scholarly journals Performance and mechanism of sinusoidal leading edge serrations for the reduction of turbulence–aerofoil interaction noise

2017 ◽  
Vol 818 ◽  
pp. 435-464 ◽  
Author(s):  
P. Chaitanya ◽  
P. Joseph ◽  
S. Narayanan ◽  
C. Vanderwel ◽  
J. Turner ◽  
...  
Keyword(s):  
Turbulent Flow ◽  
Three Dimensional ◽  
Leading Edge ◽  
Flow Speed ◽  
Integral Length Scale ◽  
Length Scale ◽  
Flat Plates ◽  
Image Velocimetry ◽  
Lift And Drag ◽  
Power Radiation

This paper presents the results of a detailed experimental investigation into the effectiveness of sinusoidal leading edge serrations on aerofoils for the reduction of the noise generated by the interaction with turbulent flow. A detailed parametric study is performed to investigate the sensitivity of the noise reductions to the serration amplitude and wavelength. The study is primarily performed on flat plates in an idealized turbulent flow, which we demonstrate captures the same behaviour as when identical serrations are introduced onto three-dimensional aerofoils. The influence on the noise reduction of the turbulence integral length scale is also studied. An optimum serration wavelength is identified whereby maximum noise reductions are obtained, corresponding to when the transverse integral length scale is approximately one-fourth the serration wavelength. This paper proves that, at the optimum serration wavelength, adjacent valley sources are excited incoherently. One of the most important findings of this paper is that, at the optimum serration wavelength, the sound power radiation from the serrated aerofoil varies inversely proportional to the Strouhal number $St_{h}=fh/U$, where $f$, $h$ and $U$ are frequency, serration amplitude and flow speed, respectively. A simple model is proposed to explain this behaviour. Noise reductions are observed to generally increase with increasing frequency until the frequency at which aerofoil self-noise dominates the interaction noise. Leading edge serrations are also shown to reduce aerofoil self-noise. The mechanism for this phenomenon is explored through particle image velocimetry measurements. Finally, the lift and drag of the serrated aerofoil are obtained through direct measurement and compared against the straight edge baseline aerofoil. It is shown that aerodynamic performance is not substantially degraded by the introduction of the leading edge serrations on the aerofoil.

Numerical Investigation of Hydroelastic Response of a Three-Dimensional Deformable Hydrofoil

2020 ◽  
Author(s):  
Saeed Hosseinzadeh ◽  
Kristjan Tabri
Keyword(s):  
Pressure Coefficient ◽  
Fluid Structure Interaction ◽  
Three Dimensional ◽  
Leading Edge ◽  
Elastic Response ◽  
Fluid Structure ◽  
Strongly Coupled ◽  
Structure Interaction ◽  
Lift And Drag ◽  
Hydroelastic Response

The present study is concerned with the numerical simulation of Fluid-Structure Interaction (FSI) on a deformable three-dimensional hydrofoil in a turbulent flow. The aim of this work is to develop a strongly coupled two-way fluid-structure interaction methodology with a sufficiently high spatial accuracy to examine the effect of turbulent and cavitating flow on the hydroelastic response of a flexible hydrofoil. A 3-D cantilevered hydrofoil with two degrees-of-freedom is considered to simulate the plunging and pitching motion at the foil tip due to bending and twisting deformation. The defined problem is numerically investigated by coupled Finite Volume Method (FVM) and Finite Element Method (FEM) under a two-way coupling method. In order to find a better understanding of the dynamic FSI response and stability of flexible lifting bodies, the fluid flow is modeled in the different turbulence models and cavitation conditions. The flow-induced deformation and elastic response of both rigid and flexible hydrofoils at various angles of attack are studied. The effect of three-dimension body, pressure coefficient at different locations of the hydrofoil, leading-edge and trailing-edge deformation are presented and the results show that because of elastic deformation, the angle of attack increases and it lead to higher lift and drag coefficients. In addition, the deformations are generally limited by stall condition and because of unsteady vortex shedding, the post-stall condition should be considered in FSI simulation of deformable hydrofoil. To evaluate the accuracy of the numerical model, the present results are compared and validated against published experimental data and showed good agreement.

Three-Dimensional Turbulent Flow in the Tip Region of an Axial Compressor Rotor Passage at a Near Stall Condition

2001 ◽  
Author(s):  
Hongwei Ma ◽  
Haokang Jiang
Keyword(s):  
Turbulent Flow ◽  
Large Scale ◽  
Three Dimensional ◽  
Axial Flow ◽  
Leading Edge ◽  
Rotating Stall ◽  
Suction Surface ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Compressor Rotor

This paper presents an experimental study of the three-dimensional turbulent flow field in the tip region of an axial flow compressor rotor passage at a near stall condition. The investigation was conducted in a low-speed large-scale compressor using a 3-component Laser Doppler Velocimetry and a high frequency pressure transducer. The measurement results indicate that a tip leakage vortex is produced very close to the leading edge, and becomes the strongest at about 10% axial chord from the leading edge. Breakdown of the vortex periodically occurs at about 1/3 chord, causing very strong turbulence in the radial direction. Flow separation happens on the tip suction surface at about half chord, prompting the corner vortex migrating toward the pressure side. Tangential migration of the low-energy fluids results in substantial flow blockage and turbulence in the rear of a rotor passage. Unsteady interactions among the tip leakage vortex, the separated vortex and the corner flow should contribute to the inception of the rotating stall in a compressor.

Unsteady Characteristics of Turbulent Flow Over a Rectangular Cavity

2007 ◽  
Author(s):  
Takayuki Mori ◽  
Kenji Naganuma
Keyword(s):  
Turbulent Flow ◽  
Cavity Length ◽  
Three Dimensional ◽  
Dominant Frequency ◽  
Rectangular Cavity ◽  
Circulating Water ◽  
Resonant Interactions ◽  
Image Velocimetry ◽  
Instantaneous Flow Field ◽  
Unsteady Characteristics

Unsteady characteristics of incompressible turbulent flow over a rectangular cavity were investigated with emphasis on its dominant frequency of oscillation and three dimensional features. Particle image velocimetry (PIV) measurements and fluctuating pressure measurements were carried out in a circulating water tunnel varying cavity length-depth ratio L/D=1 to 4 at Reθ=8,300. It is found that the dominant frequency of the fluctuation decreases with the increase of the cavity length and it exhibits broadband behavior instead of resonant one. The instantaneous flow field shows strong three dimensional distortions. Present results indicate that the spanwise distortion may weaken resonant interactions between shear layer and cavity trailing edge.

scholarly journals Role of the tip vortex in the force generation of low-aspect-ratio normal flat plates

2007 ◽  
Vol 581 ◽  
pp. 453-468 ◽  
Author(s):  
MATTHEW J. RINGUETTE ◽  
MICHELE MILANO ◽  
MORTEZA GHARIB
Keyword(s):  
Aspect Ratio ◽  
Vortex Formation ◽  
Three Dimensional ◽  
Unsteady Motion ◽  
Tip Vortex ◽  
Flat Plates ◽  
Low Aspect Ratio ◽  
Start Up ◽  
Image Velocimetry

We investigate experimentally the force generated by the unsteady vortex formation of low-aspect-ratio normal flat plates with one end free. The objective of this study is to determine the role of the free end, or tip, vortex. Understanding this simple case provides insight into flapping-wing propulsion, which involves the unsteady motion of low-aspect-ratio appendages. As a simple model of a propulsive half-stroke, we consider a rectangular normal flat plate undergoing a translating start-up motion in a towing tank. Digital particle image velocimetry is used to measure multiple perpendicular sections of the flow velocity and vorticity, in order to correlate vortex circulation with the measured plate force. The three-dimensional wake structure is captured using flow visualization. We show that the tip vortex produces a significant maximum in the plate force. Suppressing its formation results in a force minimum. Comparing plates of aspect ratio six and two, the flow is similar in terms of absolute distance from the tip, but evolves faster for aspect ratio two. The plate drag coefficient increases with decreasing aspect ratio.

Prediction of vortex lift of non-planar wings by the leading-edge suction analogy

1988 ◽  
Vol 92 (914) ◽  
pp. 154-164 ◽  
Author(s):  
B. C. Hardy ◽  
S. P. Fiddes
Keyword(s):  
Incompressible Flow ◽  
Three Dimensional ◽  
Leading Edge ◽  
Panel Method ◽  
Good Prediction ◽  
Trailing Edge ◽  
Planar Configuration ◽  
Trailing Edge Flaps ◽  
Lift And Drag ◽  
Acceptable Agreement

SummaryA three-dimensional panel method has been used to calculate edge-suction forces for thin sharp-edged wings in incompressible flow. The suction forces have been used to estimate the vortex lift on the wings by means of the leading-edge suction analogy due to Polhamus.The results for planar wings are in acceptable agreement with other methods based on the suction analogy. A limited comparison with results from experiments for non-planar wings revealed good prediction of lift and drag increments associated with the deflection of leading and trailing edge flaps for ‘conventional’ wings of high sweep, but only moderate agreement for a grossly non-planar configuration.

The motion of fibres in turbulent flow

1998 ◽  
Vol 377 ◽  
pp. 47-64 ◽  
Author(s):  
JAMES A. OLSON ◽  
RICHARD J. KEREKES
Keyword(s):  
Turbulent Flow ◽  
Fibre Length ◽  
Integral Length Scale ◽  
Length Scale ◽  
Dispersion Coefficients ◽  
Turbulent Fluid ◽  
Mean Motion ◽  
Fluid Velocities

Equations of mean and fluctuating velocities in rotation and translation have been derived for rigid thin inertialess fibres moving in a turbulent fluid. The derived equations for mean motion are general to fluid velocities that vary nonlinearly along the length of the fibre. From the equations of fluctuating fibre velocity, rotational and translational dispersion coefficients were derived. The resulting dispersion coefficients were shown to decrease as the ratio of fibre length to Lagrangian integral length scale of the turbulence increased.

Experimental Study of Tip-Gap Turbulent Flow Structure

2006 ◽  
Author(s):  
Genglin Tang ◽  
Roger L. Simpson ◽  
Qing Tian
Keyword(s):  
Turbulent Flow ◽  
Turbulent Flows ◽  
Flow Structure ◽  
Three Dimensional ◽  
Leading Edge ◽  
Suction Side ◽  
Normal Velocity ◽  
Compressor Cascade ◽  
Custom Made ◽  
Turbulent Flow Structure

Experimental results are presented from a study of the tip-gap turbulent flow structure in a low-speed linear compressor cascade wind tunnel at Virginia Tech by utilizing surface oil flow visualization, endwall pressure measurements, and instantaneous velocity measurements with a custom-made 3-orthogonal-velocity-component fiber-optic laser-Doppler velocimetry (LDV) system. Tip gap flows are pressure-driven and highly skewed three-dimensional turbulent flows. The crossflow velocity normal to the blade chord is nearly uniform in the mid tip gap and changes substantially from the pressure to suction side due to the local tip pressure loading while the TKE does not vary much across the mid tip gap. The tip gap flow correlations of streamwise and wall normal velocity fluctuations decrease significantly from the leading edge to the trailing edge of the blade due to flow skewing.

Unsteady pitching flat plates

2013 ◽  
Vol 733 ◽  
Author(s):  
Kenneth O. Granlund ◽  
Michael V. Ol ◽  
Luis P. Bernal
Keyword(s):  
Flow Field ◽  
Incidence Angle ◽  
Leading Edge ◽  
Time Base ◽  
Force Measurements ◽  
Flat Plates ◽  
Pivot Point ◽  
Unsteady Effect ◽  
Edge Vortex ◽  
Lift And Drag

AbstractDirect force measurements and qualitative flow visualization were used to compare flow field evolution versus lift and drag for a nominally two-dimensional rigid flat plate executing smoothed linear pitch ramp manoeuvres in a water tunnel. Non-dimensional pitch rate was varied from 0.01 to 0.5, incidence angle from 0 to 90°, and pitch pivot point from the leading to the trailing edge. For low pitch rates, the main unsteady effect is delay of stall beyond the steady incidence angle. Shifting the time base to account for different pivot points leads to collapse of both lift/drag history and flow field history. For higher rates, a leading edge vortex forms; its history also depends on pitch pivot point, but linear shift in time base is not successful in collapsing lift/drag history. Instead, a phenomenological algebraic relation, valid at the higher pitch rates, accounts for lift and drag for different rates and pivot points, through at least 45° incidence angle.

Flame Brush Structure of H2-Air Turbulent Premixed Flames at High Reynolds Numbers

2011 ◽  
Author(s):  
Youngsam Shim ◽  
Shoichi Tanaka ◽  
Masayasu Shimura ◽  
Naoya Fukushima ◽  
Mamoru Tanahashi ◽  
...  
Keyword(s):  
Flame Front ◽  
Layer Structure ◽  
Three Dimensional ◽  
Kinetic Mechanism ◽  
Integral Length Scale ◽  
Length Scale ◽  
Elementary Reactions ◽  
High Reynolds ◽  
Flame Brush ◽  
Turbulent Premixed

Three-dimensional direct numerical simulations (DNSs) of turbulent premixed planar, jet and V flames of hydrogen-air mixture have been conducted to investigate the flame brush and the local flame structures at high Reynolds number turbulences. The detail kinetic mechanism including 12 reactive species and 27 elementary reactions was used to represent the hydrogen-air reaction. For planar flame, flame front is highly fluctuating, and multi-layer structure, multiply-folded flame front and unburned mixture island which lead to corresponding increase of the flame brush thickness can be observed. The flame brush thickness of the planar flame is relatively uniform along the flame front, and is about 2∼3 times the integral length scale (l), which is defined from an energy spectrum. For the jet and V flames, the flame brush thicknesses grow with the streamwise direction from about 0.5∼1 times the integral length scale (l) to about 2∼3 times the integral length scale (l) due to the highly fluctuating flame front at the downstream region.

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