Guide Vane Vibrations Caused by Wakes and Blower Noise—Part 1: The Vortex Degeneration in the Asymmetrical Wakes

1976 ◽  
Vol 98 (3) ◽  
pp. 948-955
Author(s):  
Y. N. Chen ◽  
G. Baylac ◽  
R. Walther
Keyword(s):  
Flat Plate ◽  
Strouhal Number ◽  
Guide Vane ◽  
Vortex Street ◽  
Flat Plates ◽  
Dynamic Stresses ◽  
Vortex Strength ◽  
Trailing Edges ◽  
The Difference ◽  
Lock In

The symmetrical wakes beyond a guide vane cascade consisting of curved and flat plates with blunt trailing edges were investigated as far as the excited dynamic stresses in the blades and the vortex Strouhal number are concerned. The results reveal that the flat plate is more liable to be damaged by the Karman vortex street than the curved plate. However, the vortex street can be effectively suppressed by giving the trailing edge an asymmetrical form. It will be shown that this suppression orginates from the difference of the vortex strengths in the two rows of the vortex street, causing the rapid degeneration of the vortices. This leads to the suppression of the reinforcement of the vortex strength by the lock-in because of lack of stable vortex region.

Flow Over an Inclined Plate

1962 ◽  
Vol 84 (3) ◽  
pp. 380-388 ◽  
Author(s):  
F. H. Abernathy
Keyword(s):  
Flow Field ◽  
Flat Plate ◽  
Strouhal Number ◽  
Angle Of Attack ◽  
Separation Distance ◽  
Lateral Flow ◽  
Vortex Street ◽  
Arbitrary Angle ◽  
Inclined Plate ◽  
Free Vortex

A free-streamline theory for an inclined flat plate in an infinite flow field, at an arbitrary angle of attack, is presented. Measurements of the location of the free-vortex layers, of the vortex-street frequency, and of the pressure behind an inclined sharp-edge plate are reported as a function of both the angle of attack of the plate and the lateral constriction of the flow. The separation between free-vortex layers is found experimentally to be essentially independent of lateral flow constriction. A form of the Strouhal number, using this separation distance as the characteristic flow dimension, is shown to be independent of lateral constriction of the flow and of the inclination of the plate.

On the Spacing of Karman Vortices

1969 ◽  
Vol 36 (2) ◽  
pp. 370-372 ◽  
Author(s):  
D. W. Sallet
Keyword(s):  
Strouhal Number ◽  
Cross Section ◽  
Vortex Shedding ◽  
Bluff Body ◽  
Slenderness Ratio ◽  
The Body ◽  
Vortex Street ◽  
Circular Cylinders ◽  
Flat Plates ◽  
Uniform Cross Section

Equations for the absolute dimensions of the Karman vortex street are developed in terms of the coefficient of drag and the Strouhal number of the vortex shedding bluff body. The body is assumed to be of large slenderness ratio and of uniform cross section. The predicted vortex spacings are compared with the experimental results of other investigators for circular cylinders, flat plates, and a wedge.

The spacing, position and strength of vortices in the wake of slender cylindrical bodies at large incidence

1971 ◽  
Vol 50 (4) ◽  
pp. 751-783 ◽  
Author(s):  
K. D. Thomson ◽  
D. F. Morrison
Keyword(s):  
Strouhal Number ◽  
Cross Flow ◽  
Reynolds Numbers ◽  
The Body ◽  
Vortex Street ◽  
Flow Conditions ◽  
Vortex Strength ◽  
Subcritical Region ◽  
A Value ◽  
Impulse Flow

Extensive schlieren studies and yawmeter traverses of the wake behind slender cone-cylinders at large angles of incidence have shown that the flow pattern is generally steady. Under certain flow conditions, however, the wake exhibits an instability which is not understood. For cross-flow Reynolds numbers in the subcritical region the wake can be described in terms of a cross-flow Strouhal number which has a constant value of 0·2 for cross-flow Mach number components (Mc) up to 0·7 and then increases steadily to a value of 0·6 at Mc = 1·6. The strength of the wake vortices varies substantially with Mc, increasing to a maximum at Mc ≈ 0·7 and then decreasing rapidly for higher values of Mc. Schlieren photographs of the wake have been analysed by means of the impulse flow analogy and also by considering the vortices to be part of a yawed infinite vortex street. The impulse flow analogy is shown to be of use in determining the cross-flow Strouhal number but estimates of vortex strength are too high. The Kármán vortex street theory combined with the sweepback principle leads to reliable estimates of vortex strength up to Mc = 1·0.Information is given on the spacing, path and strength of the vortices shed from the body for flow conditions varying from incompressible speeds up to Mc = 1·0. Finally this information is used to determine the vortex drag of a two-dimensional circular cylinder below Mc = 1·0.

Study on the effect of leading and trailing-edge serrations on flat-plate broadband noise

2020 ◽  
Vol 51 (3) ◽  
pp. 44-51
Author(s):  
Dilip A Shah ◽  
Husain A Hamid ◽  
M Praveen Kumar ◽  
Tanmay Atul Bhise ◽  
GC Vishnu Kumar
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Flat Plate ◽  
Computational Study ◽  
Leading Edge ◽  
Broadband Noise ◽  
Flat Plates ◽  
Trailing Edge ◽  
Ansys Fluent ◽  
Trailing Edges

The results of a comparative study on the reduction of broadband noise for several combinations of a flat plate with serrations encountering a low-turbulence fluid flow are computed and documented. The four combinations under study are triangular serrations on leading-edge only, triangular serrations on trailing-edge only, triangular serrations on the leading and trailing edges, and ogival serrations on the leading and trailing edges. Serrations based on the trailing edge are normalized in terms of its chord length. A computational study was carried out using computational fluid dynamics models to simulate the variety of serrated flat plates. Commercial computational fluid dynamics software ANSYS Fluent 16.0 was used. A quantifiable reduction in the broadband noise was found in most of the variations in the serrated geometries. The particular case of the serrations considered in the present study having triangular serrations on both leading and trailing edges of the flat plate proved to be the most effective in terms of broadband noise reduction.

Effect of Flaw Dimensions on Ductile Fracture Behavior of Non-Aligned Multiple Flaws in a Plate

2011 ◽  
Author(s):  
Katsumasa Miyazaki ◽  
Kunio Hasegawa ◽  
Koichi Saito
Keyword(s):  
Ductile Fracture ◽  
Flat Plate ◽  
Fracture Behavior ◽  
Maximum Load ◽  
Surface Flaws ◽  
Fracture Tests ◽  
The Difference ◽  
Almost All ◽  
Maximum Minimum

The fitness-for-service codes require the characterization of non-aligned multiple flaws for flaw evaluation, which is performed using a flaw proximity rule. Worldwide, almost all such codes provide their own proximity rule, often with unclear technical bases of the application of proximity rule to ductile or fully plastic fracture. In particular, the effect of flaw dimensions of multiple surface flaws on fully plastic fracture of non-aligned multiple flaws had not been clear. To clarify the effect of the difference of part through-wall and through-wall flaws on the behavior of fully plastic fracture, the fracture tests of flat plate specimens with non-aligned multiple part through-wall flaws were conducted. When the flaw depth a was shallow with 0.4 in ratio of a to thickness t, the maximum load Pmax occurred at penetration of multiple flaws and the effect of vertical distance of non-aligned multiple flaws H on Pmax was not so significant. However, when flaw depth was deep with 0.8 in a/t, Pmax occurred after penetration of flaws and the effect of H on Pmax could be seen clearly. It was judged that the through-wall flaw tests were appropriate for discussion of the effect of H on Pmax and the alignment rule of multiple flaws. In addition, in order to clarify the appropriate length parameter to estimate Pmax of test specimens with dissimilar non-aligned through-wall multiple flaws, the fracture tests of plate specimens were also conducted. The effect of different flaw length on Pmax was discussed with maximum, minimum and averages of dissimilar non-aligned multiple flaw lengths. Experimental results showed that the maximum length lmax would be an appropriate length parameter to estimate Pmax, when the non-aligned multiple through-wall flaws were dissimilar.

scholarly journals A Generalized Method for Flat Plates Impact Detection and Location

2013 ◽  
Vol 543 ◽  
pp. 171-175
Author(s):  
Jose Andrés Somolinos ◽  
Rafael Morales ◽  
Carlos Morón ◽  
Alfonso Garcia
Keyword(s):  
Signal Processing ◽  
Flat Plate ◽  
Acoustic Signal ◽  
Experimental Results ◽  
Piezoelectric Sensors ◽  
Experimental Setup ◽  
Flat Plates ◽  
Impact Detection ◽  
Timing Difference

In the last years, many analyses from acoustic signal processing have been used for different applications. In most cases, these sensor systems are based on the determination of times of flight for signals from every transducer. This paper presents a flat plate generalization method for impact detection and location over linear links or bars-based structures. The use of three piezoelectric sensors allow to achieve the position and impact time while the use of additional sensors lets cover a larger area of detection and avoid wrong timing difference measurements. An experimental setup and some experimental results are briefly presented.

Experimental Study of Multiple Air Jets Impinging a Moving Flat Plate

2020 ◽  
Author(s):  
Flavia Barbosa ◽  
Senhorinha Teixeira ◽  
Carlos Costa ◽  
Filipe Marques ◽  
José Carlos Teixeira
Keyword(s):  
Heat Transfer ◽  
Flat Plate ◽  
Jet Impingement ◽  
Plate Motion ◽  
Test Facility ◽  
Flat Plates ◽  
Target Plate ◽  
Wall Jets ◽  
Air Jets ◽  
Flow Interactions

Abstract The motion of the target plate is important in some industrial applications which apply multiple jet impingement, such as reflow soldering, drying and food processing. Multiple jet impingement is widely used due to its ability to generate high heat transfer rates over large and complex areas. This convective process is characterized by several flow interactions essentially due to adjacent jets mixing prior the impingement, wall jets collision after the impingement, as well as crossflow interactions induced by the motion of the wall jets that flow through the exits of the domain. These interactions lead to strong flow recirculation, pressure gradients and boundary layer development. However, the complexity of the flow interactions is increased with the surface motion in confined space, due to the generation of strong shear regions. These interactions can induce problems and product defects due to complicated thermal behavior and non-uniform heating or cooling, being important to fully understand the process in order to reduce time and costs. This work addresses the experimental analysis of multiple air jets impinging on a moving flat plate. The experiments are conducted on a purpose-built test facility which has been commissioned, using a 2D-PIV system. Through this technique, the flow structure and velocity profiles will be analyzed in detail. The effects of the impinging plate motion on the resulting global and local velocity profile is compared with a static flat plate. The multiple jet configuration consists on air flowing through 14 circular nozzles, at a Reynolds number of 690 and 1,380. The experiments are conducted for a nozzle-to-plate distance of 8 and a jet-to-jet spacing of 2. The target plate motion remains constant throughout the experiments and equal to 0.03 m/s. The results are compared for both stationary and moving flat plates cases and express the increased complexity of the flow due to strong interaction between jets and the target surface, which affects the heat transfer performance. The results obtained experimentally are important to clearly define this complex flow and these data can be used in future works for numerical model validation.

On drag, Strouhal number and vortex-street structure

2002 ◽  
Vol 30 (6) ◽  
pp. 379-399 ◽  
Author(s):  
Boye Ahlborn ◽  
Mae L Seto ◽  
Bernd R Noack
Keyword(s):  
Strouhal Number ◽  
Vortex Street

Vortex Shedding Analysis in the Wake of a Flat Plate at Low Incidence and Low Reynolds Number

2021 ◽  
Author(s):  
Bastav Borah ◽  
Anand Verma ◽  
Vinayak Kulkarni ◽  
Ujjwal K. Saha
Keyword(s):  
Reynolds Number ◽  
Velocity Field ◽  
Flat Plate ◽  
Vortex Shedding ◽  
Low Reynolds Number ◽  
General Tendency ◽  
Flat Plates ◽  
Trailing Edge ◽  
Low Reynolds ◽  
Low Incidence

Abstract Vortex shedding phenomenon leads to a number of different features such as flow induced vibrations, fluid mixing, heat transfer and noise generation. With respect to aerodynamic application, the intensity of vortex shedding and the size of vortices play an essential role in the generation of lift and drag forces on an airfoil. The flat plates are known to have a better lift-to-drag ratio than conventional airfoils at low Reynolds number (Re). A better understanding of the shedding behavior will help aerodynamicists to implement flat plates at low Re specific applications such as fixed-wing micro air vehicle (MAV). In the present study, the shedding of vortices in the wake of a flat plate at low incidence has been studied experimentally in a low-speed subsonic wind tunnel at a Re of 5 × 104. The velocity field in the wake of the plate is measured using a hot wire anemometer. These measurements are taken at specific points in the wake across the flow direction and above the suction side of the flat plate. The velocity field is found to oscillate with one dominant frequency of fluctuation. The Strouhal number (St), calculated from this frequency, is computed for different angles of attack (AoA). The shedding frequency of vortices from the trailing edge of the flat plate has a general tendency to increase with AoA. In this paper, the generation and subsequent shedding of leading edge and trailing edge vortices in the wake of a flat plate are discussed.

Small Rotationally Symmetric Deformations of Shallow Helicoidal Shells

1955 ◽  
Vol 22 (1) ◽  
pp. 31-34
Author(s):  
Eric Reissner
Keyword(s):  
Flat Plate ◽  
Plane Stress ◽  
General Property ◽  
Middle Surface ◽  
Circular Ring ◽  
Sample Problem ◽  
Flat Plates ◽  
Transverse Bending ◽  
Rotationally Symmetric

Abstract Known solutions for transverse bending and plane stress of flat circular ring plates are generalized so as to apply to shallow helicoidal shells. The pitch of the middle surface of the shell is responsible for a coupling of what would be separate problems of plane stress and transverse bending for flat plates. Explicit results are obtained for an important sample problem. A general property of helicoidal cantilever shells is stated. Criteria are obtained indicating, in terms of the parameters of the shell (a) the range of applicability of the results obtained, and (b) the range in which the shell behaves like a flat plate.

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