In order to analyze the influence of the number of blades on the radial force characteristics of pump as turbine during the variable flow rate transition process, six impellers with different number of blades are designed. On the basis of verifying the correctness of the numerical calculation method by the external characteristic experiment, the steady and unsteady numerical simulation of each scheme is carried out by ANSYS-CFX software, the radial force characteristics on impellers with different schemes are compared and analyzed. The results show that during the transition process of variable flow rate, the radial force vector and its fluctuation range on the impeller gradually decreases with the increase of the number of blades. The radial resultant force obviously increases with the increase of time in the transition to large flow rate, and obviously decreases with the increase of time in the transition to small flow rate. The dominant frequency of the radial force is equal to leaf frequency, and the pulsation amplitude of the radial force of Z9 is the minimum in both transition processes. In the transition process of variable flow rate, when the number of blades is Z9, the efficiency is the highest, the radial force on the impeller is the minimum, and the pulsation amplitude of the radial force is also the smallest, so for this pump as turbine, the value of blade number equals 9 is the optimal.

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In this study, we analyze the flow characteristics of pulp suspensions in a sudden expansion channel, which is used as a tube bank in papermaking machines. Flow visualization using a light section method and measurements of time-averaged and fluctuating fiber concentrations, Ca and C’, and pressure, were performed. The experiments were carried out on pulp suspensions with a bulk fiber concentration (Cs) of 0–2.0 wt% in a channel with an expansion ratio of   2 at varied average velocities (Ua) of 0.046.6 m/s. We examined the effect of flow velocity on the changes in concentration and pressure distributions along the channel axis. The distribution of the pulp fiber concentration behind the sudden expansion significantly changes depending on the flow state in the upstream channel before the expansion. In particular, for low and moderate velocities, the flow field is characterized in the main flow region consisting of flocculated plug fibers and a recirculation region with a low concentration near the expansion corner by a type of streamline originated from the thin water-layer in the upstream channel. The distribution of Ca shows a tongue-shaped structure in the central part of the cross section, and C’ is large near the annulus streamline. As the velocity is further increased, the flocculated fibers gradually disperse, and the distributions of Ca and C’ become almost uniform. In addition, the uniformity of fiber concentration does not change much in the section downstream from a distance 10 times the step height from the sudden expansion plane.

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The paper depicts design philosophy of a pneumatic pressurization system configured for Inflatable Aerodynamic Decelerator (IAD). The objective is to fine tune parameters in conjunction with mathematical model allowing a better understanding of process. System configuration has been discussed and mathematical model is formulated for estimating thermodynamic properties and mass flow of gas transferring from high pressure storage to IAD through orifice. Theoretical analysis and calculations were made and compared with the simulations carried out in LMS AMESim platform. Experiments were conducted in vacuum conditions to verify pressure change in high pressure storage and in IAD and this experimental data is used for validation of mathematical model.

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In actual turbomachinery, the wider chord cascade sometimes shows a higher aerodynamic efficiency than the shorter chord one. This study tries to ascertain the underlying physical mechanism of the wide chord advantage mentioned above in terms of the boundary layer loss reduction. It is verified the boundary layer loss has the characteristics of the chord to the power of -1/n ( n > 1), therefore, the wide chord can reduce it. Next, by CFD, it is verified the boundary layer loss is surely reduced by the wide chord. Consequently it is verified the wide chord is effective to reduce the viscous loss in actual turbomachinery.

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An experimental study was performed on the fiber-concentration distributions of wood pulp liquid flowing through a divergent tube at a divergence angle of θ = 12°. The study was conducted to verify the tube’s effectiveness for application to the tube banks of papermaking machines. Experiments were conducted at bulk pulp-fiber concentrations of Cs = 0.2 - 0.6 wt % and inflow velocities of Ua = 0.1 - 2 m/s. The flow in the horizontal plane that contained the tube axis was visualized using the light-section method. In addition, the distributions of the time-averaged and fluctuating fiber concentrations (Ca and C’, respectively) were measured. We then investigated the effect of the average flow rate on the variations in the directions of flow of the concentration distributions. At a low flow rate (Ua < 0.3 m/s), the fluid of the annular water layer formed in the upstream tube divided the flow into two in the divergent tube, and the Ca and C’ distributions exhibited shapes that had considerable differences in the cross-section. When the flow velocity was increased to Ua ≥ 0.5 m/s, the shape of the Ca distribution flattened, and C’ reduced gradually in the flow direction. The results related to the non-uniformity of fiber concentration demonstrated that the divergent tube is suitable for use in a tube-bank channel of the headbox of a papermaking machine.

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Surge frequencies in compressors can vary much in dependence of many factors, such as compressor conditions, such as sizes, speeds, number of stages, and flowpath geometries, relative compressor locations, etc. The present investigation shows the basic behaviors of surge frequencies in multi-stage axial flow compressors, governed by a small number of essential parameters, which are obtained by physical insight to the phenomena and examinations in a trial-and-error manner on a number of numerical-experimental data. One of the essential parameters is a flowpath-average reduced resonance frequency, implying the number of excitations by the resonance frequency on the fluid particle in passing through the flowpath. Another one is also a reduced frequency formulated by modelling the emptying and filling actions in surge. A generalized basic framework of surge frequencies against resonance frequencies has been constructed by applying the numerical-experimental data on a wide range of conditions of the compressors and the flowpaths in terms of both parameters. The framework thus prepared can be useful for practical purposes, such as for estimation of surge frequencies and surge degeneration (stall stagnation) boundaries, and also for understanding the effects of various related factors. It can provide a rule of thumb for estimation of surge frequency in the condition of sufficiently large values of the reduced resonance frequency parameter. It could serve also as a clue to further study on the details.

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Cavitation instabilities such as rotating cavitation and cavitation surge often occur in high speed turbopumps. It has been shown by a stability analysis that the cause of cavitation instabilities is explained by the positive mass flow gain factor, representing the increase of cavity volume against the decrease (increase) of flow rate (incidence angle). The cavitation compliance, representing the increase of cavity volume in response to the decrease of inlet pressure, determines the frequency of instabilities. However, one-dimensional stability analysis cannot be directly used for the prediction of the onset point of cavitation surge when quasi-steady assumption is applied. In the present study, unsteady characteristics, i.e. the phase lag in the response of cavity volume against the flow rate/inlet pressure fluctuations, are taken into account in a stability analysis of cavitation surge in the form of lag element. The onset criterion considering the time lag is newly proposed for one-dimensional stability analysis, and the criterion is validated by comparisons with a two-dimensional stability analysis based on a singularity method applied to a free streamline theory.

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The efficiency of multiphase twin-screw pump decreases sharply under wet gas conditions (GVF>95%) with severe vibration and thermal problems. Based on the design characteristics of twin-screw pump and screw compressor, a design method of multigradient variable pitch decompression screw pump is to address these problems in this paper. This method keeps the cross section profiles of screw pump unchanged，only changes the pitch of screw. According to the design concept of decompression of screw compressor, the screw rotor is divided into three regions from the inlet to the outlet. The pitch of screw and thread width in these regions are designed separately to increase the volumetric efficiency of the screw pump and reduce the vibration. The effective clearance leakage model of twin-screw pump is simplified and modified. Considering two-phase back flow and combining mechanical model with thermodynamic model, the flow capacity, volumetric efficiency, pressure, and temperature distribution of new and conventional screw pumps are predicted by non-isothermal compression model. The calculations show that the design scheme of multi-gradient variable-pitch decompression screw pump can solve the volumetric efficiency and vibration problems under wet gas conditions fundamentally and can significantly reduce the power consumption of screw pump. However, the problem of temperature rise of screw pump still exists. Cooling system for the screw pump should be designed to continuously cool the screw pump.

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