Hydroelastic Vibrations of Flat Plates Related to Trailing Edge Geometry

1961 ◽  
Vol 83 (4) ◽  
pp. 671-678 ◽  
Author(s):  
G. H. Toebes ◽  
P. S. Eagleson
Keyword(s):  
Leading Edge ◽  
Equation Of Motion ◽  
Thin Plates ◽  
Comprehensive Treatment ◽  
Angle Of Incidence ◽  
Flat Plates ◽  
Trailing Edge ◽  
Edge Geometry ◽  
Vortex Induced Vibrations ◽  
Hydroelastic Vibrations

Vortex-induced vibrations of thin flat plates are studied as a function of trailing edge geometry. In an effort to extend the analysis to a more comprehensive treatment than that provided by the common vortex model, the vibrations are considered as hydroelastic phenomena. An equation of motion is formulated. From a qualitative analysis of this nonlinear equation some expected features of its solution are set forth. A detailed experimental determination is made of the amplitude spectra of various thin plates mounted at zero mean angle of incidence in the test section of a water tunnel and suspended by a torsion spring through their leading edge. The effects of trailing edge geometry and elastic properties of plate support are explored. Data analysis gives interesting confirmation of the formulated equation of motion. The vibration is shown to become self-excited and the degree of two dimensionality of the wake is deduced to be determinative in regard to the severity of the vibration.

Trailing-edge stall

1970 ◽  
Vol 42 (3) ◽  
pp. 561-584 ◽  
Author(s):  
S. N. Brown ◽  
K. Stewartson
Keyword(s):  
Boundary Layer ◽  
Complete Solution ◽  
Leading Edge ◽  
Asymptotic Solutions ◽  
Angle Of Incidence ◽  
Trailing Edge ◽  
Boundary Layer Equations ◽  
Order Of Magnitude ◽  
Stall Angle ◽  
Fundamental Equations

A study is made of the laminar flow in the neighbourhood of the trailing edge of an aerofoil at incidence. The aerofoil is replaced by a flat plate on the assumption that leading-edge stall has not taken place. It is shown that the critical order of magnitude of the angle of incidence α* for the occurrence of separation on one side of the plate is$\alpha^{*} = O(R^{\frac{1}{16}})$, whereRis a representative Reynolds number, for incompressible flow, and α* =O(R−¼) for supersonic flow. The structure of the flow is determined by the incompressible boundary-layer equations but with unconventional boundary conditions. The complete solution of these fundamental equations requires a numerical investigation of considerable complexity which has not been undertaken. The only solutions available are asymptotic solutions valid at distances from the trailing edge that are large in terms of the scaled variable of orderR−⅜, and a linearized solution for the boundary layer over the plate which gives the antisymmetric properties of the aerofoil at incidence. The value of α* for which separation occurs is the trailing-edge stall angle and an estimate is obtained from the asymptotic solutions. The linearized solution yields an estimate for the viscous correction to the circulation determined by the Kutta condition.

Influence of Trailing-Edge Geometry on Hydraulic-Turbine-Blade Vibration Resulting From Vortex Excitation

1960 ◽  
Vol 82 (2) ◽  
pp. 103-109 ◽  
Author(s):  
Gunnar Heskestad ◽  
D. R. Olberts
Keyword(s):  
Boundary Layer ◽  
Turbine Blade ◽  
Vortex Shedding ◽  
Hydraulic Turbine ◽  
Trailing Edge ◽  
Blade Vibration ◽  
Edge Geometry ◽  
Blade Thickness ◽  
Vortex Induced Vibrations ◽  
Approach Velocity

A study was made to determine effects of trailing-edge geometry on the vortex-induced vibrations of a model blade designed to simulate the conditions at the trailing edge of a hydraulic-turbine blade. For the type of trailing-edge flow encountered, characterized by a thick boundary layer relative to the blade thickness, the vortex-shedding frequency could not be represented by any modification of the Strouhal formula. The amplitude of the induced vibrations increased with the strength of a vortex in the von Karman vortex street of the wake; one exception was provided by a grooved edge, which is discussed in some detail. For a particular approach velocity, the vortex strength is primarily a function of the ratio of distance between separation points to boundary-layer thickness, the degree of “shielding” between regions of vortex growth, and frequency of vortex shedding.

scholarly journals The Analysis of Leading Edge Deformations on Turbomachine Blades

Energies ◽  
2019 ◽  
Vol 12 (4) ◽  
pp. 736 ◽  
Author(s):  
Le Li ◽  
Huoxing Liu
Keyword(s):  
Boundary Layer ◽  
Leading Edge ◽  
Transition Process ◽  
Aerodynamic Performance ◽  
Flat Plates ◽  
Laminar Separation ◽  
Good Design ◽  
Edge Geometry ◽  
Original Boundary ◽  
High Turbulence

With recent advancements in the development of material and manufacturing technology, the leading edge geometry of turbomachine blades has attracted widespread attention. “Sharp” leading edges always have a better aerodynamic performance, though it is prone to deformations easily. Thus, flat plates and real compressor cascades with different leading edge deformations were investigated to study the influence, which is applicable for thin blades at low speeds. Different boundary layer characteristics, including the velocity profile, transition process, and loss, are compared. The results show that there are several kinds of contradictory influence mechanisms and that the final phenomenon is closely related to the condition of the original boundary layer. In low turbulence, with large and laminar separation, the deformations can suppress separation and decrease loss. In high turbulence, with short and transitional separation, deformations can promote the transition process and increase the loss. The sensitivities of different the original leading edge shapes are also compared. This indicates that a good design always has a better robustness at low turbulence values, while it is worse at high turbulence values. The cascade experiment and simulation show that the deformation influence is similar to flat plates and that it is enlarged near the hub, which affects the corner separation.

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.

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.

Computational Study of the Risø-B1-18 Airfoil with a Hinged Flap Providing Variable Trailing Edge Geometry

2005 ◽  
Vol 29 (2) ◽  
pp. 89-113 ◽  
Author(s):  
Niels Troldborg
Keyword(s):  
Reynolds Number ◽  
Unsteady Flow ◽  
Computational Study ◽  
Turbine Blades ◽  
Aerodynamic Characteristics ◽  
Flow Conditions ◽  
Wind Turbine Blades ◽  
Trailing Edge ◽  
Edge Geometry ◽  
Fully Developed Turbulent Flow

A comprehensive computational study, in both steady and unsteady flow conditions, has been carried out to investigate the aerodynamic characteristics of the Risø-B1-18 airfoil equipped with variable trailing edge geometry as produced by a hinged flap. The function of such flaps should be to decrease fatigue-inducing oscillations on the blades. The computations were conducted using a 2D incompressible RANS solver with a k-w turbulence model under the assumption of a fully developed turbulent flow. The investigations were conducted at a Reynolds number of Re = 1.6 · 106. Calculations conducted on the baseline airfoil showed excellent agreement with measurements on the same airfoil with the same specified conditions. Furthermore, a more widespread comparison with an advanced potential theory code is presented. The influence of various key parameters, such as flap shape, flap size and oscillating frequencies, was investigated so that an optimum design can be suggested for application with wind turbine blades. It is concluded that a moderately curved flap with flap chord to airfoil curve ratio between 0.05 and 0.10 would be an optimum choice.

Effect of kinematics of orogenic wedge on kinematic evolutionary paths and deformation profiles of major shear zones: An example from the eastern Himalaya 

2021 ◽  
Author(s):  
Pritam Ghosh ◽  
Kathakali Bhattacharyya
Keyword(s):  
Shear Zone ◽  
Strain Softening ◽  
Leading Edge ◽  
Shear Zones ◽  
Deformation History ◽  
Progressive Deformation ◽  
Trailing Edge ◽  
Orogenic Wedge ◽  
Transport Direction ◽  
Evolutionary Paths

<p>We examine how the deformation profile and kinematic evolutionary paths of two major shear zones with prolonged deformation history and large translations differ with varying structural positions along its transport direction in an orogenic wedge. We conduct this analysis on multiple exposures of the internal thrusts from the Sikkim Himalayan fold thrust belt, the Pelling-Munsiari thrust (PT), the roof thrust of the Lesser Himalayan duplex (LHD), and the overlying Main Central thrust (MCT). These two thrusts are regionally folded due to growth of the LHD and are exposed at different structural positions. The hinterlandmost exposures of the MCT and PT zones lie in the trailing parts of the duplex, while the foreland-most exposures of the same studied shear zones lie in the leading part of the duplex, and thus have recorded a greater connectivity with the duplex. The thicknesses of the shear zones progressively decrease toward the leading edge indicating variation in deformation conditions. Thickness-displacement plot reveals strain-softening from all the five studied MCT and the PT mylonite zones. However, the strain-softening mechanisms varied along its transport direction with the hinterland exposures recording dominantly dislocation-creep, while dissolution-creep and reaction-softening are dominant in the forelandmost exposures. Based on overburden estimation, the loss of overburden on the MCT and the PT zones is more in the leading edge (~26km and ~15km, respectively) than in the trailing edge (~10km and ~17km, respectively), during progressive deformation. Based on recalibrated recrystallized quartz grain thermometer (Law, 2014), the estimated deformation temperatures in the trailing edge are higher (~450-650°C) than in the leading edge (350-550°C) of the shear zones. This variation in the deformation conditions is also reflected in the shallow-crustal deformation structures with higher fracture intensity and lower spacing in the leading edge exposures of the shear zones as compared to the trailing edge exposures.</p><p>The proportion of mylonitic domains and micaceous minerals within the exposed shear zones increase and grain-size of the constituent minerals decreases progressively along the transport direction. This is also consistent with progressive increase in mean R<sub>s</sub>-values toward leading edge exposures of the same shear zones. Additionally, the α-value (stretch ratio) gradually increases toward the foreland-most exposures along with increasing angular shear strain. Vorticity estimates from multiple incremental strain markers indicate that the MCT and PT zones generally record a decelerating strain path. Therefore, the results from this study are counterintuitive to the general observation of a direct relationship between higher Rs-value and higher pure-shear component. We explain this observation in the context of the larger kinematics of the orogen, where the leading edge exposures have passed through the duplex structure, recording the greatest connectivity and most complete deformation history, resulting in the weakest shear zone that is also reflected in the deformation profiles and strain attributes. This study demonstrates that the same shear zone records varying deformation profile, strain and kinematic evolutionary paths due to varying deformation conditions and varying connectivity to the underlying footwall structures during progressive deformation of an orogenic wedge.</p>

Wing Mechanics and Take-Off Preparation of Thrips (Thysanoptera)

1980 ◽  
Vol 85 (1) ◽  
pp. 129-136 ◽  
Author(s):  
C. P. ELLINGTON
Keyword(s):  
Leading Edge ◽  
Morphological Features ◽  
Inertial Forces ◽  
Wing Area ◽  
Trailing Edge ◽  
Lateral Projection ◽  
Parking Problem ◽  
Closed Position ◽  
Open Position ◽  
Fringe System

1. All of the wing fringe cilia of Thrips physapus, except those along the hindwing leading edge, pivot in elongated sockets which lock them into two positions. 2. The wings lie parallel over the abdomen when not in use, with the cilia locked in the closed position at an angle of 15-20° to the wing axis. The closing of the fringes prevents entanglement of the trailing edge cilia and lateral projection of the forewing leading edge cilia. 3. During flight the cilia are locked in the open position, doubling the wing area. The locking force is stronger than the combined aerodynamic and inertial forces on the cilia. 4. The fringes are opened by abdominal combing and closed by tibial combing. 5. The same morphological features are found in other members of the sub-order Terebrantia. Parallel wings at rest are characteristic of this suborder, and the collapsible fringe system is viewed as an effective method for parking the wings. 6. The fringes of the sub-order Tubulifera are not collapsible. The wings overlap on the abdomen at rest and a similar parking problem does not arise.

Study on the Relation Between Side Ratios of Rectangular Cross Sections and Secondary Vortices at Trailing Edge in Motion-Induced Vortex Excitation

2017 ◽  
Author(s):  
Kazutoshi Matsuda ◽  
Kusuo Kato ◽  
Kouki Arise ◽  
Hajime Ishii
Keyword(s):  
Wind Speed ◽  
Wind Tunnel ◽  
Cross Sections ◽  
Leading Edge ◽  
Trailing Edge ◽  
Wind Speeds ◽  
Smoke Flow ◽  
Flow Visualizations ◽  
Institute Of Technology ◽  
Secondary Vortices

According to the results of conventional wind tunnel tests on rectangular cross sections with side ratios of B/D = 2–8 (B: along-wind length (m), D: cross-wind length (m)), motion-induced vortex excitation was confirmed. The generation of motion-induced vortex excitation is considered to be caused by the unification of separated vortices from the leading edge and secondary vortices at the trailing edge [1]. Spring-supported test for B/D = 1.18 was conducted in a closed circuit wind tunnel (cross section: 1.8 m high×0.9 m wide) at Kyushu Institute of Technology. Vibrations were confirmed in the neighborhoods of reduced wind speeds Vr = V/fD = 2 and Vr = 8 (V: wind speed (m/s), f: natural frequency (Hz)). Because the reduced wind speed in motion-induced vortex excitation is calculated as Vr = 1.67×B/D = 1.67×1.18 = 2.0 [1], vibrations around Vr = 2 were considered to be motion-induced vortex excitation. According to the smoke flow visualization result for B/D = 1.18 which was carried out by the authors, no secondary vortices at the trailing edge were formed, although separated vortices from the leading edge were formed at the time of oscillation at the onset wind speed of motion-induced vortex excitation, where aerodynamic vibrations considered to be motion-induced vortex excitation were confirmed. It was suggested that motion-induced vortex excitation might possibly occur in the range of low wind speeds, even in the case of side ratios where secondary vortices at trailing edge were not confirmed. In this study, smoke flow visualizations were performed for ratios of B/D = 0.5–2.0 in order to find out the relation between side ratios of rectangular cross sections and secondary vortices at trailing edge in motion-induced vortex excitation. The smoke flow visualizations around the model during oscillating condition were conducted in a small-sized wind tunnel at Kyushu Institute of Technology. Experimental Reynolds number was Re = VD/v = 1.6×103. For the forced-oscillating amplitude η, the non-dimensional double amplitudes were set as 2η/D = 0.02–0.15. Spring-supported tests were also carried out in order to obtain the response characteristics of the models.

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