The Impact of Combustor Turbulence on Turbine Loss Mechanisms

Abstract

A blade row which is located downstream of a combustor has an extremely high turbulence intensity at inlet, typically above 10%. The peak turbulent length scale is also high, at around 20% of the chord of the downstream blade row. In a combustor, the turbulence is created by impinging jets in cross flow. This may result in the turbulence being anisotropic in nature. The aim of this paper is to investigate the effect of combustor turbulence on the loss mechanisms which occur in a turbine blade row. The paper has a number of important findings. The combustor turbulence is characterized and is shown to be isotropic in nature. It shows that, when no pressure gradient is present, combustor turbulence increases the loss of a turbulent boundary layer by 22%. The mechanism responsible for this change is shown to be a deep penetration of the turbulence into the boundary layer. It shows that the presence of combustor turbulence increases the profile loss and endwall loss in the turbine cascade studied by 37% and 47%, respectively. The presence of combustor turbulence also introduces a freestream loss resulting in the total loss of the turbine cascade rising by 47%. When these loss mechanisms were applied to the vane alone, of an engine representative high pressure turbine, it was found to result in a 1.3% reduction in stage efficiency.

Effect of inflow conditions on transonic turbine airfoil limit loading

“…Results show a direct correlation between inflow turbulence level and local mass-flow averaged total pressure loss coefficient. Similar to the experimental results of Folk, 21 increases in turbulence intensity caused an increase in roughly 20–40% of the mass-flow averaged total pressure loss coefficient. Interestingly, changes in turbulence intensity from 5 to 10% and turbulent length scale from 1 to 10% airfoil pitch show near identical significance.…”

“…For the case of increased turbulence intensity, there is a significant change in the predicted suction side wake profile as well as the high-pressure “shock” section of the mid-passage region for each airfoil, the pressure side remains relatively unchanged. As discussed by Folk, 21 this is a product of a change in shape factor for the suction surface boundary layer near the trailing edge. As inlet turbulence intensity is increased, the amount of turbulent penetration into the suction surface boundary layer is increased.…”

“…The flow within a turbine passage, specifically during ramping procedures experiences a wide range of both incidence and turbulence variation. 9 This is not included in these assumptions; therefore, it is unclear how these will affect the onset of choking or limit loading.…”

Turbulence Measurements Downstream of a Combustor Simulator Designed for Studies on the Combustor–Turbine Interaction

“…In the aforementioned papers, information about the turbulence of the flow at the turbine inlet was missing due to the mechanical constraints of the turbine rig that did not allow for the insertion of a hot wire, commonly considered the primary tool for such measurements. As found by previous authors [12][13][14], turbulence intensity impacts turbine loss mechanisms and increases heat transfer. Therefore, this is an important feature that has to be reproduced by combustor simulators.…”