"Вестник МГСУ"

Geometrical characteristics of obstacles on the ground, which determine the roughness of the terrain, cause the air flow turbulence. The friction level of air flow on the surface depends on the height and density of the location of obstacles, which determines the magnitude and direction of the load on a corresponding specific object. Any obstacle located in the way of the turbulent flow experiences a corresponding wind load. In the given study we have considered a multi-span one-storey industrial building as an obstacle. In order to estimate the load on the object of study caused by the wind, we decomposed the corresponding load into two components: middle and fluctuating. The first one shows the static wind load characteristics estimated according to the territorial division into districts of the Russian Federation, where the areas of calculated values of wind pressure are exhibited. Their distribution is the result of the implementation of the probabilistic model presented in the form of non-stationary random field of wind flow speeds. In order to obtain calculated values and automated processing of the value of wind load on the surface of an industrial building under blow the profiles of wind flow velocities at different heights were approximated. The resulting functional dependency on the heights is of a distinct power character. In order to describe the dynamic parameters of the process, presented in the form of the fluctuating component of wind load and the resulting reactions of structural elements of the building, we considered the random functions according to the time parameter. They represent the energy spectrum of the proportion of the wind flow power, attributable to an infinitesimal frequency band. The set of reciprocal spectral densities when selecting the points in space, each of which determines the correlation degree between the states of a random process, has allowed establishing the magnitude of the correlation coefficient of wind pressure pulsations to the entire surface of the building. When studying wind load impact on the operation of an industrial building framework, the corresponding response elements of the system are defined separately from the effects of the average and the sum of pulsation components. The combined effect which corresponds to the most unfavorable load value is achieved in case of coincidence of their signs. The present approach to the assessment of the forces caused by wind and the response to them on the part of the object became the basis of the calculation methodology as one of the components of the generalized load on the object of study.

In the article, the authors present their findings generated at the laboratory of aerodynamic and aero-acoustic testing of structural units of MGSU. The authors provide information about the principle of operation and a brief description of the experimental test bed designated for the physical research of patterns of air flows arising inside building premises of various geometric shapes. The authors also demonstrate the basic parameters of the test bed, the principle of operation of its recording devices and some of its characteristics.
The test bed is designated for the identification of characteristics of three-dimensional flows of models under research and for the verification of results of numerical studies. The measurement bed has advanced measurement and registration units. The management principle is based on the method of digital flow visualization, PIV method and Doppler flow meter implemented in the LDA anemometer. The test stand generates two or three component vector fields of turbulent gas flow velocities. It may be applicable to the study of liquids in case of research of hydraulics-related problems. Some results of the flow study are provided in the article, as well.

The article is a further research of a circular-longitudinal flow created in a cylindrical pipe by a continuous swirler called Couette vortex, which the author started to study in his previous works. The key question is how Couette modified vortex is transformed along the channel (pipe). The author regards variation of azimuthal velocities (
u) and the Heeger-Baer’s swirl number (
Sn) in turbulent irregular circular-longitudinal flow, which is described by the model of modified Couette vortex along the cylindrical channel. It is confirmed that the model of the modified Couette vortex and free-forced Burgers - Batchelor vortex show almost similar results in calculations and both vortex models can be equally used in engineering practice in calculations and the analysis of circulating and longitudinal flow operating modes (vortex flows).

This article focuses on the method of improving shear stresses calculation accuracy based on the experimental data. It was proven that shear stresses value considerably changes (even up to change of sign from positive to negative) depending on different velocity fluctuations amount (or length). Experimental database consists of velocity in turbulent flow at different times. Recommendations for practical use of methods of calculation depending on the type of engineering problems are presented. The method of finding optimal amount of the experimental database is proposed by the analysis of the values convergence of the standard deviations calculated for the whole sample and the standard deviation calculated by increasing interval. The calculation results for these intervals are at the points of the measuring system and the hypothesis about finding the optimal length of implementation is offered. The steps for further research are set out.

Swirled flows of liquid and gas are widely used in modern technology because of many of their unique aerodynamic, thermodynamic, and hydro-mechanical qualities. They are used for spraying liquid fuel mixing and dispersing liquid, aerosol formation, formation of the flame, classification of disperse materials and drying, dehydration, deaeration, cooling and heating, distillation and purification (rectification of working fluids), ash and dust-collecting, generating vapor separation of suspensions, absorption materials, separation materials, excitation of mechanical vibrations and formation of a sound signal, transportation of materials and many other technological purposes. The proposals for the use of interacting (counter vortex) swirling flows were caused by the requirements of the practice of mixing fluids and gases and quenching of excess kinetic energy of the high-speed flow of water in the high-pressure hydro spillways. The method for energy dissipation by reacting flows (jets) I based on the idea of separating the stream into parts and creating the conditions for mutual energy damping of individual parts of during subsequent reunification. As it is known, while moving from the upper pool to the lower one the water flow may dampen its energy performing useful work on the hydraulic turbines or overcoming the reaction forces, which arise when passing through the dampers. The energy of one part of a stream in interaction with the energy of the other part is used for creating the forces equivalent to the jet forces developed by quenchers. Such interaction can give the best effect in the conditions of rational breakdown of a stream and creation of the respective movement directions of its parts in relation to each other. In the cylindrical camera of counter vortex devices coaxial flows are formed consisting of two or more oppositely swirling flows of liquid or gas, the interaction of which can convert practically the whole mechanical energy source of the interacting flows into excess turbulence energy. The nature and intensity of hydro-mechanical, aerodynamic and mechanical processes occurring in the counter vortex devices provide the efficiency of their application in various branches of modern technology for mixing of single-phase and multiphase media, quenching the excess mechanical energy of the flow of liquid and gas, for disintegration of conglomerates, creating a homogeneous systems, excitation of mechanical vibrations and obtaining other effects. Authors due to the nature of their activity paid the main attention to the development, researches and creation of the designs of counter vortex quenchers of spillways energy of high-pressure water-engineering systems and counter vortex aerators of different purpose. Counter vortex devices have been tested for other purposes (homogenizer, flotators), protected by patents or circuit diagram are proposed for them.

The article is devoted to hydraulic modeling of flows with counter-rotating coaxial layers. Dynamic similarity criteria of such flows were found by the inspection analysis of the Reynolds equations. It was found that the hydrodynamic similarity criteria for physical modeling of unsteady turbulent circular-longitudinal flows with counter-rotating coaxial layers of viscous incompressible fluid are: Strouhal number - the ratio of forces of local and convective inertia, Rossby number characterizes the ratio of the azimuthal and axial velocity, Froude number - the ratio of forces of convective inertia to the forces of gravity, Euler number - the ratio of pressure forces to the convective forces of inertia, Weber number - the ratio of the convective inertia forces to surface tension forces, Reynolds number - the ratio of the convective inertia forces to the forces of molecular viscosity, Karman number - the ratio of dispersion velocity vector of fluid particles to the flow velocity. The limit value of the Reynolds number was found at the lower boundary conditions of automodel zone of such flow. It is shown that Weber and Rossby criteria for physical modeling of such flows are not determinative. It was found out that turbulent circular-longitudinal flow with counter-rotating coaxial layers are not modeled using Karman criterion. In this connection, there is a need to conduct experimental methodological research of turbulent flows with counter-rotating coaxial layers on stands equipped means of three-dimensional laser Doppler anemometry. Integral criteria of dynamic similarity of circular-longitudinal flows was considered - Heeger-Baer number (swirl number) and Abramovich number, characterizing the ratio of the angular momentum and momentum of such flows. In comparison with the swirl number, Heeger-Baer number is more preferable. Abramovich number is equal to the geometric characteristics of the local swirler as similarity criterion of circular-longitudinal incompressible fluid flows, including counter-rotating coaxial layers. Basing on summation of the angular momenta of coaxial counter-rotating layers, integral criterion of dynamic similarity of these flows was obtained. A common system of basic hydrodynamic similarity criteria was defined for physical modeling of unsteady turbulent circular-longitudinal viscous liquid flows with counter-rotating coaxial layers. For this kind of flow criterial equation was compiled.

One of the modern methods of the experimental investigation of water flows turbulence is the method of Laser Doppler Anemometry. At the present time a measuring system “LAD-056” (Russia) is operating in the laboratory of the Department of Hydraulics of MGSU. The authors conducted an analysis of the requirements to experimental data when calculating turbulent characteristics of water flows. The article shows the necessity of checking the database of ripple continuity over time and the required representation of the number of points in the implementation. The results of experiments are presented showing the importance of fixing the length of the implementation and testing time. The authors offered a method of determining the optimal spatial coordinates for the measurement to minimize the time of filling the base of experimental data. According to the methods of defining optimal coordinate domain when measuring turbulent water flows with the use of “LAD-056” in a rectangular channel with glass walls in was established that it is required to conduct measurements within the range from 0 to 120 mm from the closest side wall. In case of greater deepening it is required to use illuminators reducing deflections of laser beams.

One of the main tasks of an engineer in design of hydraulic structures is to perform an accurate calculation of losses in a moving flow of liquid, whether that be a head conduit or open channel. Modern technologies make it possible to obtain construction materials enabling to reduce resistance in motion of liquid. Thus, the shifting of motion mode from hydraulically rough into the sphere of hydraulically smooth resistance takes place. In this regard, there is a need for improvement of methods for hydraulic resistance coefficient calculation. The analysis of existing methods for calculating the hydraulic resistance coefficient was performed. Reasons for necessity of the search of modern methods for calculation of this parameter were grounded. The data array that meets the requirements of the task was received using the modern equipment. The analysis of experimental results illustrating the influence of Reynolds number and Froude number, and of ratio of the channel width to the flow depth on the hydraulic resistance coefficient was performed. The revised method of calculating the coefficient of hydraulic resistance of smooth open channels is proposed.

The article represents an overview of the field studies of the intensity and distribution of probability
of longitudinal turbulent velocity fluctuations in river flows with different sizes of beds and
hydrological characteristics. The authors demonstrate that the normalizing transformation of velocity
fluctuations performed by the local friction velocity makes it possible to get the changes of velocity
fluctuations deep inside the flow close to universal.
The authors have also identified that the intensity of turbulent velocity fluctuations exceeds
the friction velocity 2.5-3-fold in the area close to the river bottom, while their intensities demonstrate
their gradual decline closer to the surface of the flow. The authors have derived an approximation
formula, describing the change of the intensity of longitudinal velocity fluctuations
deep inside river flows.
Probability distributions of longitudinal velocity fluctuations were compared to those based on
the law of Gauss. It is proven that they have a kurtosis of a frequency curve as well as an asymmetry
in comparison with the distribution of Gauss, which are most vivid in the area close to the bottom of the flow. Due to the fact that the coefficient of asymmetry includes a third degree of velocity fluctuations,
and a kurtosis of the frequency curve, experimental identification of these characteristics
is problematic for the reason of their instability. The new information concerning the intensity and
probability properties of the river flow turbulence can be used in projecting the mixture formation and
mass exchange processes ongoing inside river flows.

Subject: the article is devoted to the study of the processes of vortex formation (microturbulence) in non-pressure pipelines of drainage systems with a corrugated surface during transportation of liquid through them. The results of experiments on the study of microturbulence and carrying capacity of water flow at small fillings and velocities in an open tray are described for the flow past point and linearly elongated obstacles. On the basis of semi-phenomenological theory of turbulence with the use of universal indicator, expressed as a criterion of turbulence, theoretical derivations are presented for determination of zone of conducting subsequent experiments in the corresponding ranges of velocities at different heights of obstacles. The assumption is made that it is necessary to theoretically study the dependence of roughness coefficient on the ratio of obstacle height to pipe diameter in a wide range of fillings. The article presents the results of field experiments to identify the efficiency of pipeline network carrying capacity as a function of the filling value at a certain character of artificial obstacles. Research objectives: theoretical and experimental study of vortex formation processes and carrying capacity of fluid flow as it moves along a non-pressure tray with a textured surface to identify the optimal regime of pipeline operation. Materials and methods: literature sources were analyzed, stands for conducting field experiments were developed. We conducted a series of experiments and set forth theoretical propositions and possibilities for improvement of transporting capacity of the flow as it moves along the gravity pipeline with different textured inner surface. To determine the flow rate, a volumetric method was used, and the degree of turbulence was estimated using photo and movie equipment based on the use of black and white effect. Results: formation of flow microturbulence during placement of single or group obstacles in an open tray was investigated, graphs were constructed and mathematical dependences of the roughness coefficient on the ratio of obstacle height to pipe diameter were obtained for different filling values. A comparison of the values of the roughness coefficient was made for real sewer pipes made of different materials with artificial roughness generated on the experimental setup. The practical absence of discrepancies between artificial and natural roughnesses in the range of self-cleaning rates of water flow and normative fillings is established. Conclusions: studies have shown that the presence of artificial roughness in the form of various types of obstacles on the inner surface of the pipeline (by height, pitch, configuration) noticeably affects the transporting capacity of water flow. This makes it possible to use a textured surface in the form of polymer hoses applied to the inner surface of pipelines during their trenchless renovation to ensure self-cleaning of pipes and improve efficiency of sediments transportation.