Calculation of High-Lift Cascades in Low Pressure Turbine Conditions Using a Three-Equation Model

2010 ◽  
Vol 133 (3) ◽  
Author(s):  
Roberto Pacciani ◽  
Michele Marconcini ◽  
Atabak Fadai-Ghotbi ◽  
Sylvain Lardeau ◽  
Michael A. Leschziner
Keyword(s):  
Reynolds Number ◽  
Kinetic Energy ◽  
Eddy Viscosity ◽  
Low Reynolds Number ◽  
Low Pressure ◽  
Equation Model ◽  
Bypass Transition ◽  
High Lift ◽  
Wide Range ◽  
Low Reynolds

A three-equation model has been applied to the prediction of separation-induced transition in high-lift low-Reynolds-number cascade flows. Classical turbulence models fail to predict accurately laminar separation and turbulent reattachment, and usually overpredict the separation length, the main reason for this being the slow rise of the turbulent kinetic energy in the early stage of the separation process. The proposed approach is based on solving an additional transport equation for the so-called laminar kinetic energy, which allows the increase in the nonturbulent fluctuations in the pretransitional and transitional region to be taken into account. The model is derived from that of Lardeau et al. (2004, “Modelling Bypass Transition With Low-Reynolds-Number Non-Linear Eddy-Viscosity Closure,” Flow, Turbul. Combust., 73, pp. 49–76), which was originally formulated to predict bypass transition for attached flows, subject to a wide range of freestream turbulence intensity. A new production term is proposed, based on the mean shear and a laminar eddy-viscosity concept. After a validation of the model for a flat-plate boundary layer, subjected to an adverse pressure gradient, the T106 and T2 cascades, recently tested at the von Kármán Institute, are selected as test cases to assess the ability of the model to predict the flow around high-lift cascades in conditions representative of those in low-pressure turbines. Good agreement with experimental data, in terms of blade-load distributions, separation onset, reattachment locations, and losses, is found over a wide range of Reynolds-number values.

Calculations of High-Lift Cascades in Low Pressure Turbine Conditions Using a Three-Equation Model

2009 ◽  
Author(s):  
Roberto Pacciani ◽  
Michele Marconcini ◽  
Atabak Fadai-Ghotbi ◽  
Sylvain Lardeau ◽  
Michael A. Leschziner
Keyword(s):  
Reynolds Number ◽  
Kinetic Energy ◽  
Low Pressure ◽  
Equation Model ◽  
Transitional Region ◽  
Bypass Transition ◽  
High Lift ◽  
Production Term ◽  
Free Stream Turbulence ◽  
Wide Range

A three-equation model has been applied to the prediction of separation-induced transition in high-lift low-Reynolds-number cascade flows. Classical turbulence models fail to predict accurately laminar separation and turbulent reattachment, and usually over-predict the separation length, the main reason for this being the slow rise of the turbulent kinetic energy in the early stage of the separation process. The proposed approach is based on solving an additional transport equation for the so-called laminar kinetic energy, which allows the increase of the non-turbulent fluctuations in the pre-transitional and transitional region to be taken into account. The model is derived from that of Lardeau and Leschziner, which was originally formulated to predict bypass transition for attached flows, subject to a wide range of free-stream turbulence intensity. A new production term is proposed, based on the mean shear and a laminar eddy-viscosity concept. After a validation of the model for a flat-plate boundary layer, subjected to an adverse pressure gradient, the T106 and T2 cascades, recently tested at the von Ka´rma´n Institute, are selected as test cases to assess the ability of the model to predict the flow around high-lift cascades in conditions representative of those in low-pressure turbines. Good agreement with experimental data, in terms of blade-load distributions, separation onset, reattachment locations and losses, is found over a wide range of Reynolds-number values.

scholarly journals An assessment of the laminar kinetic energy concept for the prediction of high-lift, low-Reynolds number cascade flows

2011 ◽  
Vol 225 (7) ◽  
pp. 995-1003 ◽  
Author(s):  
R Pacciani ◽  
M Marconcini ◽  
A Arnone ◽  
F Bertini
Keyword(s):  
Reynolds Number ◽  
Kinetic Energy ◽  
High Speed ◽  
Low Reynolds Number ◽  
Flow Region ◽  
Freestream Turbulence ◽  
High Lift ◽  
Numerical Predictions ◽  
Wide Range ◽  
Low Reynolds

The laminar kinetic energy (LKE) concept has been applied to the prediction of low-Reynolds number flows, characterized by separation-induced transition, in high-lift airfoil cascades for aeronautical low-pressure turbine applications. The LKE transport equation has been coupled with the low-Reynolds number formulation of the Wilcox's k − ω turbulence model. The proposed methodology has been assessed against two high-lift cascade configurations, characterized by different loading distributions and suction-side diffusion rates, and tested over a wide range of Reynolds numbers. The aft-loaded T106C cascade is studied in both high- and low-speed conditions for several expansion ratios and inlet freestream turbulence values. The front-loaded T108 cascade is analysed in high-speed, low-freestream turbulence conditions. Numerical predictions with steady inflow conditions are compared to measurements carried out by the von Kármán Institute and the University of Cambridge. Results obtained with the proposed model show its ability to predict the evolution of the separated flow region, including bubble-bursting phenomenon and the formation of open separations, in high-lift, low-Reynolds number cascade flows.

Low Pressure Turbine Lapse Rate Study: CFD Model vs. Rig Data

2002 ◽  
Author(s):  
J.-S. Liu ◽  
M. L. Celestina ◽  
G. B. Heitland ◽  
D. B. Bush ◽  
M. L. Mansour ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Flow Field ◽  
Fluid Dynamic ◽  
Low Reynolds Number ◽  
Low Pressure ◽  
Lapse Rate ◽  
Bypass Transition ◽  
Blade Row ◽  
Low Reynolds ◽  
Lp Turbine

As an aircraft engine operates from sea level take-off (SLTO) to altitude cruise, the low pressure (LP) turbine Reynolds number decreases. As Reynolds number is reduced the condition of the airfoil boundary layer shifts from bypass transition to separated flow transition. This can result in a significant loss. The LP turbine performance fall-off from SLTO to altitude cruise, due to the loss increase with reduction in Reynolds number, is referred to as a lapse rate. A considerable amount of research in recent years has been focused on understanding and reducing the loss associated with the low Reynolds number operation. A recent 3-1/2 stage LP turbine design completed a component rig test program at Honeywell. The turbine rig test included Reynolds number variation from SLTO to altitude cruise conditions. While the rig test provides detailed inlet and exit condition measurements, the individual blade row effects are not available. Multi-blade row computational fluid dynamics (CFD) analysis is used to complement the rig data by providing detailed flow field information through each blade row. A multi-blade row APNASA model was developed and solutions were obtained at the SLTO and altitude cruise rig conditions. The APNASA model predicts the SLTO to altitude lapse rate within 0.2 point compared to the rig data. The global agreement verifies the modeling approach and provides a high confidence level in the blade row flow field predictions. Additional Reynolds number investigation with APNASA will provide guidance in the LP turbine Reynolds number research areas to reduce lapse rate. To accurately predict the low Reynolds number flow in the LP turbine is a challenging task for any computational fluid dynamic (CFD) code. The purpose of this study is to evaluate the capability of a CFD code, APNASA, to predict the sensitivity of the Reynolds number in LP turbines.

Computational Analysis of a High-Lift and Low Reynolds Number Airfoil at Turbulent Atmospheric Conditions

2009 ◽  
Author(s):  
Mazharul Islam ◽  
M. Ruhul Amin ◽  
Yasir M. Shariff
Keyword(s):  
Reynolds Number ◽  
Wind Turbines ◽  
Turbulence Intensity ◽  
Computational Analysis ◽  
Low Reynolds Number ◽  
Experimental Results ◽  
High Lift ◽  
Wide Range ◽  
Low Reynolds ◽  
Low Reynolds Number Airfoil

Selection of airfoil is crucial for better aerodynamic performance and design of aerodynamic applications such as wind turbine and aircrafts. In this paper, a high-lift and low-Reynolds number airfoil has been selected and investigated through computational analysis for applying it for small-sized wind turbines as blades. The S1223 airfoil, designed by the University of Illinois at Urbana-Champaign, was chosen for its high-lift characteristics at low Reynolds number typically encountered by the small wind turbines. CFD work is performed with S1223 airfoil profile over a wide range of conditions of interest to analyze the performance of the airfoil using the Spalart-Allmaras turbulence model. The results obtained from the simulation works have been compared with experimental data for validation purpose. It has been found that the Spalart-Allmaras model conforms well with the experimental results, though the values of lift coefficients (Cl) are slightly less than the experimental results. In the present analysis, velocity distributions are analyzed at different angle of attacks for different turbulence intensities. It has been observed that there is vortex shedding around the trailing edge of the airfoil for both turbulence levels. It has been observed in the present study that due to increase in turbulence intensity, both the maximum lift coefficient and the stall angle increases significantly. It has been found after investigating the effect of turbulence intensity over lift-to-drag coefficient ratio that it drastically decreases due to increase in turbulence intensity up to certain value (about 3.5%), then it starts decreasing in gradual manner.

Effects of periodic wakes on the endwall secondary flow in high-lift low-pressure turbine cascades at low Reynolds numbers

2017 ◽  
Vol 233 (1) ◽  
pp. 354-368 ◽  
Author(s):  
Xiao Qu ◽  
Yanfeng Zhang ◽  
Xingen Lu ◽  
Ge Han ◽  
Ziliang Li ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Secondary Flow ◽  
Low Reynolds Number ◽  
Reynolds Numbers ◽  
Low Pressure ◽  
High Lift ◽  
Low Pressure Turbine ◽  
Low Reynolds ◽  
High Reynolds

Periodic wakes affect not only the surface boundary layer characteristics of low-pressure turbine blades and profile losses but also the vortex structures of the secondary flow and the corresponding losses. Thus, understanding the physical mechanisms of unsteady interactions and the potential to eliminate secondary losses is becoming increasingly important for improving the performance of high-lift low-pressure turbines. However, few studies have focused on the unsteady interaction mechanism between periodic wakes and endwall secondary flow in low-pressure turbines. This paper verified the accuracy of computational fluid dynamics by comparing experimental results and those of the numerical predictions by taking a high-lift low-pressure turbine cascade as the research object. Discussion was focused on the interaction mechanisms between the upstream wakes and secondary flow within the high-lift low-pressure turbine. The results indicated that upstream wakes have both positive and negative effects on the endwall flow, where the periodic wakes can decrease significantly the size of the separation bubble, prevent the formation of secondary vorticity structures at relatively high Reynolds numbers (100,000 and 150,000), and reduce the cross-passage pressure gradient of cascade. In addition, periodic wakes can improve the cascade incidence characteristic in terms of reducing the overturning and underturning of the secondary flow at downstream of the cascade all of which are beneficial for decreasing the endwall secondary losses, whereas more endwall boundary layer is involved in the main flow passage due to the wake transport, resulting in increased strength of the secondary flow at low Reynolds number of 25,000 and 50,000. Compared with the results without wakes, the total pressure loss for unsteady condition at the cascade exit decreases by 2.7% and 6.1% at high Reynolds number of 100,000 and 150,000, respectively. However, the secondary loss at unsteady flow conditions increases at low Reynolds number of 25,000 and 50,000.

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