Investigation of the axial force on a varying-speed centrifugal pump impeller

Centrifugal impeller has high efficiency but obvious axial force problems because of the axial-to-radial flow direction change. It is easy to cause the over loading of thrust bearing and damage shaft system. Especially in varying-speed centrifugal pumps, the mechanism, characteristics, and influence of impeller axial force is complex. Therefore, experimental and numerical studies are conducted to resolve these problems in this case. The impeller axial force is comparatively investigated by analyzing zonal components, visualizing internal flow, and resolving pressure attenuation law in clearances. This study provides a new test scheme based on force sensors for measuring the impeller axial force. The results show that the variation tendency of impeller axial force is similar to that of pump head. Flow patterns show that streamline-rotation angle decreases with the increase of flow rate in clearances. As the key factor affecting impeller axial force, the static pressure distribution in the clearances can be divided into specific variation stages to specify the mechanism. Specially in this varying-speed case, the blade axial force shifts from positive to negative with the decrease of rotation speed from high to low. This study provides a good reference for solving the axial force problems for centrifugal pumps.

Conjugate heat transfer numerical study of the ejector by means of SU2 solver

In this paper, the test supersonic ejector with conjugate heat transfer in solid bodies has been studied numerically. An extensive numerical campaign by means of open-source SU2 solver is performed to analyze the fluid dynamics of the ejector flowfield accounting for the heat conduction in solids. The fluid domain simulation is carried out by employing compressible RANS treatment whilst the heat distribution in solids is predicted by simultaneous solving the steady heat conduction equation. The working fluid is R245fa and all simulations are performed accounting for real gas properties of the refrigerant. Experimental data against numerical results comparison showed close agreement both in terms mass flow rates and static pressure distribution along the walls. Within the CFD trials, the most valuable flow parameters at a wall vicinity are compared: distribution across the boundary layer of the temperature and the turbulent kinetic energy specific dissipation rate, boundary layer displacement and momentum thicknesses. A comprehensive analysis of the simulation results cases with adiabatic walls against cases with heat permeable walls revealed the actual differences of the flow properties in the wall vicinity. However, the ejector performance has not changed noticeably while accounting for the heat conduction in solids.

The Tip Clearance Cavitation Mechanism of a High-Speed Centrifugal Pump with a Splitter-Bladed Inducer

For a high-speed centrifugal pump, cavitation occurs easily. To equip a high-performance splitter-bladed inducer upstream of the pump is an effective method to suppress cavitation. In this paper, an external characteristics experiment of the high-speed centrifugal pump with a splitter-bladed inducer is carried out, and the corresponding numerical calculations are completed. The research shows that the results of the numerical calculation are credible. Numerical cavitation calculations under eight different tip clearance conditions are carried out. First, it is found that the tip clearance (TC) has a certain impact on the head of the centrifugal pump. When TC is in a small range, the clearance leakage is small, and the impact on the head of the pump is not so obvious, which can give the pump a higher performance. Second, it is found that TC has a certain influence on the static pressure distribution in the cascade passage of the splitter-bladed inducer. When TC is in a certain range, the increasement in TC will aggravate the cavitation at the suction surface of the long blades near the inlet. When it exceeds the certain range, it will cause cavitation at the outlet of the inducer. At last, it is found that the cavitation’s severity and position of the inducer are closely related to TC. TC affects the magnitude and position of vorticity in the inducer’s passage. In this paper the flow mechanism of TC is revealed, and its research results can provide theoretical basis and technical support for the design of the tip clearance of the inducers.

Impeller in suction pipe Thai Phaya-Nakh for agriculture

Purpose The suction pipes are important in agriculture and are used widely in water management and agricultural–mechanical industry in ASEAN. Thus, this paper aims to present design of new impeller in suction pipe and include shape blade impeller to optimize for suction head, which has been higher than efficiency local-type by the performance. It mostly depends on the hydrodynamic characteristics, e.g. lift, drag and ratio, which is known as the “Thai Phaya-Nakh pipe”. Design/methodology/approach By approach NACA methodology and use applied technique: leading edge of blade, skew-line, cambered-line, developed area and advanced number etc., for analyzing data which the result of CFD simulation. Findings The models were tested in field by using motor at rotation speed 1500 rpm and found that the summarized average suction efficiency of the new impeller was estimated to be 72%, which has been greater than that of the local-type impeller with an average suction efficiency of 28% to 2.6 times. In addition, the amount of required electrical energy was reduced by 18%. Originality/value Then after analyzing the data from the static pressure distribution flow rate of impeller models, it is found that the new curved impeller has higher flow rate than the local type impeller. Thus, this study suggests the shape new impeller has higher flow rate than the local type impeller.

Influence of Opposing Dilution Jets on Effusion Cooling

The gas turbine combustion process reaches gas temperatures that exceed the melting temperature of the combustor liner materials. Cooling the liner is critical to combustor durability and is often accomplished with double-walled liners that contain both impingement and effusion holes. The liner cooling is complicated with the interruption of the effusion cooling by large dilution jets that facilitate the combustion process. Given the presence of the dilution jets, it is important to understand the effect that the dilution jet has on the opposing wall in respect to the effusion film. This research includes measurements of the local static pressure distribution for a range of dilution jet momentum flux ratios to investigate the impact that the opposing dilution jet has on the effusion film. The interactions with the effusion cooling were also evaluated by measuring the overall cooling effectiveness across the panel. Measurements show that the opposing dilution jets did impact the liner at dilution jet momentum flux ratios that were greater than 20. The impacts at high momentum flux ratios were indicated through increased local static pressures measured on the surface of the combustor liner. Furthermore, the dilution touchdown decreased the overall cooling effectiveness of the effusion cooling. Results also indicated that the opposing dilution jets changed position on the liner as the dilution jet momentum flux ratio changes.

A Study of Influences of Inlet Total Pressure Distortions On Clearance Flow in an Axial Compressor

The rotating distortion generated by upstream wakes or low speed flow cells is a kind of phenomenon in the inlet of middle and rear stages of an axial compressor. Highly complex inflow can obviously affect the performance and the stability of these stages, and is needed to be considered during compressor design. In this paper, a series of unsteady computational fluid dynamics (CFD) simulations is conducted based on a model of an 1-1/2 stage axial compressor to investigate the effects of the distorted inflows near the casing on the compressor performance and the clearance flow. Detailed analysis of the flow field has been performed and interesting results are concluded. The distortions, such as total pressure distortion in circumferential and radial directions, can block the tip region so that the separation loss and the mixing loss in this area are increased, and the efficiency and the total pressure ratio are dropped correspondingly. Besides, the distortions can change the static pressure distribution near the leading edge of the rotor, and make the clearance flow spill out of the rotor edge more easily under near stall condition, especially in the cases with co-rotating distortions. This phenomenon can be used to explain why the stall margin is deteriorated with nonuniform inflows.

Static Pressure Distribution on Long Cylinders as a Function of the Yaw Angle and Reynolds Number

This paper addresses the challenges of pressure-based sensing using axisymmetric probes whose axes are at small angles to the mean flow. Mean pressure measurements around three yawed circular cylinders with aspect ratios of 28, 64, and 100 were made to determine the effect of changes in the yaw angle, γ, and freestream velocity on the average pressure coefficient, C¯pN, and drag coefficient, CDN. The existence of four distinct types of circumferential pressure distributions—subcritical, transitional, supercritical, and asymmetric—were confirmed, along with the appropriateness of scaling C¯pN and CDN on a streamwise Reynolds number, Resw, based on the freestream velocity and the fluid path length along the cylinder in the streamwise direction. It was found that there was a distinct difference in the values of CDN and C¯pN at identical Resw values for cylinders yawed between 5° and 30°, and for cylinders at greater than a 30° yaw. For γ < 5°, there did not appear to be any large-scale vortices in the near wake, and CDN and C¯pN appeared to become independent of Resw. Over the range of 5° ≤ γ ≤ 30°, there was a complex interplay of freestream speed, yaw angle, and aspect ratio that affected the formation and shedding of Kármán-like vortices.

Coaxial Circular Jets—A Review

This review article focuses on the near-field flow characteristics of coaxial circular jets that, despite their common usage in combustion processes, are still not well understood. In particular, changes in outer to inner jet velocity ratios, ru, absolute jet exit velocities and the nozzle dimensions and geometry have a profound effect on the near-field flow that is characterized by shear as well as wake instabilities. This review starts by presenting the set of equations governing the flow field and, in particular, the importance of the Reynolds stress distributions on the static pressure distribution is emphasized. Next, the literature that has led to the current stage of knowledge on coaxial jet flows is presented. Based on this literature review, several regions in the near-field (based on ru) are identified in which the inner mixing layer is either governed by shear or wake instabilities. The latter become dominant when ru≈1. For coaxial jets issued into a quiescent surrounding, shear instabilities of the annular (outer) jet are always present and ultimately govern the flow field in the far-field. We briefly discuss the effect of nozzle geometry by comparing the flow field in studies that used a blockage disk to those that employed thick inner nozzle lip thickness. Similarities and differences are discussed. While impinging coaxial jets have not been investigated much, we argue in this review that the rich flow dynamics in the near-field of the coaxial jet might be put to an advantage in fine-tuning coaxial jets impinging onto surfaces for specific heat and mass transfer applications. Several open questions are discussed at the end of this review.

Study of Wall Static Pressure Distribution on Flat Surface by Impinging Submerged Jet from Non-circular Orifice

The distribution of wall static and stagnation (CP and CPO) pressure coefficient on a flat rectangular element by impinging air jet from the hexagonal orifice is obtained from experimentation. The past research studies helped to identify key parameters such as orifice geometry, jet exit-to-plate-distance (Z/dj), test section inclination (θ), jet Reynold number (Re), lateral distance-to-jet diameter (X/dj), test surface type and geometry, for better and acceptable results. The experimental outcome helps to know the effect of identified key parameters on wall static and stagnation pressure on a rectangular test plate in a confined flow path. The independent nature of wall static pressure is observed for all jet Reynold number (10000 ≤ Re ≤ 50000). Higher pressure coefficient values were observed at lower Z/dj = 1, X/dj = 0 and θ = 0. A significant drop in CP values are seen with the increase in Z/dj, X/dj and θ. The experimental CP and CPO contribution of confined flow are compared against the unconfined flow, around 48% to 58% enhancement is observed when confinement is used. Experimental pressure drop measurements across orifice were made and pressure loss coefficient (PC) for hexagonal orifice of confined and unconfined condition are reported.

Mechanism of the Absent Air Column in Three Products Hydrocyclone Screen (TPHS): Experiment and Simulation

Three products hyrdrocyclone screen (TPHS) has been proposed for particle separation based on size. In TPHS, a cylindrical screen was embedded in a conventional hydrocyclone (CH) to combine the centrifugal classification and screening to particle separation based on size. The industrial application of TPHS indicates its better device performance than CH. Although, the earlier studies reveal some common understanding for TPHS, the information of the absent air column remains unknown. Hence, the combination of physical experiment and numerical simulation was considered involving a 75 mm TPHS for this knowledge gap. First, both the computational fluid dynamics (CFD) simulation with Reynolds stress mode and the physical experiment with a high-definition camera illustrate the development process details of a flow field in TPHS. That is, the water was imported along the tangential inlet into TPHS; then under the effects of the feed chamber wall and gravity, the liquid phase spiraled downward until the cylindrical screen passed through the sieve; as the liquid moved to the spigot, it could be discharged in time due to the small underflow port, thus the volume fraction of air rapidly reduced from 1 to 0; subsequently the water filled the TPHS and the absent air column could be observed. Furthermore, the distribution comparisons of air volume fraction and static pressure show that TPHS displayed the absent air core with the negative static pressure in the center region along the z-axis, while CH displayed the opposite features. In addition, despite the different inlet velocity, TPHS consistently presented the vanished air column which could be ascribed to the fact that the present cylindrical screen resulted in positive static pressure distribution inside TPHS.