Study on Axial Clearance Size and Leakage of Canned Motor Pump under Axial Force Self-Balance State

Canned motor pump is widely used in chemical industry. Due to the particularity of its application, it is necessary to ensure that the medium does not leak completely. If the axial force of impeller is too large, it will directly affect the performance of canned motor pump. Therefore, the floating impeller could be used in the pump to balance the axial force. In this paper, the relationship between axial clearance and leakage rate at the key part of canned motor pump is studied by means of numerical calculation and experimental verification. It is found that the fitting curve is highly consistent with the calculated value, which provided a good theoretical basis for further study of axial clearance control axial force and experimental axial force self-balance. In addition, the leakage rate increases with the increase of axial clearance. The static pressure in the axial clearance first increases and then decreases with the decrease of radius, and the maximum static pressure value is about 10.5% ∼ 15.8% near the clearance inlet. This study is of great significance to the theoretical research on the self-balance state of axial force of impeller.

Influence of Axial Clearance on Water-Jet Axial Flow Pump

Three dimensional Reynolds averaged N-S equation and S-A turbulent model were adopted to simulate the flow field and hydraulic performance of the waterjet axial flow pump with the different impeller axial clearance. The numerical research results show that with the increase of axial clearance size, total pressure and static pressure rise at first and then decreases, torque and shaft power remain basically unchanged, the efficiency decreases gradually, the suction surface separation zone of stator expanded under the design condition. When the axial clearance is 30mm, the pump hydraulic performance and flow field are the best, and stator load distribution is the most uniform. When the axial clearance is 40–50mm the load of the lower part of stator leading edge is reduced greatly, which is not conducive to maintain static blade strength and maintain the stator rectifying action.

Abnormal Wear Mechanism and Improvement of High-Speed Cylindrical Roller Bearing

This paper presents the dynamic differential equations of cylindrical roller bearing, considering the dynamic unbalance mass of roller and the contact between the roller end face and the inner ring rib. The influence of bearing working condition and structural parameters on the P V value of roller end face and the slip speed of roller working surface were analysed. The theoretical analysis and experimental results both show that the large amount of roller’s dynamic unbalance mass due to the difference in chamfering size on both sides of the roller and the deviation of the bearing axial clearance are the main causes of abnormal wear on the roller working surface and end face.

Stiffness characteristics of crossed roller bearings with roller roundness deformation

This study investigated the stiffness characteristics of crossed-roller bearings (XRBs) subjected to various loading and boundary conditions. A five degree-of-freedom XRB model was adopted that considers the effect of roller roundness deformation, which was developed by the authors in a prior study. The analytical formulation for a fully occupied (5 × 5) stiffness matrix of XRB was obtained. Extended simulations were performed to determine the XRB stiffness and internal load distribution considering the effects of the external loads, axial preloads, axial clearance, and angular misalignment. The numerical results confirmed that the bearing stiffness possessed significant nonlinearity with respect to the external loads. Increasing the axial clearance reduced the stiffness of the bearing under radial and moment loading, but it did not affect the stiffness of the pure axially loaded bearing. The stiffness of the bearing with axial clearance increased consistently with the misalignment angle. The stiffness behavior of the preloaded bearing depended on the misalignment angle.

Calculation of Pressure Pulsations in the Flow Part of the First Stage of an Axial Turbine in the Rotor-Stator Interaction Zone

A serious problem in the development of reusable liquid-propellant rocket engines (LRE) is the provision of a high resource and reliability of gas turbines of turbopump, which supply fuel to the combustion chamber. This problem can be solved by reducing the level of pressure pulsations in the interaction zone of the turbine rotor-stator and dynamic loads acting on the working and stator blades. In this regard, a useful tool is the method of numerical simulation of the unsteady turbulent flow of a compressible gas in the turbine flow path with the determination of the amplitude of pressure pulsations in the axial clearance between the stator and rotor blade cascades. The calculation model includes the Navier-Stokes equations and equation of energy. Density, thermal conductivity and diffusion coefficient are linearly dependent on temperature and concentration. Calculations were performed on different meshes, proving the mesh convergence of the method upon reaching the quasi-stationary regime. The calculation results show that the pressure pulsations vary greatly with the axial clearance, and the main frequency of the pressure pulsations in the spectrum is the blade passing frequency. The frequency of dynamic moment acting on the blade also coincides with the indicated frequency.

Multi-Parameter Measurement of Rotors Using the Doppler Effect of Frequency-Swept Interferometry

The Doppler effect of frequency-swept interferometry (FSI) is often seen as an obstacle to the dynamic ranging accuracy. However, the potential of this obstacle is rarely noticed and used. In this paper, by combining the periodical characteristics of the rotational Doppler effect, an FSI-based multi-parameter measurement method for the rotor is proposed. Through the establishment of the rotational Doppler formula of FSI, it is found that the frequency, direct component, and amplitude of the dynamic distance given by FSI can be utilized to estimate the angular velocity, axial clearance, and tilt angle of the rotor, respectively. A rotor platform and a fiber-optic FSI system were constructed, and a series of experiments were carried out to verify the proposed method. The experimental results showed that the relative errors of the measured axial clearance, angular velocity, and tilt angle were less than 3.5%. This work provides a new perspective on the multi-parameter measurement of the rotor and makes it possible to directly perform multi-parameter measurement inside the space-confined rotating machinery as only a single small-size fiber-optic probe is needed.

Numerical and experimental investigation of notch-induced high-speed precise shearing of 42CrMo bar

A notch-induced high-speed precise shearing method was developed for high-strength metal bars, which prefabricated V-shape circumferential notches in batch on the bar surface to make stress concentration, and applied a high-speed load to complete separation on a new type of electric-pneumatic counter hammer. The FE simulation and experimental tests were conducted; the influences of loading speed, notch depth, and axial clearance were analyzed on the fracture behavior and blank quality; the microfracture mechanism was further investigated. The results showed that the circumferential notch inhibited the plastic distortion and obtained high precision chamfered billets, with a roundness error of 1.34%, flatness error of 0.34 mm, and incline angle of 0.87°. Besides, the surface notch effectively reduced Max. impact force and fracture energy. The fractography revealed that: for the notched bar, the cracks initiated from the thin extrusion layers at the bilateral-notch tips, and from micro extrusion and intrusion at the top-notch tip. The predominant microfracture mechanism involves microvoid coalescence and forming of quasi-parabolic dimples along with the shear stress.

Investigating the Effect of the Axial Clearance Magnitude Between the Covering Disc of the Runner and the Centrifugal Compressor Body on the Gas Dynamics in a Low-Discharge Stage Prototype

The paper presents the results of numerically investigating viscous gas flow in a simulated low-discharge stage of a super high-pressure type compressor, using the ANSYS CFX software package. We studied the low-discharge centrifugal compressor stage prototype designed and tested at the Compressor, Vacuum and Refrigerating Technology Department of Peter the Great St. Petersburg Polytechnic University. In order to conduct the numerical experiment, we performed a mesh independence study. We compared the properties obtained in the numerical investigation to the experimental data. In our mathematical simulation the magnitude of the axial clearance between the covering disc of the runner and the compressor body varies in the range of 1--5.5 mm; we estimate the effect that varying this number has on the loss complex characteristic 1 + βfriction + βleakage

Methods to Have Tighter Clearance in Gas Turbine: Turbine Section

Typically, Gas turbine clearance between stator and rotor parts are governed by radial clearance which determines performance, cooling flow requirements, part performance etc. These clearances must be optimized to meet product requirements. Clearance which are kept too tight at assembly condition causes excessive rubbing during starting or shutdown of gas turbine which results in excessive heat generation and damage to rotating and statoric parts. In some cases, rubbing could cause tip liberations and damages to flow path which results in aero dynamic losses. Similarly, if rotor tip clearance is large at assembly condition results in aerodynamic losses. While designing component design at interface locations, tip clearance should be kept as minimum as possible to have proper balance between tip rubs at low speed and aero dynamic loss. In this paper describes the experience of Baker Hughes, wherein different design options which are considered to arrive at optimized clearance in low pressure turbine section of Gas turbine have been discussed. Typically, in low pressure turbine wherein the turbine airfoils were provided with tip rails and shrouds are brazed with honeycombs. These were allowed to rub during startup of Gas turbine engine and provide a tighter clearance at steady state operating condition. In this paper, to have tighter clearance in operating condition few methods of incorporating axial clearance in addition to radial tip clearance are discussed. By incorporating tighter axial clearance, it was found to be evident that performance estimated has improved compared to having only radial tip clearance. This paper also describes design considerations for honeycomb pertaining to axial clearance control and the methods for rubbing tip shroud with honeycomb. This paper highlights worm chart developed for a rotor blade and stator shroud configuration and highlight benefit of axial clearance control mechanism. This paper also covers different designs of heat dissipation methods in tip rails of a bucket while it is rubbing with honeycomb. In this paper, based analytical case study proves that, when axial clearance was made tighter, it reduces leakage flows and improves Low pressure turbine stage efficiency significantly.