Comments on Milgram: “Calculation of Attached or Partially Separated Flow Around Airfoil Sections”

1978 ◽  
Vol 22 (01) ◽  
pp. 64-65
Author(s):  
Fabio R. Goldschmied
Keyword(s):  
Experimental Verification ◽  
A Priori ◽  
Separated Flow ◽  
Leading Edge ◽  
Suction Side ◽  
Separated Flows ◽  
Two Dimensional ◽  
The Subject ◽  
Edge Separation ◽  
Theoretical Results

The title paper presents a relatively unified potential flow theory for attached and partially separated (trailing-edge separation) two-dimensional, incompressible airfoil sections. The partially separated flows are characterized by nonreattaching flow separation from a point on the suction side of the airfoil downstream from the leading edge; it is required that the location of this separation point and the corresponding separation pressure be specified a priori. Figures 5 and 6 of the subject paper present the test data and the theoretical results for the NACA 63–018 airfoil at 15- and 18-deg angle of attack, respectively, as the only experimental verification for partially separated flows.

Three-Dimensional and Rotational Aerodynamics on the NREL Phase VI Wind Turbine Blade

2008 ◽  
Vol 130 (3) ◽  
Author(s):  
Alvaro Gonzalez ◽  
Xabier Munduate
Keyword(s):  
Wind Turbine ◽  
Turbine Blade ◽  
Three Dimensional ◽  
Separated Flow ◽  
Leading Edge ◽  
Wind Turbine Blade ◽  
Trailing Edge ◽  
Rotating Blade ◽  
Nrel Phase Vi ◽  
Edge Separation

This work undertakes an aerodynamic analysis over the parked and the rotating NREL Phase VI wind turbine blade. The experimental sequences from NASA Ames wind tunnel selected for this study respond to the parked blade and the rotating configuration, both for the upwind, two-bladed wind turbine operating at nonyawed conditions. The objective is to bring some light into the nature of the flow field and especially the type of stall behavior observed when 2D aerofoil steady measurements are compared to the parked blade and the latter to the rotating one. From averaged pressure coefficients together with their standard deviation values, trailing and leading edge separated flow regions have been found, with the limitations of the repeatability of the flow encountered on the blade. Results for the parked blade show the progressive delay from tip to root of the trailing edge separation process, with respect to the 2D profile, and also reveal a local region of leading edge separated flow or bubble at the inner, 30% and 47% of the blade. For the rotating blade, results at inboard 30% and 47% stations show a dramatic suppression of the trailing edge separation, and the development of a leading edge separation structure connected with the extra lift.

Part II: Steady aerofoil-spoiler characteristics

1987 ◽  
Vol 91 (908) ◽  
pp. 359-366
Keyword(s):  
Separated Flow ◽  
Experimental Results ◽  
Surface Singularity ◽  
Separation Region ◽  
Two Dimensional ◽  
Trailing Edge ◽  
Singularity Method ◽  
Total Head ◽  
Low Speeds ◽  
Theoretical Results

Summary A surface singularity method has been formulated to predict two-dimensional spoiler characteristics at low speeds. Vorticity singularities are placed on the aerofoil surface, on the spoiler surface, on the upper separation streamline from the spoiler tip and on the lower separation streamline from the aerofoil trailing edge. The separation region is closed downstream by two discrete vortices. The flow inside the separation region is assumed to have uniform total head. The downstream extent of the separated wake is an empirical input. The flows both external and internal to the separated regions are solved. Theoretical results have been obtained for a range of spoiler-aerofoil configurations which compare reasonably with experimental results. The model is deficient in that it predicts a higher compression ahead of the spoiler than obtained in practice. Furthermore, there is a minimum spoiler angle below which a solution is not possible; it is thought that this feature is related to the physical observation that at small spoiler angles, the separated flow from the spoiler reattaches on the aerofoil upper surface ahead of the trailing edge.

Base Heat Transfer in Two-Dimensional Subsonic Fully Separated Flows

1971 ◽  
Vol 93 (4) ◽  
pp. 342-348 ◽  
Author(s):  
John W. Mitchell
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Experimental Investigation ◽  
Vortex Shedding ◽  
Separated Flow ◽  
Flow Region ◽  
Separated Flows ◽  
Two Dimensional ◽  
Layer Behavior ◽  
Low Speed Wind Tunnel

An experimental investigation of the heat transfer from the base of a two-dimensional wedge-shaped body to the separated-flow region was conducted in a low-speed wind tunnel. The Stanton number has been determined as a function of Reynolds number for two geometries that are representative of heat-exchanger surfaces. The heat transfer is found to be comparable in magnitude to that for attached flows. An analysis based on the mechanisms of vortex shedding and boundary-layer behavior is developed. The analysis agrees fairly well with the data and indicates the parameters governing base heat transfer.

Effect of Hole Diameter on Nozzle Endwall Film Cooling and Associated Phantom Cooling

2015 ◽  
Author(s):  
Luzeng Zhang ◽  
Juan Yin ◽  
Kevin Liu ◽  
Moon Hee-Koo
Keyword(s):  
Film Cooling ◽  
High Speed ◽  
Leading Edge ◽  
Suction Side ◽  
Hole Diameter ◽  
Two Dimensional ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Injection Angle ◽  
Blowing Ratio

Flow fields near the turbine nozzle endwall are highly complex due to the passage vortices and endwall cross flows. Consequently, it is challenging to provide proper cooling to the endwall surfaces. An effective way to cool the endwall is to have film cooling holes forward of the leading edge, often called “inlet-film cooling”. This paper presents the results of an experimental investigation on how the film hole diameter affects the film effectiveness on nozzle endwall and associated phantom cooling effectiveness on airfoil suction side. The measurements were conducted in a high speed linear cascade, which consists of three nozzle vanes and four flow passages. Double staggered rows of film injections, which were located upstream from the nozzle leading edge, provided cooling to the contoured endwall surfaces. Film cooling effectiveness on the endwall surface and corresponding phantom cooling effectiveness on the airfoil suction side were measured separately with a Pressure Sensitive Paint (PSP) technique through the mass transfer analogy. Four different film hole diameters with the same injection angle and the same pitch to diameter ratio were studied for up to six different MFR’s (mass flow ratios). Two dimensional film effectiveness distributions on the endwall surface and two dimensional phantom cooling distributions on the airfoil suction side are presented. Film/phantom cooling effectiveness distributions are pitchwise/spanwise averaged along the axial direction and also presented. The results indicate that both the endwall film effectiveness and the suction side phantom cooling effectiveness increases with the hole diameter (as decreases in blowing ratio for a given MFR) up to a specific diameter, then starts decreasing. An optimal value of the film hole diameter (blowing ratio) for the given injection angle is also suggested based on current study.

Unsteady Mechanisms of Compressor Corner Separation Over a Range of Incidences Based on Hybrid LES/RANS

2013 ◽  
Author(s):  
Zhong-Nan Wang ◽  
Xin Yuan
Keyword(s):  
Separated Flow ◽  
Suction Side ◽  
Separated Flows ◽  
Resonance Structure ◽  
Separation Flow ◽  
Trailing Edge ◽  
Flow Physics ◽  
Unsteady Separation ◽  
Large Pressure ◽  
Corner Flows

The separation flow pattern in compressor corners is well known but its nature is not fully understood. In this paper, the numerical simulation based on hybrid LES/RANS was performed to improve our understanding about the unsteady separation structure and its dynamic mechanisms of compressor corner flows, subject to a range of incoming flow incidences. In the simulation, the attached boundary layer near the walls was modeled by RANS, while the large separated flows in the corner were resolved by LES. The simulation was carefully validated by the experimental data before flow physics investigation. The unsteady separation structures and its effects were then investigated step by step, from phenomena observation to mechanisms analysis. First, the overall separation behavior and its associated flow physics was visualized and analyzed. It was found that the unsteady separation structure was distinct from the steady view. Some additional vortex structures, normally smeared out in the steady averaging process, were crucial in the unsteady dynamic process. These small but critical vortices corresponded to large intermittency in the separation size and strength. As the incidences increased, the vortex structure became much more complex due to the enhanced interaction of these vortices. Second, the turbulence behavior was examined in the separated regions. Anisotropy and non-equilibrium of turbulence were found to be dominant in the separation region due to non-homogenous shear of the separated flow. It posed a big challenge for conventional RANS prediction. Finally, the unsteadiness of corner separated flows was fully analyzed over a range of incidences. It was found that the unsteadiness came from two sources: the suction side separation and the wake shedding. The unsteadiness increased with the incidences. The two unsteady sources interacted with each other at high incidences, which led to a big unsteady resonance structure near the blade trailing edge. The resonance was responsible for a large pressure variation, implying the enhanced noise generation near the blade trailing edge.

A theoretical investigation of enhanced lift in the presence of thin aerofoil stall

1999 ◽  
Vol 103 (1023) ◽  
pp. 237-244 ◽  
Author(s):  
W. W. H. Yeung ◽  
G. V. Parkinson
Keyword(s):  
Flat Plate ◽  
Flow Model ◽  
Separated Flow ◽  
Leading Edge ◽  
Geometrical Parameters ◽  
Separation Flow ◽  
Attached Flow ◽  
Positive Angle ◽  
Edge Separation ◽  
Potential Flow Model

Abstract A theoretical study is presented for the investigation of a potential-flow model for enhancing lift over a flat-plate aerofoil experiencing thin aerofoil stall. Rather than suppressing the leading-edge separation, flow is assumed to separate tangentially at the leading edge and made to reattach smoothly at the tip of a forward-facing fence joining the plate tangentially on its upper surface to avoid any unnecessary stagnated flow. The length of the fence and its location from the leading edge form two geometrical parameters. At any positive angle of attack, the resulting bounding streamline emanating from the leading edge and terminating at the tip of the fence is simulated by using suitable mathematical singularities subject to boundary conditions such as attaining a finite velocity at each critical point of the conformal mapping involved, and the condition of finite pressure gradient at reattachment, when applicable. Computational results from varying these two geometrical parameters indicate that the lift from each model is enhanced, as compared with the attached flow model around a simple flat plate and the original separated flow model by Kirchhoff.

An Experimental Investigation of Cavitation Inception and Development on a Two-Dimensional Eppler Hydrofoil

1999 ◽  
Vol 122 (1) ◽  
pp. 164-173 ◽  
Author(s):  
J.-A. Astolfi ◽  
P. Dorange ◽  
J.-Y. Billard ◽  
I. Cid Tomas
Keyword(s):  
Reverse Flow ◽  
Pressure Coefficient ◽  
Large Angle ◽  
Separated Flow ◽  
Leading Edge ◽  
Angle Of Incidence ◽  
Two Dimensional ◽  
Velocity Measurements ◽  
Cavitation Inception ◽  
Minimum Pressure

Cavitation inception and development on a two-dimensional foil with an Eppler E817 cross section issued from an inverse calculus have been experimentally investigated. The foil is theoretically designed to have a wide cavitation-free bucket allowing a large range of cavitation-free angle of incidence (Eppler, R., 1990, Airfoil Design and Data, Springer-Verlag, Berlin). The inception cavitation numbers, the noise level, the velocity distribution, the minimum pressure coefficient, the cavitation patterns (bubble, leading edge “band type” cavitation, attached sheet cavity), together with the sheet cavity length have been experimentally determined. Effects on the velocity field have been studied too with a slightly developed cavitation. For angles of incidence larger than 1 deg, a great difference exists between the inception cavitation number and the theoretical minimum pressure coefficient. However it is in agreement with the measured one obtained from velocity measurements (for 0 deg<α<6 deg). Discrepancy between theory and experiment on scale models is generally attributed to a flow separation at the leading edge. Although there are some indications of a separated flow at the leading edge, the velocity measurements do not show reverse flow with clearly detected negative velocities excepted for a large angle of incidence equal to 10 deg. Concerning sheet cavity development, the length cavity is found to scale as [σ/2α−αiσ]−m with m close to 2, for length cavities that do not exceed half the foil chord and for σ/2α−αiσ larger than about 30. [S0098-2202(00)00201-7]

Heat transfer from turbulent separated flows

1967 ◽  
Vol 27 (1) ◽  
pp. 97-109 ◽  
Author(s):  
D. B. Spalding
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Reynolds Number ◽  
Separated Flow ◽  
Separated Flows ◽  
Two Dimensional ◽  
Hydrodynamic Properties ◽  
One Dimensional ◽  
Actual Mechanism ◽  
Turbulent Separated Flow

A power-law relation is derived between the Stanton number and the Reynolds number, expressing the law of heat transfer for a wall adjacent to a region of turbulent separated flow. The derivation is based on Prandtl's (1945) proposal for the laws of dissipation, diffusion and generation of turbulent kinetic energy. The constants appearing in these laws are determined by reference to experimental data for the hydrodynamic properties of the constant-stress and the linear-stress layers.The agreement between the resulting predictions and the experimental data of other workers is sufficiently good to suggest that the actual mechanism of heat transfer from separated flows has much in common with that which is postulated. Closer agreement can be expected only after the present one-dimensional analysis has been superseded by a two-dimensional one.

On the steady separated flow around an inclined flat plate

1997 ◽  
Vol 333 ◽  
pp. 403-413 ◽  
Author(s):  
W. W. H. YEUNG ◽  
G. V. PARKINSON
Keyword(s):  
Flat Plate ◽  
Bluff Body ◽  
Separation Bubble ◽  
Separated Flow ◽  
Leading Edge ◽  
Source Model ◽  
Pressure Distributions ◽  
Wide Range ◽  
Trailing Edges ◽  
Edge Separation

An inviscid analytic model is proposed for the steady separated flow around an inclined flat plate. With the plate normal to the stream, the model reduces to the wake-source model of Parkinson & Jandali originally developed for flow external to a symmetrical two-dimensional bluff body and its wake. At any other inclination, the Kutta condition is satisfied at both leading and trailing edges of the plate, and, in the limit that the angle of attack approaches zero, classical airfoil theory is recovered. A boundary condition is formulated based on some experimental results of Abernathy, but no additional empirical information is required. The predicted pressure distributions on the wetted surface for a wide range of angle attack are found to be in good agreement with experimental data, especially at smaller angles of attack. An extension to include a leading-edge separation bubble is explored and results are satisfactory.

Two-dimensional unsteady leading-edge separation on a pitching airfoil

AIAA Journal ◽  
1994 ◽  
Vol 32 (4) ◽  
pp. 673-681 ◽  
Author(s):  
P. Ghosh Choudhuri ◽  
D. D. Knight ◽  
M. R. Visbal
Keyword(s):  
Leading Edge ◽  
Two Dimensional ◽  
Pitching Airfoil ◽  
Edge Separation
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