Aeroelastic Dynamics of a NACA 0012 Airfoil in the Transitional Reynolds Number Regime

2006 ◽  
Author(s):  
Dominique Poirel ◽  
Yael Harris ◽  
Aze´mi Benaissa
Keyword(s):  
Surface Roughness ◽  
Reynolds Number ◽  
Degrees Of Freedom ◽  
Initial Conditions ◽  
Reynolds Numbers ◽  
Flow Structures ◽  
Hot Wire ◽  
Initial Work ◽  
Naca 0012 ◽  
The Relationship

The work discussed herein is a focused extension of a series of studies that were carried out at the Aeroelasticity Laboratory of the Royal Military College of Canada in recent years. Initial work revealed the presence of self-excited oscillations over certain ranges of airspeed when a NACA 0012 airfoil was immersed in the laboratory’s wind tunnel and allowed to oscillate freely in both pitch and heave. The range of airspeeds tested corresponded to Reynolds numbers in the low-to-moderate regime. While the aeroelastic apparatus is capable of two-degrees-of-freedom motion, the present work concerns only the motion of the airfoil when it is constrained to rotate in pure pitch. A parametric investigation is presently being undertaken to more fully comprehend the airfoil’s pitch behaviour, specifically the amplitude and frequency of its oscillations which are observed in the following range of chord based Reynolds numbers: 5.0 × 104 ≤ Rec ≤ 1.2 × 105. This paper focuses on the effect of the stiffness of the springs used in the apparatus. Other parameters such as surface roughness, turbulence intensity, temperature and initial conditions are also briefly discussed. In conjunction with the pitch oscillation measurements, preliminary results reveal vortices to be present in the wake. In an attempt to determine the frequency and character of these flow structures, as well as to understand the relationship between the airfoil motion and wake dynamics, hot-wire anemometry measurements have been performed.

Effect of Surface Roughness on Gaseous Flow Through Microchannels

2000 ◽  
Author(s):  
Stephen E. Turner ◽  
Hongwei Sun ◽  
Mohammad Faghri ◽  
Otto J. Gregory
Keyword(s):  
Surface Roughness ◽  
Reynolds Number ◽  
Friction Factor ◽  
Reynolds Numbers ◽  
Helium Flow ◽  
Local Pressure ◽  
Aspect Ratios ◽  
Corrugated Surfaces ◽  
Flow Through ◽  
Effect Of Surface

Abstract This paper presents an experimental investigation on nitrogen and helium flow through microchannels etched in silicon with hydraulic diameters between 10 and 40 microns, and Reynolds numbers ranging from 0.3 to 600. The objectives of this research are (1) to fabricate microchannels with uniform surface roughness and local pressure measurement; (2) to determine the friction factor within the locally fully developed region of the microchannel; and (3) to evaluate the effect of surface roughness on momentum transfer by comparison with smooth microchannels. The friction factor results are presented as the product of friction factor and Reynolds number plotted against Reynolds number. The following conclusions have been reached in the present investigation: (1) microchannels with uniform corrugated surfaces can be fabricated using standard photolithographic processes; and (2) surface features with low aspect ratios of height to width have little effect on the friction factor for laminar flow in microchannels.

Supercritical Reynolds number simulation for two-dimensional flow over circular cylinders

1975 ◽  
Vol 70 (3) ◽  
pp. 529-542 ◽  
Author(s):  
Edmond Szechenyi
Keyword(s):  
Surface Roughness ◽  
Reynolds Number ◽  
Reynolds Numbers ◽  
Practical Significance ◽  
Circular Cylinders ◽  
Wind Tunnels ◽  
Bluff Bodies ◽  
Wide Range ◽  
Two Dimensional Flow ◽  
Different Diameters

In wind-tunnel tests on bluff bodies the Reynolds number is often limited to values that are very much smaller than those of the flows being simulated. In such cases the experiments may have no practical significance whatsoever since both the fluctuating and the steady aerodynamic phenomena can vary considerably with Reynolds number.This difficulty was encountered in an investigation of supercritical incompressible flow over cylinders, and an attempt at artificially increasing the Reynolds number by means of surface roughness was made. In order to evaluate this simulation technique, the influence of various grades of surface roughness on the aerodynamic forces acting on cylinders of different diameters was studied over a wide range of Reynolds numbers in two very different wind tunnels. The results allow very positive conclusions to be drawn.

Hot-wire spatial resolution issues in wall-bounded turbulence

2009 ◽  
Vol 635 ◽  
pp. 103-136 ◽  
Author(s):  
N. HUTCHINS ◽  
T. B. NICKELS ◽  
I. MARUSIC ◽  
M. S. CHONG
Keyword(s):  
Reynolds Number ◽  
Boundary Layers ◽  
Spatial Resolution ◽  
Reynolds Numbers ◽  
Energy Spectra ◽  
Small Scale ◽  
Wire Length ◽  
Hot Wire ◽  
Wide Range ◽  
Near Wall

Careful reassessment of new and pre-existing data shows that recorded scatter in the hot-wire-measured near-wall peak in viscous-scaled streamwise turbulence intensity is due in large part to the simultaneous competing effects of the Reynolds number and viscous-scaled wire length l+. An empirical expression is given to account for these effects. These competing factors can explain much of the disparity in existing literature, in particular explaining how previous studies have incorrectly concluded that the inner-scaled near-wall peak is independent of the Reynolds number. We also investigate the appearance of the so-called outer peak in the broadband streamwise intensity, found by some researchers to occur within the log region of high-Reynolds-number boundary layers. We show that the ‘outer peak’ is consistent with the attenuation of small scales due to large l+. For turbulent boundary layers, in the absence of spatial resolution problems, there is no outer peak up to the Reynolds numbers investigated here (Reτ = 18830). Beyond these Reynolds numbers – and for internal geometries – the existence of such peaks remains open to debate. Fully mapped energy spectra, obtained with a range of l+, are used to demonstrate this phenomenon. We also establish the basis for a ‘maximum flow frequency’, a minimum time scale that the full experimental system must be capable of resolving, in order to ensure that the energetic scales are not attenuated. It is shown that where this criterion is not met (in this instance due to insufficient anemometer/probe response), an outer peak can be reproduced in the streamwise intensity even in the absence of spatial resolution problems. It is also shown that attenuation due to wire length can erode the region of the streamwise energy spectra in which we would normally expect to see kx−1 scaling. In doing so, we are able to rationalize much of the disparity in pre-existing literature over the kx−1 region of self-similarity. Not surprisingly, the attenuated spectra also indicate that Kolmogorov-scaled spectra are subject to substantial errors due to wire spatial resolution issues. These errors persist to wavelengths far beyond those which we might otherwise assume from simple isotropic assumptions of small-scale motions. The effects of hot-wire length-to-diameter ratio (l/d) are also briefly investigated. For the moderate wire Reynolds numbers investigated here, reducing l/d from 200 to 100 has a detrimental effect on measured turbulent fluctuations at a wide range of energetic scales, affecting both the broadband intensity and the energy spectra.

Evolution of zero-pressure-gradient boundary layers from different tripping conditions

2015 ◽  
Vol 783 ◽  
pp. 379-411 ◽  
Author(s):  
I. Marusic ◽  
K. A. Chauhan ◽  
V. Kulandaivelu ◽  
N. Hutchins
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Boundary Layers ◽  
Initial Conditions ◽  
Reynolds Numbers ◽  
Streamwise Velocity ◽  
Mean Flow ◽  
Flow Parameters ◽  
The Mean ◽  
Inflow Conditions

In this paper we study the spatial evolution of zero-pressure-gradient (ZPG) turbulent boundary layers from their origin to a canonical high-Reynolds-number state. A prime motivation is to better understand under what conditions reliable scaling behaviour comparisons can be made between different experimental studies at matched local Reynolds numbers. This is achieved here through detailed streamwise velocity measurements using hot wires in the large University of Melbourne wind tunnel. By keeping the unit Reynolds number constant, the flow conditioning, contraction and trip can be considered unaltered for a given boundary layer’s development and hence its evolution can be studied in isolation from the influence of inflow conditions by moving to different streamwise locations. Careful attention was given to the experimental design in order to make comparisons between flows with three different trips while keeping all other parameters nominally constant, including keeping the measurement sensor size nominally fixed in viscous wall units. The three trips consist of a standard trip and two deliberately ‘over-tripped’ cases, where the initial boundary layers are over-stimulated with additional large-scale energy. Comparisons of the mean flow, normal Reynolds stress, spectra and higher-order turbulence statistics reveal that the effects of the trip are seen to be significant, with the remnants of the ‘over-tripped’ conditions persisting at least until streamwise stations corresponding to $Re_{x}=1.7\times 10^{7}$ and $x=O(2000)$ trip heights are reached (which is specific to the trips used here), at which position the non-canonical boundary layers exhibit a weak memory of their initial conditions at the largest scales $O(10{\it\delta})$, where ${\it\delta}$ is the boundary layer thickness. At closer streamwise stations, no one-to-one correspondence is observed between the local Reynolds numbers ($Re_{{\it\tau}}$, $Re_{{\it\theta}}$ or $Re_{x}$ etc.), and these differences are likely to be the cause of disparities between previous studies where a given Reynolds number is matched but without account of the trip conditions and the actual evolution of the boundary layer. In previous literature such variations have commonly been referred to as low-Reynolds-number effects, while here we show that it is more likely that these differences are due to an evolution effect resulting from the initial conditions set up by the trip and/or the initial inflow conditions. Generally, the mean velocity profiles were found to approach a constant wake parameter ${\it\Pi}$ as the three boundary layers developed along the test section, and agreement of the mean flow parameters was found to coincide with the location where other statistics also converged, including higher-order moments up to tenth order. This result therefore implies that it may be sufficient to document the mean flow parameters alone in order to ascertain whether the ZPG flow, as described by the streamwise velocity statistics, has reached a canonical state, and a computational approach is outlined to do this. The computational scheme is shown to agree well with available experimental data.

Investigation of Large-Scale Structures Behind a Single Tube (Finned and Foamed Tube) Using Two-Point Correlations

2014 ◽  
Author(s):  
Iman Ashtiani Abdi ◽  
Morteza Khashehchi ◽  
Kamel Hooman
Keyword(s):  
Reynolds Number ◽  
Large Scale ◽  
Cross Flow ◽  
Reynolds Numbers ◽  
Finned Tube ◽  
Flow Structures ◽  
Analysis Tool ◽  
Standard Case ◽  
Statistical Analysis Tool ◽  
Point Correlation

Flow structures downstream of a finned-tube are compared to those of an identical pipe; with the same diameter and length, covered with a foam layer. The standard case of cross-flow over a bare tube, i.e. no surface extension, is also tested as a benchmark. Experiments are conducted in a wind tunnel at Reynolds numbers of 4000 and 16000. Particle image velocimetry (PIV) was used for flow visualization on two different perpendicular planes. To characterize the size of the flow structures downstream of the tube, for each of the aforementioned case, two-point correlation, as a statistical analysis tool, has been used. It has been observed that by decreasing the Reynolds number, the flow structures are further stretched in streamwise direction for both bare and finned-tube cases. This is, however, more pronounced with the former. Interestingly, with a foam-wrapped tube the sizes of the flow structures are found to be independent of the Reynolds number. Finally, the structure sizes are smaller in the case of the foam-wrapped tube compared to those of finned-tube.

Transitory Behavior of Synthetic Jets

2005 ◽  
Author(s):  
Michael Amitay ◽  
Florine Cannelle
Keyword(s):  
Reynolds Number ◽  
Steady State ◽  
Input Signal ◽  
Mass Flux ◽  
Reynolds Numbers ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Hot Wire ◽  
Stroke Length ◽  
Zero Net Mass Flux

The transitory behavior of an isolated synthetic (zero net mass flux) jet was investigated experimentally using PIV and hot-wire anemometry. In the present work, the synthetic jet was produced over a broad range of length- and time-scales, where three formation frequencies, f = 300, 917, and 3100Hz, several stroke lengths (between 5 and 50 times the slit width) and Reynolds numbers (between 85 and 408) were tested. The transitory behavior, following the onset of the input signal, in planes along and across the slit was measured. It was found that the time it takes the synthetic jet to become fully developed depends on the stroke length, formation frequency and Reynolds number. In general, the transients consist of four stages associated with the merging of vortices in both cross-stream and spanwise planes that grow in size, which lead to the pinch off of the leading vortex before the jet reaches its steady-state.

scholarly journals A Detailed Study: CFD Analysis of NACA 0012 at Varying Angles of Attack

2021 ◽  
Vol 9 (VII) ◽  
pp. 2330-2336
Author(s):  
Vani Sadadiwala
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Wind Tunnel ◽  
Computational Analysis ◽  
Cfd Analysis ◽  
Reliable Source ◽  
Relationship Of ◽  
Naca 0012 ◽  
The Relationship ◽  
Symmetric Profile

This work reflects the study and detailed analysis of NACA 0012 airfoil at different angles of attack with a constant value of Reynolds Number. The geometrical designing of the airfoil is done using FreeCad and the computational analysis is carried out using Simflow 4.0- OpenFoam Interface. The analysis is fully based upon the concepts of FEM and CFD. The velocity is kept constant with various angles of attack. CFD methods are reliable source of analysis and hence can be replaced with the experimental wind tunnel methods. Boundary layer approaches were taken into consideration using the meshing techniques. The main purpose of this work is to study the symmetric profile of NACA 0012 with varying angles and the behaviour of 0012 at specific conditions. At the end, various graphs are plotted depicting the relationship of Angle of Attack with other dimensionless quantities.

scholarly journals Dynamics of spatially localized states in transitional plane Couette flow

2019 ◽  
Vol 867 ◽  
pp. 414-437 ◽  
Author(s):  
Anton Pershin ◽  
Cédric Beaume ◽  
Steven M. Tobias
Keyword(s):  
Reynolds Number ◽  
Couette Flow ◽  
Initial Conditions ◽  
Reynolds Numbers ◽  
Localized States ◽  
Transition To Turbulence ◽  
Dynamical Structure ◽  
Plane Couette Flow ◽  
Homoclinic Snaking ◽  
Chaotic Transients

Unsteady spatially localized states such as puffs, slugs or spots play an important role in transition to turbulence. In plane Couette flow, steady versions of these states are found on two intertwined solution branches describing homoclinic snaking (Schneider et al., Phys. Rev. Lett., vol. 104, 2010, 104501). These branches can be used to generate a number of spatially localized initial conditions whose transition can be investigated. From the low Reynolds numbers where homoclinic snaking is first observed ($Re<175$) to transitional ones ($Re\approx 325$), these spatially localized states traverse various regimes where their relaminarization time and dynamics are affected by the dynamical structure of phase space. These regimes are reported and characterized in this paper for a $4\unicode[STIX]{x03C0}$-periodic domain in the streamwise direction as a function of the two remaining variables: the Reynolds number and the width of the localized pattern. Close to the snaking, localized states are attracted by spatially localized periodic orbits before relaminarizing. At larger values of the Reynolds number, the flow enters a chaotic transient of variable duration before relaminarizing. Very long chaotic transients ($t>10^{4}$) can be observed without difficulty for relatively low values of the Reynolds number ($Re\approx 250$).

Experimental Measurements of the Wake of a Sphere at Subcritical Reynolds Numbers

2021 ◽  
Vol 143 (6) ◽  
Author(s):  
Robert Muyshondt ◽  
Thien Nguyen ◽  
Y. A. Hassan ◽  
N. K. Anand
Keyword(s):  
Reynolds Number ◽  
Spectral Analysis ◽  
Kinetic Energy ◽  
Cross Correlation ◽  
Reynolds Numbers ◽  
Velocity Fields ◽  
Stereoscopic Particle Image Velocimetry ◽  
Recirculation Region ◽  
Flow Structures ◽  
Vortex Identification

Abstract This work experimentally investigated the flow phenomena and vortex structures in the wake of a sphere located in a water loop at Reynolds numbers of Re = 850, 1,250, and 1,700. Velocity fields in the wake region were obtained by applying the time-resolved stereoscopic particle image velocimetry (TR-SPIV) technique. From the acquired TR-SPIV velocity vector fields, the statistical values of mean and fluctuating velocities were computed. Spectral analysis, two-point velocity–velocity cross-correlation, proper orthogonal decomposition (POD) and vortex identification analyses were also performed. The velocity fields show a recirculation region that decreases in length with an increase of Reynolds numbers. The power spectra from the spectral analysis had peaks corresponding to a Strouhal number of St = 0.2, which is a value commonly found in the literature studies of flow over a sphere. The two-point cross-correlation analysis revealed elliptical structures in the wake, with estimated integral length scales ranging between 12% and 63% of the sphere diameter. The POD analysis revealed the statistically dominant flow structures that captured the most flow kinetic energy. It is seen that the flow kinetic energy captured in the smaller scale flow structures increased as Reynolds number increased. The POD modes contained smaller structure as the Reynolds number increased and as mode order increased. In addition, spectral analysis performed on the POD temporal coefficients revealed peaks corresponding to St = 0.2, similar to the spectral analysis on the fluctuating velocity. The ability of POD to produce low-order reconstructions of the flow was also utilized to facilitate vortex identification analysis, which identified average vortex sizes of 0.41D for Re1, 0.33D for Re2, and 0.32D for Re3.

Measurements of Turbulent Transport in a Square Channel with One Ribbed Wall

2022 ◽  
Author(s):  
Sebastian Ruck ◽  
Frederik Arbeiter
Keyword(s):  
Reynolds Number ◽  
Shear Stress ◽  
Shear Layer ◽  
Reynolds Shear Stress ◽  
Turbulent Transport ◽  
Reynolds Numbers ◽  
Flow Structures ◽  
Channel Height ◽  
Height Ratio ◽  
Square Channel

Abstract The velocity field of the fully developed turbulent flow in a one-sided ribbed square channel (rib-height-to-channel-height ratio of k/h = 0.0667, rib-pitch-to-rib-height ratio of p/k = 9) were measured at Reynolds numbers (based on the channel height h and the mean bulk velocity uB) of Reh = 50 000 and 100 000 by means of Laser-Doppler-Anemometry (LDA). Triple velocity correlations differed slightly between both Reynolds numbers when normalized by the bulk velocity and the channel height, similarly to the first- and second-order statistical moments of the velocity. Their near-wall behavior reflected the crucial role of turbulent transport near the rib crest and within the separated shear layer. Sweep events occurred with the elongated flow structures of the flapping shear layer and gained in importance towards the channel bottom wall, while strong ejection events near the rib leading and trailing edges coincided with flow structures bursting away from the wall. Despite the predominant occurrence of sweep events close to the ribbed wall within the inter-rib spacing, ejection events contributed with higher intensity to the Reynolds shear stress. Ejection and sweep events and their underlying transport phenomena contributing to the Reynolds shear stress were almost Reynolds number-insensitive in the resolved flow range. The invariance to the Reynolds number can be of benefit for the use of scale-resolving simulation methods in the design process of rib structures for heat exchange applications.

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