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1.
Two-point correlation measurements of the wall normal fluctuating velocities were made in two-dimensional (2-D) and pressure-driven
three-dimensional (3-D) turbulent boundary layers. These data are needed for characterization and modeling of active-motion
length scales, especially for 3-D flows. The fine-probe-volume data were measured using two custom-designed laser-Doppler-velocimeter
fiber-optic probes. The data are relatively free of noise, signal broadening, and bias effects.
Favorable comparisons with direct-numerical-simulation (DNS) results in the near-wall region of the 2-D flow validate the
experimental techniques used here. For a given fixed probe location, non-dimensional correlation values scale best on the
probe separation. For both the 2-D and 3-D cases, peak correlations lie along a line inclined away from the wall at 11° and
8°, respectively, which suggests the existence of an outgoing characteristic line affected by only the upstream flow. The
decay of the correlation coefficient occurs nearer the wall than away from the wall relative to the fixed probe location.
The variations for the 3-D flow correlations are similar to the 2-D variations, but with longer Δ x
+and Δ y
+ decay distances, probably because of the 3-D flowacceleration. While the spanwise variation of the correlationcoefficients
is symmetric about the fixed point for the 2-D case asdictated by reciprocity, the 3-D case shows a large asymmetry for spanwise
variations Δ z
+ < 68. The profiles at higher Δ z
+ are more symmetric. In general, at a given y the maximum correlation is skewed toa non-zero Δ z. It appears that the skewing of the correlation coefficient in the z direction tracks the sign of
.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
2.
各向同性湍流内颗粒碰撞率的直接模拟研究 总被引:1,自引:0,他引:1
对 Re_{\lambda } 约为51均匀各向同性湍流内 St_{k}(=\tau_{p}/\tau_{k})
为 0 ~10.0 的
有限惯性颗粒的碰撞行为进行了直接数值模拟,以研究湍流对有限惯性
颗粒碰撞的影响. 结果表明,具有一定惯性颗粒的湍流碰撞率完全不同于零惯性的轻颗粒
(St_{k}=0) 和可忽略湍流作用的重颗粒 (St{k} \to \infty) , 其变化趋势极其复杂:
在Stk为 0~1.0 之间,颗粒的碰撞率随 St 的增加而近乎线性地剧烈增长,在
Stk≈1.0 3.0(对应的StE=τp/Te≈0.5)附近,颗粒碰撞率出现两个峰值,在Stk>3.0以后,颗粒的碰撞率随惯性增
大而逐渐趋向于重颗粒极限;在峰值处,有限惯性颗粒的平均碰撞率的峰值较轻颗粒增强了
30倍左右. 为进一步分析湍流作用下颗粒碰撞率的影响因素,分别使用可能发生碰撞
的颗粒对的径向分布函数和径向相对速度来量化颗粒的局部富集效应和湍流掺混效应,表明
St_{k} \approx 1.0 时局部富集效应最为强烈,使得颗粒的碰撞率出现第1个峰值;
湍流掺混效应则随着颗粒Stk的增大而渐近增大;局部富集和湍流掺混联合作用的结果,
使得颗粒碰撞率在 St_{k} \approx 3.0 附近出现另一个峰值. 相似文献
3.
4.
5.
人工扰动信号在湍流边界层中的衰减 总被引:3,自引:1,他引:2
将人工扰动引入湍流流场,使用功率谱分析方法,研究边界层外层的较大频率范围内的人工扰动信号沿流向和法向的衰减,获得了人工扰动在湍流边界层中的衰减趋势. 相似文献
6.
The transitional turbulent regime in confined flow between a rotating and a stationary disc is studied using direct numerical
simulation. Besides its fundamental importance as a three-dimensional prototype flow, such flows frequently arise in many
industrial devices, especially in turbomachinary applications. The present contribution extends the DNS simulation into the
turbulent flow regime, to a rotational Reynolds number Re =3 × 105. An annular rotor-stator cavity of radial extension ΔR and height H, is considered with L = 4.72(L = ΔR/H) and Rm = 2.33 (Rm = (R
1+ R
0)/ΔR). The direct numerical simulation is performed by integrating the time-dependent Navier–Stokes equations until a statistically
steady state is reached. A three-dimensional spectral method is used with the aim of providing both very accurate instantaneous
fields and reliable statistical data. The instantaneous quantities are analysed in order to enhance our knowledge of the physics
of turbulent rotating flows. Also, the results have been averaged so as to provide target turbulence data for any subsequent
modelling attempts at reproducing the flow.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
7.
The high-speed transport of thin-sheet materials occurs in avariety of industrial processes. In this paper the method of matchedasymptotic expansions is used to solve the low tension, large-deflectionshape of a convected strip hanging under gravity. To leading order theequations for the deflection in the boundary layer and in the centre ofthe span are nonlinear. Previous treatments of this problem have notaccurately solved the leading-order equation within the boundary layer.The composite analytic solution of the full nonlinear equation isobtained and compares well with numerical solutions. 相似文献
8.
沟槽面与光滑面湍流边界层特性比较 总被引:3,自引:0,他引:3
应用LDV技术对沟槽面及光滑面湍流边界层流速和湍流度分布进行了精细的测量,实验结果表明:与光滑面相比,沟槽面湍流边界层时均流速分布对数公式中具有较大的积分常数C值,且沟槽面湍流度最大值较小,但其出现的位置距壁面较远。另外,偏斜因子及平坦因子的分布特性区别不大,但是在近壁区内沟槽面结果波动较大。 相似文献
9.
Spatial Direct Numerical Simulation of the Large Vortical Structures in Forced Plumes 总被引:1,自引:0,他引:1
Direct numerical simulation (DNS) of forced plumes arising frominput of both momentum and buoyancy into an ambient fluid is presented.The large vortical structures in the near field of thermal and reactiveplumes are investigated. Boundary conditions associated with the spatialDNS of open-boundary buoyant flows that are compatible with the modernnon-dissipative, high-order, finite-difference schemes have beendeveloped. The governing equations for flow and combustion at the plumecenterline are put into a special form to circumvent the singularity atthe axis associated with the cylindrical coordinates. Mixing is found tobe stronger in the planar thermal plume than in the axisymmetric case.An explanation is provided based on the vorticity budget. Axisymmetricreactive plumes with a one-step reaction governed by the Arrheniuskinetics have also been studied. The unsteady effects of chemical heatrelease and combustion-induced buoyancy on the flow structures areinvestigated. Budgets of the vorticity transport are examined to revealthe mechanisms leading to the formation and evolution of large vorticalstructures in forced plumes. It is found that volumetric expansion dueto chemical heat release tends to destroy vorticity, whilecombustion-induced buoyancy under the gravitational effect generatesvorticity. The gravitational term in the vorticity transport equation isfound to be the main mechanism for the buoyant flow instability and thedevelopment of counter-rotating vortices in reactive plumes. 相似文献
10.
湍流边界层流场与噪声实验研究 总被引:5,自引:0,他引:5
在重力式水洞中进行了水翼及半翼湍流边界层流场与噪声的实验研究。测量了水翼及半翼边界层附近的湍流脉动速度场;测量了半翼翼型表面三点处的压力脉动及其辐射噪声,测量了水翼内部测点的噪声及外部辐射噪声,在不同流速、不同攻角、光滑和粗糙翼面的情况下都进行了测量分析。试验结果发现,上述因素对模型的边界层湍流速度场有显著影响,15度攻角时,翼面附近湍流强度要比0度时大得多,粗糙翼面附近的湍流强度比光滑的大,而湍流强度随来流速度的变化不大,u(来流)方向和v方向的湍流强度量级相当;一般地,翼面压力脉动、翼内部噪声及外部噪声都是随来流速度的增大而增大,随攻角的增大而增大,粗糙翼面时的结果要比光滑翼面的大。从压力脉动与噪声测量结果与相应的流场测量结果比较可知,可以从湍流区域的湍流强度来判断出声源强度的定性变化。 相似文献
11.
利用一套以位移传感器为主的弹性平衡装置,测量几种不同表面形状设计的平板在充分发展的二维湍流边界层中的减阻效果,并对其减阻机理进行研究。结果表明,大涡破碎器 LEBU(Large Eddy Break-up)和其它减阻装置的形状和布置对表面摩擦阻力有较大影响,在有些设计状态下的平板得到了净减阻。 相似文献
12.
Coherent structures in a tripped turbulent boundary layer havebeen analysed by applying a new conditional sampling algorithm tolarge-eddy simulation (LES) data. The space-time development of theevents and structural characteristics were examined. The new conditionalsampling scheme is shown to be very effective in the eduction of thecoherent eddy structures, allowing the simultaneous detection, trackingand averaging of several three-dimensional (3-D) structures. Alignmentof the triggering events in all spatial directions and flip-averaging(spatial reflection of the samples) enhance significantly the extractionof detailed features of the structures. The detection method minimisesthe smearing of the spatial details and avoids imposing artificialsymmetry, which is often intrinsic to other conditional samplingschemes.The results show the existence of cigar-shapedstreamwise vortices which are directly associated with negative pressurefluctuation peaks (positive source term of the pressure Poissonequation). They are inclined at 12° to the wall andtilted laterally at an angle of 7° to the streamwisedirection. The streamwise vortices induce ejections and sweeps throughan advection mechanism due to the tilting or inclination of thevortices. There is no evidence of hairpin vortices in either theconditional averages or instantaneous flow fields. Near-wall shearlayers are found to be related to the positive pressure fluctuationpeaks as a result of complex interactions between ejection and sweepevents. The shear layer structure has an inclination of10°, being located between two tilted, streamwisevortices of opposite direction of rotation.The presentresults are very close to other Direct Numerical Simulation studiesusing different conditional sampling schemes. Conceptual models for thestreamwise vortices and shear layer structures are proposed to accountfor the results. 相似文献
13.
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
14.
The results of an experimental investigation of the effect of the streamwise pressure gradient in a turbulent boundary layer on the permissible height of the surface roughness of bodies in an incompressible fluid flow are presented. The permissible roughness Reynolds number for which the characteristics of the turbulent boundary layer remain the same as in the case of flow past a smooth surface is determined. 相似文献
15.
A new turbulent injection procedure dedicated to fully compressible direct numerical simulation (DNS) or large eddy simulation (LES) solvers is proposed. To avoid the appearance of spurious acoustic waves, this method is based on an accurate tracking of the turbulent structures crossing the boundary at the inlet of the domain. A finite difference DNS solver has been coupled with a spectral simulation in which a statistically stationary homogeneous turbulence evolves to provide fluctuating boundary conditions.A new turbulence forcing method, dedicated to spectral solvers, has been developed as well to control the major properties of the injected flow (turbulent kinetic energy, dissipation rate and integral length scale). One-dimensional Navier–Stokes characteristic boundary conditions extended to non-stationary flows are coupled with the injection procedure to evaluate is potential in four various configurations: spatially decaying turbulence, dispersion of vaporizing sprays, propagation of one- and two-phase V-shape turbulent flames. 相似文献
16.
对流边界层湍流特性的数值研究 总被引:2,自引:0,他引:2
采用大涡模拟方法研究了存在逆温层的情况下大气对流边界层的湍流特性。实际大气边界层中出现逆温层是较常见的,逆温层会导致大气边界层湍流结构的变化,从而影响大气的湍流扩散和输运特性。本文比较了不同逆温梯度的工况,着重分析了逆温层对边界层中热量逆梯度输运(counter gradient heat transportation,CGHT)的影响。计算结果表明:逆温梯度越大,对流边界层的发展越受到抑制;逆温层高度降低会影响整个对流边界层的温度抬升;逆温梯度越大,垂直速度方差越小;在逆温梯度较大的情况下,其逆梯度输运区域要略微低一些,初步分析认为是由于逆温层对热对流的抑制造成的;对于逆温层高度不同的情况,高度越低的逆温层对逆梯度输运的抑制作用更明显。 相似文献
17.
Let v=v(x) be a non-trivial bounded steady solution of a viscous scalar conservation law u
t+f(u)
x
=u
xx on a half-line R+, with a Dirichlet boundary condition. The semi-group of this IBVP is known to be contractive for the distance d(u, u)u–u1 induced by L
1(R+). We prove here that v is asymptotically stable with respect to d: if u
0–vL
1, then u(t)–v10 as t+. When v is a constant, we show that this property holds if and only if f(v)0. These results complement our study of the Cauchy problem [2]. 相似文献
18.
19.
Zhihua Wang Pei He Yu Lv Junhu Zhou Jianren Fan Kefa Cen 《Flow, Turbulence and Combustion》2010,84(4):669-686
Direct numerical simulation(DNS) of spatially developing round turbulent jet flow with Reynolds number 4,700 was carried out.
Over 20 million grid points were used in this simulation. Fully compressible three-dimensional Navier–Stokes equations were
solved. High order explicit spatial difference schemes and Runge–Kutta time integration scheme were used to calculate derivatives
and time marching, respectively. Non-reflecting boundary conditions and exit zone techniques were adopted. Some refined computational
grids were used in order to capture the smallest turbulent structures near the centerline of the jet. Low level disturbance
were imposed on the jet inflow velocity to trigger the developing of turbulence. Turbulent statistics such as mean velocity,
Reynolds stresses, third order velocity moments were obtained and compared with experimental data. One-dimensional velocity
autospectra was also calculated. The inertial region where the spectra decays according to the k − 5/3 was observed. The quantitative profiles of mean velocity and all of the third order velocity moments which were difficult
to measure via experimental techniques were presented here in detail. The jet flow was proven to be close to fully self-similar
around 19 jet diameters downstream of jet exit. The statistic data and revealed flow feature obtained in this paper can provide
valuable reference for round turbulent jet research. 相似文献
20.
N.A. Adams 《Theoretical and Computational Fluid Dynamics》1998,12(2):109-129
A numerical procedure for the direct numerical simulation of compressible turbulent flow and shock–turbulence interaction
is detailed and analyzed. An upwind-biased finite-difference scheme with a compact centered stencil is used to discretize
the convective part of the Navier–Stokes equations. The scheme has a uniformly high approximation order and allows for a spectral-like
wave resolution while dissipating nonresolved wave numbers. When hybridized with an essentially nonoscillatory scheme near
discontinuities, the scheme becomes shock–capturing and its resolution properties are preserved. Diffusive parts are discretized
with symmetric compact finite differences and an explicit Runge–Kutta scheme is used for time-advancement. The peculiarities
of efficient upwinding and coupling procedures are described and validation results are given. Using direct numerical simulation
data, some aspects of turbulent supersonic compression ramp flow are studied to demonstrate the effectiveness of the simulation
procedure.
Received 13 November 1997 and accepted 14 May 1998 相似文献