No description available.

No description available.

No description available.

No description available.

This thesis describes an experimental study of the transient heat transfer from both a free disc and a rotating cavity. Measured disc surface temperatures - from heating, cooling and quasi-steady tests - were used as boundary conditions for the solution of Fourier's conduction equation. The local and average Nusselt numbers were obtained from the computed temperature distribution, inside the disc, at each time-step. A finite element model was used to predict the thermocouple disturbance errors in the measured Nusselt numbers. The experimental technique was verified using a free disc, which comprised a 762 mm diameter, steel disc rotating in air at speeds of up to 3000 rev/min. For the free disc, the experimental results from the cooling tests were found to be less affected by thermocouple disturbance errors than those from the heating or quasi-steady tests. The measured Nusselt numbers from the cooling tests were in close agreement with established theoretical correlations. The rotating cavity comprised two steel discs, 762 mm in diameter, separated by an axial distance of 102 mm, and bounded at the circumference by an outer shroud. The cavity was supplied with a radial outflow of air, with a maximum flow rate of 0.6 kg/s, and rotated at speeds of up to 2000 rev/min. In some tests, known as the 0.1 radius ratio tests, air entered the cavity axially, through a central inlet pipe of 38.1 mm radius. In other tests, known as the 0.5 radius ratio tests, air entered the cavity axially, but a porous inner shroud was located inside the cavity at a radius of 190 mm. For the rotating cavity, flow visualisation showed the flow structure to consist of an inner source region, Ekman layers on each disc and an outer sink region. The size of the source region was found to depend on the radius ratio, and could be predicted by a simple theoretical model. For the 0.1 radius ratio tests, three regimes of heat transfer have been identified: the 'wall jet', the 'free disc' and the 'Ekman layer' regimes. The measured Nusselt numbers in those regimes were consistent with available experimental and theoretical expressions. For the 0.5 radius ratio tests, the wall jet and free disc regimes were not observed, and the heat transfer in the Ekman layers was found to be lower than for the 0.1 radius ratio cavity.

This thesis records an investigation into the flow and heat transfer occurring in a rapidly rotating cylindrical cavity, which forms a simple model of the space between two compressor discs in a gas turbine engine. The main effort has been directed towards the development and application of a computer program for the solution of the governing equations. In addition, analytical solutions for laminar flow between two infinite rotating discs have also been derived, and some temperature data from a test engine have been analysed to obtain estimates of the rate of convective heat transfer. The computer program, which is based on a standard finite difference technique for the calculation of recirculating two-dimensional flow, incorporates two novel features. Step changes in grid size have been employed to economise on the total number of grid points required, and the solution for the pressure field is given special treatment in order to obtain convergence of the iterative method at-high rotational speeds. Laminar flow predictions are presented for radial throughflow and for the buoyancy-induced recirculation in a sealed'cavity. Comparisons with experimental and analytical results confirm the accuracy of the numerical work, and the additional information that is available from the numerical solutions has given a-useful insight into the nature of the flow. Numerical results for turbulent flow in a rotating cavity, obtained using a two equation model of turbulence, did not agree with experimental measurements. Subsequent attempts to reproduce other workers' numerical predictions for the flow between a rotating and a stationary disc, and the flow caused by a disc rotating in an infinite environment, also failed to produce agreement.

The thesis is part of a wider study of turbulent natural convection in cavities undertaken by the U.K. Atomic Energy Authority, to provide experimental data for the verification of computer codes needed in the design of Fast Breeder Reactors. The objectives of the present work were to design and construct a large rectangular air cavity in order to measure distributions of temperature, velocity and local heat transfer rates within the cavity. The cavity was designed to operate with eitherisothermal hot and cold walls, or a uniform heat flux hot wall and an isothermal cold wall. These walls were 3m high and liii wide and the distance between them (cavity thickness) was adjustable between .i.m and .5m. The horizontal and vertical side walls were as nearly adiabatic as possible. Temperature and velocity profiles were measured, at different heights in the vertical mid-plane, with 25j.un diameter themocouples and standard DISA hot-wire anemometer probes respectively. These measurements were for isothermal walls and cavity thickness of .5m. The low velocities and large temperature variations of the flow required a special low speed jet to be designed and constructed for calibrating the hot wires. The calibrations were for velocities up to l.Om/s at temperatures between ambient and 70°C with the flow direction set vertically upwards for the probe used near the hot wall and downwards for the probe used near the cold wall. The experimental data were recorded in digital form on magnetic tapes, using a PDP/ll based data logging system. Statistical analysis of these measurements, involving the local heat transfer rates, mean and standard deviation of temperatures and velocities, frequency spectra, etc. were later carried out on the QMC ICL 2980 computer. The data are compared with results from other experiments including some with a variety of different working fluids, and with the predictions of available computer codes.

No description available.

This thesis describes a combined theoretical and experimental study of the fluid dynamics and heat transfer in a rotating cylindrical c~vity. Experimental results were obtained using a cavity comprising two discs of 762mm diameter, separated by an axial gap up to 152mm, and a peripheral shroud. The cavity was rotated up to 2200 rev/min and cooling air was used, in either an axial throughflow or a radial outflow mode, to cool the heated downstream disc of the cavity. Flow visualisation r~vealed the presence of vortex breakdown for the axial throughflow case and revealed four regimes of flow in the radial outflow case. LDA measurements, made during radial outflow, compared well with the results predicted from approximate solutions of the laminar and turbulent boundary layer equations. For the axial throughflow case, a number of heat transfer tests were conducted with different inlet and outlet conditions and some correlations were obtained for the mean Nusselt numbers. For the radial outflow case, four regimes of heat transfer were identified, and correlations of the mean Nusselt numbers were obtained for each regime. In particular, the results for regime II (the 'Ekman layer regime')agreed closely with the approximate boundary layer model, and the results for regime IV (the 'free convection regime') were consistent with those obtained for the axial throughflow case

No description available.