Abstract:In this paper, we have investigated numerically the interaction between secondary flow and a normal compression shock in a transonic turbine cascade. We observe that the sudden deceleration caused by the compression shock triggers an instability in weaker regions of the vortex system. This instability forms a pattern of concentric rings of elevated vorticity, which, in turn, cause the shock to deform into the same concentric wave-like pattern. The same pattern appears in the entropy distribution just downstrea… Show more
“…Given the complex flow conditions at the trailing edge caused by unsteady trailing edge vortex shedding and subsequent interaction with shock structures this is difficult to predict computationally. 7 Supercritical loading is the fourth and final stage, with the trailing edge pressure surface shock completely departing the base pressure region and the flow within the passage becoming completely choked.Figure 1.Stages to limit loading: Terminology.…”
To better understand airfoil limit loading and the effect inflow conditions have on local efficiency, a computational fluid dynamic investigation was performed for four different transonic turbine airfoils under sub-critical, critical, and supercritical conditions. A computational baseline was established using data previously collected at the Pratt and Whitney Canada High-Speed Wind Tunnel at Carleton University near design conditions using the Reynolds-Averaged Naiver-Stokes shear stress transport k − ω turbulence model with γ transition. The effects of inflow conditions on aerodynamic performance were examined by varying incidence by ± 20°, mainstream turbulence intensity from 5 to 20% and mainstream turbulent length scale from 1 to 100% of the airfoil pitch. Quantitative data of mass-flow averaged Mach numbers, mass-flow averaged flow angles, surface isentropic Mach number distributions and mass-flow averaged total pressure loss coefficients were collected and are presented alongside flow visualizations of numerical Schlieren images to allow for a detailed description of the entire flow domain. Similar to previous experimental work the limit loading pressure ratio and the mass-flow averaged outlet flow angle were strongly correlated with the airfoil outlet metal angle. The influence of inflow conditions was minimal on the exit flow profile with the exception of the mass-flow averaged total pressure loss coefficients. Results show incidence variation to change the total pressure loss coefficient depending on the airfoil, whereas, turbulence intensity and turbulent length scale predicted a drastic increase in loss with increased turbulence level for all airfoils considered.
“…Given the complex flow conditions at the trailing edge caused by unsteady trailing edge vortex shedding and subsequent interaction with shock structures this is difficult to predict computationally. 7 Supercritical loading is the fourth and final stage, with the trailing edge pressure surface shock completely departing the base pressure region and the flow within the passage becoming completely choked.Figure 1.Stages to limit loading: Terminology.…”
To better understand airfoil limit loading and the effect inflow conditions have on local efficiency, a computational fluid dynamic investigation was performed for four different transonic turbine airfoils under sub-critical, critical, and supercritical conditions. A computational baseline was established using data previously collected at the Pratt and Whitney Canada High-Speed Wind Tunnel at Carleton University near design conditions using the Reynolds-Averaged Naiver-Stokes shear stress transport k − ω turbulence model with γ transition. The effects of inflow conditions on aerodynamic performance were examined by varying incidence by ± 20°, mainstream turbulence intensity from 5 to 20% and mainstream turbulent length scale from 1 to 100% of the airfoil pitch. Quantitative data of mass-flow averaged Mach numbers, mass-flow averaged flow angles, surface isentropic Mach number distributions and mass-flow averaged total pressure loss coefficients were collected and are presented alongside flow visualizations of numerical Schlieren images to allow for a detailed description of the entire flow domain. Similar to previous experimental work the limit loading pressure ratio and the mass-flow averaged outlet flow angle were strongly correlated with the airfoil outlet metal angle. The influence of inflow conditions was minimal on the exit flow profile with the exception of the mass-flow averaged total pressure loss coefficients. Results show incidence variation to change the total pressure loss coefficient depending on the airfoil, whereas, turbulence intensity and turbulent length scale predicted a drastic increase in loss with increased turbulence level for all airfoils considered.
“…The approach shown here is used to assess shock-wave vortex interaction in Mimic et al (2019) where it is found to produce similarly satisfactory results.…”
The aim of this work is the decomposition, quantification, and analysis of losses related to the axial gap size effect. Both experimental data and unsteady RANS calculations are investigated for axial gaps equal to 20 %, 50 % and 80 % of the stator axial chord. A framework for identifying sources of loss typical in turbomachinery is derived and utilized for the low-pressure turbine presented. The analysis focuses on the dependency of these losses on the axial-gap variation. It is found that two-dimensional profile losses increase for smaller gaps due to higher wake-mixing losses and unsteady wake-blade interaction. Losses in the end-wall regions, however, decrease for smaller gaps. The total system efficiency can be described by a superposition of individual loss contributions, the optimum of which is found for the smallest gap investigated. It is concluded that these loss contributions are characteristic for the medium aspect-ratio airfoils and operating conditions investigated. This establishes a deeper physical understanding for future investigations into the axial-gap size effect and its interdependency with other design parameters.
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