Leading-Edge Surface-Manipulated Flow Separation from an Airfoil

2008 ◽  
Vol 45 (6) ◽  
pp. 2171-2173 ◽  
Author(s):  
Hong J. Zhang ◽  
Yu Zhou
Keyword(s):  
Flow Separation ◽  
Leading Edge ◽  
Edge Surface

Leading Edge Surface Pressures from Airfoils in a Turbulent Flow

2004 ◽  
Author(s):  
Jonathan L. Gershfeld ◽  
Thomas C. Mathews
Keyword(s):  
Turbulent Flow ◽  
Leading Edge ◽  
Edge Surface

scholarly journals Flow past a square-section cylinder with a wavy stagnation face

2001 ◽  
Vol 426 ◽  
pp. 263-295 ◽  
Author(s):  
RUPAD M. DAREKAR ◽  
SPENCER J. SHERWIN
Keyword(s):  
Reynolds Number ◽  
Cross Flow ◽  
Leading Edge ◽  
Reynolds Numbers ◽  
Physical Structure ◽  
Near Wake ◽  
Hairpin Vortices ◽  
Independent State ◽  
Flow Past ◽  
Edge Surface

Numerical investigations have been performed for the flow past square-section cylinders with a spanwise geometric deformation leading to a stagnation face with a sinusoidal waviness. The computations were performed using a spectral/hp element solver over a range of Reynolds numbers from 10 to 150.Starting from fully developed shedding past a straight cylinder at a Reynolds number of 100, a sufficiently high waviness is impulsively introduced resulting in the stabilization of the near wake to a time-independent state. It is shown that the spanwise waviness sets up a cross-flow within the growing boundary layer on the leading-edge surface thereby generating streamwise and vertical components of vorticity. These additional components of vorticity appear in regions close to the inflection points of the wavy stagnation face where the spanwise vorticity is weakened. This redistribution of vorticity leads to the breakdown of the unsteady and staggered Kármán vortex wake into a steady and symmetric near-wake structure. The steady nature of the near wake is associated with a reduction in total drag of about 16% at a Reynolds number of 100 compared with the straight, non-wavy cylinder.Further increases in the amplitude of the waviness lead to the emergence of hairpin vortices from the near-wake region. This wake topology has similarities to the wake of a sphere at low Reynolds numbers. The physical structure of the wake due to the variation of the amplitude of the waviness is identified with five distinct regimes. Furthermore, the introduction of a waviness at a wavelength close to the mode A wavelength and the primary wavelength of the straight square-section cylinder leads to the suppression of the Kármán street at a minimal waviness amplitude.

scholarly journals Flow Separation Control of Backward-Facing Step Airfoil NACA0015 by Blowing Technique

2019 ◽  
Vol 12 (1) ◽  
pp. 99-119
Author(s):  
Khuder N. Abed
Keyword(s):  
Flow Separation ◽  
Numerical Study ◽  
Leading Edge ◽  
Distribution Coefficients ◽  
Open Circuit ◽  
Experimental Investigations ◽  
Backward Facing Step ◽  
Ansys Fluent ◽  
Flow Separation Control ◽  
Naca 0015

The aim of this paper is to control the flow separation above backward-facing step (BFS) airfoil type NACA 0015 by blowing method. The flow field over airfoil has been studied both experimentally and computationally. The study was divided into two parts: a practical study through which NACA 0015 type with a backward -facing step (located at 44.4% c from leading edge) on the upper surface containing blowing holes parallel to the airfoil chord was used. The tests were done over two-dimensional airfoil in an open circuit suction subsonic wind tunnel with flow velocity 25m/s to obtain the pressure distribution coefficients. A numerical study was done by using ANSYS Fluent software version 16.0 on three models of NACA 0015, the first one has backward-facing step without blowing, the second with single blowing holes and the third have multi blowing holes technique. Both studies (experimental and numerical) were done at low Reynolds number (Re=4.4x105) and all models have chord length 0.27m.The experimental investigations and CFD simulations have been performed on the same geometry dimensions, it has been observed that the flow separation on the airfoil can be delayed by using  velocity blowing (30m/s) on the upper surface. The multi blowing holes with velocity improved the aerodynamics properties.The multi blowing holes and single blowing hole thesame effect onpressure distribution coefficients

Study of three types of wave leading edge on the performance of industrial turbine blade cascade

2020 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Hamed Ghandi ◽  
Reza Aghaei Togh ◽  
Abolghasem Mesgarpoor Tousi
Keyword(s):  
Turbine Blade ◽  
Flow Separation ◽  
Numerical Solutions ◽  
Incidence Angle ◽  
Leading Edge ◽  
Content Type ◽  
Passive Flow Control ◽  
Passive Flow ◽  
Geometrical Features ◽  
Control Methodology

Purpose The blade profile and its geometrical features play an important role in the separation of the boundary layer on the blade. Modifying the blade geometry, which might lead to the delay or elimination of the flow separation, can be considered as a passive flow control methodology. This study aims to find a novel and inexpensive way to reduce loss with appropriate modifications on the leading edge of the turbine blade. Design/methodology/approach Three types of wave leading edges were designed with different wavelengths and amplitudes. The selected numbers for the wave characteristics were based on the best results of previous studies. Models with appropriate and independent meshing have been simulated and studied by a commercial software. The distribution of the loss at different planes and mid-plane velocity vectors were shown. The mass flow average of loss at different incidence angles was calculated for the reference blade and modified ones for the sake of comparison. Findings The results show that in all three types of modified blades compared to the reference blade, the elimination of flow separation is observed and therefore the reduction of loss at the critical incidence angle of I = –15°. As the amplitude of the wave increased, the amount of loss growing up, while the increase in wavelength caused the loss to decrease. Originality/value The results of the present numerical analysis were validated by the laboratory results of the reference blade. The experimental study of modified blades can be used to quantify numerical solutions.

scholarly journals Numerical Simulation of the Anti-Icing Performance of Electric Heaters for Icing on the NACA 0012 Airfoil

Aerospace ◽  
2020 ◽  
Vol 7 (9) ◽  
pp. 123
Author(s):  
Sho Uranai ◽  
Koji Fukudome ◽  
Hiroya Mamori ◽  
Naoya Fukushima ◽  
Makoto Yamamoto
Keyword(s):  
Numerical Simulation ◽  
Lift Coefficient ◽  
Heating Surface ◽  
Leading Edge ◽  
Simulation Method ◽  
Chord Length ◽  
Ice Accretion ◽  
Suction Surface ◽  
Edge Surface ◽  
Naca 0012

Ice accretion is a phenomenon whereby super-cooled water droplets impinge and accrete on wall surfaces. It is well known that the icing may cause severe accidents via the deformation of airfoil shape and the shedding of the growing adhered ice. To prevent ice accretion, electro-thermal heaters have recently been implemented as a de- and anti-icing device for aircraft wings. In this study, an icing simulation method for a two-dimensional airfoil with a heating surface was developed by modifying the extended Messinger model. The main modification is the computation of heat transfer from the airfoil wall and the run-back water temperature achieved by the heater. A numerical simulation is conducted based on an Euler–Lagrange method: a flow field around the airfoil is computed by an Eulerian method and droplet trajectories are computed by a Lagrangian method. The wall temperature distribution was validated by experiment. The results of the numerical and practical experiments were in reasonable agreement. The ice shape and aerodynamic performance of a NACA 0012 airfoil with a heater on the leading-edge surface were computed. The heating area changed from 1% to 10% of the chord length with a four-degree angle of attack. The simulation results reveal that the lift coefficient varies significantly with the heating area: when the heating area was 1.0% of the chord length, the lift coefficient was improved by up to 15%, owing to the flow separation instigated by the ice edge; increasing the heating area, the lift coefficient deteriorated, because the suction peak on the suction surface was attenuated by the ice formed. When the heating area exceeded 4.0% of the chord length, the lift coefficient recovered by up to 4%, because the large ice near the heater vanished. In contrast, the drag coefficient gradually decreased as the heating area increased. The present simulation method using the modified extended Messinger model is more suitable for de-icing simulations of both rime and glaze ice conditions, because it reproduces the thin ice layer formed behind the heater due to the runback phenomenon.

Investigations of the Flow Through a High Pressure Ratio Centrifugal Impeller

2002 ◽  
Author(s):  
Gernot Eisenlohr ◽  
Hartmut Krain ◽  
Franz-Arno Richter ◽  
Valentin Tiede
Keyword(s):  
High Pressure ◽  
Flow Separation ◽  
Pressure Ratio ◽  
Leading Edge ◽  
Centrifugal Impeller ◽  
Angle Distribution ◽  
Blade Angle ◽  
Minor Variation ◽  
Design Point ◽  
High Pressure Ratio

In an industrial research project of German and Swiss Turbo Compressor manufacturers a high pressure ratio centrifugal impeller was designed and investigated. Performance measurements and extensive laser measurements (L2F) of the flow field upstream, along the blade passage and downstream of the impeller have been carried out. In addition to that, 3D calculations have been performed, mainly for the design point. Results have been presented by Krain et al., 1995 and 1998, Eisenlohr et al., 1998 and Hah et al.,1999. During the design period of this impeller a radial blade at the inlet region was mandatory to avoid a rub at the shroud due to stress reasons. The measurements and the 3D calculations performed later, however, showed a flow separation at the hub near the leading edge due to too high incidence. Additionally a rather large exit width and a high shroud curvature near the exit caused a flow separation near the exit, which is enlarged by the radially transported wake of the already addressed hub separation. Changes to the hub blade angle distribution to reduce the hub incidence and an adaptation of the shroud blade angle distribution for the same impeller mass-flow at the design point were investigated by means of 3D calculations first with the same contours at hub and shroud; this was followed by calculations with a major change of the shroud contour including an exit width change with a minor variation of the hub contour. These calculations showed encouraging results; some of them will be presented in conjunction with the geometry data of the original impeller design.

Film Cooling on Highly Loaded Blades With Main Flow Separation—Part I: Heat Transfer

2012 ◽  
Vol 135 (1) ◽  
Author(s):  
Reinaldo A. Gomes ◽  
Reinhard Niehuis
Keyword(s):  
Heat Transfer ◽  
Flow Separation ◽  
Film Cooling ◽  
Separation Bubble ◽  
Leading Edge ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Main Flow ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness

Film cooling experiments were run at the high speed cascade wind tunnel of the University of the Federal Armed Forces Munich. The investigations were carried out with a linear cascade of highly loaded turbine blades. The main objectives of the tests were to assess the film cooling effectiveness and the heat transfer in zones with main flow separation. Therefore, the blades were designed to force the flow to detach on the pressure side shortly downstream of the leading edge and reattach at about half of the axial chord. In this zone, film cooling rows are placed among others for a reduction of the size of the separation bubble. The analyzed region on the blade is critical due to the high heat transfer present at the leading edge and at the reattachment line after the main flow separation. Film cooling can contribute to a reduction of the size of the separation bubble reducing aerodynamic losses, however, in general, it increases heat transfer due to turbulent mixing. The reduction of the size of the separation bubble might also be twofold, since it acts like a thermal insulator on the blade and reducing the size of the bubble might lead to a stronger heating of the blade. Film cooling should, therefore, take both into account: first, a proper protection of the surface and second, reducing aerodynamic losses, diminishing the extension of the main flow separation. While experimental results of the adiabatic film cooling effectiveness were shown in previous publications, the local heat transfer is analyzed in this paper. Emphasis is also placed upon analyzing, in detail, the flow separation process. Furthermore, the tests comprise the analysis of the effect of different outlet Mach and Reynolds numbers and film cooling. In part two of this paper, the overall film cooling effectiveness is addressed. Local heat transfer is still difficult to predict with modern numerical tools and this is especially true for complex flows with flow separation. Some numerical results with the Reynolds averaged Navier-Stokes (RANS) and large eddy simulation (LES) show the capability of a commercial solver in predicting the heat transfer.

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