD), a numerical simulation model of the three-car marshalling high-speed maglev train is established to study the aerodynamic characteristics and the flow field structure. The results show that the airflow through the suspension gap impacts directly on the windward side of the suspension frame of the head car at a speed of 500 km/h. This creates a differential pressure drag which increases the aerodynamic drag of the head car significantly. A large area of the positive pressure area is formed at the bottom of the car body due to the airflow turbulence of the suspension frame, leading to a large increase in the aerodynamic lift force of the head car that is much higher than that of the middle car and the tail car. According to the results, three different types of deflector devices are proposed to control the airflow through the gap by changing the structure of the nose of the head car, which can significantly improve the pressure distribution on the train surface. The aerodynamic drag, aerodynamic lift and pitch moment of the train are effectively and synergistically reduced. Compared with the original maglev train, all three types of deflector devices (plate, short wedge, long wedge) can achieve both aerodynamic drag and lift forces reduction, among which the best long wedge deflector device can reduce the overall aerodynamic drag force by 3.6%, the head car aerodynamic lift by 40.6% and the head car pitch moment by 80.3%, with the best comprehensive aerodynamic characteristics.

Mechanism of expanded equal-section inclined hood to reduce initial compression wave by high-speed maglev passing through the tunnel

MA Zhihao, JING Xuelei, DU Yingchun, MEI Yuangui

2023, 37(1): 100-112. doi: 10.11729/syltlx20220123

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Abstract:
The initial compression wave is generated when the high-speed rail vehicle enters the tunnel. The compression wave propagates to the exit of the tunnel at the speed of sound and radiates outward to form a micropressure wave, which brings serious environmental problems. Using the three-dimensional unsteady, compressible flow N–S equation and the SST k–ω turbulence model, and taking the maglev train with a speed of 600 km/h as the research object, the initial compression wave generated by maglev train entering the tunnel with extended equal-section hood, extended equal-section oblique hood and no hood was simulated. The mitigation effect and mechanism of the inclined end and the oblique angle of the hood on the initial compression wave were analyzed. The following conclusions are mainly drawn: the formation of the maximum pressure gradient of the initial compression wave is directly related to the entrance of the part of the train into the tunnel/hood where the change rate of the cross-sectional area of the train head is the maximum, which corresponds to the maximum change rate of the flow in the tunnel. The maximum gradient of the compression wave can be greatly reduced by setting the extended constant section hood, and the relief rate is 49.92%. Changing the vertical port of the expanded isocross section hood to the positive oblique port can further improve the mitigation rate. When the oblique angle is 10°, 20°, 30° and 39°, the increase of the mitigation rate is 12.93%, 10.32%, 8.18% and 6.28%, respectively. It is suggested that the oblique hood has the most obvious effect on the peak pressure gradient of the initial compression wave when the oblique angle is 10°, and the total relief rate is 62.85%. In this paper, the coupling analysis method of the change rate of the cross section area of the head, the air flow rate and the compression wave at the observation point, and the mutual mapping relationship between the head shape and the air flow rate, which affect the maximum pressure gradient of the initial compression wave, can reasonably explain the mechanism of the hood at the entrance to the cave to reduce the initial compression wave. It provides a new method for further optimization of the train head shape and design of different types of hood and analysis of aerodynamic effects.

2023 Vol. 37, No. 1