An approximate method to compute mean velocity profiles in turbulent flows is developed. This approach is based on the equation connecting the Reynolds stress and mean velocity. By using the measured values of pressure drop and average (bulk) flow velocity, such characteristics of a turbulent flow as the mean velocity and Reynolds stress distributions were calculated and compared with the experimental measurements in different pipes and channels for various fluids and gases. These show good agreement for a wide range of Reynolds numbers.
We investigate the spatio-temporal quantity of coherence for turbulent velocity fluctuations at spatial distances of the order or larger than the integral length scale $l_{0}$. Using controlled laboratory experiments, an exponential decay as a function of distance is observed with a decay rate which depends on the flow properties. The same law is observed in two different flows indicating that it can be a generic property of turbulent flows.
Logarithmic distribution of mean velocity and turbulent kinetic energy in a pipe flow
基于李群相似理论,发展了一种适用于湍流管流中动量和能量分布的相似理论,得到了平均速度和湍流动能的渐近对数分布。在很宽的Re范围内的通道和管道数据产生0.45是通用的卡门常数。发现了一个新的表征外动力学的空间不变量,并通过可靠的实验数据进行了验证。对于高Re实验数据(高达4000万),该理论以99%的准确度预测平均速度剖面(MVP),并为Hullmak等人最近观察到的对数动能分布提供了定量解释(Phys. Rev. Lett. 108,094501)。
The Prevalence of Similarity of the Turbulent Wall-bounded Velocity Profile
卡斯蒂略和乔治(卡斯蒂略,L。和乔治,W,AIAA J. 39,41(2001))开发了用于描述湍流外边界层区域的流动控制方程方法。该方法被用来制定相似准则的平均速度和雷诺剪应力剖面。以该标准为指导,Castillo、George及其同事检查了大量的实验数据集,并声称当用Zagarola和Smits(Zagarola,M.和Smits,A.,J.Fluid Mech.373,33(1998))速度参数。在这里的工作中,它表明,他们的成功在许多这些数据集显示缩放的配置文件的相似性是有缺陷的,由于一个相似性的问题,当一个相结合的缺陷配置文件和Zagarola和Smits类型的速度缩放参数。同样的问题在文献中的其他论文中也被发现,事实上可能很普遍。我们的结论是,湍流速度剖面的相似性是不普遍的卡斯蒂略,乔治,和同事声称。这个结果对于湍流边界层的尺度化的公认范例有影响。
We study intermittency of circulation moments in turbulent superfluid helium by using experimental grid turbulence and numerical simulations of the Hall-Vinen-Bekarevich-Khalatnikov model. More precisely, we compute the velocity circulation $Γ_r$ in loops of size $r$ laying in the inertial range. For both, experimental and numerical data, the circulation variance shows a clear Kolmogorov scaling $\langle Γ_r^2 \rangle \sim r^{8/3}$ in the inertial range, independently of the temperature. Scaling exponents of high-order moments are comparable, within error bars, to previously reported anomalous…
Reported in the paper are results of unsteady three-dimensional direct numerical simulations of laminar and turbulent, lean hydrogen-air, complex-chemistry flames propagating in forced turbulence in a box. To explore the eventual influence of thermo-diffusive instability of laminar flames on turbulent burning velocity, (i) a critical length scale Λn that bounds regimes of unstable and stable laminar combustion is numerically determined by gradually decreasing the width Λ of computational domain until a stable laminar flame is obtained and (ii) simulations of turbulent flames are performed by v…
This study presents a deep learning-based framework to reconstruct high-resolution turbulent velocity fields from extremely low-resolution data at various Reynolds numbers using the concept of generative adversarial networks (GANs). A multiscale enhanced super-resolution generative adversarial network (MS-ESRGAN) is applied as a model to reconstruct the high-resolution velocity fields, and direct numerical simulation (DNS) data of turbulent channel flow with large longitudinal ribs at various Reynolds numbers are used to evaluate the performance of the model. The model is found to have the cap…
This paper describes an experimental investigation, by means of hot-wire anemometry, of the characteristics of velocity and temperature in a rotating turbulent boundary layer under isothermal and non-isothermal conditions. The ranges of experimental parameters are: Reynolds number from 10000 to 25000, rotational speed from 0 to 150 rpm, and y+ from 1.8 to 100. The relative temperature difference is held constant at 0.1. Detailed velocity and temperature distributions in the boundary layer are measured in the rotating state, and a new criterion for boundary layer segmentation under rotation is …
We consider analytically pair structure function of turbulent pulsations on the background of a coherent geostrophic vortex in a fast rotating fluid. The statistics of the turbulent pulsation is determined by their dynamics which is the dynamics of inertia waves affected by the differential rotation in the vortex and weak viscous damping. Our consideration is restricted by the smallest scales, where the velocity field remains smooth. We establish the anisotropy of the structure function. The velocity gradient of the turbulent pulsations achieves its largest value for the radial direction and i…
Anisotropy and multifractality in velocity and temperature time series sampled at multiple heights in the roughness sublayer (RSL) over a boreal mixed-coniferous forest are reported. In particular, a turbulent-stress invariant analysis along with a scalewise version of it are conducted to elucidate the nature of relaxation of large-scale anisotropy to quasi-isotropic states at small scales. As the return to isotropy is linked to nonlinear interactions and correlations between different fluctuating velocity components across scales, we study the velocity and temperature time series by using mul…
An experimental Lagrangian study based on particle tracking velocimetry has been completed in an incompressible turbulent round water jet freely spreading into water. The jet is seeded with tracers only through the nozzle: inhomogeneous seeding called nozzle seeding. The Lagrangian flow tagged by these tracers therefore does not contain any contribution from particles entrained into the jet from the quiescent surrounding fluid. The mean velocity field of the nozzle seeded flow, $\langle \boldsymbol{U_φ} \rangle$, is found to be essentially indistinguishable from the global mean velocity field …
Strong rotation makes an underlying turbulent flow quasi-two-dimensional that leads to the upscale energy transfer. Recent numerical simulations show that under certain conditions, the energy is accumulated at the largest scales of the system, forming coherent vortex structures known as condensates. We analytically describe the interaction of a strong condensate with weak small-scale turbulent pulsations and obtain an equation that allows us to determine the radial velocity profile $U(r)$ of a coherent vortex. When external rotation is fast, the velocity profiles of cyclones and anticyclones a…