The world is becoming more dynamic and connected with ever increasing demands for air and road travel. Both are enabled by technologies such as gas turbines and internal combustion engines. To minimise the environmental impact requires improvements in the thermal efficiency of these technologies throughout their operating regimes. Here, we interpret this to mean the variation (or switching) of the relevant internal engine air flows, as an enabler for the engines to always be at the peak of their efficiency for the widely varying operating conditions. However, the difficulty arises from the fact that the air flow speeds are high (>200 m/s), air is both hot (600K+) and high pressure (20 bar+) and potentially requires high modulation rates (>200Hz).
In this research grant we have set out to develop the fundamental building blocks required to underpin more adaptable engines. These include:
Classically Switched Fluidic Valves
Fluidic valves are no-moving parts valves that utilise the Coanda effect for their operation. Conventional devices use a small proportion of control flow (<20%) to switch the main flow.
This diagram shows a sketch of the classical switched vortex valve (SVV) with the control ports in low resistance (radial) state. The device can be switched into high resistance (tangential state) by temporary injection of the transverse jet into the CR pot, or by the extraction of the main jet through the CT port.
Diagram showing the CFD of low loss (radial state).
Diagram showing the CFD of high loss (tangential state).
Example of a Perspex fluidic switch vortex valve.
Plasma Fluidic Valves
On this project, we have developed plasma controlled fluidic valves where the switching of the device states is obtained through the careful control of plasma in the entrainment region. This has the advantage that such devices can be used in hot high pressure environments such as those found in jet engines.
Examples of 4 times and 2 engine scale devices.
Piezo Fluidic Valves
Another class of devices developed under this grant utilises sound instead of sparks for switching. Examples of such devices are shown below.
Active Tip Leakage Control
Our advances in high momentum flux fluidic switching devices have raised the opportunity for no-moving parts actuation in turbines. This allows the application of cooling air to be optimised and introduced only where it controls the over-tip leakage flow. A potential increase in turbine row efficiency through the careful application of through-casing cooling air injection has been demonstrated using unsteady CFD.
Experimental testing of the switches to carry out injection from the casing is currently being undertaken in the Oxford Rotor Facility (ORF), a 60% scale, 1 ½ stage high pressure rig refurbished under this grant. Two downstream fast-response total pressure rakes produce pseudo-rotor relative total pressure maps, allowing the impact of the cooling air injection on aerodynamic loss to be directly observed. An innovative cassette-within-cassette design allows the cooling configuration to be changed without first removing the instrumentation. For the active modulation cases, ten switch packs permit active injection over a two blade passage sector, with an additional preceding two passages of passive blowing to establish the flow.
Steady air injection cassette.
Unsteady air injection cassette during assembly.
- Nicholls, C. and Bacic, M. “Closed loop control of a piezo-fluidic amplifier”, AIAA Aviation, Atlanta, USA, 25-29 June, 2018
- Tang B. M. T., Bacic M., and Ireland P. T., Effect of Active Modulation of Through-Casing Coolant Injection on Turbine Efficiency, in Proceedings of ASME Turbo Expo 2017: Turbomachinery Technical Conference and Exposition Volume 5B: Heat Transfer Charlotte, North Carolina, USA, June 26–30, 2017
- Mair M., Turner J., Bacic M., and Ireland P., Switching Dynamics of a Fluid Diverter Valve Using Ultrasonic Excitation for Active Flow Control, 47th AIAA Fluid Dynamics Conference, AIAA AVIATION Forum, Denver, Colorado (AIAA 2017-4309)
- Li-Wei Chen, James Turner, Marko Bacic, Peter Ireland (2016) “Experimental and Numerical Studies of a Plasma Fluidic Device for Active Flow Control,” 8th AIAA Flow Control Conference, Washington, D.C.