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1.
An active turbulence generating grid, based on the rotating-vane design of Makita (1991), was developed for a large wind tunnel. At 2.14 m square, the grid is the largest of this type ever developed. To improve
the isotropy of the turbulence generated, the grid was placed in the wind tunnel contraction. Measurements show that the grid
produces a closely uniform mean flow and homogeneous isotropic turbulence to within two integral scales from the wall. By
systematically varying the flow speed and parameters controlling the random motion of the vanes, grid turbulence with a wide
variety of characteristics was produced and the dependence of those characteristics on the operating parameters of the grid
revealed. Taylor Reynolds numbers of the grid turbulence varied from 100 to 1,360 and integral scales from 5 to almost 70 cm.
The extreme cases represent some of the highest Reynolds number and largest scale homogeneous turbulent flows ever generated
in a wind tunnel. 相似文献
2.
Large eddy simulation (LES) is carried out to investigate the turbulent boundary-layer flows over a hill-shaped model with
a steep or relatively moderate slope at moderately high Reynolds numbers (Re = O(103)) defined by the hill height and the velocity at the hill height. The study focuses on the effects of surface roughness and
curvature. For Sub-grid Scale (SGS) modeling of LES, both the dynamic Smagorinsky model (DSM) and the dynamic mixed model
(DMM) are applied. The behavior of the separated shear layer and the vortex motion are affected by the oncoming turbulence,
such that the shear layer comes close to the ground surface, or the size of a separation region becomes small because of the
earlier instability of the separated shear layer. Appropriate measures are required to generate the inflow turbulence. The
methods of Lund et al. (J. Comput. Phys., 140:233–258, 1998) and Nozawa and Tamura (J. Wind Eng. Ind. Aerodyn., 90:1151–1162, 2002; The 4th European and African Conference on Wind Engineering, 1–6, 2005) are employed to simulate the smooth- and rough-wall turbulent boundary layers in order to generate time-sequential
data of inflow turbulence. This paper discusses the unsteady phenomena of the wake flows over the smooth and rough 2D hill-shaped
obstacles and aims to clarify the roughness effects on the flow patterns and the turbulence statistics distorted by the hill.
Numerical validation is conducted by comparing the simulation results with wind tunnel experiment data for the same hill shape
at almost the same Re. The applicability of DSM and DMM are discussed, focusing on the recirculation region behind a steep hill. 相似文献
3.
A note on wind-tunnel turbulence measurements with DPIV 总被引:1,自引:1,他引:0
At moderate Reynolds numbers (104 ≤ Re ≤ 105), the performance of lifting surfaces is strongly affected by the potential for laminar boundary layer separation and subsequent
reattachment and the use of high-quality, low-turbulence wind tunnels is essential in characterising flight at comparatively
small scales (where the wing chord may be from 1 to 5 cm in length) and low speeds (on the order of 10 m/s). Measurement of
the existing turbulence levels in such facilities is hard and has not been achieved using DPIV methods due to the relatively
small bandwidth of measurable velocities. A series of experiments is reported here where DPIV sampling parameters are driven
beyond their normal range in an attempt to measure turbulence levels in a low turbulence wind tunnel. The results show that
DPIV can measure the background turbulence, and therefore its instantaneous structure. The measurements also reveal certain
challenges in investigating the aerodynamic performance of small-scale flying devices. 相似文献
4.
Turbulence measurements are reported on the three-dimensional turbulent boundary layer along the centerline of the flat endwall
in a 30° bend. Profiles of mean velocities and Reynolds stresses were obtained down to y
+≈2 for the mean flow and y
+≈8 for the turbulent stresses. Mean velocity data collapsed well on a simple law-of-the-wall based on the magnitude of the
resultant velocity. The turbulence intensity and turbulent shear stress magnitude both increased with increased three-dimensionality.
The ratio of these two quantities, the a
1 structure parameter, decreased in the central regions of the boundary layer and showed profile similarity for y
+<50. The shear stress vector angle lagged behind the velocity gradient vector angle in the outer region of the boundary layer,
however there was an indication that the shear stress vector tends to lead the velocity gradient vector close to the wall.
Received: 16 July 1996/Accepted: 14 July 1997 相似文献
5.
Measurements using stereo particle image velocimetry are presented for a developing turbulent boundary layer in a wind tunnel
with a Mach 2.75 free stream. As the boundary layer exits from the tunnel nozzle and moves through the wave-free test section,
small initial departures from equilibrium turbulence relax, and the boundary layer develops toward the equilibrium zero-pressure-gradient
form. This relaxation process is quantified by comparison of first and second order mean, fluctuation, and gradient statistics
to classical inner and outer layer scalings. Simultaneous measurement of all three instantaneous velocity components enables
direct assessment of the complete turbulence anisotropy tensor. Profiles of the turbulence Mach number show that, despite
the M = 2.75 free stream, the incompressibility relation among spatial gradients in the velocity fluctuations applies. This result
is used in constructing various estimates of the measured-dissipation rate, comparisons among which show only remarkably small
differences over most of the boundary layer. The resulting measured-dissipation profiles, together with measured profiles
of the turbulence kinetic energy and mean-flow gradients, enable an assessment of how the turbulence anisotropy relaxes toward
its equilibrium zero-pressure-gradient state. The results suggest that the relaxation of the initially disturbed turbulence
anisotropy profile toward its equilibrium zero-pressure-gradient form begins near the upper edge of the boundary layer and
propagates downward through the defect layer. 相似文献
6.
Babanin and Haus (J Phys Oceanogr 39:2675–2679, 2009) recently presented evidence of near-surface turbulence generated below steep non-breaking deep-water waves. They proposed
a threshold wave parameter a
2ω/ν = 3,000 for the spontaneous occurrence of turbulence beneath surface waves. This is in contrast to conventional understanding
that irrotational wave theories provide a good approximation of non-wind-forced wave behaviour as validated by classical experiments.
Many laboratory wave experiments were carried out in the early 1960s (e.g. Wiegel 1964). In those experiments, no evidence of turbulence was reported, and steep waves behaved as predicted by the high-order irrotational
wave theories within the accuracy of the theories and experimental techniques at the time. This contribution describes flow
visualisation experiments for steep non-breaking waves using conventional dye techniques in the wave boundary layer extending
above the wave trough level. The measurements showed no evidence of turbulent mixing up to a value of a
2ω/ν = 7,000 at which breaking commenced in these experiments. These present findings are in accord with the conventional understandings
of wave behaviour. 相似文献
7.
Saša Kenjereš 《Theoretical and Computational Fluid Dynamics》2009,23(6):471-489
We conducted a large eddy simulation (LES) of a locally applied electromagnetic control of turbulent thermal convection of
an electrically conductive fluid (electrolyte solution) inside of a slender enclosure. Generic configurations, consisting
of two or three magnets of opposite polarities located below the lower wall, and two oppositely charged electrodes along the
side walls, are considered. The neutral situation (pure thermal convection) is selected to be in turbulent regime at Ra = 107, Pr = 7. A magnetically extended Smagorinsky type model for the subgrid turbulent stresses and a simple-gradient diffusion model
for the subgrid turbulent heat fluxes are used. Different intensities of applied DC current through electrodes are imposed.
The effects of the resulting Lorentz force on flow, turbulence reorganisation and wall-heat transfer are analysed. It is demonstrated
that significant flow and turbulence structure reorganisation takes place in the proximity of the lower horizontal wall and
in the central parts of the enclosure—even for weak DC current of I = 1 A. Significant turbulence increase, generated by the elevated electromagnetic mixing, produced significant enhancements
of the wall-heat transfer—up to 70% for the 2-magnet configuration. 相似文献
8.
A thre-dimensional direct numerical simulation is combined with a laboratory study to describe the turbulent flow in an enclosed
annular rotor-stator cavity characterized by a large aspect ratio G = (b − a)/h = 18.32 and a small radius ratio a/b = 0.152, where a and b are the inner and outer radii of the rotating disk and h is the interdisk spacing. The rotation rate Ω considered is equivalent to the rotational Reynolds number Re = Ωb
2/ν= 9 .5 × 104 (ν the kinematic viscosity of water). This corresponds to a value at which experiment has revealed that the stator boundary
layer is turbulent, whereas the rotor boundary layer is still laminar. Comparisons of the computed solution with velocity
measurements have given good agreement for the mean and turbulent fields. The results enhance evidence of weak turbulence
by comparing the turbulence properties with available data in the literature (Lygren and Andersson, J Fluid Mech 426:297–326,
2001). An approximately self-similar boundary layer behavior is observed along the stator. The wall-normal variations of the structural
parameter and of characteristic angles confirm that this boundary layer is three-dimensional. A quadrant analysis (Kang et
al., Phys Fluids 10:2315–2322, 1998) of conditionally averaged velocities shows that the asymmetries obtained are dominated by Reynolds stress-producing events
in the stator boundary layer. Moreover, Case 1 vortices (with a positive wall induced velocity) are found to be the major
source of generation of special strong events, in agreement with the conclusions of Lygren and Andersson (J Fluid Mech 426:297–326,
2001). 相似文献
9.
The influence of the shear number on the turbulence evolution in a stably stratified fluid is investigated using direct numerical
simulations on grids with up to 512 × 256 × 256 points. The shear number SK/ε is the ratio of a turbulence time scale K/ε to the shear time scale 1/S. Simulations are performed at two initial values of the Reynolds number Re
Λ= 44.72 and Re
Λ= 89.44. When the shear number is increased from small to moderate values, the nondimensional growth rate γ= (1/SK)dK/dt of the turbulent kinetic energy K increases since the shear forcing and its associated turbulence production is larger. However, a further increase of the
shear number from moderate to large values results in a reduction of the growth rate γ and the turbulent kinetic energy K shows long-time decay for sufficiently large values of the shear number. The inhibition of turbulence growth at large shear
numbers occurs for both initial values of the Reynolds number and can be explained with the predominance of linear effects
over nonlinear effects when the shear number is sufficiently high. It is found that, at the higher initial value of the Reynolds
number, the reduction of the growth rate occurs at a higher value of the shear number. The shear number is found to affect
spectral space dynamics. Turbulent transport coefficients decrease with increasing shear number.
Received 23 June 1998 and accepted 25 February 1999 相似文献
10.
Y.F. Yao T.G. Thomas N.D. Sandham J.J.R. Williams 《Theoretical and Computational Fluid Dynamics》2001,14(5):337-358
This paper describes a direct numerical simulation (DNS) study of turbulent flow over a rectangular trailing edge at a Reynolds
number of 1000, based on the freestream quantities and the trailing edge thickness h; the incoming boundary layer displacement thickness δ* is approximately equal to h. The time-dependent inflow boundary condition is provided by a separate turbulent boundary layer simulation which is in good
agreement with existing computational and experimental data. The turbulent trailing edge flow simulation is carried out using
a parallel multi-block code based on finite difference methods and using a multi-grid Poisson solver. The turbulent flow in
the near-wake region of the trailing edge has been studied first for the effects of domain size and grid resolution. Then
two simulations with a total of 256 × 512 × 64 (∼ 8.4×106) and 512 × 1024 × 128 (∼ 6.7×107) grid points in the computational domain are carried out to investigate the key flow features. Visualization of the instantaneous
flow field is used to investigate the complex fluid dynamics taking place in the near-wake region; of particular importance
is the interaction between the large-scale spanwise, or Kármán, vortices and the small-scale quasi-streamwise vortices contained
within the inflow boundary layer. Comparisons of turbulence statistics including the mean flow quantities are presented, as
well as the pressure distributions over the trailing edge. A spectral analysis applied to the force coefficient in the wall
normal direction shows that the main shedding frequency is characterized by a Strouhal number based on h of approximately 0.118. Finally, the turbulence kinetic energy budget is analysed.
Received 4 March 1999 and accepted 27 October 2000 相似文献
11.
An experimental study was conducted to examine the effects of surface roughness and adverse pressure gradient (APG) on the
development of a turbulent boundary layer. Hot-wire anemometry measurements were carried out using single and X-wire probes in all regions of a developing APG flow in an open return wind tunnel test section. The same experimental conditions
(i.e., T
∞, U
ref, and C
p) were maintained for smooth, k
+ = 0, and rough, k
+ = 41–60, surfaces with Reynolds number based on momentum thickness, 3,000 < Re
θ < 40,000. The experiment was carefully designed such that the x-dependence in the flow field was known. Despite this fact, only a very small region of the boundary layer showed a balance
of the various terms in the integrated boundary layer equation. The skin friction computed from this technique showed up to
a 58% increase due to the surface roughness. Various equilibrium parameters were studied and the effect of roughness was investigated.
The generated flow was not in equilibrium according to the Clauser (J Aero Sci 21:91–108, 1954) definition due to its developing nature. After a development region, the flow reached the equilibrium condition as defined
by Castillo and George (2001), where Λ = const, is the pressure gradient parameter. Moreover, it was found that this equilibrium condition can be used
to classify developing APG flows. Furthermore, the Zagarola and Smits (J Fluid Mech 373:33–79, 1998a) scaling of the mean velocity deficit, U
∞δ*/δ, can also be used as a criteria to classify developing APG flows which supports the equilibrium condition of Castillo
and George (2001). With this information a ‘full APG region’ was defined. 相似文献
12.
The evolution of energies and fluxes in homogeneous turbulence with baroclinic instability is analyzed using the linear theory. The mean flow corresponds to a vertical shear having a uniform mean velocity gradient, ?U i /?x j = S δ i1 δ j3, a system rotation about the vertical axis with rate Ω, Ω i = Ωδ i3, and uniform buoyancy gradients in the spanwise ${(\partial B{/}\partial x_2\,{=}\, N_h^2\,{=}\,-2\Omega S)}The evolution of energies and fluxes in homogeneous turbulence with baroclinic instability is analyzed using the linear theory.
The mean flow corresponds to a vertical shear having a uniform mean velocity gradient, ∂U
i
/∂x
j
= S
δ
i1
δ
j3, a system rotation about the vertical axis with rate Ω, Ω
i
= Ωδ
i3, and uniform buoyancy gradients in the spanwise (?B/?x2 = Nh2 = -2WS){(\partial B{/}\partial x_2\,{=}\, N_h^2\,{=}\,-2\Omega S)} and vertical (?B/?x3 = Nv2){(\partial B{/}\partial x_3\,{=}\,N_v^2)} directions. Computations based on the rapid distortion theory (RDT) are performed for several values of the rotation number
R = 2Ω/S and the Richardson number Ri = Nv2/S2 < 1{R_i\,{=}\,N_v^2/S^2 <1 }. It is shown that, during an initial phase, the energies and the buoyancy fluxes are sensitive to the effects of pressure
and viscosity. At large time, the ratios of energies, as well as the normalized fluxes, evolve to an asymptotically constant
value, while the pressure–strain correlation scaled with the product of the turbulent kinetic energy by the shear rate approaches
zero. Accordingly, an analytical parametric study based on the “pressure-less” approach (PLA) is also presented. The analytical
study indicates that, when R
i
< 1, there is an exponential instability and equilibrium states of turbulence, in agreement with RDT. The energies and the
buoyancy fluxes grow exponentially for large times with the same rate (γ in St units). The asymptotic value of the ratios of energies yielded by RDT is well described by its PLA counterpart derived analytically.
At R
i
= 0, the asymptotic value of γ increases with increasing R approaching 2 for high rotation rates. At low rotation rates, an important contribution to the kinetic energy comes from
the streamwise kinetic energy, whereas, at high rotation rates, the contribution of the vertical kinetic energy is dominant.
When 0 < R
i
< 1 and R 1 0{R\ne 0}, the asymptotic value of γ decreases as R
i
increases so as it becomes zero at R
i
= 1. 相似文献
13.
The effect of the jet-to-cross-flow velocity ratio, R, on the turbulent wake and Kármán vortex shedding for a cylindrical stack of aspect ratio AR=9 was investigated in a low-speed wind tunnel using thermal anemometry. The cross-flow Reynolds number was ReD=2.3×104, the jet Reynolds number ranged from Red=7.6×103 to 4.7×104, and R was varied from 0 to 3. The stack was partially immersed in a flat-plate turbulent boundary layer, with a boundary layer thickness-to-stack-height ratio of δ/H=0.5 at the location of the stack. From the behaviour of the turbulent wake and the vortex shedding, the flow around the stack could be classified into three regimes depending on the value of R, which were the downwash (R<0.7), cross-wind-dominated (0.7R<1.5), and jet-dominated (R1.5) flow regimes. Each flow regime had a distinct structure to the mean velocity (streamwise and wall-normal directions), turbulence intensity (streamwise and wall-normal directions), and Reynolds shear stress fields, as well as the variation of the Strouhal number and the power spectrum along the stack height. 相似文献
14.
H. C. H. Ng J. P. Monty N. Hutchins M. S. Chong I. Marusic 《Experiments in fluids》2011,51(5):1261-1281
Single normal hot-wire measurements of the streamwise component of velocity were taken in fully developed turbulent channel
and pipe flows for matched friction Reynolds numbers ranging from 1,000 ≤ Re
τ ≤ 3,000. A total of 27 velocity profile measurements were taken with a systematic variation in the inner-scaled hot-wire
sensor length l
+ and the hot-wire length-to-diameter ratio (l/d). It was observed that for constant l
+ = 22 and l/d >~200l/d \gtrsim 200, the near-wall peak in turbulence intensity rises with Reynolds number in both channels and pipes. This is in contrast to
Hultmark et al. in J Fluid Mech 649:103–113, (2010), who report no growth in the near-wall peak turbulence intensity for pipe flow with l
+ = 20. Further, it was found that channel and pipe flows have very similar streamwise velocity statistics and energy spectra
over this range of Reynolds numbers, with the only difference observed in the outer region of the mean velocity profile. Measurements
where l
+ and l/d were systematically varied reveal that l
+ effects are akin to spatial filtering and that increasing sensor size will lead to attenuation of an increasingly large range
of small scales. In contrast, when l/d was insufficient, the measured energy is attenuated over a very broad range of scales. These findings are in agreement with
similar studies in boundary layer flows and highlight the need to carefully consider sensor and anemometry parameters when
comparing flows across different geometries and when drawing conclusions regarding the Reynolds number dependency of measured
turbulence statistics. With an emphasis on accuracy, measurement resolution and wall proximity, these measurements are taken
at comparable Reynolds numbers to currently available DNS data sets of turbulent channel/pipe flows and are intended to serve
as a database for comparison between physical and numerical experiments. 相似文献
15.
An active grid for turbulence generation of several rotatable axes with surmounted vanes that can be driven via stepper or
servo motors is presented. We investigate the impact of different excitation protocols for the grid. Using such protocols
that already have the intermittent structure of turbulence, higher intermittent flows can be achieved. This concept can also
be used to generate turbulent flows of high turbulence intensities (>25%) exhibiting integral length scales beyond the typical
size of the test section of the wind tunnel. Similar two-point correlations measured by the intermittent statistics of velocity
increments that are characteristic for flows of high Reynolds number, i.e. in the atmospheric boundary layer, can be reproduced. 相似文献
16.
Wind turbines operate in the surface layer of the atmospheric boundary layer, where they are subjected to strong wind shear
and relatively high turbulence levels. These incoming boundary layer flow characteristics are expected to affect the structure
of wind turbine wakes. The near-wake region is characterized by a complex coupled vortex system (including helicoidal tip
vortices), unsteadiness and strong turbulence heterogeneity. Limited information about the spatial distribution of turbulence
in the near wake, the vortex behavior and their influence on the downwind development of the far wake hinders our capability
to predict wind turbine power production and fatigue loads in wind farms. This calls for a better understanding of the spatial
distribution of the 3D flow and coherent turbulence structures in the near wake. Systematic wind-tunnel experiments were designed
and carried out to characterize the structure of the near-wake flow downwind of a model wind turbine placed in a neutral boundary
layer flow. A horizontal-axis, three-blade wind turbine model, with a rotor diameter of 13 cm and the hub height at 10.5 cm,
occupied the lowest one-third of the boundary layer. High-resolution particle image velocimetry (PIV) was used to measure
velocities in multiple vertical stream-wise planes (x–z) and vertical span-wise planes (y–z). In particular, we identified localized regions of strong vorticity and swirling strength, which are the signature of helicoidal
tip vortices. These vortices are most pronounced at the top-tip level and persist up to a distance of two to three rotor diameters
downwind. The measurements also reveal strong flow rotation and a highly non-axisymmetric distribution of the mean flow and
turbulence structure in the near wake. The results provide new insight into the physical mechanisms that govern the development
of the near wake of a wind turbine immersed in a neutral boundary layer. They also serve as important data for the development
and validation of numerical models. 相似文献
17.
H.-J. Kaltenbach 《Theoretical and Computational Fluid Dynamics》2003,16(3):187-210
A three-dimensional separated flow behind a swept, backward-facing step is investigated by means of DNS for Re
H
= C
∞
H/ν = 3000 with the purpose to identify changes in the statistical turbulence structure due to a variation of the sweep angle
α from 0° up to 60°. With increasing sweep angle, the near-wall turbulence structure inside the separation bubble and downstream
of reattachment changes due to the presence of an edge-parallel mean flow component W. Turbulence production due to the spanwise shear ∂W/∂y at the wall becomes significant and competes with the processes caused by impingement of the separated shear-layer. Changes
due to a sweep angle variation can be interpreted in terms of two competing velocity scales which control the global budget
of turbulent kinetic energy: the step-normal component U
∞ = C
∞cosα throughout the separated flow region and the velocity difference C
∞ across the entire shear-layer downstream of reattachment. As a consequence, the significance of history effects for the development
into a two-dimensional boundary layer decreases with increasing sweep angle. For α ≥50°, near-wall streaks tend to form inside
the separated flow region.
Received 7 November 2000 and accepted 9 July 2002 Published online 3 December 2002
RID="*"
ID="*" Part of this work was funded by the Deutsche Forschungsgemeinschaft within Sfb 557. Computer time was provided by the
Konrad-Zuse Zentrum (ZIB), Berlin.
Communicated by R.D. Moser 相似文献
18.
Laser-Doppler measurements were conducted in a plane turbulent wall jet at a Reynolds number based on inlet velocity, Re
0, of 9600. The initial development as well as the fully developed flow was studied. Special attention was given to the near-wall
region, including the use of small measuring volumes and the application of specific near-wall data corrections, so that wall
shear stresses were determined directly from the mean velocity gradient at the wall using only data below y
+=4. It was possible to resolve the inner peak in the streamwise turbulence intensity as well as the inner (negative) peak
in the shear stress. Limiting values of (u′)+ and uv
+ were determined. Turbulence data from the outer region of the flow were compared to earlier hot wire measurements and large
differences in the normal turbulence intensity and the shear stress were found. These differences can be attributed to high
turbulence intensity effects on the hot-wires.
Received: 17 October 1996 / Accepted: 8 December 1997 相似文献
19.
The inner part of a neutral atmospheric boundary layer has been simulated in a wind tunnel, using air injection through the wind tunnel floor to thicken the boundary layer. The flow over both a rural area and an urban area has been simulated by adapting the roughness of the wind tunnel floor. Due to the thickening of the boundary layer the scaling factor of atmospheric boundary layer simulation with air injection is considerably smaller than that without air injection. This reduction of the scaling factor is very important for the simulation of atmospheric dispersion problems in a wind tunnel.The time-mean velocity distribution, turbulence intensity, Reynolds stress and turbulence spectra have been measured in the inner part of the wind tunnel boundary layer. The results are in rather good agreement with atmospheric measurements.Nomenclature
d
Zero plane displacement, m
-
h
Height of roughness elements, m
-
k
Von Kármán's constant
-
n
Frequency of turbulence velocity component, s–1
-
S
u(n)
Energy spectrum for longitudinal turbulence velocity component, m2 s–1
-
S
v(n)
Energy spectrum for lateral turbulence velocity component, m2 s–1
-
S
w(n)
Energy spectrum for vertical turbulence velocity component, m2 s–1
-
U
o
Free stream velocity outside the boundary layer, m s–1
-
Time-mean velocity inside the boundary layer, m s–1
-
u*
Wall-friction velocity, m s–1
-
u
Longitudinal turbulence intensity, m s–1
-
v
Lateral turbulence intensity, m s–1
-
w
Vertical turbulence intensity, m s–1
-
Reynolds stress, m2 s–2
-
z
Height above earth's surface or wind tunnel floor, m
-
z
o
Roughness length, m
-
Thickness of inner part of boundary layer, m
-
Thickness of boundary layer, m
-
Kinematic viscosity, m2 s–1 相似文献
20.
Wind-blown sand is a typical example of two-phase particle-laden flows. Owing to lack of simultaneous measured data of the
wind and wind-blown sand, interactions between them have not yet been fully understood. In this study, natural sand of 100–125 μm
taken from Taklimakan Desert was tested at the freestream wind speed of 8.3 m/s in an atmospheric boundary layer wind tunnel.
The captured flow images containing both saltating sand and small wind tracer particles, were separated by using a digital
phase mask technique. The 2-D PIV (particle imaging velocimetry) and PTV (particle tracking velocimetry) techniques were employed
to extract simultaneously the wind velocity field and the velocity field of dispersed sand particles, respectively. Comparison
of the mean streamwise wind velocity profile and the turbulence statistics with and without sand transportation reveal a significant
influence of sand movement on the wind field, especially in the dense saltating sand layer (y/δ < 0.1). The ensemble-averaged streamwise velocity profile of sand particles was also evaluated to investigate the velocity
lag between the sand and the wind. This study would be helpful in improving the understanding of interactions between the
wind and the wind-blown sand. 相似文献