An experimental study of heat transfer and hydraulic losses in a channel with one wall being a surface with trench dimple was carried out. The working surface had four rows of dimples located alternately at angles of 45° and −45° to the channel axis. In the laminar regime, the transfer of heat and the losses of pressure turned out to be close to the parameters of a smooth channel. In the turbulent regime, a 1.5-fold enhancement of heat transfer with respect to the transfer of heat in a smooth channel was obtained. The dependence of the increase in pressure losses on the Reynolds number qualitatively agreeing with the dependence for the channels with sandy roughness is obtained.

The most popular way to transport natural gas is to use pipelines. However, complex spatial configuration of pipeline systems, as well as regulating devices and gate valves, break the uniformity and symmetry of the velocity profile, induce swirling flows, generate acoustic disturbance, and promote amplification of acoustic noise. It is almost impossible to estimate and take into account all these effects in gas metering. Therefore, the measurement uncertainty in complex conditions can be as high as 20%. It is reasonable to employ flow conditioners (FC) in order to increase the measurement accuracy. Their function is to form the flow with known characteristics. The existing FC models, however, were designed to deal with a limited set of flow histories and typically require calibration in combination with a flow meter. There are almost no FCs able to deal with a wide spectrum of flow histories and mitigate the effect of acoustics on the measurement accuracy. The study submits an approach to the design of the flow passage inside FC that addresses the described problems. The proposed FC has a cartridge containing a set of coaxial perforated streamwise cylinders nested within one another with a varied pitch along the diameter. An experimental model of the device demonstrated its effectiveness in velocity profile conditioning and reproducibility of profiles in steady and unsteady flows in pipelines of different spatial configurations. The Reynolds number range considered in the study spans from the lower threshold, at which the majority of flow meters operate, to the values at which the flow becomes self-similar. The acoustic efficiency was estimated for the frequency range of 5 Hz to 120 kHz. In general, the experimental model met all challenges successfully. At the same time, the shape of velocity profiles downstream of the device is somewhat different from the developed velocity profile in straight pipes. This problem will require optimization of the device geometry, which will be addressed in the future research.

The effect of confinement of flow over the transversal coordinate on cross flow past a circular cylinder at the Reynolds numbers from 40 to 255 (based on the cylinder diameter and the undisturbed flow velocity) is studied numerically and experimentally. In the experiments, the cylinder was located in a rectangular channel and, in the case of numerical simulation, three types of the boundary conditions, namely, the periodic boundary conditions and the slip and no-slip conditions were imposed on the side walls confining the flow. Particular attention is concentrated on the vertical flow structure in the cylinder wake. It is shown that spiral vortices that travel in the plane of symmetry of the channel are formed only in the case of no-slip boundary conditions in the region of junction of the cylinder and the side walls. Under their interaction, vortex clusters are formed in the center of channel and some indications to flow turbulization can be observed in the wake. Under the periodic boundary conditions and the slip conditions on the side walls, there are no spiral vortices and, in the Re range from 200 to 250, the A and B modes of three-dimensional instability and turbulence transition are implemented in the cylinder wake. The effect of the channel width and the type of boundary conditions on the side walls on the vortex wake structure behind the cylinder and integral flow parameters is estimated.

The effect of confinement of flow over the transversal coordinate on cross flow past a circular cylinder at the Reynolds numbers from 40 to 255 (based on the cylinder diameter and the undisturbed flow velocity) is studied numerically and experimentally. In the experiments, the cylinder was located in a rectangular channel and, in the case of numerical simulation, three types of the boundary conditions, namely, the periodic boundary conditions and the slip and no-slip conditions were imposed on the side walls confining the flow. Particular attention is concentrated on the vertical flow structure in the cylinder wake. It is shown that spiral vortices that travel in the plane of symmetry of the channel are formed only in the case of no-slip boundary conditions in the region of junction of the cylinder and the side walls. Under their interaction, vortex clusters are formed in the center of channel and some indications to flow turbulization can be observed in the wake. Under the periodic boundary conditions and the slip conditions on the side walls, there are no spiral vortices and, in the Re range from 200 to 250, the A and B modes of three-dimensional instability and turbulence transition are implemented in the cylinder wake. The effect of the channel width and the type of boundary conditions on the side walls on the vortex wake structure behind the cylinder and integral flow parameters is estimated.

The purpose of this study is to sample a procedure for numerical simulation and calculation of the processes of mixing in pipes of a T-junction (tee) of natural gas with the so-called “stripped” components, such as methane, hydrogen, and nitrogen, to obtain a mixture that can be used as a fuel at thermal power plants. The specific of fuel gas mixing is high Reynolds numbers of the simulated flows, which can be as high as Re = (5–10) × 10 6 . An analysis is presented of some experimental and modern computational studies of the processes of flow mixing in pipes and T-junctions. It is pointed out that the application of various well-accepted models for eddy viscosity or Reynolds stresses in the numerical simulation on the basis of Reynolds-averaged conservation equations yields a satisfactory agreement with experimental data on mixing flows in a T-mixer only with an unjustified decrease of the turbulent Schmidt (Prandtl) number to the value 0.1 or an increase of the known constant of turbulence models C μ by a factor of 9. It can be concluded that eddy-resolving methods are unsuitable for the investigation of mixing processes in fuel pipeline joints due to high Reynolds numbers and a great length of the main pipe. An analysis of the predictions has revealed large fluctuations in the local ratio of the generation rate of the turbulent kinetic energy to the rate of its dissipation and a sharp decrease in its value averaged over the pipe cross section at a distance of several diameters from the starting point of mixing, which is not characteristic of pipe flows, mixing layers, or jets. An attempt was made to improve the predictive capabilities of the standard k –ε model for developed turbulence, while keeping the turbulent Schmidt number Sc_t and the constant С μ within the substantiated limits. An empirical formula for Sc_t and a modification of the standard k –ε model, which takes into account the variability of С μ according to the Rodi dependence carefully verified against data on various free flows, are proposed. Experimental investigations of isothermal mixing of air flows in a tee mixer, one of which contained tracers in the form of glycerin-based liquid microdroplets, were carried out. The profiles of hydrodynamic characteristics of the flow downstream of the tee were measured by the planar optical SIV method at a distance of 5.5 D from the axis of the pipes' intersection. To verify the modified k –ε model, numerical simulation was performed of the mixing of gases and liquids in a tee mixer, and the predictions were compared with the experiment. The results are presented of the calculation of natural gas mixing in a tee mixer with a methane-hydrogen fraction from petrochemical facilities.

Experiments on the efficiency of several design versions of flow conditioners with folded perforated plates were carried out. The efficiency was estimated from the standpoint of reduced influence of acoustic noise on ultrasonic gas flowmeter performance, decreased pressure loss, elimination of flow field distortion, and combination of these factors.

The paper elaborates on experimental testing of the effect of the mixing chamber length of the cylindrical flow conditioner on the shape of velocity profiles in the downstream pipeline section. The study estimates the parameters of the assembly consisting of the cylindrical flow conditioner and the pipe section connecting it to the flow meter from the standpoint of its compactness.

Heat transfer in diverging channels is essentially different from the one in channels of constant cross section. The mechanism of heat transfer enhancement in diverging channels compared to the channels of constant cross section is based on increased turbulence intensity. The present paper suggests new approach to the analysis and generalization of heat transfer data. Heat transfer on the wall of a diverging channel should be considered similarly to heat transfer from a plate instead of heat transfer in a channel. The data on heat transfer coefficient on the wall of a plane diverging channel at different expansion angles can be generalized by the Stanton number as a function of the Reynolds number and Kays acceleration parameter, St similar to f(Re, K). This function has characteristic sections along the wall that are typical of laminar, transitional and turbulent boundary layers. Stanton and Reynolds numbers based on the distance from the inlet and the velocity at the diverging channel inlet can be employed for data generalization in all the considered ranges of geometries and flow regimes. Kinematic structure of flow is examined to reveal hydrodynamic mechanisms behind heat transfer formation. Optical measurements provide the profiles of velocities and turbulence parameters in characteristic sections of the channel. Mechanism of turbulent structure formation in diverging channels is examined. Correlation between hydrodynamics and heat transfer is analyzed. Correlation between local coefficients of heat transfer and near-wall Reynolds stress is revealed. (c) 2022 Elsevier Ltd. All rights reserved.

Experimental study examines the structure of nominally laminar flows subjected to sinusoidal variation of flow rate in smooth pipes. An experimental setup employed for this purpose provides high stability of flow rate variation pattern and is able to reproduce flow reversal during a fraction of pulsation period. The Reynolds number based on the highest cross-section average velocity over the pulsation period is 1200. SIV technique is used to measure the instantaneous vector fields of velocity in two regimes of pulsating flow. While there is no flow reversal in the first regime, it occupies approximately 0.4 of the pulsation period in the second regime. The increase in the amplitude of high-frequency fluctuation of velocity is documented in both regimes near the pipe wall within the Stokes layer. Evolution of the shape of velocity profiles and fluctuation amplitude profiles depending on the pulsation phase is presented. Our analysis suggests that forced sinusoidal pulsation of flow rate at the considered parameters results in the onset of instability and signs of transition to turbulence in the near-wall flow in the smooth pipe. We describe possible mechanism of turbulization of the near-wall flow under the impact of forced flow rate pulsation.

The oscillating flow of a viscous incompressible fluid in a rigid circular pipe with local constriction has been studied numerically. Fluid viscosity and density, channel diameter and constriction, as well as amplitude-frequency characteristics of the flow rate are identical to those of the blood flow in the human popliteal artery with stenosis. Reynolds number in the area of stenosis is Re ≈ 5·103, dimensionless pulsation frequency is Sh = 0.43·10−3, and normalized constriction of the channel is δ = d/D = 0.4. The flow under consideration is characterized by the fact that during one oscillation period, the fluid flow rate changes direction four times. This contributes to laminar-turbulent transition when the jet discharges from a constriction throat into the main flow. Qualitative features and quantitative parameters of pulsating flow have been determined including distribution of friction stresses along the channel wall.

New approach to maintaining liquid flow rate stability in primary standard calibration facility is proposed. It takes advantage of primary standards with constant static head and does not require high-altitude installation of the pressure tank. To implement the proposed approach, the pressure tank is installed in the water pipeline of the Standard between the pumping station and the measurement pipeline. Pressure in the air cushion above the liquid in this tank is maintained automatically, as well as the liquid level in the pressure tank. It has been demonstrated that in order to stabilize the flow, it is sufficient to employ the controlling impacts in the form of air supply/withdrawal and adjustment of variable-frequency drives of pumps. The air is supplied and withdrawn from the air cushion by a set of critical flow nozzles, which are activated depending on the absolute pressure of air in the cushion. The liquid level in the tank is controlled by adjustment of variable-frequency drives of pumps based on the information on the hydrostatic head (liquid level) in the tank. Experimental study of the flow stabilization system of the National Primary Standard GET 63–2017 for mass and volume of liquid, mass and volumetric flow rates of liquid (Kazan, Russia) confirmed high efficiency of the proposed approach.

Heat transfer and turbulence in channel flows past either a single rib or a rib array installed on the wall have been studied experimentally. It has been revealed that the local heat transfer coefficient behind a rib and a rib array is statistically closely related to RMS fluctuations of the vertical component of velocity in the near-wall region. This result points to a possible way to control the hydrodynamics aiming at heat transfer enhancement in turbulent flows in the channels with discrete roughness.

The paper describes a new experimental setup intended for simulation of blood flow through stenosis or distal end of anastomosis. The setup is able to reproduce flow rate pulsations with a wave form identical to the one of real blood flow during a cardiac cycle, including the high-amplitude antegrade peak and flow reversal. The design of experimental setup provides stable average flow rate in the test section and repeatability of simulated flow regimes.

Experiments and direct numerical simulation were employed to study the near wake of a circular cylinder in a cross flow in a rectangular channel. The gap between the cylinder and the channel wall was varied. Moderate Reynolds numbers were considered. The analysis of experimental results in combination with numerical simulation revealed the common patterns in the vortical structure of flow behind the cylinder, namely the tornado-like vortices formed in the region where the cylinder was attached to the sidewalls of the channel. The effect of the cylinder location on the onset of Karman vortex street was estimated. The formation mechanism of tornado-like vortices was described.

In the present paper, we report on the results of an experimental study of the transfer of heat and flow structure in the inter-tube space of in-line and staggered tube (cylinder) bundles in a pulsating external flow. For two values of the relative pitch in the bundles, the average heat transfer of a cylinder, and the distributions of the components of flow velocity and rms pulsations of that velocity in the inter-tube space, were measured. It is found that the change in the heat transfer of a bundle cylinder under forced flow unsteadiness correlates well with the level of the energy of velocity pulsations in the cylinder wake. The possibility of enhancement of heat transfer in a cylinder bundle using forced flow oscillations is demonstrated.

Turbulent characteristics of a near wake behind a circular cylinder in a cross flow at Re = 3900 were considered. This regime of flow past cylinders has been widely discussed in the literature; however, the published experimental data and numerical simulation results experience some controversy. Furthermore, there is a shortage of reliable experimental data, e.g. the available descriptions of experimental setups and conditions are not enough for testing of numerical methods. The present paper fills this gap to a large extent. Experiments were carried out using a relatively new smoke image velocimetry (SIV) technique, which provides time-resolved measurements of instantaneous two-dimensional velocity vector fields in complex turbulent flows with high spatial resolution of the order of Kolmogorov scale. Distributions of flow statistics over different cross sections of the cylinder wake were obtained. Comparative analysis of SIV measurements and previously published experimental and DNS data was performed. The sources of differences in distributions of turbulence statistics were analysed. Key regularities in evolution of velocity profiles in the cylinder wake were revealed. Some features were discovered in the distributions of transverse velocity component and fluctuating flow parameters that had not been previously captured by other measurement methods. Physical mechanisms and their origins are described.

The paper presents the experimental data on velocity fluctuation spectra and reattachment lengths observed in turbulent flows past low-profile elements of discrete roughness mounted on the wall. The discrete roughness elements were shaped as semicircular spanwise ribs with the height of 2% of the hydraulic diameter of the channel. It has been revealed that such ribs make the velocity fluctuations increase manifold at the height of rib tops in the range of non-dimensional frequency St=0.6-1.2 that favors the reattachment length reduction and heat transfer augmentation.