The research work covered by this thesis includes a series of semi-empirical investigations, associated with certain aerodynamic aspects of the design of multi-purpose mine shafts; it was carried out mainly by model studies, in a 1:12 scale special purpose wind tunnel, designed and constructed for the purpose.
The first part of the programme involved a project investigation for the sponsoring company (Mount Isa Mines Limited). Alternative shaft configurations, employing various shapes and degrees of streamlining of buntons, were tested. The last test yielded a result representing a reduction of 59 per cent of the drag resistance offered by standard bluff rolled steel joist shapes, in a somewhat similar configuration. This result shows the value of narrowing and of streamlining of buntons in the design of new shafts.
In another investigation, various arrangements of brattice partitions were tested. These yielded results of pragmatic interest. One anomalous result demanded serious enquiry; this anomaly was checked by another method, and then investigated by the use of interference (or splitter) plates. A possible solution was found, showing that, where interference plates are used (resembling a thin brattice partition), they should be "bounded" or "fenced".
The investigation with interference plates showed that some of the results achieved were at variance with those of previous workers. For instance, a wake splitter plate (a), used in conjunction with a streamlined body, was increasingly effective as the length was increased (even beyond the recognized downstream distance of five diameters); and (b), used in connection with a bluff body, had no effect within five diameters, but was progressively effective beyond this general distance.
A further interesting result (for which a provisional patent has been applied) showed that an interference plate, mounted in front of a bluff body, significantly reduced the drag, whether or not a wake splitter plate (of effective length) was also used. This approach arose from an intensive study of the observed action of a thin brattice partition in a model shaft. It is suggested that such a forward splitter plate tends to maintain laminar conditions in the boundary layer, thereby delaying separation (or reducing the "ferocity" of separation) and reducing drag- As would be expected, a forwards splitter plate is of no value when used with streamlined bodies. This set of results should be of particular advantage to mining companies seeking to reduce the resistance of existing shafts equipped with bluff buntons.
The programme also included the compilation of drag coefficients (as observed in the wind tunnel) of some regular standard shapes (for control purposes) and of shapes of particular use in mine shaft design.
Arising from these experiments, the results of some further observations were recorded, as under:
(a) for specimens of the same frontal shape and width, an increase in length (in the direction of airflow) resulted in lower aerodynamic drag;
(b) for semi-streamlined specimens, halved transversely and artificially restored to their original full length by an interference plate, an even lower value of drag coefficient was obtained; this did not occur with bluff specimens;
(c) where two (or more) similar specimens were placed in the air stream in line, the overall value of drag was reduced, thereby indicating that the second was shielded from the dynamic pressure of the air stream by the preceding specimen; this reduction in drag led to a measure of the shielding factor;
(d) the shielding effect diminished as the spacing interval increased, until, at a certain point, it became negligible; and
(e) the drag coefficient per specimen was reduced, and the shielding factor was increased, as the number of specimens in an assembly was increased, at various spacing intervals.
The above set of results should contribute to a deeper understanding of some of the parameters involved in the design of mine hoisting shafts.
Finally, the use of the Bromilow formula was validated (by reference to shaft model tests, and observed values of drag coefficient), as an effective approximate- method of predicting shaft resistance, in any hypothetical array of shaft furniture, within certain prescribed limitations, as a basis for the (preliminary) design of mine hoisting shafts.