The effect of shroud extensibility on the vibrational characteristics of turbine blade packets.

The thesis presents a comprehensive study of the vibrational characteristics of turbine blade packet systems. A number of turbine blade packet systems are considered although the discussion is essentially restricted to those packets where the binding is made by a shroud capping the tip of the blades. A theoretical system is chosen for investigation which has one more variable than the most complex system used by previous investigators. Using this additional variable, the extensibility of the shroud, a set of transcendental characteristic equations is evolved and put into a form suitable for numerical solution. In the process of this development it is shown that the characteristic values depend on four parameters of which the number of blades in the packet is independent of the other three parameters. Using these parameters the behaviour of the characteristic values is investigated over a range exceeding the ranges of equivalent commercial blades. The results of these calculations are compared with results obtained from experimental tests on actual blade packet systems. These comparisons show in certain cases good agreement and in other cases almost no agreement with the predicted values. It is concluded that the variation in agreement between the theoretical and the experimental results is due to two factors dependent on the placing in the parameter space. One is the inadequacy of the theory where the shroud is massive and flexible and the other is the lack of a suitable specimen manufacturing technique