Performance of choked unsteady ejector-nozzles for use in pressure-gain combustors

If the conventional steady flow combustor of a gas turbine is replaced with a device which achieves a pressure gain during the combustion process then the thermal efficiency of the cycle is raised. All such 'Pressure Gain Combustors' (e.g. PDEs, pulse combustors or wave rotors) are inherently unsteady flow devices. For such a device to be practically installed in a gas turbine it is necessary to design a downstream row of turbine vanes which will both accept the combustors unsteady exit flow and deliver a flow which the turbine rotor can accept. The design requirements of such a vane are that its exit flow both retains the maximum time-mean stagnation pressure gain (the pressure gain produced by the combustor is not lost) and minimises the amplitude of unsteadiness (reduces unsteadiness entering the downstream rotor). In this paper the exit of the pressure gain combustor is simulated with a cold unsteady jet. The first stage vane is simulated by a one-dimensional choked ejector nozzle with no turning. The time-mean and rms stagnation pressure at nozzle exit is measured. A number of geometric configurations are investigated and it is shown that the optimal geometry both maximizes time mean stagnation pressure gain (75% of that in the exit of the unsteady jet) and minimizes the amplitude of unsteadiness (1/3 of that in the primary jet). The structure of the unsteady flow within the ejector nozzle is determined computationally. Copyright © 2009 by J Heffer and R Miller.

A transonic vane for use downstream of a pressure gain combustor

Replacing a conventional combustor in a gas turbine with one that produces a pressure gain could significantly raise cycle efficiency. For this efficiency gain to be achieved the exit flow from the combustor must be coupled to the downstream turbine such that the pressure gain produced by the combustor is retained and such that the turbine efficiency is maintained. The exit flow from a pressure gain combustor will often contain a high velocity unsteady jet. It has previously been proposed that ejectors should be used to harness the energy in the unsteady jet, this paper proposes combining an ejector with the first stage vane, producing a single compact component that preserves the combustion driven pressure gain and delivers a suitable flow to the turbine so that its efficiency is not compromised. This novel component has been experimentally tested for the first time. The performance of this first prototype design is found to be low due to high levels of loss generated by secondary flows. However possible mitigation strategies are discussed. It is shown that the unsteadiness at exit form the ejector-vane is reduced compared to the inlet flow. If a pulse combustor were incorporated into a gas turbine, it is unlikely that the level of unsteadiness experienced in a downstream rotor will be significantly larger that that due to the periodic passing of upstream wakes. Copyright © 2010 by Jonathan Heffer.

Mandrel peeling of a flexible laminate with a pressure-sensitive adhesive: Comparison of experiment with numerical analysis

Mandrel peel tests with mandrels or rollers of varying diameters have been carried out using Mylar backing of several thicknesses and a commercial synthetic acrylic adhesive. The results are critically compared with the numerical predictions of the peeling software package ICPeel. In addition, a finite element model of the mandrel peeling process has been completed which gives good agreement with experiment provided appropriate mechanical properties of adherend and adhesive are used which must include the effects of adherent constraint. The influence of the thickness of the backing is also considered and both experiment and analysis confirm that there is a backing thickness at which the peel force for a laminate of this sort will show a maximum. © 2010 Blackwell Publishing Ltd.