Matthew Stickland

Performance of a centrifugal pump running in inverse mode

Abstract This paper presents the functional characterization of a centrifugal pump used as a turbine. It shows the characteristics of the machine involved at several rotational speeds, comparing the respective flows and heads. In this way, it is possible to observe the influence of the rotational speed on efficiency, as well as obtaining the characteristics at constant head and runaway speed. Also, the forces actuating on the impeller were studied. An uncertainty analysis was made to assess the accuracy of the results. The research results indicate that the turbine characteristics can be predicted to some extent from the pump characteristics, that water flows out of the runner free of swirl flow at the best efficiency point, and that radial stresses are lower than in pump mode.

Hub Height Ocean Winds over the North Sea Observed by the NORSEWInD Lidar Array: Measuring Techniques, Quality Control and Data Management

In the North Sea, an array of wind profiling wind lidars were deployed mainly on offshore platforms. The purpose was to observe free stream winds at hub height. Eight lidars were validated prior to offshore deployment with observations from cup anemometers at 60, 80, 100 and 116 m on an onshore met mast situated in flat terrain. The so-called “NORSEWInD standard” for comparing lidar and mast wind data includes the criteria that the slope of the linear regression should lie within 0.98 and 1.01 and the linear correlation coefficient higher than 0.98 for the wind speed range 4–16 m∙s−1. Five lidars performed excellently, two slightly failed the first criterion and one failed both. The lidars were operated offshore from six months to more than two years and observed in total 107 months of 10-min mean wind profile observations. Four lidars were re-evaluated post deployment with excellent results. The flow distortion around platforms was examined using wind tunnel experiments and computational fluid dynamics and it was found that at 100 m height wind observations by the lidars were not significantly influenced by flow distortion. Observations of the vertical wind profile shear exponent at hub height are presented.

An investigation into the mechanical damping characteristics of catenary contact wires and their effect on aerodynamic galloping instability

Abstract Measurement of the damped oscillation of a section of the UK East Coast Main Line (ECML) catenary/contact wire system was undertaken, and the natural frequency and mechanical damping were found to be 1.4Hz and 0.05 respectively. This information was used to assess the effect of increasing the mechanical damping ratio on the susceptibility of the system to an aerodynamic galloping instability. The section of line tested was known to gallop at wind speeds of approximately 40 mile/h, and theoretical and experimental work verified this. A friction damper arm was designed and three units were fitted to the section of line affected. The introduction of increased mechanical damping was found to raise the mechanical damping coefficient of the line to between 0.095 and 0.18, and the mathematical analysis produced a theoretical wind speed for galloping oscillation of between 75 and 141 mile/h respectively. For over a year since the units were fitted, no problems with galloping instability have been observed.

An investigation into the aerodynamic characteristics of catenary contact wires in a cross-wind:

Abstract An experimental analysis of the aerodynamic characteristics of catenary contact wires is presented. The aerodynamic data obtained were used to calculate the Glauert-Den Harthog criterion for one-dimensional galloping. Utilizing this criterion, the susceptibility to galloping instability of a number of contact wire cross-sections was assessed. The analysis showed that a galloping oscillation can only be induced in a cross-wind when the wire is worn and the flow approaches the wire at an angle of between 7 and 14° to the horizontal. This analysis suggested an explanation for the large-scale oscillations experienced by catenary wires on elevated railway tracks in exposed positions, where the close proximity of the embankment to the wire generates large angles of attack in the flow field around the contact wire.

Design optimisation of a regenerative pump using numerical and experimental techniques

Purpose – Regenerative pumps are the subject of increased interest in industry as these pumps are low‐cost, low‐specific speed, compact and able to deliver high heads with stable performance characteristics. However, these pumps have a low efficiency (35‐50 per cent). The complex flow field within the pumps represents a considerable challenge to detailed mathematical modelling. Better understanding of the flow field would result in improvement of the pump efficiency. The purpose of this paper is to consider a numerical and experimental analysis of a regenerative pump to simulate the flow field and math pump performance.Design/methodology/approach – This paper outlines the use of a commercial computational fluid dynamics (CFD) code to simulate the flow field within the regenerative pump and compare the CFD results with new experimental data. A novel rapid manufacturing process is used to consider the effect of impeller geometry changes on the pump efficiency.Findings – The CFD results demonstrate that it i...

A one-dimensional numerical model for the momentum exchange in regenerative pumps

The regenerative pump is a rotor-dynamic turbomachine capable of developing high heads at low flow rates and low specific speeds. In spite of their low efficiency, usually less than 50 %, they have found a wide range of applications as compact single-stage pumps with other beneficial features. The potential of a modified regenerative pump design is presented for consideration of the performance improvements. In this paper the fluid dynamic behaviour of the novel design was predicted using a one-dimensional model developed by the authors. Unlike most one-dimensional models previously published for regenerative pumps, the momentum exchange is computed numerically. Previous one-dimensional models relied on experimental data and correction factors; the model presented in this paper demonstrates accurate prediction of the pump performance characteristics without the need for correction with experimental data. The validity of this approach is highlighted by the comparison of computed and measured results for two different regenerative pump standards. The pump performance is assessed numerically without the need of correction factors or other experimental data. This paper presents an approach for regenerative pumps using a physically valid geometry model and by resolving the circulatory velocity in peripheral direction.

A computational fluid dynamics model to evaluate the inlet stroke performance of a positive displacement reciprocating plunger pump

A computational fluid dynamics model of the middle chamber of a triplex positive displacement reciprocating pump is presented to assess the feasibility of a transient numerical method to investigate the performance of the pump throughout the 180° of crank rotation of the inlet stroke. The paper also investigates, by means of computational fluid dynamics, the pressure drop occurring in the pump chamber during the first part of the inlet stroke in order to gain a better understanding of the mechanisms leading to cavitation. The model includes the compressibility of the working fluid and the lift of the inlet valve as a function of the pressure field on the inlet valve surfaces. It also takes into account the valve spring preload in the overall balance of forces moving the valve. Simulation of the valve motion was achieved by providing the solver with two user-defined functions. The plunger lift–time history was defined by the crank diameter and connecting rod length. This paper will demonstrate the feasibility and reasonable accuracy of the method adopted by comparison with experimental data.

An experimental and numerical investigation of natural convection melting

The melting of a vertical ice cylinder in water is investigated in this paper. The experiments were carried out in a water-filled cylindrical Perspex barrel with adiabatic walls for Rayleigh numbers of 0.22x108 and 0.475x108. The ice crystal is suspended in the water and experimental images of the natural convection melting process were obtained using both shadowgraphy and particle image velocimetry (PIV) techniques. This data is compared with a numerical model which attempts to capture the melt-front on a fixed computational grid. The numerical model takes into account the density inversion effects in the water. The results show the applicability of PIV to this type of flow and demonstrate a simple numerical model to effectively resolve the melting phenomenon.

The development of a three-dimensional imaging system and its application in computer aided design workstations

This paper details the application of a three dimensional imaging system known as planar contour imaging (PCI) to the presentation of images created by computer aided design (CAD) software. The three dimensional computational models were generated within a commercially available CAD/CAM software package from Delcam plc and then converted to stereo lithographic (.stl) format. The .stl file was then converted into a real, three dimensional, image by PCI. It was found that, in the same way that a user looks at a two dimensional image, the selection of the correct type and amount of data presented to the viewer was critical. However, when the image was refined, the three dimensional image was found to produce an impressive representation of the computational dataset.

An advanced CFD model to study the effect of non-condensable gas on cavitation in positive displacement pumps

Abstract An advanced transient CFD model of a positive displacement reciprocating pump was created to study its behavior and performance in cavitating condition during the inlet stroke. The “full” cavitation model developed by Singhal et al. was utilized, and a sensitivity analysis test on two air mass fraction amounts (1.5 and 15 parts per million) was carried out to study the influence of the dissolved air content in water on the cavitation phenomenon. The model was equipped with user defined functions to introduce the liquid compressibility, which stabilizes the simulation, and to handle the two-way coupling between the pressure field and the inlet valve lift history. Estimation of the performance is also presented in both cases.