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The breakdown of laminar flow in the clearance space of a journal is considered, and the point of transition is considered in relation to experiments carried out with ‘bearings’ of large clearance. Experiments involving flow visualization with very large clearance ratios of 0.05 to 0.3 show that the laminar regime gives way to cellular or ring vertices at the critical Reynolds number predicted by G. I. Taylor for concentric cylinders even in the presence of an axial flow and at a rather higher Reynolds number in the case of eccentric cylinders. The effect of the transition on the axial flow between the cylinders is small. The critical speed for transition as deduced by Taylor, is little affected by moderate axial flows and is increased by eccentricity. The effect of critical condition on the axial‐flow characteristics of the bearing system appears to be negligible, again for moderate axial flows. Assuming that the results can be extrapolated to clearances applicable to bearing operation, the main conclusion of this paper is that the breakdown of laminar flow, which is a practical possibility in very high‐speed bearings, is delayed by eccentric operation.

The purpose of this paper is to reduce the drag loss and study the effects of operating conditions and groove parameters such as flow rate and temperature of automatic transmission fluid, clearance between plates, groove depth and groove ratio on the drag torque of a wet clutch for vehicles, parametric analysis of the drag torque model of wet multi-plate friction clutch with groove consideration.

Both experimental and numerical research was carried out in this work. Parametric groove models, full film lubrication flow model and pressure distribution model are established to investigate the effects of the grooves on drag torque of a wet clutch. Multigrid method is used to simplify the solution.

In this paper, a drag torque model of a wet multi-plate friction clutch based on the basic theory of viscous fluid dynamics is examined through experimental and numerical methods that take grooves into account, and the change trend of drag torque with operating conditions and groove parameters is analyzed.

Multigrid method is used to solve the governing equations, which simplifies the solution process because of the restrictions and interpolation operations between the adjacent layers of coarser and fine grids. These works provide insight into the effect regularity of operating conditions and groove parameters on drag torque of a wet multi-plate friction clutch. Furthermore, variable test conditions and sufficient experimental data are the main functions in the experimental research.

For an axial-flow compressor rotor, the upstream inflow conditions will vary as the aircraft faces harsh flight conditions (such as taking off, landing or maneuvering) or the whole compressor operates at off-design conditions. With the increase of upstream boundary layer thickness, the rotor blade tip will be loaded and the increased blade load will deteriorate the shock/boundary layer interaction and tip leakage flows, resulting in high aerodynamic losses in the tip region. The purpose of this paper is to achieve a better flow control for tip secondary flows and provide a probable design strategy for high-load compressors to tolerate complex upstream inflow conditions.

This paper presents an analysis and application of shroud wall optimization to a typical transonic axial-flow compressor rotor by considering the inlet boundary layer (IBL). The design variables are selected to shape the shroud wall profile at the tip region with the purpose of controlling the tip leakage loss and the shock/boundary layer interaction loss. The objectives are to improve the compressor efficiency at the inlet-boundary-layer condition while keeping its aerodynamic performance at the uniform condition.

After the optimization of shroud wall contour, aerodynamic benefits are achieved mainly on two aspects. On the one hand, the shroud wall optimization has reduced the intensity of the tip leakage flow and the interaction between the leakage and main flows, thereby decreasing the leakage loss. On the other hand, the optimized shroud design changes the shock structure and redistributes the shock intensity in the spanwise direction, especially weakening the shock near the tip. In this situation, the shock/boundary layer interaction and the associated flow separations and wakes are also eliminated. On the whole, at the inlet-boundary-layer condition, the compressor with optimized shroud design has achieved a 0.8 per cent improvement of peak efficiency over that with baseline shroud design without sacrificing the total pressure ratio. Moreover, the re-designed compressor also maintains the aerodynamic performance at the uniform condition. The results indicate that the shroud wall profile has significant influences on the rotor tip losses and could be properly designed to enhance the compressor aerodynamic performance against the negative impacts of the IBL.

The originality of this paper lies in developing a shroud wall contour optimization design strategy to control the tip leakage loss and the shock/boundary layer interaction loss in a transonic compressor rotor. The obtained results could be beneficial for transonic compressors to tolerate the complex upstream inflow conditions.

The purpose of this paper is to study the pressure fluctuation characteristics in the sidewall gaps of a centrifugal dredging pump in detail and discover the excitation sources.

An unsteady numerical simulation with shear–stress transport–scale-adaptive simulation (SAS-SST) model was conducted for a centrifugal pump considering the sidewall gaps. The numerical codes were validated by a model test carried out in China Water Resources Beifang Investigation, Design and Research Co., Ltd. Fast Fourier transform was used to obtain the frequency components of the pressure fluctuation.

Pressure fluctuation characteristics inside the pump were analyzed for a condition near the design point. In the sidewall gaps, the circumferential, radial and axial distribution of the pressure fluctuation amplitude follow different laws. The non-axisymmetrical distribution of pressure fluctuation in the sidewall gaps shows that the unsteady flow in the volute casing which has a non-axisymmetrical geometry imposes an evident effect on the flow field in the sidewall gaps and the interaction between the main flow and the clearance flow cannot be neglected. There are several frequency components appearing as the dominant frequencies at different locations in the sidewall gaps, but the relatively stronger pressure fluctuations are all dominated by the rotating frequency. It indicates that the rotating impeller, which originally makes the shrouds rotate, is the primarily excitation source of the pressure fluctuations in the sidewall gaps.

The pressure fluctuation characteristics in the sidewall gaps of centrifugal pumps were first comprehensively analyzed. Unsteady flows in the sidewall gaps should be considered during the design and operation of centrifugal pumps.

The balanced vane pump is a common transmission component in hydraulic systems. Since the physicochemical properties of water and seawater are different from that of mineral oil, some problems can occur, for instance, poor lubrication, more leakage, and more corrosion. The paper aims to demonstrate the technical feasibility for the water hydraulic vane pump.

The material combinations were selected based on related research in literature. The volumetric efficiency and suction performance were measured in the current experiment. The relations between gap clearances and leakage flow, the contact and the friction forces between a vane tip and a cam contour were simulated based on mathematic models.

The soft‐hard material combinations in the prototype pump show preferable friction characteristics during tests. The axial clearances are the main channels of leakage flow. Pin type vane pump can reduce the contact force of the vane tip.

This paper outlines some key problems of the water hydraulic vane pump, such as the friction pair material,the structure, and the contact force of the vane tip by means of testing the basic performance of pump and mathematic model.

A non‐contact end‐effector was applied to lift three different materials which have different physical properties. These materials are mica (as rigid material), carton (as semi‐rigid material) and non‐rigid material (woven fabric). This end‐effector operates on the principle of generating a high‐speed air flow between nozzles and the specimen surface thereby creating a vacuum which levitates the materials with no mechanical contact. In this paper, the handling results of these materials are compared with each other. The changes in the physical behavior of lifting materials were observed during the experimental work. The effect of the various air flow rates on the non‐contact handling clearance gap between the nozzle and the materials were also investigated. As a result, it was observed that the non‐contact end‐effector could be applied to handle different flat materials.

This paper aims to study the lubrication and sealing performance on the textured piston pair under the cross action of the shape and structure parameters. This paper further carries out the optimization design of low energy consumption hydraulic impact piston pair.

Based on the characteristics of the ring gap seal piston pair, the flow field analysis model of the whole film gap is established for its periodic treatment. The friction power loss of the piston pair is defined as the evaluation index of the lubrication performance and the leakage power loss as the evaluation index of the sealing performance. The orthogonal test design and CFD software were used to analyze the lubrication and sealing performance of the textured piston pair.

The cross action of shape and structure factors has a great influence of the lubrication and sealing performance on the textured piston pair. Clearance and shape parameters have great influence on it, while seal length and depth diameter ratio have little influence. The sealing performance of conical textured piston pair is good, while the lubrication performance of square textured piston pair is good. The primary and secondary order of influence of shape and structure on energy consumption on piston pair is B (seal clearance) > C (texture shape) > D (area ratio) > A (seal length) > E (depth diameter ratio).

Breaking the defect of local optimization design on traditional piston pair structure, then find the matching relationship of structural parameters on textured piston pair. Further improve the lubrication and sealing performance of the piston pair, and provide reference for the global optimization design of the low energy consumption hydraulic impact piston pair.

A method for optimizing net positive suction head required of axial‐flow pumps has been proposed by the present author, which is based on the two‐dimensional potential flow model and without considering the tip gap effect. The objective of the paper is to confirm if the method is just and feasible for the case of viscous fluid flow in impellers with tip gap.

A series of steady, three‐dimensional, noncavitating and cavitating, turbulent, incompressible flows of water through two axial‐flow pump impellers were calculated by using CFD code Fluent. The two impellers included a reference one with constant circulation at outlet and an optimized one with variable circulation designed with the author's method and code. In computations, the throttling and unthrottling approaches were used, respectively. Comparison of hydraulic performance, averaged flow variables at the impeller inlet and exit, flow in the tip gap, flow variables on blade surfaces and suction performance between the optimized and reference impellers was made.

It was confirmed that the optimized impeller has better hydraulic and suction performances. The method for optimizing with variable flow circulation profile along blade span at the outlet to impeller is proper and practical. Additionally, an unstable regime in the head curves of two impellers is presented. In the regime, a stall occurs on the pressure side of the blade and a hysteresis exists, which causes a hysteresis‐loop.

The effect of suction entry on flow is represented approximately by using a free‐vortex and uniform axial velocity. The diffusing component behind the impellers is not taken into account. The unsteadiness of flow is not considered, which would have a connection with stall pattern in an axial‐flow impeller.

The hydraulic and suction performances and flow variables of two axial‐flow pump impellers with tip clearance are obtained successfully with CFD. Stall and hysteresis as well as hysteresis‐loop in head curve are observed by using throttling and unthrottling approaches.

The geometric parameters of the compressor blade have a noteworthy influence on compressor stability, which should be meticulously designed. However, machining inaccuracies cause the blade geometric parameters to deviate from the ideal design, and the geometric deviation exhibits high randomness. Therefore, the purpose of this study is to quantify the uncertainty and analyze the sensitivity of the impact of blade geometric deviation on compressor stability.

In this work, the influence of blade geometric deviation is analyzed based on a subsonic compressor rotor stage, and three-dimensional numerical simulations are used to compute samples with different geometric features. A method of combining Halton sequence and non-intrusive polynomial chaos is adopted to carry out uncertainty quantitative analysis. Sobol’ index and Spearman correlation coefficient are used to analysis the sensitivity and correlation between compressor stability and blade geometric deviation, respectively.

The results show that the compressor stability is most sensitive to the tip clearance deviation, whereas deviations in the leading edge radius, trailing edge radius and chord length have minimal impact on the compressor stability. And, the effects of various blade geometric deviations on the compressor stability are basically independent and linearly superimposed.

This work provided a new approach for uncertainty quantification in compressor stability analysis. The conclusions obtained in this work provide some reference value for the manufacturing and maintenance of rotor blades.

Herringbone groove thrust bearings are typically used in high-speed, light-load applications, such as spindle motors for hard disk drives. In the past researches, the effect of shaft misalignment was little considered. This study aims to reveal effects of shaft misalignment on the microscopic flow regime in the water-lubricated herringbone groove thrust bearing.

The liquid film in a thrust herringbone groove bearing was investigated by computational fluid dynamics. The effects of micro-grooves on the flow field were carefully explored. Two-dimensional liquid films at four different sites were examined for obtaining the rich flow field properties.

The distributions of pressure, temperature and water vapor volume fraction were obtained, the micro hydrodynamic effects were formed by the herringbone grooves and the effects of the shaft misalignment on lubrication and sealing performance could be found.

The influence of misalignment on the herringbone groove thrust bearing performance was investigated in detail. The obtained results could give the reference guideline for the bearing design.