Mechanisms of surface pressure distribution within a laminar separation bubble at different Reynolds numbers

2015 ◽  
Vol 27 (2) ◽  
pp. 023602 ◽  
Author(s):  
Donghwi Lee ◽  
Soshi Kawai ◽  
Taku Nonomura ◽  
Masayuki Anyoji ◽  
Hikaru Aono ◽  
...  
Keyword(s):  
Pressure Distribution ◽  
Surface Pressure ◽  
Separation Bubble ◽  
Reynolds Numbers ◽  
Laminar Separation Bubble ◽  
Laminar Separation ◽  
Surface Pressure Distribution

Detailed Numerical Characterization of the Suction Side Laminar Separation Bubble for a High-Lift Low Pressure Turbine Blade by Means of RANS and LES

2016 ◽  
Author(s):  
Fabio Bigoni ◽  
Stefano Vagnoli ◽  
Tony Arts ◽  
Tom Verstraete
Keyword(s):  
Large Eddy Simulation ◽  
Separation Bubble ◽  
Suction Side ◽  
Reynolds Numbers ◽  
Laminar Separation Bubble ◽  
High Lift ◽  
Laminar Separation ◽  
Low Pressure Turbine ◽  
Eddy Simulation ◽  
Large Eddy

The scope of this work is to obtain a deep insight of the occurrence, development and evolution of the laminar separation bubble which occurs on the suction side of the high-lift T106-C low pressure turbine blade operated at correct engine Mach and Reynolds numbers. The commercial codes Numeca FINE/Turbo and FINE/Open were used for the numerical investigation of a set of three different Reynolds numbers. Two different CFD approaches, characterized by a progressively increasing level of complexity and detail in the solution, have been employed, starting from a steady state RANS analysis and ending with a Large Eddy Simulation. Particular attention was paid to the study of the open separation occurring at the lowest Reynolds number, for which a Large Eddy Simulation was performed in order to try to correctly capture the involved phenomena and their characteristic frequencies. In addition, the potentialities of the codes employed for the analysis have been assessed.

An Experimental Study of Perpendicular Acoustic Disturbances Effect on Flow Over an Aerofoil at Low Reynolds Numbers

2012 ◽  
Author(s):  
M. Serdar Genç ◽  
M. Tuğrul Akpolat ◽  
H. Hakan Açıkel ◽  
İlyas Karasu
Keyword(s):  
Wind Tunnel ◽  
Test Section ◽  
Separation Bubble ◽  
Reynolds Numbers ◽  
Acoustic Excitation ◽  
Laminar Separation Bubble ◽  
Laminar Separation ◽  
Low Reynolds Numbers ◽  
Acoustic Control ◽  
Maximum Coefficient

In this study, the effect of perpendicular acoustic excitation on laminar separation bubble over a NACA2415 aerofoil and stall characteristics of the aerofoil was investigated experimentally at low Reynolds numbers (50000 and 75000) and various angles of attack on the aerofoil using force measurement, pressure measurement and smoke-wire flow visualization techniques. The experiments of resonance characteristics of test section of the wind tunnel showed that the frequencies used for acoustic control were not equal to the peak (resonance) frequencies of the wind tunnel test section. The experimental results of acoustic control showed that when acoustic excitation of a certain frequency was applied, the length of the laminar separation bubble was shortened owing to the energy added to the flow by acoustic excitation. Because of the shortened laminar separation bubble, coefficient of lift was increased. Furthermore, at the stall angles the separated flow was forced to reattach to the surface of the aerofoil, so the stall angle was increased from 12° to 17° and maximum coefficient of lift was increased from 1.16 to 1.24 at Re = 50000 and from 13° to 18° and maximum coefficient of lift was increased from 1.18 to 1.34 at Re = 75000.

Investigation of laminar separation bubble over a supercritical airfoil in an incompressible flow

2021 ◽  
pp. 095440622110207
Author(s):  
Massoud Tatar ◽  
Mehran Masdari ◽  
Mojtaba Tahani
Keyword(s):  
Boundary Layer ◽  
Surface Pressure ◽  
Separation Bubble ◽  
Second Derivative ◽  
Laminar Separation Bubble ◽  
Laminar Separation ◽  
Supercritical Airfoil ◽  
Time Frequency ◽  
Transition Points ◽  
Hot Film

Supercritical airfoils have an unknown behavior at incompressible flow regime and Reynolds numbers lower than those related to their design point at transonic condition. In this work, boundary layer transition is studied over a supercritical airfoil by means of hot-film and pressure measurements completed with numerical simulations. The experiments are performed at chord-based Reynolds number of [Formula: see text]and Mach number of [Formula: see text] at different angles of attack. Hot-film measurement over the upper surface of the supercritical airfoil is carried out and the transition points are computed using the standard deviation of the signals. The upper surface pressure is also recorded and a peak in its second derivative is presented as the transition point generated by the laminar separation bubble mechanism. Moreover, an appropriate time-frequency analysis is applied to the hot-film signals to get an insight into the spectral content and development of the transitional boundary layer structures. On the other hand, two numerical codes are employed and the transition points obtained from numerical simulations are compared with the experimental outcomes. Results express a rapid change of the bubble position over the upper surface, as the angle of attack is increased to the value of [Formula: see text]. Laminar separation bubble is observed in the surface pressure distribution data and is well identified using its second derivative along the streamwise direction. The spectral characteristics of the boundary layer are satisfactorily explored including the streamwise fluctuations within the laminar flow, intermittent behavior of the transitional zone and the wide range of the spectrum in turbulent flow, thanks to the time-frequency analysis. A promising agreement is observed between the transition points computed by both the numerical and experimental studies and confirms the accuracy of findings achieved by the second derivative of surface pressure data, hot-film measurements and the reliability of the employed numerical transition models for optimization studies.

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