Turbulent Motion Research Articles

Dissimilar turbulent momentum and heat transfer associated with viscoelastic vibration in channel flow

This experimental study on the momentum and heat transfer in drag-reducing turbulent channel flow of surfactant solution, i.e., viscoelastic fluid, has revealed a viscoelastic vibration (VEV) as a novel type of ordered turbulent motion in the wall vicinity where the elastic energy is transformed into turbulent kinetic energy. The VEV is a wave-like motion of low-frequency modes in the streamwise direction and causes zero average Reynolds shear stress. However, thermal diffusion occurs continuously due to the movement of a fluid lump owing to the VEV via the additional action of pressure.

Total mechanical energy budget in open-channel transitions with turbulent flows

Abstract The issue of mechanical energy budget has received a lot of attention in open-channel flows which are frequently turbulent. Turbulent motions play a major role in the total mechanical energy of the flow field. It is difficult to evaluate total mechanical energy balance and energy loss for 3-D turbulent flows in irregular open channels due to the formation of vortices and the presence of secondary currents. In 3-D turbulent flows, the effect of these phenomena has often been considered as the empirical coefficient of energy loss. In this study, these details in the total mechanical energy budget are investigated through theoretical analysis and numerical simulation, a new form of the total mechanical energy equation and a relationship for the energy loss in 3-D turbulent flows are derived, and their applications are examined in open-channel transitions. For this purpose, the Navier-Stokes equations are solved numerically, and the results are used to obtain the various terms in the total mechanical energy balance equation and analyze the details. The relationships derived in this study generally support the concept of the total mechanical energy budget to comprehend the turbulence parameters affecting the mechanical energy balance in various open-channel flows.

Theoretical Estimates of the Critical Reynolds Number in the Flow around the Sphere on the Basis of Theory of Stochastic Equations and Equivalence of Measures

The aim of this investigation is to show the solution for the critical Reynolds number in the flow around the sphere on the basis of theory of stochastic equations and equivalence of measures between turbulent and laminar motions. Solutions obtained by numerical methods (DNS, LES, RANS) require verification and in this case the theoretical results have special value. For today in the scientific literature, there is J. Talor’s implicit formula connecting the critical Reynolds number with the parameters of the initial fluctuations in the flow around the sphere. Here the derivation of the explicit formula is presented. The results show a satisfactory correspondence of the obtained theoretical dependence for the critical Reynolds number to the experiments in the flow around the sphere.

HYDRO-GAS-DYNAMIC MODEL OF MOTION OF GAS-SATURATED LIQUID IN A CENTRIFUGAL POROUS PUMP


 
 
 An approach has been developed to the formation of a theoretical model of the movement of a gas- saturated liquid in the flow path of a porous centrifugal pump, as an assembly of the system for feeding the reaction mass of liquid-propellant rocket engines. The developed approach is based on a physical model of the turbulent motion of a gas-liquid mixture, within which conservation equations are used. Two models are proposed that describe the movement of a gas-liquid mixture in the flow path of a centrifugal porous pump in a two-phase one- dimensional formulation and a quasi-homogeneous one, complementing each other. A porous impeller of a closed- type centrifugal pump of constant width is considered. The energy losses of the gas-liquid mixture flow at the inlet to the pump impeller, as well as the losses of disk friction associated with rotation in a fixed housing, are not taken into account. The parameters of the viscous and inertial hydraulic resistance coefficients of the porous body are used. In particular, the influence of the static pressure gradient in a gas-saturated liquid and the friction force on the accumulation of gas at the inlet to the impeller and the stability of the liquid supply by the pumping unit is noted. The use of the developed approach makes it possible, by calculation methods, to evaluate the values of parameters characterizing the movement of gas-liquid media in centrifugal porous pumps of the designed systems for feeding propellant components to liquid-propellant rocket engines, to reduce the amount of experimental testing of new and modernized propulsion systems for space stages and launch vehicles.
 
 

Assessment and application of wavelet-based optical flow velocimetry (wOFV) to wall-bounded turbulent flows

The performance of a wavelet-based optical flow velocimetry (wOFV) algorithm in extracting high accuracy and high-resolution velocity fields from tracer particle images in wall-bounded turbulent flows is assessed. wOFV is first evaluated using synthetic particle images generated from a channel flow DNS of a turbulent boundary layer. The sensitivity of wOFV to the regularization parameter (lambda) is quantified and results are compared to cross-correlation-based PIV. Results on synthetic particle images indicated different sensitivity to under-regularization or over-regularization depending on which region of the boundary layer is being analyzed. Nonetheless, tests on synthetic data revealed that wOFV can modestly outperform PIV in vector accuracy across a broad lambda range. wOFV showed clear advantages over PIV in resolving the viscous sublayer and obtaining highly accurate estimates of the wall shear stress and thus normalizing boundary layer variables. wOFV was also applied to experimental data of a developing turbulent boundary layer. Overall, wOFV revealed good agreement with both PIV and a combined PIV + PTV method. However, wOFV was able to successfully resolve the wall shear stress and correctly normalize the boundary layer streamwise velocity to wall units where PIV and PIV + PTV showed larger deviations. Analysis of the turbulent velocity fluctuations revealed spurious results for PIV in close proximity to the wall, leading to significantly exaggerated and non-physical turbulence intensity in the viscous sublayer region. PIV + PTV showed only a minor improvement in this aspect. wOFV did not exhibit this same effect, revealing that it is more accurate in capturing small-scale turbulent motion in the vicinity of boundaries. The enhanced vector resolution of wOFV enabled improved estimation of instantaneous derivative quantities and intricate flow structure both closer to the wall and more accurately than the other velocimetry methods. These aspects show that, within a reasonable lambda range that can be verified using physical principles, wOFV can provide improvements in diagnostics capability in resolving turbulent motion occurring in the vicinity of physical boundaries.Graphical abstract

Amplitude modulation in particle-laden atmospheric surface layers

Particle effects on the amplitude modulation are investigated in this study based on observational data with various mass loading acquired from long-term measurements of aeolian sandstorms in high-Reynolds-number ($Re_{\tau }\sim O(10^6)$) near-neutral atmospheric surface layers. In both particle-laden and unladen flows, in addition to the positive top–down modulation behaviour in the logarithmic region, a significant modulation effect that exists for some specific motions is also found for the single-point amplitude modulation. The most energetic turbulent motions exhibit the strongest modulation effect, and the modulating signals do not change with the small-scale motions being modulated. In particle-laden flows, the length of the most energetic structure is almost constant, thus the scales of the modulating signal and carrier signal are hardly affected by particles. However, the addition of particles changes the distribution of energy between multi-scale turbulent motions. The kinetic energy of the large-scale component is less enhanced than the total kinetic energy by particles. This leads to a reduced energy proportion of the large-scale component and an augmented one of the small-scale component. Moreover, the particles produce a large damping in the degree of the amplitude modulation and move down the positions of the modulating signals and carrier signals corresponding to the strongest inter-layer modulation, but the damping is weakened with the wall-normal distance due to the decreased mass loading. This study may provide a more general insight into the modulation mechanism between multi-scale turbulent motions and the effect of particles on turbulence.

Regular rotation and low turbulence in a diverse sample of z ∼ 4.5 galaxies observed with ALMA

ABSTRACT The discovery of galaxies with regularly rotating discs at redshifts ≥4 has been a puzzling challenge to galaxy formation models that tend to predict chaotic gas kinematics in the early Universe as a consequence of gas accretion, mergers, and efficient feedback. In this work, we investigated the kinematics of five highly resolved galaxies at z ∼ 4.5 observed with ALMA in the [C ii] 158 $\mu$m emission line. The sample is diverse: AzTEC1 (starburst galaxy), BRI1335-0417 (starburst and quasar host galaxy), J081740 (normal star-forming galaxy), and SGP38326 (two starburst galaxies in a group). The five galaxies show velocity gradients, but four were found to be rotating discs, while the remaining, AzTEC1, is likely a merger. We studied the gas kinematics of the discs using 3DBAROLO and found that they rotate with maximum rotation velocities between 198 and 562 km s−1, while the gas velocity dispersions, averaged across the discs, are between 49 and 75 km s−1. The rotation curves are generally flat and the galaxies have ratios of ordered-to-random motion (V/σ) between 2.7 and 9.8. We present CANNUBI, an algorithm for fitting the disc geometry of rotating discs in 3D emission-line observations prior to modelling the kinematics, with which we find indications that these discs may have thicknesses of the order of 1 kpc. This study shows that early disc formation with a clear dominance of rotation with respect to turbulent motions is present across a variety of galaxy types.

Toward quantifying turbulent vertical airflow and sensible heat flux in tall forest canopies using fiber-optic distributed temperature sensing

Abstract. The paper presents a set of fiber-optic distributed temperature sensing (FODS) experiments to expand the existing microstructure approach for horizontal turbulent wind direction by adding measurements of turbulent vertical component, as well as turbulent sensible heat flux. We address the observational challenge to isolate and quantify the weaker vertical turbulent motions from the much stronger mean advective horizontal flow signals. In the first part of this study, we test the ability of a cylindrical shroud to reduce the horizontal wind speed while keeping the vertical wind speed unaltered. A white shroud with a rigid support structure and 0.6 m diameter was identified as the most promising setup in which the correlation of flow properties between shrouded and reference systems is maximized. The optimum shroud setup reduces the horizontal wind standard deviation by 35 %, has a coefficient of determination of 0.972 for vertical wind standard deviations, and a RMSE of less than 0.018 ms−1 when compared to the reference. Spectral analysis showed a fixed ratio of spectral energy reduction in the low frequencies, e.g., <0.5 Hz, for temperature and wind components, momentum, and sensible heat flux. Unlike low frequencies, the ratios decrease exponentially in the high frequencies, which means the shroud dampens the high-frequency eddies with a timescale <6 s, considering both spectra and cospectra together. In the second part, the optimum shroud configuration was installed around a heated fiber-optic cable with attached microstructures in a forest to validate our findings. While this setup failed to isolate the magnitude and sign of the vertical wind perturbations from FODS in the shrouded portion, concurrent observations from an unshrouded part of the FODS sensor in the weak-wind subcanopy of the forest (12–17 m above ground level) yielded physically meaningful measurements of the vertical motions associated with coherent structures. These organized turbulent motions have distinct sweep and ejection phases. These strong flow signals allow for detecting the turbulent vertical airflow at least 60 % of the time and 71 % when conditional sampling was applied. Comparison of the vertical wind perturbations against those from sonic anemometry yielded correlation coefficients of 0.35 and 0.36, which increased to 0.53 and 0.62 for conditional sampling. This setup enabled computation of eddy covariance-based direct sensible heat flux estimates solely from FODS, which are reported here as a methodological and computational novelty. Comparing them against those from eddy covariance using sonic anemometry yielded an encouraging agreement in both magnitude and temporal variability for selected periods.

Convective and Turbulent Motions in Nonprecipitating Cu. Part III: Characteristics of Turbulence Motions

Abstract Velocity field in a nonprecipitating Cu under BOMEX conditions, simulated by SAM with 10-m resolution and spectral bin microphysics is separated into the convective part and the turbulent part, using a wavelet filtering. In Part II of the study properties of convective motions of this Cu were investigated. Here in Part III of the study, the parameters of cloud turbulence are calculated in the cloud updraft zone at different stages of cloud development. The main points of this study are (i) application of a fine-scale LES model of a single convective cloud allowed a direct estimation of turbulence parameters using the resolved flow in the cloud and (ii) the separation of the resolved flow into the turbulence flow and the nonturbulence flow allowed us to estimate different turbulent parameters with sufficient statistical accuracy. We calculated height and time dependences of the main turbulent parameters such as turbulence kinetic energy (TKE), spectra of TKE, dissipation rate, and the turbulent coefficient. It was found that the main source of turbulence in the cloud is buoyancy whose contribution is described by the buoyancy production term (BPT). The shear production term (SPT) increases with height and reaches its maximum near cloud top, and so does BPT. In agreement with the behavior of BPT and SPT, turbulence in the lower cloud part (below the inversion level) is weak and hardly affects the processes of mixing and entrainment. The fact that BPT is larger than SPT determines many properties of cloud turbulence. For instance, the turbulence is nonisotropic, so the vertical component of TKE is substantially larger than the horizontal components. Another consequence of the fact that BPT is larger than STP manifests itself in the finding that the turbulence spectrum largely obeys the −11/5 Bolgiano–Obukhov scaling. The classical Kolmogorov −5/3 scaling dominates for the low part of a cloud largely at the dissolving stage of cloud evolution. Using the spectra obtained we evaluated an “effective” dissipation rate which increases with height from nearly zero at cloud base up to 20 cm2 s−3 near cloud top. The coefficient of turbulent diffusion was found to increase with height and ranged from 5 m2 s−1 near cloud base to 25 m2 s−1 near cloud top. The possible role of turbulence in the process of lateral entrainment and mixing is discussed. Significance Statement 1) This study investigates the turbulent structure of Cu using a 10-m-resolution LES model with spectral bin microphysics, 2) the main source of turbulence is buoyancy, 3) turbulence in cumulus clouds (Cu) is nonisotropic, 4) turbulence reaches maximum intensity near cloud top, 5) turbulence spectrum obeys largely the −11/5 Bolgiano–Obukhov scaling, and 6) the main turbulent parameters are evaluated.

Convection and intermittency noise in water temperature near a deep Mediterranean seafloor

Turbulent and internal wave motions are important for the exchange of momentum, heat, and suspended matter in the deep sea, which is generally stably stratified in density. Turbulence-generation models involve shear of vertical current differences that deforms stratified waters and convection that is driven by (unstable) buoyancy. In general, shear generation is found more in the interior of the well-stratified ocean, while convection is known to occur near the sea surface, e.g., via nighttime cooling. Far below the surface, the Western Mediterranean Sea is very weakly stratified and offers opportunity to observationally study the deep-sea convection. An opportunistic small set of high-resolution temperature sensors demonstrate not only classic internal-wave-induced turbulence but also convection attributed to geothermal heating and spectral properties that relate to various chaos-theory models, such as 1/σ pink noise (σ denoting frequency), mainly found lying at (0.01 m above) the seafloor, and 1/σ2 Brownian noise, mainly found on a moored line at about 100 m above the seafloor. Near-inertial temperature variations are observed to occur down to the seafloor, thereby disturbing the local convective turbulence regime to shear-dominated one temporarily. The integral turbulence timescale is generally smaller (with dominant higher frequency motions) at the seafloor than about 100 m above it.

Inflationary and Phase-transitional Primordial Magnetic Fields in Galaxy Clusters

Primordial magnetic fields (PMFs) are possible candidates for explaining the observed magnetic fields in galaxy clusters. Two competing scenarios of primordial magnetogenesis have been discussed in the literature: inflationary and phase-transitional. We study the amplification of both large- and small-scale correlated magnetic fields, corresponding to inflation- and phase transition–generated PMFs, in a massive galaxy cluster. We employ high-resolution magnetohydrodynamic cosmological zoom-in simulations to resolve the turbulent motions in the intracluster medium. We find that the turbulent amplification is more efficient for the large-scale inflationary models, while the phase transition–generated seed fields show moderate growth. The differences between the models are imprinted on the spectral characteristics of the field (such as the amplitude and the shape of the magnetic power spectrum) and therefore also on the final correlation length. We find a one order of magnitude difference between the final strengths of the inflation- and phase transition–generated magnetic fields, and a factor of 1.5 difference between their final coherence scales. Thus, the final configuration of the magnetic field retains information about the PMF generation scenarios. Our findings have implications for future extragalactic Faraday rotation surveys with the possibility of distinguishing between different magnetogenesis scenarios.

Influence of Atmospheric Flow Structure on Optical Turbulence Characteristics

This article discusses the quality of astronomical images under conditions of moderate small-scale turbulence and varying meso-scale airflows above the Baikal Astrophysical Observatory (BAO). We applied a Weather Research and Forecasting (WRF) Model, as well as statistical estimations of the Fried parameter from the differential motion of the solar images. The simulations were performed with a fairly high horizontal resolution within a large area of 1600 × 1600 km. A high horizontal resolution provides representative estimations of atmospheric characteristics and correct accounting of large-scale air advection. We considered the influence of atmospheric motions over the cold water area of Lake Baikal, as well as meso-scale vortex structures over rough terrain on solar image quality. A better understanding of structured turbulent small-scale motions and optical turbulence over rough terrain may help to develop advanced methods for diagnostics and prediction of image quality. For the first time, we have shown that the BAO is located at the periphery of a meso-scale atmospheric vortex structure with an anticyclonic direction of airflows in the daytime. An increase in image quality was associated with weakening airflows over Lake Baikal and a decrease in the intensity of wind speed fluctuations. Calculated spectra of atmospheric turbulence in the daytime were close to the classical form. At night and in the morning, the spectra had a steeper slope on small scales. Deformations of the spectra were due to the suppression of turbulence under stable stratification of the atmosphere. The characteristic horizontal scales of the transition from “−5/3” to ∼“−3” spectral slope were 2–2.5 km. The results obtained using the WRF model and analysis of optical turbulence strength (namely, the Fried parameter) indicated that the parameterization schemes used in the WRF model were accurate.

CFD Simulation Study on the Air Side of a CO2 Evaporator in a Motor Train Unit Air Conditioning System

At present, China’s high-speed rail is in a period of rapid development. Most of the refrigerants used in Chinese motor train units at this stage are still R134a and R407c, which have an impact on the environment. In response to the environmental protection concept of green travel, it is of great significance to study the air conditioning system of motor train units using CO2 refrigerant. Using CFD simulation analysis technology, the heat transfer performance of the air side of the CO2 finned tube evaporator used in the air conditioning system of the motor train unit is studied. We select the air outlet temperature, pressure drop, heat transfer factor, and resistance factor as the objective function, in addition, monitoring points are set up in the air flow channel to monitor the turbulent flow field and pipe wall pressure. Our research shows that the cooling capacity of the CO2 evaporator can reach up to 29.76 kW, which can meet the heat exchange required in the air conditioning system of the motor train unit. In order to obtain a better structure and the conditions of the heat transfer effect, structural optimization was conducted. The simulation results demonstrate several trends: (i) With the augment of the air inlet velocity, the cooling capacity of the evaporator increases and the heat exchange effect improves; when the air inlet ve > 2.2 m/s, the effect of continuing to augment ve on heat exchange is weak. (ii) Following appropriate reduction of the diameter of the heat exchange tube, the wind resistance is reduced and the cooling capacity of the evaporator is improved. (iii) With the enlargement of the fin spacing, the turbulent motion in the flow channel can be fully developed, there is a peak in the change in the heat exchange tube area optimization factor, and the optimal fin spacing is between 1.6 mm and 1.7 mm; at this time, the average turbulent kinetic energy of the air side is larger and the turbulent dissipation rate is smaller. These results provide a reference for the practical application of CO2 refrigerant in the motor train unit.

Two saturated states of the vertical shear instability in protoplanetary disks with vertically varying cooling times

Abstract Turbulence in protoplanetary disks plays an important role in dust evolution and planetesimal formation. The vertical shear instability (VSI) is one of the candidate hydrodynamic mechanisms that can generate turbulence in the outer disk regions. The VSI requires rapid gas cooling in addition to vertical shear. A linear stability analysis suggests that the VSI may not operate around the midplane where gas cooling is inefficient. In this study, we investigate the nonlinear outcome of the VSI in disks with a linearly VSI-stable midplane region. We perform two-dimensional global hydrodynamical simulations of an axisymmetric disk with vertically varying cooling times. The vertical cooling time profile determines the thicknesses of the linearly VSI-stable midplane layer and unstable layers above and below the midplane. We find that the thickness of the midplane stable layer determines the vertical structure of VSI-driven turbulence in the nonlinear saturated state. We identify two types of final saturated state: (i) T states, characterized by vertical turbulent motion penetrating into the VSI-stable midplane layer, and (ii) pT states, characterized by turbulent motion confined in the unstable layers. The pT states are realized when the midplane VSI-stable layer is thicker than two gas scale heights. We also find that the VSI-driven turbulence is largely suppressed at all heights when the VSI-unstable region lying above and below the midplane is thinner than two gas scale heights. We present empirical formulas that predict the strength of VSI-driven turbulence as a function of the thicknesses of the unstable and stable layers. These formulas will be useful for studying how VSI-driven turbulence and dust grains controlling the disk cooling efficiency evolve simultaneously.

Energy and Information Fluxes at Upper Ocean Density Fronts

We present large eddy simulations of a midlatitude open ocean front using a modified state-of-the-art computational fluid dynamics code. We investigate the energy and information fluxes at the submesoscale/small-scale range in the absence of any atmospheric forcing. We find submesoscale conditions (Ro∼1, Ri∼1) near the surface within baroclinic structures, related to partially imbalanced frontogenetic activity. Near the surface, the simulations show a significant scale coupling on scales larger than ∼103 (m). This is manifested as a strong direct energy cascade and intense mutual communication between scales, where the latter is evaluated using an estimator based on Mutual Information Theory. At scales smaller than ∼103 (m), the results show near-zero energy flux; however, at this scale range, the estimator of mutual communication still shows values corresponding with a significant level of communication between them. This fact motivates investigation into the nature of the self-organized turbulent motion at this scale range with weak energetic coupling but where communication between scales is still significant and to inquire into the existence of synchronization or functional relationships between scales, with emphasis on the eventual underlying nonlocal processes.

Multi-scale flow structure and its effect on momentum flux in the coastal marine atmospheric boundary layer

To accurately calculate the turbulent exchange coefficient, the contribution of multi-scale turbulent transportation needs to be considered, especially in the complex terrain of the coastal area. In September 2019, a comprehensive observation experiment on the offshore atmospheric boundary layer was carried out at the Yangmeikeng Ecological Monitoring Station and Sai Chung Gulf. Through scale decomposition, it is shown that the turbulent motion in the atmospheric boundary layer in the coastal area is affected by the underlying surface, such as that of the coastal land or the sea–land boundary. This is the main reason behind the phenomenon whereby different scales make different contributions to momentum flux. Different multi-scale characteristics of turbulent structures on the underlying surface affect the drag coefficient. Through wavelet transform and finite element method, the characteristics of the multi-scale flow structures produced by the complicated offshore terrain are analysed. It is found that large-scale flow structures enhance the pulsating intensity at the small scale, but the large-scale coherence characteristics are different from those at the small scale. In summary, in comparing these three sites, the flux exchange on the roof is greatest, followed by that on the tower. In the Gulf, the flux exchange is mainly dependent on small-scale structures, which are linked with the smallest values.

Model for calculating the hydraulic parameters of channels with a dynamically stable section

In today's climate change conditions, it is difficult to imagine agriculture as separate from irrigated agriculture. When taking water from the river, transferring a large number of river sediments along with water to crop fields through irrigation networks requires high carrying capacity and resistance to deformation from irrigation channels. In this process, correct assessment of the factors affecting the sedimentation of the flow and ensuring that the velocity in the channel is at the limit values determines the dynamic strength of the channels. In the paper, based on the analysis of some models representing suspended turbulent flow motion and a new generalized mathematical model based on the theory of interfering media, the equation for calculating the relative width of the channel (β) for two-phase turbulent flow containing suspended sediments and the interaction of the riverbed is taken into account. It was found that the results of this equation were very close to the results of field studies compared to existing computational methods compared with the values of field studies conducted on dynamically stable section channels and the values calculated by existing computational methods.

Theoretical Aspects of Turbulent Flows in Pipeline

Abstract The paper presents the results of theoretical studies on turbulent water motion in pipelines, obtained by the analysis of experimental data regarding hydraulic patterns of turbulent flows. The authors suggest to evaluate the relevant parameters on the basis of the molecular and turbulent viscosity indicators, with the introduction of the conditional relative thickness of the boundary layer on the pipeline walls into the calculations. On this basis, the authors specified semi-empirical relationships for the distribution of averaged velocities in the pipe cross-sections, and revealed new theoretical relationships between the main parameters of turbulent pipe flows. The research confirmed the adequacy of these relationships given the good agreement of the calculated averaged velocity values with the experimental data which formed a basis for the current standards for hydraulic calculations of water supply pipes. For hydraulically smooth pipes, the authors derived an explicit dependence of the hydraulic friction coe cient on the Reynolds number, which almost completely corresponds to the well-known Prandtl-Colebrook equation that has an implicit form. The presented research allowed to determine numerical values and analytical relationships between parameters, which enabled evaluating turbulent flows in hydraulically smooth pipes in a new way.

Interaction of turbulent kinetic energy and coherent motion in the near field of the cylinder wake

The far aim of the study is to experimentally assess the exchange of turbulent kinetic energy (TKE) of a wake behind a cylinder, as a function of the upstream flow. The wake behind the obstacle is composed of coherent motion (CM) and random motion (RM). Coherent motion, reminiscent of the Von Kármán street, interacts with the random flow, thus inducing locally enhanced turbulent cascade. This energy exchange between CM and RM is reflected by the kinetic energy budget at one point, and two points in space. In the experimental setup, a cylinder is placed in a closed loop wind tunnel to create a Von Kármán vortex street. The Reynolds number, based on the cylinder diameter and the free main stream velocity, is equal to Re = 2000. Two-dimensional, two-components in-plane velocity fields are measured behind the cylinder by Particle Image Velocimetry (PIV). Two sets of measurements are explored: without and with synchronization, based on the CM. For synchronization, a microphone is used. CM is reconstructed, by filtering the flow at 9 phase shifts, for a detailed insight.

Velocity distribution and hydrodynamic drag in turbulent flow

This work aims to study the vertical velocity distribution in the near-wall layer of a pipe, channel, and boundary layer of a flat plate because these issues are of great practical and theoretical importance. Until now, engineering calculations of turbulent flows have been based on empirical formulas derived in the last century. The theory of turbulent fluid motion has not been completed, and the issues of velocity distribution and hydraulic resistance remain open for further study. It is known that velocity distribution in the flow is intricately linked to hydraulic resistance. Therefore, the study’s objectives also include determining the position of the point of maximum turbulent tangential stresses and comparing the change in tangential stresses with the logarithmic velocity profile. Based on calculation and analytical methods, we have researched the distribution of the turbulent component of the tangential stress along the depth of the flow. Derived an expression determining the position of the maximum point of the turbulent component of the tangential stress for smooth tubes. The contribution of the viscous component of the tangential stress at different points along the flow depth has been evaluated. The calculation results determining the position of the maximum point of the turbulent component of the tangential stress were compared with experimental data on velocity distribution in the flow. With the decrease of the hydraulic resistance coefficient, the point of maximum turbulent tangential stresses shifts towards the solid flow boundary. Based on the results of comparing the maximum turbulent tangential stresses with the total tangential stress, we can conclude that the contribution of the viscous component of the tangential stress to the total amount of friction and its influence on velocity distribution is significant. The angular coefficient of the velocity profile for the flow core is determined.