Robert Read

Flame Imaging of Gas-Turbine Relight

High-altitude relight inside a lean-direct-injection gas-turbine combustor is investigated experimentally by highspeed imaging. Realistic operating conditions are simulated in a ground-based test facility, with two conditions being studied: one inside and one outside the combustor ignition loop. The motion of hot gases during the early stages of relight is recorded using a high-speed camera. An algorithm is developed to track the flame movement and breakup, revealing important characteristics of the flame development process, including stabilization timescales, spatial trajectories, and typical velocities of hot gas motion. Although the observed patterns of ignition failure are in broad agreement with results from laboratory-scale studies, other aspects of relight behavior are not reproduced in laboratory experiments employing simplified flow geometries and operating conditions. For example, when the spark discharge occurs, the air velocity below the igniter in a real combustor is much less strongly correlated to ignition outcome than laboratory studies would suggest. Nevertheless, later flame development and stabilization are largely controlled by the cold flowfield, implying that the location of the igniter may, in the first instance, be selected based on the combustor cold flow. Copyright

Relight Imaging at Low Temperature, Low Pressure Conditions

High-altitude relight inside a lean, direct-injection, gas turbine combustor is investigated experimentally by high-speed imaging. Ignition testing is conducted at two operating conditions: a ‘safe’ point at which relight is possible, and an ‘unsafe’ condition where ignition is precluded by the large air mass flow rate. Image processing software has been developed to analyze the motion and breakup of the imaged flame. At the safe condition, the developing flame kernels are typically swept downstream and towards the fuel-injector center-line, before moving upstream. The comparatively large gas-phase velocity at the unsafe condition causes rapid disintegration of the ignition kernel. At neither condition does the size of the spark kernel determine ignition outcome. Good agreement is demonstrated between the measured spark-centroid velocity and CFD predictions of gas-phase velocity below the igniter tip.

An overset grid approach to linear wave-structure interaction

A finite-difference based approach to wave-structure interaction is reported that employs the overset approach to grid generation. A two-dimensional code that utilizes the Overture C++ library has been developed to solve the linear radiation problem for a floating body of arbitrary form. This software implementation has been validated by performing time-domain simulations to evaluate the dynamic forces applied to a half-submerged cylinder and a rectangular barge in response to a prescribed motion. A Gaussian displacement is used to introduce a range of wave frequencies, thereby allowing the measurement of the body response over the frequency range of interest. The radiation added-mass and damping coefficients of both bodies have been evaluated and compared to exact analytical solutions. The numerical and analytical results show good agreement when the modes of excitation and response are the same. The cross-coupled results are in qualitative agreement, but show some quantitative variations that may be related to slight differences in the fluid domain geometry. For both the cylinder and the barge, the effects of bottom slope on the coefficients are found to be minimal.Copyright

Planar Laser-Induced Fluorescence Fuel Imaging During Gas-Turbine Relight

This experimental study investigates the influence of fuel distribution on ignition outcome during high-altitude relight of a gas turbine. Planar laser-induced fluorescence is used to image fuel inside a lean direct-injection combustor under realistic conditions. A novel apparatus is developed to permit planar laser-induced fluorescence imaging, in which large quantities of poorly atomized fuel impinges on the internal surfaces of the combustor. Results reveal high variability in atomization quality. In the absence of flame, small droplets are confined to areas of recirculating flow, whereas large droplets impact on the walls. All fuel is introduced through a pilot air-blast atomizer close to the injector centerline. However, comparatively little fuel is apparent near the igniter tip because the outside swirlers of the fuel injector create a fast-moving stream of fuel-free air that flows directly below the upper combustor wall. The droplet size and fuel concentration in the main recirculation zone do not ...