Effect of the inlet gas volume fraction on the turbulent dissipation characteristics in the multiphase pump

The internal flow of the multiphase pump is complicated owing to its specific structure. To reveal the effect of the inlet gas volume fraction (IGVF) on the turbulent dissipation characteristics, the method of combining numerical simulation based on k-ε turbulence model with experiment was adopted, and the turbulent dissipation of the multiphase pump was quantitatively and qualitatively analyzed in both the pure water and gas-liquid two phases condition. Results showed the vortexes were primarily distributed in the diffusers at different inlet gas volume fractions (IGVFs), near the middle of the first diffuser and the outlet of the next diffuser. At the same time, the larger value of the turbulent dissipation than that in the impellers was concentrated in the inlet and outlet of the impellers and diffusers. In addition, the effect of IGVFs on the turbulent dissipation increased gradually from the hub to the shroud at the inlet section of the first impeller. Moreover, the turbulent dissipation became increasingly unsymmetrical from the hub to the shroud at the outlet section of the first impeller.

Numerical Analysis of Slope Stability Due to Excavation of Diversion Tunnel at Pamukkulu Dam Site, Indonesia

Located in the Takalar Regency of South Sulawesi Province, the Pamukkulu Dam is planned to use a tunnel type as its diversion structure. One of the critical parts in the tunnel construction is the stability of portal slopes. This research aimed to estimate the effect of tunnel excavation on the stability of the portal inlet and outlet slopes under static and earthquake loads by using the finite element method. The slope stability analyses were carried out under conditions of prior to and after tunnel excavation. The input parameters used were laboratory test results in the forms of index properties and mechanical properties taken from rock core drilling samples, completed with the rock mass quality parameters based on the Geological Strength Index (GSI) classification. The Mohr-Coulomb failure criterion was used to model strength of the soil, while the Generalized Hoek-Brown failure criterion was used to model strength of the rocks. The results of rock cores analysis using the GSI method showed that the inlet tunnel slope consisted of four types of materials, namely residual soil, fair quality of basalt lava, good quality of basalt lava, and very good quality of basalt lava. Meanwhile, the outlet portal slope consisted of three types of materials, namely residual soil, good quality basalt lava, and very good quality basalt lava. The calculated horizontal seismic coefficient for the pseudo-static slope stability analysis was 0.0375. The analysis results of slope stability in the Y1 inlet section had a critical Strength Reduction Factor (SRF) value of 2.35 in a condition prior to the tunnel excavation and a critical SRF value of 2.34 after the tunnel excavation. The Y2 outlet section had a critical SRF value of 13.27 in a condition before tunnel excavation and a critical SRF value of 5.55 after the tunnel excavation. The earthquake load addition at the Y1 inlet section showed a critical SRF value of 2.05, both before and after the tunnel excavation. The Y2 outlet section showed a critical SRF value of 11.49 before the tunnel excavation and a critical SRF value of 5.54 after the tunnel excavation. The numerical analysis results showed that earthquake load reduced critical SRF values of the slopes. At the Y1 inlet section, the tunnel excavation did not have a significant effect on slope stability. It was demonstrated by an extremely small decrease in a critical SRF value of 0.43% for a condition without an earthquake load and an unchanged critical SRF in a condition with an earthquake load. At the Y2 outlet section, the tunnel excavation had a more significant effect on the slope stability. It was exhibited by the decrease in the critical SRF value of 58.18% in a condition without an earthquake load and a decrease in the critical SRF value of 51.78% in a condition with an addition of an earthquake load. However, the analysis of slope stability for both sections showed that all design slopes were above the required allowable safety factor value.

Characteristics of Air Resistance in Aerostatic Bearings

The definition of air resistance is nonuniform when analyzing the bearing capacity, stiffness, and stability of an orifice throttling aerostatic restrictor. In this study, a capillary tube similar to the inlet section of an aerostatic restrictor is used as the research object, and the Bernoulli equation under adiabatic conditions is established. Through an experiment, the pressure and temperature of the capillary tube inlet and outlet and the flow through the capillary tube are measured. Based on the air resistance definition, the empirical formula of the coefficient k is obtained, and the theoretical air resistance of the capillary path is calculated. The relative error between the theoretical air resistance and experimental air resistance is kept within 10%. The comparison results verify the accuracy of the air resistance theory and provide a basis for the subsequent establishment of a universal definition of air resistance. Subsequently, air resistance can be used to design aerostatic bearings and help improve their characteristics.

Numerical Analysis of Erosion Wear of Water with Particles in Elbows

In this paper, the numerical analysis of erosion wear of water with particles in elbow is carried out based on fluent. The influence of different inlet velocity and bending angle on pipeline erosion, and the distribution of pressure field and velocity field in the pipeline are studied. The main conclusions are as follows: the erosion of elbow section is more serious than that of inlet section and outlet section of pipeline. With the increase of inlet velocity, the maximum erosion rate of elbow section gradually increases, and the maximum velocity and maximum pressure inside the elbow section also increase. When other conditions are certain, different bending angles make the elbow receive different erosion effects. When the bending angle is larger, the pipeline erosion rate is relatively more uniform. Study on erosion helps to reduce the impact of fluid on the wall and improve the safety and reliability of engineering.

The effect of oscillating turbulent inflow on the shape of downstream turbulence

Large Eddy Simulations (LES) has been widely applied and used in several decades to simulate a turbulent boundary layer in the numerical domain. In this study, we aimed to make a synthetic inflow generator (SIG) yielding an appropriate property of turbulent boundary layer in the inlet section and making quick development in the downstream of a three-dimensional domain. In order to achieve turbulent boundary layer quickly in a limited domain, the oscillating term was implemented in the well-defined boundary layer, which was expected to make faster convergence in the calculation. Cholesky decomposition was also applied to possess turbulent statistics such as the randomness and correlation of turbulent flow. In a result, the oscillating inflow did not show the faster convergence, but it indicated a possibility to improve statistical quantities in the downstream. In addition, regarding the mean flow characteristics were very close to the calculation without the oscillating flow. On the other hand, the turbulent statistics were improved depending on the oscillating magnitude.

Dust Concentration Changing Regularities and Dust Reduction Technology by Spray Negative Pressure in Fully Mechanized Mining Face

The dust concentration changing regularities are the basis to take dust depression measures, which is greatly influenced by the airflow. In the software of FLUENT, the value of ventilation velocity is set as a constant, which cannot express the real ventilation. According to the flow characteristics of the sublayer and data from Nicholas’ experiment, the ventilation velocity distribution formula of sublayer in the inlet section of fully mechanized caving coal face is deduced. The boundary condition of velocity is given by UDF. Taking the 3top1110 fully mechanized caving coal face as an example, the dust distribution in the process of coal mining and hydraulic support shifting was studied. According to the dust-spray coupling experiment, three types of nozzle are chosen based on the efficiency of dust suppression. Combining the dust migration rule and the characteristics of nozzles, the negative pressure-secondary dust suppression devices of spray were developed and applied. And the above measures have lowered the dust concentration effectively.

Experiment on Pressure Pulsation of Axial Flow Pump System with Different Runaway Head

The runaway condition is a damage condition for pumps and turbines which can induce the wake vortex, reverse flow, and severe pressure pulsation. This study aimed to research the characteristics of pressure pulsation of axial flow pumps under different runaway conditions, and the runaway model test was performed with different blade angles and heads. Moreover, four pressure sensors were uniformly arranged at the impeller inlet section to eliminate the random error. The time domain and frequency domain analysis were the main methods to obtain the change regulations. Results showed that the pressure pulsation under the runaway condition are mainly influenced by the rotation frequency, blade passing frequency, and wake vortex frequency. The dimensionless pressure pulsation coefficient of rotation frequency and wake vortex frequency increased obviously with the runaway head increasing, but changed little with different blade angles. In addition, the dimensionless pressure coefficient of wake vortex frequency of the sensors around the impeller inlet section differed a lot, which means that the wake vortex core is not in center of the rotation axis. The average dimensionless pressure pulsation coefficient of wake vortex frequency is higher than that of rotation frequency with the same runaway head, owing to the severer wake vortex.

Validation setup for the investigation of aeroacoustic and vibroacoustic sound emission of confined turbulent flows

Confined flows induce sound at certain flow conditions, which can be annoying in electric vehicles due to the absence of combustion noise. Noise in internal flow may occur due to unfavorable flow-guiding geometries caused by the complex packaging required in engine compartments of modern vehicles. The flow-induced sound is emitted at duct openings (e.g., ventilation inside the passenger cabin). It also originates from the vibroacoustic emissions of the flow-guiding structure excited by the flow. We propose a modular validation procedure for aeroacoustic simulations of confined flows. The experimental setup includes the vibroacoustic emission of the involved flow-guiding structure. The test rig consists of a sensor system, a high-pressure blower, modular pipe sections, and absorbers, which decouple the system from blower noise and avoid acoustic reflections at the pipe exit. A sufficiently long straight inlet section ensures fully developed flow conditions entering the investigated region. For capturing the vibroacoustic sound radiation of the flow-guiding structure, the measurement object and the surrounding microphones are encapsulated in a wooden box, lined with micro-perforated plates. Measurement results of a straight pipe and a pipe with a half-moon-shaped orifice are presented. Additionally, the sound generation is reproduced by Lighthill's aeroacoustic analogy applying a hybrid approach.

GENERATION OF SYNTHETICAL MEDICAL DATA BY MDR-ANALYSIS

Purpose: The purpose of this article is to determine the dependence of the rate of gel formation on the type of reagent-inhibitor of the gel formation process, and to study the kinetic dependences of gel formation of silicate compositions in the presence of compounds that regulate the rate of gel formation. Research methods: Direct and reverse titration, potentiometric titration, pH-metry, determination of the dynamic viscosity on a rotational viscometer, axial compression method to determine the elastic modulus were used to study the possibility of using chemical reagents as gelation inhibitors. Results: The possibility of using inorganic and organic additives to slow down the gel formation process and the effect of these additives on the strength of the gel, their thermodynamic parameters have been researched. Discussion: The adding of organic acids into the silicate composition as "crosslinking agents" slows down the gel formation process, while replacing hydrochloric acid with other gel acids that slow down the gel formation process does not lead to a decrease in the strength characteristics of these systems compared to the standard. It was found that with an increase in the gelation time, the strength of the gels decreases, and the syneresis increases; the adding of inhibitor additives insignificantly worsens the filterability of silicate compositions, which in general have bad filterability, leading to an increase in resistance during filtration at the inlet section of the sample. Observations have shown that the addition of additives-inhibitors does not affect the thermal stability of gels, regardless of the additives' nature.