Examination of Reynolds number effect on the development of round jet flow

In this study, the Reynolds number effect on the development of round jet flow is presented. The jet is produced from a smoothly contracting round nozzle and the flow structure is controlled by varying the air blower speed in order to obtain various Reynolds numbers (Re). The flow Reynolds number considered varies between 1140 and 9117. Mean velocity measurements were taken using hot-wire probe at different axial and lateral distances (0≤x/d≤50, where x is the downstream distance and d is the nozzle diameter) for the jet flow and at for 0≤x/d≤30 in long pipe attached to the nozzle. Measurements reveal that Reynolds number dictate the potential core length such that the higher the Reynolds number, the lower the potential core which is a measure of mixing of jet and ambient fluid. It shows that further away from the jet exit section, potential core decreases as Reynolds number increases, the velocity profile has a top hat shape very close to the nozzle exit and the shape is independent of Reynolds number. It is found that potential core extends up to x/d=8 for Reynolds number of 1140 as against conventional near field 0≤x/d≤6. This may suggest effect of very low Reynolds number. However, further investigation is required to ascertain this at extremely low Reynolds numbers. It is also observed that further away from the jet exit section, the higher the downstream distance, the higher the jet half-width (R1/2). Furthermore, the flow in the pipe shows almost constant value of normalised axial centerline velocity for a longer distance and this clearly indicates that there is mass redistribution rather than entrainment of ambient fluid. Overall, the Reynolds number controls the magnitude rather than the wavelength of the oscillation

Analysis on Leakage Characteristics of Labyrinth Piston Clearance in Reciprocating Labyrinth Compressor

In this paper, the piston clearance leakage model in reciprocating labyrinth compressor is established, and the leakage characteristics of labyrinth piston are analysed. The results show that in the labyrinth entrance section, the gas velocity decreases greatly, and the throttling effect is the most obvious. In the middle section of the labyrinth, the flow velocity descending gradient decreases. In the exit section, the flow rate begins to increase. When the labyrinth clearance is less than or equal to 0.1 mm, the clearance changes has little effect on the leakage. When the clearance is greater than 0.1 mm, the leakage increases rapidly with the clearance increasing. When the piston operates eccentrically, the leakage will increase by 1.5 ∼ 2 times compared with the non-eccentric operation. Therefore, the eccentric operation of the piston should be avoided as much as possible and the clearance should be reduced.

Variation characteristic of the Yellow River water resources in Ningxia section

The subject of rapid economic and social development impact of global climate change and the upper reaches of the Yellow River in the past decade, Ningxia Yellow River water into Gansu substantial reduced, resulting in Ningxia exit water also reduced to varying degrees, but the water entry and exit difference (water consumption) has increased. In this paper, comparative analysis of the Yellow River in Ningxia Section from 2001 to 2012 and from 1956 to 1995 data, found the average years of entry water by about 18%, leaving an average of about 23% less water for many years, Ningxia Yellow River water consumption increased by about 48%. Water impact from Meili Canal, Qixing canal, Qing Tongxia east and west main canal, 211.73 m3/s annual flux above Qing Tongxia Reservoir was evacuated by 2001 to 2012, more water in irrigated areas back from Shi Zui Shan section of the Yellow River once again return to the Yellow River, flow in the Ningxia exit section of the Yellow River than Qing Tongxia station extra 102.99 m3/s; the point of view during the year, due to the irrigation water from late March, the entry water becomes greater than exit water of the Yellow River in Ningxia section, effective irrigation due to precipitation increases in August, the difference between entry water and exit water becomes narrow, with the withdrawal of water regression in irrigated areas in downstream segment, thus result of the Shi Zuishan exit section flow than the entry of water cross section in varying degrees of increases in September, October and December.

Impact of Tunnel Groups on Pupil Diameter of Drivers on Mountainous Freeway in China: A Real-World Driving Study

A real-world driving experiment was performed in the Wen-Ma section of the G4217 Rong-Chang Freeway situated in the Sichuan Province to investigate the impact law of the pupil diameter of drivers in tunnel groups on the mountainous freeway. The eye-movement data of drivers were collected, and the percentage of pupil diameter variable (PPDV) was used as a visual characteristic index. The analysis of the overall change in the PPDV of drivers in the experimental sections demonstrated that the PPDV in tunnel groups differed significantly between the nontunnel sections and single tunnel sections. Subsequently, a related model for the PPDV of drivers and the length of the connecting zone between tunnels was established, its reliability evaluated, and the smooth mutation value obtained on the basis of the mutation theory. Thereafter, a tunnel group definition standard based on the visual effect of drivers was developed. A six-zone approach was devised for the analysis of tunnel groups, and the result revealed that the different zones in the tunnel group have different impact on PPDV of drivers. The results revealed that the different zones of tunnel group have different impact on PPDV of drivers. Furthermore, lighting transition facilities should be set in the exit section of tunnel. The PPDV of drivers was negatively correlated with the length of the connecting zone of tunnel groups, and 100 m is the recommended safety length threshold for the connecting zone of tunnel groups.

Dynamics of exit section of automatic mill of pipe rolling line

Nonuniformity of pipe wall thickness is one of significant indices, determining quality of hot-rolled seamless pipes. One of the reasons of increased nonuniformity arising is dynamics of exit section mechanisms of pipe rolling line (PRL). Results of study of mandrel holding mechanism dynamics of PRL presented. Dynamic models of exit section, accounting parameters of technological process and inertia of a rolled hollow billet elaborated, which enabled to determine the character of dynamic processes at the exit section of PRL automatic mill. Differential equations of exit section elements motion at the exit section of PRL automatic mill were made up. The solution of the differential equations system was obtained in a numerical form by application of Runge‒Kutta method for correspondent dynamic models of exit section based on the example of calculations for ТПА-350 automatic mill. The pattern of dynamic processes arising at the exit section was specified at realization of the whole technological process of a hollow billet rolling at automatic mill, taking into consideration alternative action from the side of deformation center and mass of the rolled hollow billet. It was shown, that the specified solution of the task for three advanced dynamic models of mechanical system considerably differs from those of the known mathematical models. It was established, that the dynamics of the mandrel holding mechanism of ТПА-350 automatic mill equivalently form the mechanism of finished pipes geometry forming. Analysis of dynamic models of the mill exit section enabled to select the necessary technological and dynamic parameters of the mechanical system, to determine stable modes of hollow billets rolling at the ТПА-350 automatic mill. Results of the study of dynamics of exit section ТПА-350 automatic mill presented. A scheme of modernization of the exit section ТПА-350 automatic mill proposed, which enables to realize rational modes of operation accounting level of mechanical system dynamics and to control quality (geometric parameters) of the rolled pipes.

Drivers in Expressway Superlong Tunnels: The Change Patterns of Visual Features and the Discriminant Model of Driving Safety

A real-vehicle experiment was carried out in the superlong highway tunnel environment to study the change patterns of driver’s visual features, tracked by eye tracking devices, and the discriminant model of driver’s safety status. On the basis of statistical analysis, a single index and a comprehensive index discriminant model, both based on a C4.5 decision tree, were established. The results showed that compared with the non-tunnel highway sections, the driver’s pupil size was larger, and the gaze duration was longer in the tunnel section. Driver’s pupil size was larger in mid-tunnel section than in the entrance section and exit section. Gazes at the exit section were mainly short gazes. Compared to the exit section, driver’s pupil size changed more dramatically in the entrance section, and the gaze duration was longer. The single visual parameter indicator could clearly discriminate the driver’s safety status in the mid-tunnel section and the non-tunnel sections, while the dual-index-based identification model could clearly discriminate the safety status in each highway sections. The study deepens the research on the driver information perception model in superlong highway tunnels. Also, the study provides a theoretical basis for establishing a visual-feature-based real-time safety status discriminant.