A DNS of acoustic field emitted from a near-wall turbulent flow

2001 ◽  
Author(s):  
Yutaka Miyake ◽  
Koichi Tsujimoto ◽  
Yoshiaki Miyamoto ◽  
Tetsuji Ryo
Keyword(s):  
Turbulent Flow ◽  
Acoustic Field ◽  
Near Wall

APPLICATION OF THE HIGH-RESOLUTION RANS/ILES TECHNOLOGY FOR FLOW SIMULATION AND THE NEARBY ACOUSTIC FIELD OF NEAR-WALL JETS AND MIXING LAYERS

2016 ◽  
Vol 47 (2) ◽  
pp. 159-183 ◽  
Author(s):  
Leonid Aleksandrovich Bendersky ◽  
Dmitriy Aleksandrovich Lyubimov ◽  
Irina Vasilevna Potekhina ◽  
Alena Eduardovna Fedorenko
Keyword(s):  
High Resolution ◽  
Acoustic Field ◽  
Flow Simulation ◽  
Mixing Layers ◽  
Wall Jets ◽  
Near Wall

scholarly journals Heat Transfer in Highly Turbulent Separated Flows: A Review

Energies ◽  
2021 ◽  
Vol 14 (4) ◽  
pp. 1005
Author(s):  
Viktor I. Terekhov
Keyword(s):  
Heat Transfer ◽  
Turbulent Flow ◽  
Separated Flow ◽  
Separated Flows ◽  
Turbulence Characteristic ◽  
Wall Jets ◽  
Average Heat ◽  
Free Stream Turbulence ◽  
External Turbulence ◽  
Near Wall

The study of flows with a high degree of turbulence in boundary layers, near-wall jets, gas curtains, separated flows behind various obstacles, as well as during combustion is of great importance for increasing energy efficiency of the flow around various elements in the ducts of gas-dynamic installations. This paper gives some general characteristics of experimental work on the study of friction and heat transfer on a smooth surface, in near-wall jets, and gas curtains under conditions of increased free-stream turbulence. Taking into account the significant effect of high external turbulence on dynamics and heat transfer of separated flows, a similar effect on the flow behind various obstacles is analyzed. First of all, the classical cases of flow separation behind a single backward-facing step and a rib are considered. Then, more complex cases of the flow around a rib oriented at different angles to the flow are analyzed, as well as a system of ribs and a transverse trench with straight and inclined walls in a turbulent flow around them. The features of separated flow in a turbulized stream around a cylinder, leading to an increase in the width of the vortex wake, frequency of vortex separation, and increase in the average heat transfer coefficient are analyzed. The experimental results of the author are compared with data of other researchers. The structure of separated flow at high turbulence—characteristic dimensions of the separation region, parameters of the mixing layer, and pressure distribution—are compared with the conditions of low-turbulent flow. Much attention is paid to thermal characteristics: temperature profiles across the shear layer, temperature distributions over the surface, and local and average heat transfer coefficients. It is shown that external turbulence has a much stronger effect on the separated flow than on the boundary layer on a flat surface. For separated flows, its intensifying effect on heat transfer is more pronounced behind a rib than behind a step. The factor of heat transfer intensification by external turbulence is most pronounced in the transverse cavity and in the system of ribs.

Highly resolved experimental results of the separated flow in a channel with streamwise periodic constrictions

2016 ◽  
Vol 796 ◽  
pp. 257-284 ◽  
Author(s):  
Christian J. Kähler ◽  
Sven Scharnowski ◽  
Christian Cierpka
Keyword(s):  
Turbulent Flow ◽  
Flow Separation ◽  
Flow Direction ◽  
Separated Flow ◽  
Mean Flow ◽  
Complex Flow ◽  
Flow Measurements ◽  
Flow Features ◽  
Wall Flow ◽  
Near Wall

The understanding and accurate prediction of turbulent flow separation on smooth surfaces is still a challenging task because the separation and the reattachment locations are not fixed in space and time. Consequently, reliable experimental data are essential for the validation of numerical flow simulations and the characterization and analysis of the complex flow physics. However, the uncertainty of the existing near-wall flow measurements make a precise analysis of the near-wall flow features, such as separation/reattachment locations and other predicted near-wall flow features which are under debate, often impossible. Therefore, the periodic hill experiment at TU Munich (ERCOFTAC test case 81) was repeated using high resolution particle image velocimetry and particle tracking velocimetry. The results confirm the strong effect of the spatial resolution on the near-wall flow statistics. Furthermore, it is shown that statistically stable values of the turbulent flow variables can only be obtained for averaging times which are challenging to realize with highly resolved large eddy simulation and direct numerical simulation techniques. Additionally, the analysis implies that regions of correlated velocity fluctuations with rather uniform streamwise momentum exist in the flow. Their size in the mean flow direction can be larger than the hill spacing. The possible impact of the correlated turbulent motion on the wake region is discussed, as this interaction might be important for the understanding and control of the flow separation dynamics on smooth bodies.

Characteristics of the leading Lyapunov vector in a turbulent channel flow

2018 ◽  
Vol 849 ◽  
pp. 942-967 ◽  
Author(s):  
Nikolay Nikitin
Keyword(s):  
Turbulent Flow ◽  
Buffer Layer ◽  
Stokes Equations ◽  
Initial Conditions ◽  
Spatial Scales ◽  
Plane Channel ◽  
Base Flow ◽  
Lyapunov Vector ◽  
Perturbation Growth ◽  
Near Wall

The values of the highest Lyapunov exponent (HLE)$\unicode[STIX]{x1D706}_{1}$for turbulent flow in a plane channel at Reynolds numbers up to$Re_{\unicode[STIX]{x1D70F}}=586$are determined. The instantaneous and statistical properties of the corresponding leading Lyapunov vector (LLV) are investigated. The LLV is calculated by numerical solution of the Navier–Stokes equations linearized about the non-stationary base solution corresponding to the developed turbulent flow. The base turbulent flow is calculated in parallel with the calculation of the evolution of the perturbations. For arbitrary initial conditions, the regime of exponential growth${\sim}\exp (\unicode[STIX]{x1D706}_{1}t)$which corresponds to the approaching of the perturbation to the LLV is achieved already at$t^{+}<50$. It is found that the HLE increases with increasing Reynolds number from$\unicode[STIX]{x1D706}_{1}^{+}\approx 0.021$at$Re_{\unicode[STIX]{x1D70F}}=180$to$\unicode[STIX]{x1D706}_{1}^{+}\approx 0.026$at$Re_{\unicode[STIX]{x1D70F}}=586$. The LLV structures are concentrated mainly in a region of the buffer layer and are manifested in the form of spots of increased fluctuation intensity localized both in time and space. The root-mean-square (r.m.s.) profiles of the velocity and vorticity intensities in the LLV are qualitatively close to the corresponding profiles in the base flow with artificially removed near-wall streaks. The difference is the larger concentration of LLV perturbations in the vicinity of the buffer layer and a relatively larger (by approximately 80 %) amplitude of the vorticity pulsations. Based on the energy spectra of velocity and vorticity pulsations, the integral spatial scales of the LLV structures are determined. It is found that LLV structures are on average twice narrower and twice shorter than the corresponding structures of the base flow. The contribution of each of the terms entering into the expression for the production of the perturbation kinetic energy is determined. It is shown that the process of perturbation development is essentially dictated by the inhomogeneity of the base flow, as well as by the presence of transversal motion in it. Neglecting of these factors leads to a significant underestimation of the perturbation growth rate. The presence of near-wall streaks in the base flow, on the contrary, does not play a significant role in the development of the LLV perturbations. Artificial removal of streaks from the base flow does not change the character of the perturbation growth.

Neural Network Modeling for Near Wall Turbulent Flow

2002 ◽  
Vol 182 (1) ◽  
pp. 1-26 ◽  
Author(s):  
Michele Milano ◽  
Petros Koumoutsakos
Keyword(s):  
Neural Network ◽  
Turbulent Flow ◽  
Network Modeling ◽  
Neural Network Modeling ◽  
Near Wall

Simplified theory of the near-wall turbulent layer of Newtonian and drag-reducing fluids

1982 ◽  
Vol 119 ◽  
pp. 423-441 ◽  
Author(s):  
M. A. Goldshtik ◽  
V. V. Zametalin ◽  
V. N. Shtern
Keyword(s):  
Velocity Profile ◽  
Turbulent Flow ◽  
Drag Reduction ◽  
Outer Boundary ◽  
Viscous Sublayer ◽  
Viscous Layer ◽  
Mean Velocity ◽  
Turbulent Layer ◽  
The Mean ◽  
Near Wall

We propose a simplified theory of a viscous layer in near-wall turbulent flow that determines the mean-velocity profile and integral characteristics of velocity fluctuations. The theory is based on the concepts resulting from the experimental data implying a relatively simple almost-ordered structure of fluctuations in close proximity to the wall. On the basis of data on the greatest contribution to transfer processes made by the part of the spectrum associated with the main size of the observed structures, the turbulent fluctuations are simulated by a three-dimensional running wave whose parameters are found from the problem solution. Mathematically the problem reduces to the solution of linearized Navier-Stokes equations. The no-slip condition is satisfied on the wall, whereas on the outer boundary of a viscous layer the conditions of smooth conjunction with the asymptotic shape of velocity and fluctuation-energy profiles resulting from the dimensional analysis are satisfied. The formulation of the problem is completed by the requirement of maximum curvature of the mean-velocity profile on the outer boundary applied from stability considerations.The solution of the problem does not require any quantitative empirical data, although the conditions of conjunction were formulated according to the well-known concepts obtained experimentally. As a result, the near-wall law for the averaged velocity has been calculated theoretically and is in good agreement with experiment, and the characteristic scales for fluctuations have also been determined. The developed theory is applied to turbulent-flow calculations in Maxwell and Oldroyd media. The elastic properties of fluids are shown to lead to near-wall region reconstruction and its associated drag reduction, as is the case in turbulent flows of dilute polymer solutions. This theory accounts for several features typical of the Toms effect, such as the threshold character of the effect and the decrease in the normal fluctuating velocity. The analysis of the near-wall Oldroyd fluid flow permits us to elucidate several new aspects of the drag-reduction effect. It has been established that the Toms effect does not always result in thickening of the viscous sublayer; on the contrary, the most intense drag reduction takes place without thickening in the viscous sublayer.

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