Showing papers by "Terrence W. Simon published in 2005"

Flow Measurements in a First Stage Nozzle Cascade Having Endwall Contouring, Leakage, and Assembly Features

Abstract: This work supports new gas turbine designs for improved performance by evaluating the use of endwall contouring in a cascade that is representative of a first stage stator passage. Contouring accelerates the flow, reducing the thickness of the endwall inlet boundary layer to the turbine stage and reducing the strength of secondary flows within the passage. Reduction in secondary flows leads to less mixing in the endwall region. This allows improved cooling of the endwall and airfoil surfaces with injected and leakage flows. The present paper documents component misalignment and leakage flow effects on the aerodynamic losses within a passage having one contoured and one straight endwall. Steps on the endwall and leakage flows through the endwall can lead to thicker endwall boundary layers, stronger secondary flows and possibly additional vortex structures in the passage. The paper compares losses with steps of various geometries and leakage of various flow rates to assess their importance on aerodynamic losses in this contoured passage. In particular, features associated with the combustor-to-turbine transition piece and the slashface gap, a gap between two vane segments on the vane platform, are addressed. An n-factorial study is used to quantify the importance of such effects on aerodynamic losses.Copyright © 2005 by ASME

Heat transfer measurements in a first stage nozzle cascade having endwall contouring, leakage and assembly features

Abstract: This work supports new gas turbine designs for improved performance by evaluating sealing flow effects in a cascade representative of a contoured first stage stator passage. Contouring accelerates the flow, reducing the thickness of the endwall inlet boundary layer to the turbine stage and reducing the strength of secondary flows within the passage. Injected flows, used to seal gaps and cool surfaces, may affect endwall boundary layers, increase secondary flows and possibly create additional vortex structures in the passage. The present paper documents injected flow effects on the endwall heat transfer within a passage with one contoured and one straight endwall. The paper discusses heat transfer distributions measured with different leakage flow rates. In particular, leakage is from the gap between the combustor and turbine sections and from the gap at the assembly joint on the vane platform between two vanes.© 2005 ASME

CFD for Jet Impingement Heat Transfer With Single Jets and Arrays

Abstract: CFD experiments were conducted for heat transfer with jet impingement over solid surfaces. The parameters include: 1) Jet Reynolds number from 3,000 to 23,000, 2) Jet-to-target-plate spacing (z/d), from 2 to 14 (single jet), d is jet diameter, 3) Target plate shape: 3a) flat, 3b) concave, 3c) convex, (single jet), 4) One row of seven jets impinging on a flat surface, the channel has one end closed (at 24d away from the most upstream jet axis), 5) Three rows of seven jets each in-line arrangement impinging on a flat surface, the channel has one end closed (at 24d away from the most upstream jet axis). Four CFD models (utilizing FLUENT commercial code) have been considered: 1) laminar flow (no turbulent transport), and turbulent flow with turbulence modeling by 2) the standard k–e model, 3) the k–ω model, and 4) the v2 –f model. The predictions of Nu number for each case were compared with experimental data available from the literature. It is shown that the v2 –f model gives the best overall performance, though the k–ω model gives good predictions for most of the flow, with the exception of near the stagnation zone for some cases. The models are in much better agreement (with the data) as z/d grows and at larger radial locations from the jet axis, as expected. For multiple jets in one row (z/d = 2), again the v2 –f showed the best overall agreement with the experimental data. The k–ω model is not as good while k–e clearly overpredicts the Nusselt numbers. For multiple jets in three inline rows (z/d = 5), all the three models were in overall agreement with the experimental data. However, k–e and k–ω exhibit an important phenomenon, reported by the experiments: a decrease of the stagnation Nu from the upstream jet to the downstream ones. The v2 –f model did not reproduce this feature.Copyright © 2005 by ASME

Flow Measurements in a First Stage Nozzle Cascade Having Leakage and Assembly Features: Effects of Endwall Steps and Leakage on Aerodynamic Losses

Abstract: This work supports new gas turbine designs for improved performance by evaluating endwall leakage and assembly features in a cascade that is representative of a first stage stator passage. The present paper documents component misalignment and leakage flow effects on the aerodynamic losses within a passage having one contoured and one straight endwall. Steps on the endwall and leakage flows through the endwall can lead to thicker endwall boundary layers, stronger secondary flows and possibly additional vortex structures in the passage. The paper compares losses with steps of various geometries and leakage of various flow rates to assess their importance on aerodynamic losses in this contoured passage. In particular, features associated with the combustor-to-turbine transition piece and the slash-face gap, a gap between two vane segments on the vane platform, are addressed.Copyright © 2005 by ASME

Transition in Low-Pressure Turbines: Effects of Unsteady Acceleration and Turbulence Intensity

Abstract: Wakes generated by upstream airfoil rows create an unsteady flowfield to downstream rows of a low-pressure turbine. Pressure gradients and local turbulence intensity levels imposed on the airfoil surface boundary layers change as the wakes pass through the passage. Separation and laminar-to-turbulent transition onset locations and transition path characteristics also change during the wake passing cycle. The effects of unsteady acceleration (composed of spatial acceleration and temporal acceleration) and time variations in turbulence intensity on transition onset and transition path are described

Influence of Wake Passing Frequency and Elevated Turbulence Intensity on Transition.

Abstract: Experimental results from a study of the effects of passing wakes upon laminar-to-turbulent transition in a low-pressure turbine passage are presented. The test section simulates the effects of unsteady wakes resulting from rotor-stator interaction In turbine blade boundary layers and separated flow regions over suction surfaces. Single-wire thermal anemometry techniques are used to measure time-resolved and phase-averaged wall-normal profiles of streamwise velocity, turbulence intensity, and intermittency at multiple streamwise locations over the turbine airfoil suction surface. The Reynolds number based on suction surface length and stage exit velocity is 5 X 10 4 . This low Reynolds number would apply to small engines flying at high altitude