Simon M. Fraser

STEREOSCOPIC DISPLAY USING A 1.2-M DIAMETER STRETCHABLE MEMBRANE MIRROR

A glasses-free stereoscopic display has been developed in which a large diameter concave Stretchable Membrane Mirror (SMM) is used both as a viewing screen and optical element. SMMs offer considerable advantages over traditional imaging optics in terms of reduced weight and cost, and are revolutionary in their ability to vary their radius of curvature to give a wide range of mirror f/Nos. This is achieved by controlling the magnitude of an applied pressure difference which acts over an edge clamped metallized polyester membrane, forming the basis of a SMM. A stereoscopic display has been developed in which a 1.2-m diameter SMM is membrane, forming the basis of a SMM. A stereoscopic display has been developed in which a 1.2-m diameter SMM is used. Stereo pairs are projected at the surface of the mirror and viewed through a pari of virtual viewing windows. Such a configuration minimizes light loss, giving a very bright image against the specular reflecting surface of the SMM. The image can be formed in front/on/behind the plane of the SMM, making both real and very large sized virtual images possible. Several formats ranging form simple stereo photographs to live stereo video feed in a telepresence display have been viewed using this system.

The radial spread and axial decay of temperature in turbulent condensing jets

Radial and axial time-averaged temperature distributions in turbulent steam jets discharged into ambient air under unchoked/choked and saturated/superheated nozzle exit conditions have been measured with the aid of a fine thermocouple. Centreline decay and half-width spreading rates were calculated for these two-phase (liquid and vapour), two-fluid (air and water) jets and compared with data from the literature for non-condensing jets. Condensing jets exhibit higher spreading rates but much lower decay rates compared to non-condensing jets. A significant temperature increase due to condensation was observed. This increase in temperature became smaller with increased superheat and hence reduced condensation. Preliminary computational fluid dynamics (CFD) simulations were also performed using various simplifying assumptions.

Membrane-mirror-based display for viewing 2D and 3D images

Stretchable Membrane Mirrors (SMMs) have been developed at the University of Strathclyde as a cheap, lightweight and variable focal length alternative to conventional fixed- curvature glass based optics. A SMM uses a thin sheet of aluminized polyester film which is stretched over a specially shaped frame, forming an airtight cavity behind the membrane. Removal of air from that cavity causes the resulting air pressure difference to force the membrane back into a concave shape. Controlling the pressure difference acting over the membrane now controls the curvature or f/No. of the mirror. Mirrors from 0.15-m to 1.2-m in diameter have been constructed at the University of Strathclyde. The use of lenses and mirrors to project real images in space is perhaps one of the simplest forms of 3D display. When using conventional optics however, there are severe financial restrictions on what size of image forming element may be used, hence the appeal of a SMM. The mirrors have been used both as image forming elements and directional screens in volumetric, stereoscopic and large format simulator displays. It was found that the use of these specular reflecting surfaces greatly enhances the perceived image quality of the resulting magnified display.

Buoyancy-Induced Flow Through a Narrow Chamber Containing an Internal Heat Source: Comparison of Experimental Measurements and Numerical Simulations

Natural convection ventilation of a rectangular chamber containing a heated rectangular body has been investigated both experimentally and computationally. The heated square blockage within the partial enclosure was adjacent to the adiabatic lower surface of the chamber and the three exposed surfaces of the block were such as to give a constant heat flux. The air inlet and outlet were located at the bottom and top of the chamber vertical walls respectively, and were of equal area. Velocity measurements were performed using laser Doppler anemometry (LDA) with a one-component He–Ne laser connected to a burst spectrum analyser (BSA). Detailed velocity profiles were measured at the inlet, outlet and at several locations inside the chamber. Temperatures of the heated air at the outlet were measured with a chromel–alumel (type K) bare wire thermocouple probe. Three-dimensional laminar and turbulent (k–e model) numerical simulations were obtained by solving the governing equations using the computational fluid dynamics (CFD) code PHOENICS. Comparisons of experimental and computational results showed very good agreement in most of the flow field.

LDA measurements and numerical simulation of the induced flow through a rectangular chamber containing a vertical cylindrical heat source

Experimental (LDA) and computational (CFD) investigations of steady, laminar natural convection in a horizontally vented chamber containing a vertical heated cylinder at the center are reported. The heated cylinder was located on the lower adiabatic wall of the chamber and was 2/3 the height of the chamber. The cylinder surfaces were maintained at a constant temperature. The chamber inlet and outlet were located at the bottom and top of facing vertical walls, respectively. In this study, experiments were conducted using laser-Doppler anemometry (LDA) with a two-component Ar-Ion laser connected to two burst spectrum analyzers (BSA). Velocity profiles (of both vertical and horizontal velocity components) were measured at the inlet, outlet and at other locations inside the chamber. For the numerical simulation (3-D, steady-state, laminar) the governing equations were solved using the computational fluid dynamics code PHOENICS. Comparison of the experimental data with computational results showed satisfactory agreement and the importance that LDA measurements have in verifying CFD simulations.

Computational Fluid Dynamics Interface

Computational Fluid Dynamics (CFD) has made tremendous advances during the last twenty years due to the increasing speed and reducing cost of the computer hardware. The software has also been improved substantially with more user-friendly pre- and postprocessors and improved solvers. The major difference between solid mechanics and fluid mechanics, using either finite element or finite difference techniques, is that the equations for fluid mechanics are more difficult to represent by the above approximation techniques; in particular when there is no acknowledged equation to represent the fluid flow phenomenon, such as turbulence, the simulations require to be validated before a confidence level can be established. High quality data such as can be obtained with laser anemometry is required in order to validate CFD applications.

Interface between experimental data and CFD simulated data

Modern instruments such as laser anemometers connected to automatic traversing and data collection systems generate large amounts of data which can be difficult to interpret. An interface has been developed which makes use of existing commercial software to display the data in multi-dimensional vector format.

LDA measurements and CFD simulation of an annular impinging jet

Laser Doppler anemometry (LDA) is a useful experimental tool which is capable of providing high quality data for validating Computational Fluid Dynamic (CFD) simulations. Previous work with a mixed-flow pump had shown that there is a considerable discrepancy between the LDA data and the CFD simulation if the standard turbulence model is not modified to allow for the additional effect of the centrifugal action. Prior to the investigation of a cyclone separator in which the flow has a very high centrifugal action, it was decided to investigate a simpler flow consisting of an annular jet impinging on a flat plate in which the curvature of the jet can be controlled by the distance between the jet exit and the impinging plate. By comparing the results of LDA and simulation of the annular jet with different amounts of curvature it was expected that a transition level would be found at which a modified model would be required. The flow from an annular jet impinging on a plate can be simply analyzed in terms of the internal pressure which is generated by the rate of change of momentum due to the jet being turned through 90 degrees. However the detailed velocity distribution and variation of pressure across the jet cannot be obtained from simple analysis and require the use of a CFD code. The commercial code PHOENICS has been used in this investigation and the experimental data was obtained using a DANTEC single component fiber optic LDA system.