Investigation into Aerodynamic Characteristics and Flow Structures of Rectangular Flat-Plate Wing with Very Small Aspect Ratios at Full Angles of Attack

An experimental study is made of natural convection oscillations in gallium melts enclosed by right circular cylinders with differentially heated end walls. Cases heated from below are examined for angles of inclination (φ) ranging from 0 deg (vertical) to 75 deg with aspect ratios Ar (height/diameter) of 2, 3, and 4. Temperature measurements are made along the circumference of the cylinder to detect the oscillations, from which the oscillatory flow structures are inferred. The critical Rayleigh numbers and oscillation frequencies are determined. For Ar=3 and φ = 0 deg, 30 deg the supercritical flow structures are discussed in detail.

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Investigation of Wedge Probe Wall Proximity Effects: Part 2—Numerical and Analytical Modeling

Journal of Engineering for Gas Turbines and Power ◽

10.1115/1.2817027 ◽

1997 ◽

Vol 119 (3) ◽

pp. 605-611 ◽

Cited By ~ 2

Author(s):

P. D. Smout ◽

P. C. Ivey

Keyword(s):

Large Scale ◽

Three Dimensional ◽

Outer Wall ◽

Aerodynamic Characteristics ◽

Proximity Effects ◽

Wake Flow ◽

Scale Model ◽

Flow Structures ◽

Flow Features ◽

Wall Proximity

An experimental study of wedge probe wall proximity effects is described in Part 1 of this paper. Actual size and large-scale model probes were tested to understand the mechanisms responsible for this effect, by which free-stream pressure near the outer wall of a turbomachine may be overindicated by up to 20 percent dynamic head. CFD calculations of the flow over two-dimensional wedge shapes and a three-dimensional wedge probe were made in support of the experiments, and are reported in this paper. Key flow structures in the probe wake were identified that control the pressures indicated by the probe in a given environment. It is shown that probe aerodynamic characteristics will change if the wake flow structures are modified, for example by traversing close to the wall, or by calibrating the probe in an open jet rather than in a closed section wind tunnel. A simple analytical model of the probe local flows was derived from the CFD results. It is shown by comparison with experiment that this model captures the dominant flow features.

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Unsteady RANS Simulation of Turbulent Flow and Heat Transfer in Ribbed Coolant Passages of Different Aspect Ratios

Volume 3: Turbo Expo 2004 ◽

10.1115/gt2004-53986 ◽

2004 ◽

Author(s):

A. K. Saha ◽

Sumanta Acharya

Keyword(s):

Heat Transfer ◽

Secondary Flow ◽

Rotation Number ◽

Large Scale ◽

Density Ratio ◽

Navier Stokes ◽

Flow Structures ◽

Flow And Heat Transfer ◽

Aspect Ratios ◽

Unsteady Rans

The flow and heat transfer in ribbed coolant passages of aspect ratios (AR) of 1:1, 4:1, and 1:4 are numerically studied through the solution of the Unsteady Reynolds Averaged Navier-Stokes (URANS) equations. The ribs are oriented normal to the flow and arranged in a staggered configuration on the leading and trailing surfaces. The URANS procedure can resolve large-scale bulk unsteadiness, and utilizes a two equation k-ε model for the turbulent stresses. Both Coriolis and centrifugal buoyancy effects are included in the simulations. The computations are carried out for a fixed Reynolds number of 25000 and density ratio of 0.13 while the Rotation number has been varied between 0.12–0.50. The average duct heat transfer is the highest for the 4:1 AR case. For this case, the secondary flow structures consist of multiple roll cells that direct flow both to the trailing and leading surfaces. The 1:4 AR duct shows flow reversal along the leading surface at high rotation numbers with multiple rolls in the secondary flow structures near the leading wall. For this AR, the potential for conduction-limited heat transfer along the leading surface is identified. At high rotation number, both the 1:1 and 4:1 AR cases exhibit loss of axial periodicity over one inter-rib module. The friction factor reveals an increase with the rotation number for all aspect ratio ducts, and shows a sudden jump in its value at a critical rotation number because of either loss of spatial periodicity or the onset of backflow.

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Investigation of Wedge Probe Wall Proximity Effects: Part 2 — Numerical and Analytical Modelling

Volume 5: Manufacturing Materials and Metallurgy; Ceramics; Structures and Dynamics; Controls, Diagnostics and Instrumentation; Education; General ◽

10.1115/96-gt-147 ◽

1996 ◽

Author(s):

Peter D. Smout ◽

Paul C. Ivey

Keyword(s):

Large Scale ◽

Three Dimensional ◽

Outer Wall ◽

Aerodynamic Characteristics ◽

Proximity Effects ◽

Wake Flow ◽

Scale Model ◽

Flow Structures ◽

Flow Features ◽

Wall Proximity

An experimental study of wedge probe wall proximity effects is described in Part 1 of this paper. Actual size and large scale model probes were tested to understand the mechanisms responsible for this effect, by which free stream pressure near the outer wall of a turbomachine may be over indicated by upto 20% dynamic head. CFD calculations of the flow over two-dimensional wedge shapes and a three-dimensional wedge probe were made in support of the experiments, and are reported in this paper. Key flow structures in the probe wake were identified which control the pressures indicated by the probe in a given environment. It is shown that probe aerodynamic characteristics will change if the wake flow structures are modified, for example by traversing close to the wall, or by calibrating the probe in an open jet rather than in a closed section wind tunnel. A simple analytical model of the probe local flows was derived from the CFD results. It is shown by comparison with experiment that this model captures the dominant flow features.

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Three-dimensional instabilities in oscillatory flow past elliptic cylinders

Journal of Fluid Mechanics ◽

10.1017/jfm.2016.319 ◽

2016 ◽

Vol 798 ◽

pp. 371-397 ◽

Cited By ~ 1

Author(s):

José P. Gallardo ◽

Helge I. Andersson ◽

Bjørnar Pettersen

Keyword(s):

Circular Cylinder ◽

Flow Direction ◽

Three Dimensional ◽

Circular Cylinders ◽

Flow Structures ◽

Three Dimensional Flow ◽

Elliptical Cross ◽

Dimensional Flow ◽

Aspect Ratios ◽

Flow Past

We investigate the early development of instabilities in the oscillatory viscous flow past cylinders with elliptic cross-sections using three-dimensional direct numerical simulations. This is a classical hydrodynamic problem for circular cylinders, but other configurations have received only marginal attention. Computed results for some different aspect ratios ${\it\Lambda}$ from 1 : 1 to 1 : 3, all with the major axis of the ellipse aligned in the main flow direction, show good qualitative agreement with Hall’s stability theory (J. Fluid Mech., vol. 146, 1984, pp. 347–367), which predicts a cusp-shaped curve for the onset of the primary instability. The three-dimensional flow structures for aspect ratios larger than 2 : 3 resemble those of a circular cylinder, whereas the elliptical cross-section with the lowest aspect ratio of 1 : 3 exhibits oblate rather than tubular three-dimensional flow structures as well as a pair of counter-rotating spanwise vortices which emerges near the tips of the ellipse. Contrary to a circular cylinder, instabilities for an elliptic cylinder with sufficiently high eccentricity emerge from four rather than two different locations in accordance with the Hall theory.

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On High-Performance Airfoil at Very Low Reynolds Number

Journal of Robotics and Mechatronics ◽

10.20965/jrm.2016.p0273 ◽

2016 ◽

Vol 28 (3) ◽

pp. 273-285

Author(s):

Katsuya Hirata ◽

◽

Ryo Nozawa ◽

Shogo Kondo ◽

Kazuki Onishi ◽

...

Keyword(s):

Reynolds Number ◽

Flat Plate ◽

High Performance ◽

Low Reynolds Number ◽

Three Dimensional ◽

Reynolds Numbers ◽

Aerodynamic Characteristics ◽

Slow Flow ◽

Low Reynolds Numbers ◽

Low Reynolds

[abstFig src='/00280003/02.jpg' width=""300"" text='Iso-Q surfaces of very-slow flow past an iNACA0015' ] The airfoil is often used as the elemental device for flying/swimming robots, determining its basic performances. However, most of the aerodynamic characteristics of the airfoil have been investigated at Reynolds numbers Re’s more than 106. On the other hand, our knowledge is not enough in low Reynolds-number ranges, in spite of the recent miniaturisation of robots. In the present study, referring to our previous findings (Hirata et al., 2011), we numerically examine three kinds of high-performance airfoils proposed for very-low Reynolds numbers; namely, an iNACA0015 (the NACA0015 placed back to front), an FPBi (a flat plate blended with iNACA0015 as its upper half) and an FPBN (a flat plate blended with the NACA0015 as its upper half), in comparison with such basic airfoils as a NACA0015 and an FP (a flat plate), at a Reynolds number Re = 1.0 × 102 using two- and three-dimensional computations. As a result, the FPBi shows the best performance among the five kinds of airfoils.

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