The impact of streamwise convex curvature on the supersonic turbulent boundary layer

2017 ◽  
Vol 29 (11) ◽  
pp. 116106 ◽  
Author(s):  
Qian-cheng Wang ◽  
Zhen-guo Wang ◽  
Yu-xin Zhao
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Convex Curvature ◽  
The Impact

Dynamics of Aeolian Sand Streamers and Airflow Turbulence over a Beach Surface

2021 ◽  
Author(s):  
Andreas Baas
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Temporal Variability ◽  
Large Scale ◽  
Sonic Anemometer ◽  
Dynamic Structure ◽  
Sand Transport ◽  
Video Imagery ◽  
Spatio Temporal ◽  
The Impact

<p>Sand transport by wind over granular beds displays dynamic structure and organisation in the form of streamers (aka ‘sand snakes’) that appear, meander and intertwine, and then dissipate as they are advected downwind. These patterns of saltating grain populations are thought to be initiated and controlled by coherent flow structures in the turbulent boundary layer wind that scrape over the bed surface raking up sand into entrainment. Streamer behaviour is thus fundamental to understanding sand transport dynamics, in particular its strong spatio-temporal variability, and is equally relevant to granular transport in other geophysical flows (fluvial, submarine).</p><p>This paper presents findings on streamer dynamics and associated wind turbulence observed in a field experiment on a beach, with measurements from 30Hz video-imagery using Large-Scale Particle Image Velocimetry (LS-PIV), combined with 50Hz wind measurements from 3D sonic anemometry and co-located sand transport rate monitoring using an array of laser particle counters (‘Wenglors’), all taking place over an area of ~10 m<sup>2</sup> and over periods of several minutes. The video imagery was used to identify when and where streamers advected past the sonic anemometer and laser sensors so that relationships could be detected between the passage of turbulence structures in the airflow and the length- and time-scales, propagation speeds, and sand transport intensities of associated streamers. The findings form the basis for a phenomenological model of streamer dynamics under turbulent boundary layer flows that predicts the impact of spatio-temporal variability on local measurement of sand transport.</p>

scholarly journals Active control of multiscale features in wall-bounded turbulence

2019 ◽  
Vol 36 (1) ◽  
pp. 12-21 ◽  
Author(s):  
Xiaotong Cui ◽  
Nan Jiang ◽  
Xiaobo Zheng ◽  
Zhanqi Tang
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Turbulent Energy ◽  
Streamwise Velocity ◽  
Discrete Wavelet ◽  
Wall Region ◽  
Mean Velocity ◽  
Pzt Actuator ◽  
The Impact ◽  
Near Wall

Abstract This study experimentally investigates the impact of a single piezoelectric (PZT) actuator on a turbulent boundary layer from a statistical viewpoint. The working conditions of the actuator include a range of frequencies and amplitudes. The streamwise velocity signals in the turbulent boundary layer flow are measured downstream of the actuator using a hot-wire anemometer. The mean velocity profiles and other basic parameters are reported. Spectra results obtained by discrete wavelet decomposition indicate that the PZT vibration primarily influences the near-wall region. The turbulent intensities at different scales suggest that the actuator redistributes the near-wall turbulent energy. The skewness and flatness distributions show that the actuator effectively alters the sweep events and reduces intermittency at smaller scales. Moreover, under the impact of the PZT actuator, the symmetry of vibration scales’ velocity signals is promoted and the structural composition appears in an orderly manner. Probability distribution function results indicate that perturbation causes the fluctuations in vibration scales and smaller scales with high intensity and low intermittency. Based on the flatness factor, the bursting process is also detected. The vibrations reduce the relative intensities of the burst events, indicating that the streamwise vortices in the buffer layer experience direct interference due to the PZT control.

Pressure fluctuations produced by forward steps immersed in a turbulent boundary layer

2014 ◽  
Vol 756 ◽  
pp. 384-421 ◽  
Author(s):  
Manuj Awasthi ◽  
William J. Devenport ◽  
Stewart A. L. Glegg ◽  
Jonathan B. Forest
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Pressure Fluctuations ◽  
Field Measurements ◽  
Reynolds Numbers ◽  
Step Height ◽  
Stream Velocity ◽  
Step Size ◽  
High Reynolds ◽  
The Impact

AbstractExperiments have been performed on the disturbance of a high-Reynolds-number turbulent boundary layer by three forward steps with sizes close to 3.8, 15 and 60 % of the boundary layer thickness. Particular attention is focused on the impact of the steps on the fluctuating surface pressure field. Measurements were made from 5 boundary layer thicknesses upstream to 22 boundary layer thicknesses downstream of the step, a distance equivalent to over 600 step heights for the smallest step size. Flow speeds of 30 and $\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}60\ \mathrm{m}\ {\mathrm{s}}^{-1}$ were studied, corresponding to boundary layer momentum thickness Reynolds numbers of 15 500 and 26 600 and step size Reynolds numbers from 6640 to 213 000. The steps produce a disturbance to the boundary layer pressure spectrum that scales on step size and decays remarkably slowly with distance downstream. When normalized on step height and free-stream velocity, the disturbance is self-similar and appears to develop almost independently of the enveloping boundary layer. The disturbance is still clearly visible at 150 step heights downstream of the mid-size step. Pressure correlations show the disturbance to be characterized by organized quasiperiodic motions that become visible well downstream of reattachment. The coherence and scale of these motions, as seen in the wall pressure correlations, scales on the step height and thus their visibility relative to the boundary layer grows rapidly as the step size is increased.

Turbulent boundary layer relaxation from convex curvature

1990 ◽  
Vol 211 ◽  
pp. 529-556 ◽  
Author(s):  
Amy E. Alving ◽  
Alexander J. Smits ◽  
Jonathan H. Watmuff
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Large Scale ◽  
Stable State ◽  
Relaxation Behaviour ◽  
Mean Flow ◽  
Mean Velocity ◽  
Measuring Station ◽  
The Mean ◽  
Convex Curvature

A study was undertaken to examine the flat plate relaxation behaviour of a turbulent boundary layer recovering from 90° of strong convex curvature (δ0/R = 0.08), for a length of ≈ 90δ0 after the end of curvature, where δ0 is the boundary layer thickness at the start of the curvature. The results show that the relaxation behaviour of the mean flow and the turbulence are quite different. The mean velocity profile and skin friction coefficient asymptotically approach the unperturbed state and at the last measuring station appear to be fully recovered. The turbulence relaxation, however, occurs in several stages over a much longer distance. In the first stage, a stress ‘bore’ (a region of elevated stress) is generated near the wall, and the bore thickens with distance downstream. Eventually it fills the whole boundary layer, but the stress levels continue to rise beyond their self-preserving values. Finally the stresses begin a gradual decline, but at the last measuring station they are still well above the unperturbed levels, and the ratios of the Reynolds stresses are distorted. These results imply a reorganization of the large-scale structure into a new quasi-stable state. The long-lasting effects of curvature highlight the sensitivity of a boundary layer to its condition of formation.

Saltating particles in a turbulent boundary layer: experiment and theory

2009 ◽  
Vol 625 ◽  
pp. 47-74 ◽  
Author(s):  
M. CREYSSELS ◽  
P. DUPONT ◽  
A. OULD EL MOCTAR ◽  
A. VALANCE ◽  
I. CANTAT ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Wind Speed ◽  
Turbulent Boundary Layer ◽  
Particle Concentration ◽  
Low Velocity ◽  
Wind Speeds ◽  
Image Velocimetry ◽  
The University ◽  
Velocity Moments ◽  
The Impact

The work presented here focuses on the analysis of a turbulent boundary layer saturated with saltating particles. Experiments were carried out in a wind tunnel 15m long and 0.6m wide at the University of Aarhus in Denmark with sand grains 242 μm in size for wind speeds ranging from the threshold speed to twice its value. The saltating particles were analysed using particle image velocimetry (PIV) and particle-tracking velocimetry (PTV), and vertical profiles of particle concentration and velocity were extracted. The particle concentration was found to decrease exponentially with the height above the bed, and the characteristic decay height was independent of the wind speed. In contrast with the logarithmic profile of the wind speed, the grain velocity was found to vary linearly with the height. In addition, the measurements indicated that the grain velocity profile depended only slightly on the wind speed. These results are shown to be closely related to the features of the splash function that characterizes the impact of the saltating particles on a sandbed. A numerical simulation is developed that explicitly incorporates low-velocity moments of the splash function in a calculation of the boundary conditions that apply at the bed. The overall features of the experimental measurements are reproduced by simulation.

INVESTIGATION OF THE POSSIBILITY OF TURBULENT BOUNDARY LAYER DRAG REDUCTION UNDER THE IMPACT OF DIELECTRIC BARRIER DISCHARGE

2012 ◽  
Vol 43 (5) ◽  
pp. 551-569
Author(s):  
Mikhail Naumovich Kogan ◽  
Vladimir Mikhailovich Litvinov ◽  
Tatiana Anatolyevna Pimenova ◽  
Aleksandr Aleksandrovich Uspenskii
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Drag Reduction ◽  
Dielectric Barrier Discharge ◽  
Barrier Discharge ◽  
Dielectric Barrier ◽  
The Impact
Sign in / Sign up

Export Citation Format

Share Document