| Résumé: | <p>Active modulation of coolant flow rates would improve cycle efficiencies for jet engines. This thesis presents a proof of concept multistage fluidic device, the staged switched vortex valve (staged SVV), which modulates flow rates by switching between high and low flow impedance states. It is shown that the device can be actively switched between states using conventional mass flow injection and, with minimal modifications, 200 Hz acoustic tones.</p>
<p>A grey-box model of the staged switched vortex valve is developed as part of the investigation. This model encapsulates the complex fluid interactions associated with the vortex chamber and the diverter switch sections within black-box objects tuned with steady-state and transient characteristics. The model convincingly reproduces pressures and mass flow rates associated with steady conditions, switching events and self-excited oscillatory instabilities. Furthermore, the model can predict the conditions that will trigger switching and oscillatory instabilities.</p>
<p>The model is used in conjunction with the physical device to investigate the effects inter-stage duct impedances and sub-switching control signals can have on the stability and performance of the staged SVV. It is discovered that an appropriately sized inter-stage impedance can be used to improve the steady-state performance, with a localised constriction area ratio of 0.25 in one of the ducts affecting a 3.8% increase in the device’s turn-down ratio (TDR). However, the resulting increase in inter-stage pressure losses also makes the device more susceptible to self-excited oscillations. Sub-switching acoustic signals can also be used to improve steady-state performance. A 5.6% increase in the TDR is achieved by applying a 640 Hz acoustic tone to the unattached side of the pilot diverter section. Moreover, sub-acoustic tones can also be used to stabilise the staged SVV and suppress self-excited oscillations.</p>
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