Brian T. Bohan

Analysis of Flow Migration in an Ultra-Compact Combustor

The Ultra Compact Combustor (UCC) has the potential to offer improved thrust-to-weight and overall efficiency in a turbojet engine. The thrust-to-weight improvement is due to a reduction in engine weight by shortening the combustor section through the use of the revolutionary UCC design. The improved efficiency is achieved by using an increased fuel-to-air mass ratio, and allowing the fuel to fully combust prior to exiting the UCC system. Furthermore, g-loaded combustion offers increased flame speeds that can lead to smaller combustion volumes. The circumferential combustion of the fuel in the UCC cavity results in hot gases present at the outside diameter of the core flow. This orientation creates an issue in that the flow from the circumferential cavity needs to migrate radially and blend with the core flow to present a uniform temperature distribution to the high-pressure turbine rotor. A computational fluid dynamics (CFD) analysis is presented for the flow patterns in the combustor section of a representative fighter-scale engine. The analysis included a study of secondary flows, cavity flow characteristics, shear layer interactions and mixing properties. An initial understanding of primary factors that impact the radial migration is presented. Computational comparisons were also made between an engine realistic condition and an ambient pressure rig environment.

Impact of an Upstream Film-Cooling Row on Mitigation of Secondary Combustion in a Fuel Rich Environment

In advanced gas turbine engines that feature very short combustor sections, an issue of fuel-rich gases interacting with the downstream turbine components can exist. Specifically, in combustors with high fuel-to-air ratios, there are regions downstream of the primary combustion section that will require the use of film-cooling in the presence of incompletely reacted exhaust. Additional combustion reactions resulting from the combination of unburnt fuel and oxygen-rich cooling films can cause significant damage to the turbine. Research has been accomplished to understand this secondary reaction process. This experimental film-cooling study expands the previous investigations by attempting to reduce or mitigate the increase in heat flux that results from secondary combustion in the coolant film. Two different upstream cooling schemes were used to attempt to protect a downstream fan-shaped cooling row. The heat flux downstream was measured and compared between ejection with air compared to nitrogen in the form of a heat flux augmentation. Planar Laser Induced Fluorescence (PLIF) was used to measure relative OH concentration in the combustion zones to understand where the reactions occurred. A double row of staggered normal holes was unsuccessful at reducing the downstream heat load. The coolant separated from the surface generating a high mixing regime and allowed the hot unreacted gases to penetrate underneath the jets. Conversely, an upstream slot row was able to generate a spanwise film of coolant that buffered the reactive gases off the surface. Essentially no secondary reactions were observed aft of the shaped coolant hole ejection with the protective slot upstream. A slight increase in heat transfer was attributed to the elevated freestream temperature resulting from reactions above the slot coolant. Creating this full sheet of coolant will be a key toward future designs attempting to control secondary reactions in the turbine.

Impact of an Upstream Film-Cooling Row on Mitigation of Secondary Combustion in a High Fuel-Air Environment

In advanced gas turbine engines that feature very short combustor sections, an issue of fuel-rich gases interacting with downstream components exists. In all of these engines there are regions downstream of the primary combustion section that will require the use of film-cooling in the presence of incompletely reacted exhaust. This will lead to the possibility of additional combustion reactions resulting from the combination of unburnt fuel and oxygen-rich cooling films. Research has been accomplished to understand this secondary reaction process. This experimental film-cooling study expands the previous investigations by attempting to reduce or remove the negative effects that result from secondary combustion in the coolant film. An upstream row of holes was added to a row of previously tested shaped coolant holes to understand if the reactions could be mitigated at the downstream locations. Several combinations of cooling schemes were investigated and the heat flux downstream was measured. Planar Laser Induced Fluorescence (PLIF) was used to measure OH concentration in the combustion zones to understand where the reactions occurred. It was discovered that creating a full sheet of air upstream could effectively protect the downstream row from the negative impacts of the fuel-rich crossflow.© 2012 ASME