Loading Distribution Effects on Separated Flow Transition of Ultra-High-Lift Turbine Blades

2014 ◽  
Vol 30 (3) ◽  
pp. 845-856 ◽  
Author(s):  
F. Satta ◽  
D. Simoni ◽  
M. Ubaldi ◽  
P. Zunino ◽  
F. Bertini
Keyword(s):  
Turbine Blades ◽  
Separated Flow ◽  
Flow Transition ◽  
High Lift

Aerodynamic Performance of a Very High Lift Low Pressure Turbine Airfoil (T106C) at Low Reynolds and High Mach Number With Effect of Free Stream Turbulence Intensity

2012 ◽  
Vol 134 (6) ◽  
Author(s):  
Jan Michálek ◽  
Michelangelo Monaldi ◽  
Tony Arts
Keyword(s):  
Mach Number ◽  
Turbulence Intensity ◽  
Free Stream ◽  
Separated Flow ◽  
Aerodynamic Performance ◽  
Flow Transition ◽  
High Lift ◽  
Free Stream Turbulence ◽  
Low Pressure Turbine ◽  
Very High

A detailed experimental analysis of the effects of the Reynolds number and free-stream turbulence intensity on the aerodynamic performance of a very high-lift, mid-loaded low-pressure turbine blade (T106C) is presented in this paper. The study was carried out on a large scale linear cascade in the VKI S1/C high-speed wind tunnel, operating at high exit Mach number (0.65) with a range of low Reynolds numbers (80,000–160,000) and three levels of free-stream turbulence intensity (0.8–3.2%). In the first part of the paper, the overall aerodynamic performance of the airfoil is presented, based on mid-span measurements performed by means of static pressure taps, hot-film sensors and a five-hole probe traversing downstream of the cascade. Some specific features of separated flow transition are also discussed for selected cases. The second part presents the analysis of the results in terms of correlations derived for the characteristic points of boundary layer separation and transition. A comparison with some previously published prediction models is shown. The large variety of boundary conditions provides a unique database for validating codes dealing with separated flow transition in turbomachinery.

Effects of Surface Groove on Separated Flow Transition on a High-Lift Low-Pressure Turbine Profile Under Steady Inflow Conditions

2009 ◽  
Author(s):  
Hualing Luo ◽  
Weiyang Qiao ◽  
Kaifu Xu
Keyword(s):  
Boundary Layer ◽  
Separated Flow ◽  
Low Pressure ◽  
Separation Point ◽  
Flow Transition ◽  
Suction Surface ◽  
High Lift ◽  
Low Pressure Turbine ◽  
Surface Groove ◽  
Inflow Conditions

LES (Large-Eddy Simulation) computations for a high-lift low-pressure turbine profile equipped with the span-wise groove on the suction surface are done to investigate the mechanism of the surface groove for separated flow transition control under steady inflow conditions, employing the dynamic Smagorinsky model. In addition to the baseline case (no groove), three groove positions which depend on the relative position of the groove trailing edge and the separation point on the suction surface are considered at two Reynolds numbers (Re, based on the inlet velocity and axial chord length). The results show that all grooves can reduce the calculated loss for Re = 50000, due to the further upstream transition inception in the separated shear layer. The analyses indicate two kinds of control mechanism such as the thinning of boundary layer behind the groove and the introduction of disturbances within the groove, depending on the groove position and Reynolds number. At Re = 50000, for the groove located upstream of the separation point, the reason for the further upstream transition inception location is the thinning of boundary layer behind the groove, and for the groove located downstream of the separation point, the reason is the introduction of disturbances within the groove. At Re = 100000, disturbances can also be generated within the groove located upstream of the separation point, promoting earlier transition inception.

Effects of Periodic Unsteadiness, Free-Stream Turbulence, and Flow Reynolds Number on Separation-Bubble Transition

2003 ◽  
Author(s):  
S. K. Roberts ◽  
M. I. Yaras
Keyword(s):  
Reynolds Number ◽  
Free Stream ◽  
Separation Bubble ◽  
Turbine Blades ◽  
Separated Flow ◽  
Suction Side ◽  
Streamwise Velocity ◽  
Flow Transition ◽  
Free Stream Turbulence ◽  
Flow Reynolds Number

This paper presents measurements of the combined effects of free-stream turbulence and periodic streamwise velocity variations on separation-bubble transition. The measurements were performed on a flat plate at two values of flow Reynolds number, with a streamwise pressure distribution similar to those encountered on the suction side of axial turbine blades. The experiment was designed to facilitate independent control of turbulence and periodic velocity fluctuations in the free-stream. The free-stream turbulence intensity was varied from 0.4% to 4.5%, and the periodic unsteadiness corresponded to Strouhal numbers of 0.0, 2.4 and 4.0. Based on the results, the relative importance of free-stream turbulence and periodic unsteadiness on the streamwise locations of separation, transition and reattachment points are quantified. Existing mathematical models for predicting separated-flow transition and reattachment are then evaluated in this context.

Aerodynamic Performance of a Very High Lift Low Pressure Turbine Airfoil (T106C) at Low Reynolds and High Mach Number With Effect of Free Stream Turbulence Intensity

2010 ◽  
Author(s):  
Jan Micha´lek ◽  
Michelangelo Monaldi ◽  
Tony Arts
Keyword(s):  
Mach Number ◽  
Turbulence Intensity ◽  
Free Stream ◽  
Separated Flow ◽  
Aerodynamic Performance ◽  
Flow Transition ◽  
High Lift ◽  
Free Stream Turbulence ◽  
Low Pressure Turbine ◽  
Very High

A detailed experimental analysis of the effects of the Reynolds number and free-stream turbulence intensity on the aerodynamic performance of a very high-lift, mid-loaded low-pressure turbine blade (T106C) is presented in this paper. The study was carried out on a large scale linear cascade in the VKI S1/C high-speed wind tunnel, operating at high exit Mach number (0.65) with a range of low Reynolds numbers (80,000–160,000) and three levels of free-stream turbulence intensity (0.8–3.2%). In the first part of the paper, the overall aerodynamic performance of the airfoil is presented, based on mid-span measurements performed by means of static pressure taps, hot-film sensors and a 5-hole probe traversing downstream of the cascade. Some specific features of separated flow transition are also discussed for selected cases. The second part presents the analysis of the results in terms of correlations derived for the characteristic points of boundary layer separation and transition. A comparison with some previously published prediction models is shown. The large variety of boundary conditions provides a unique database for validating codes dealing with separated flow transition in turbomachinery.

An Experimental Investigation of the Separated-Flow Transition Under High-Lift Turbine Blade Pressure Gradients

2011 ◽  
Vol 88 (1-2) ◽  
pp. 45-62 ◽  
Author(s):  
Daniele Simoni ◽  
Marina Ubaldi ◽  
Pietro Zunino ◽  
Davide Lengani ◽  
Francesco Bertini
Keyword(s):  
Experimental Investigation ◽  
Turbine Blade ◽  
Separated Flow ◽  
Flow Transition ◽  
Pressure Gradients ◽  
High Lift

scholarly journals Numerical analysis of high-lift configurations with oscillating flaps

2021 ◽  
Author(s):  
Johannes Ruhland ◽  
Christian Breitsamter
Keyword(s):  
Reynolds Number ◽  
Flow Separation ◽  
Separated Flow ◽  
Navier Stokes ◽  
Rotational Axis ◽  
High Lift ◽  
Hinge Point ◽  
Reduced Frequency ◽  
Flap Deflection ◽  
The Impact

AbstractThis study presents two-dimensional aerodynamic investigations of various high-lift configuration settings concerning the deflection angles of droop nose, spoiler and flap in the context of enhancing the high-lift performance by dynamic flap movement. The investigations highlight the impact of a periodically oscillating trailing edge flap on lift, drag and flow separation of the high-lift configuration by numerical simulations. The computations are conducted with regard to the variation of the parameters reduced frequency and the position of the rotational axis. The numerical flow simulations are conducted on a block-structured grid using Reynolds Averaged Navier Stokes simulations employing the shear stress transport $$k-\omega $$ k - ω turbulence model. The feature Dynamic Mesh Motion implements the motion of the oscillating flap. Regarding low-speed wind tunnel testing for a Reynolds number of $$0.5 \times 10^{6}$$ 0.5 × 10 6 the flap movement around a dropped hinge point, which is located outside the flap, offers benefits with regard to additional lift and delayed flow separation at the flap compared to a flap movement around a hinge point, which is located at 15 % of the flap chord length. Flow separation can be suppressed beyond the maximum static flap deflection angle. By means of an oscillating flap around the dropped hinge point, it is possible to reattach a separated flow at the flap and to keep it attached further on. For a Reynolds number of $$20 \times 10^6$$ 20 × 10 6 , reflecting full scale flight conditions, additional lift is generated for both rotational axis positions.

Redesign of High-Lift LP-Turbine Airfoils for Low Speed Testing

2010 ◽  
Author(s):  
Michele Marconcini ◽  
Filippo Rubechini ◽  
Roberto Pacciani ◽  
Andrea Arnone ◽  
Francesco Bertini
Keyword(s):  
Separated Flow ◽  
Low Pressure ◽  
High Lift ◽  
Low Speed ◽  
Low Pressure Turbine ◽  
Wide Range ◽  
Flow Configurations ◽  
Artificial Neural Network Ann ◽  
Lp Turbine ◽  
Turbine Airfoils

Low pressure turbine airfoils of the present generation usually operate at subsonic conditions, with exit Mach numbers of about 0.6. To reduce the costs of experimental programs it can be convenient to carry out measurements in low speed tunnels in order to determine the cascades performance. Generally speaking, low speed tests are usually carried out on airfoils with modified shape, in order to compensate for the effects of compressibility. A scaling procedure for high-lift, low pressure turbine airfoils to be studied in low speed conditions is presented and discussed. The proposed procedure is based on the matching of a prescribed blade load distribution between the low speed airfoil and the actual one. Such a requirement is fulfilled via an Artificial Neural Network (ANN) methodology and a detailed parameterization of the airfoil. A RANS solver is used to guide the redesign process. The comparison between high and low speed profiles is carried out, over a wide range of Reynolds numbers, by using a novel three-equation, transition-sensitive, turbulence model. Such a model is based on the coupling of an additional transport equation for the so-called laminar kinetic energy (LKE) with the Wilcox k–ω model and it has proven to be effective for transitional, separated-flow configurations of high-lift cascade flows.

scholarly journals On the prospects of improving the numerical analysis of symmetric airfoils at low Reynolds numbers and high angles of attack by a LES approach: the case of NACA0021 profile

2020 ◽  
Vol 197 ◽  
pp. 08015
Author(s):  
Simone Giaccherini ◽  
Filippo Mariotti ◽  
Lorenzo Pinelli ◽  
Michele Marconcini ◽  
Alessandro Bianchini
Keyword(s):  
Turbine Blades ◽  
Separated Flow ◽  
Reynolds Numbers ◽  
Aerodynamic Performance ◽  
Operating Conditions ◽  
High Fidelity ◽  
Complex Flow ◽  
Energy Applications ◽  
Low Reynolds ◽  
High Angles Of Attack

The working conditions of airfoils along modern wind turbine blades are putting new focus on the importance of properly characterizing the aerodynamic performance of different airfoil families also at high angles of attack (AoAs) beyond stall and at Reynolds numbers much lower (from few thousands to one million) than those commonly analyzed before. Several test cases are showing that even higher-order computational methods (like RANS/URANS CFD) are unable to properly capture the complex flow physics taking place past the blades, when deep stall occurs or when the AoA changes so rapidly to provoke the onset of dynamic stall. To fill this gap, the use of high-fidelity methods, like the Large Eddy Simulation (LES) is proposed, even though it implies a massive increase of the calculation cost. In order to analyze the prospects of using LES in comparison to RANS for low Reynolds, high AoAs, this work presents an in-depth study of the NACA 0021 aerodynamics at the Reynolds number of 80,000, by means of both traditional RANS approaches and high-fidelity (LES) simulations using the OpenFOAM suite. The selected airfoil has been showing in fact several issues in the correct characterization of its performance in similar conditions in many recent wind energy applications. The LES approach showed the ability to overcome the limitations of traditional RANS simulations, improving the accuracy of the results and reducing their dispersion thanks to the fact that the flow structures in the separated-flow regions are properly captured. Overall, this work underlines that accurate investigations of the aerodynamic performance of the NACA 0021 at low Reynolds require multiple sensitivity studies when RANS approaches are used, and suggests the use of LES simulations in order to increase the accuracy of estimations, especially when studying the stalledflow operating conditions of the airfoil.

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