Experimental Study of Characteristics of Flow Field in Rod Bundle Channel Under Blocking Conditions

The rod bundle fuel is characterized by compact structure and narrow flow passage. The fragments and corrosion products, flowing with the coolant, can cause local blockage accident, threaten the integrity of the fuel cladding. Therefore, it is necessary to use the Particle Image Velocimetry (PIV) to visualize and measure the flow fields downstream of the blockages. The results show that partial blockages will cause flow reversal. In the backflow zone, vortices are generated downstream of the blockage, causing increase in the resistance. The length of backflow zone increases with the increase of the Reynolds number. The wake area formed downstream of the blockage presented periodic changes with the time and the period is about 0.8s. For the blockage of the interior subchannels, in the backflow zone, two rows of asymmetrically distributed vortices, and the vortices interfere with each other and cause squeeze deformation. For the blockage of the side and corner sub-channels, the formed vortices have irregular shape and nonuniformed distribution, and the flow field is more complex and changeable. This is believed to be caused by the high intensity turbulence and the influence of the wall.

Influence of Different Lateral Bending Angles on the Flow Pattern of Pumping Station Lateral Inflow

A model of the pumping station lateral inflow forebay was established to explore the influence of different lateral bending angles of the pumping station lateral inflow. The lateral bending angles were set at 45° and 60°, and the two schemes were calculated separately. Analyzing the results of the numerical simulation showed that the flow patterns of the diversion passages of different schemes were good, but the advancing mainstream of the 1# inlet passage near the sidewall was seriously deviated after entering the forebay. Most of the water can flow smoothly into the inlet passage, while a small part of the water flowed into the sidewall and formed a backflow, resulting in a large-scale backflow zone near the left sidewall of the forebay. Moreover, the flow in the backflow zone was turbulent, which affected the water inlet conditions of the 1# water flow passage. Comparing the water inlet conditions of the water passage with the numerical simulation results of 45° and 60° bending angles showed that the larger the lateral bending angle of the forebay was, the worse the flow pattern of the water flow, and the more unfavorable the pump operation.

Application of Computer Graphics Flow Visualization Methods in Vortex Rope Investigations

Computer graphics visualization techniques for application on data from Computational Fluid Dynamics (CFD) simulations of the vortex rope, a phenomenon present in hydraulic turbines operating in off-design conditions, were devised. This included not only objects for visualization (what to visualize) but also methods of the visualization itself (how to do it). By means of advanced methods based particularly on volume rendering of Eulerian fields in combination with Lagrangian objects, various phenomena were captured, such as the motion of the vortex rope or the backflow zone. The data came from simulations using a scale-resolving hybrid turbulence model, the Stress-Blended Eddy Simulation. In such detailed simulations and other applications involving complex three-dimensional structures, proper visualization methods are needed to leverage the content captured in the resultant data.

Investigation on backflow phenomenon in the aerostatic journal bearing

In this work, the backflow phenomenon exhibited in the gas journal bearings is investigated. The effect of operational parameters such as eccentricity ratio ɛ, axial velocity of the bearing vz, misalignment angles [Formula: see text] and [Formula: see text] on the backflow behavior, and load force and axial friction force of the bearing are studied numerically. The differential transformation method and finite difference method are utilized to solve the dimensionless Reynolds equations required in the analysis. The performance parameters such as pressure distribution, gas flow rate, load force, and axial friction force are examined in the numerical simulations. The investigation reveals that when the bearing is operated in normal working zone, the load force F increases significantly with an increase in eccentricity ɛ; however, F may only increase slightly when the bearing operates in the backflow zone. It is suggested that the pressure Ps should be set greater than 5.0, Pc smaller than or equal to 3.0 to avoid the backflow behavior. The axial friction force [Formula: see text] is largely determined by the pressure [Formula: see text], and increases as pressure Pc increases.

The effects of the lower outlet on the flow field of small gas–liquid cylindrical cyclone

In this study, the effects of the lower outlet on the flow field of small gas–liquid cylindrical cyclones are investigated using Reynold stress turbulence model. Under the same operating conditions, four configurations with different outlet styles and angles are established. The time-averaged tangential velocity, axial velocity, and root mean square velocity are compared, respectively. It is shown that many local secondary flow patterns are present in small gas–liquid cylindrical cyclones, and those flow patterns may cause serious energy losses. The lower outlet mainly influences the gas–liquid cylindrical cyclones flow field in the central region. The small gas–liquid cylindrical cyclones with single rectangular outlet provides a steady flow field and a large backflow zone, which are helpful in improving the separation efficiency. According to the simulations, a single rectangular lower outlet is the optimal one for small gas–liquid cylindrical cyclones.

Vaneless Diffuser Flow With Extremely Distorted Inlet Profile

The exit flow distribution of 90-deg centrifugal compressor impellers is distorted in peripheral direction as well as over the diffuser depth. First, there are the rotating jet-and-wake regions behind each impeller channel. Second, the flow has a completely distorted inlet profile from the front to the back wall of the diffuser. Measurements of static and total pressure, total temperature, and flow angle profiles along the whole diffuser length have been carried out in a high specific speed compressor. The results show great angle and total pressure differences in the first part of the diffuser and a backflow zone near the front wall. At the end of the diffuser, a separation zone was located. It is shown that by means of a one-dimensional calculation method, using a dissipation factor, the measured representative mean values of the diffuser flow can be determined very well in the regions where no separation occurs.