A numerical analysis of buoyancy-driven melting and freezing

A numerical investigation of transient natural convective heat transfer with coupled phase change is presented. The numerical model attempts to capture the solid-fluid interface using a fixed-grid solution and is applied to two pure substance cases found in published literature, one considering the melting of 95% pure Lauric acid and the other involving the freezing of water. The governing equations are solved in a manner such that if the temperature falls below the freezing isotherm then the convection terms in the equations of motion are effectively disengaged. Variations in the specific heat of the material are incorporated in order to account for the phase change. A non-Boussinesq approach is considered which accounts for any density extrema in the flow, particularly for the density inversion found in water. In both of the cases considered the phase change occurs between fixed temperature boundaries and Rayleigh numbers rest well within the laminar flow regime. From the results obtained it is demonstrated that a relatively simple numerical technique can be applied to capture the physics of buoyancy-driven melting and freezing and that the results are in reasonable concurrence with experimental data

A novel method for the provision of flight experience and flight testing for undergraduate aeronautical engineers at the University of Strathclyde

The Department of Mechanical Engineering at the University of Strathclyde has developed a novel flight experience/test course for undergraduate Aeronautical Engineers. In common with similar courses at undergraduate level the course contains practical instruction in how an aircraft is flown, an analysis of its stall characteristics and an assessment of an aircraft's performance and stability. However, uniquely, the Strathclyde course consists of dual instructional flights in two seat gliders. This paper contains a detailed description of the flight experience/test course developed at Strathclyde and its incorporation into the undergraduate curriculum. A critical analysis of its delivery is also presented

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

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

Comparison of the computed flow field around a bubble growing at an orifice using PIV techniques

For bubbles growing rapidly at orifices, the inertia of the liquid displacement and the resultant liquid flow field contribute to the production of an inertia force which tends to retard bubble movement. It is therefore the purpose of this paper to report on a study to examine the validity of liquid velocity fields predicted by potential flow methods and measurements made using Particle Image Velocimetry (PIV) techniques. Air bubbles are generated in water at atmospheric conditions from a 1 mm diameter orifice. The process is transient and occurs over a period of approximately 80 msecs. Therefore a combination of high speed video techniques and PIV image processing has been used to determine the liquid velocity vector fields during the bubble growth, detachment and translation periods. This paper will present a summary of the experimental techniques and the theoretical model and discuss the results of the study

Design optimisation of a regenerative pump using numerical and experimental techniques

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. The complex flow-field within the pump represents a considerable challenge to detailed mathematical modelling. This paper outlines the use of a commercial 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. The CFD results demonstrate that it is possible to represent the helical flow field for the pump which has only been witnessed in experimental flow visualisation until now. The CFD performance results also demonstrate reasonable agreement with the experimental tests. The ability to use CFD modelling in conjunction with rapid manufacturing techniques has meant that more complex impeller geometry configurations can now be assessed with better understanding of the flow-field and resulting efficiency

A PIV and CFD analysis of natural convection ice 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

Development of a regenerative pump impeller using rapid manufacturing techniques

This paper presents a method of rapid manufacture used in the development of a regenerative pump impeller. Rapid manufacturing technology was used to create complex impeller blade profiles for testing as part of a regenerative pump optimisation process. Regenerative pumps are the subject of increased interest in industry. Ten modified impeller blade profiles, relative to the standard radial configuration, were evaluated with the use of computational fluid dynamics and experimental testing. Prototype impellers were needed for experimental validation of the CFD results. The manufacture of the complex blade profiles, using conventional milling techniques, is a considerable challenge for skilled machinists. The complexity of the modified blade profiles would normally necessitate the use of expensive CNC machining with 5 asis capability. With an impeller less than 75mm in diameter and a maximum blade thickness of 1.3mm, a rapid manufacturing technique enabled production of complex blade profiles that were dimensionally accurate and structurally robust enough for testing. As more advanced rapid prototyping machines become available in the study in the future, e.g. 3D photopolymer jetting machine, the quality of the parts, particularly in terms of surface finish, will improve and the amount of post processing operations will reduce. This technique offers the possibility to produce components of increased complexity whilst ensuring quality, strength, performance and speed of manufacture. The ability to manufacture complex blade profiles that are robust enough for testing, in a rapid and cost effective manner is proving essential in the overall design optimisation process for the pump

Numerical and experimental design study of a regenerative pump

This paper presents the use of a commercial CFD code to simulate the flow-field within the regenerative pump and compare the CFD results with new experimental data. 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. The complex flow-field within the regenerative pump represents a considerable challenge to detailed mathematical modelling. This paper also presents a novel rapid manufacturing process used to consider the effect of impeller geometry changes on the pump efficiency. Ten modified impeller blade profiles, relative to a standard radial configuration, were evaluated. The CFD performance results demonstrate reasonable agreement with the experimental tests. The CFD results also demonstrate that it is possible to represent the helical flow field for the pump which has been witnessed only in experimental flow visualisation until now. The ability to use CFD modelling in conjunction with rapid manufacturing techniques has meant that more complex impeller geometry configurations can now be assessed with better understanding of the flow-field and resulting efficiency

Design study of a novel regenerative pump using experimental and numerical techniques

This paper presents a numerical and experimental analysis of a new regenerative pump design. The complex flow-field within regenerative pumps represents a significant challenge to previous published mathematical models. The new pump design incorporates a new axial inlet and outlet port. The experimental and numerical results demonstrate that it is not only possible to resolve the flowfield for this pump type but also demonstrates this pump as a viable alternative to other kinetic rotodynamic machines. The use of the latest rapid manufacturing techniques have enabled the production of the complex geometry of the axial ports required for the new configuration

Sessile water droplets on insulating surfaces subject to high AC stress effect of contact angle

Surface pollution of outdoor high-voltage insulators is an important cause of flashover. We have undertaken an experimental study of electrical breakdown at the edges of a sessile water droplet on a planar, polymeric, insulating surface when subject to AC stress, parallel to the insulator surface, up to 2MV/m. The static contact angle between droplet and surface was varied by controlling the physical properties of the droplet and by inclining the insulator plane from the horizontal. The partial discharge activity from the water droplet was investigated using a combination of high-speed video camera, operated at up to 3,000 frames per second, and an electrical partial discharge detection system. We have used this to examine the location of partial discharge at the edges of the water droplet