Correlation analysis for the research of local characteristics of a turbulent flow

The paper describes the temperature-correlation velocimetry technique applied to the flow of water or liquid metal. The method allows simultaneous measurement of temperature signals and local values of a longitudinal velocity component in the flow. This approach is a simple and reliable method for measuring velocity in flows of optically impermeable fluids. At the same flow conditions, different coolants have different spatial-temporal characteristics that are processed using a temperature-correlation technique. This work is devoted to the development of an algorithm for formulating a set of practical recommendations for the use of this technique to measure velocity and to determine a metrological characteristic in various conditions. For calibration, water and mercury are used as model liquids. The data obtained are presented in the form of fields of temperature and intensity of temperature fluctuations. Autocorrelation and cross-correlation functions are compared for two investigated liquids under the same conditions.

CALCULATION OF TWO-SPEED FLOW OF TWO-PHASE OPEN FLOW

In this article the mathematical model of unsteady flow the two-phase open stream taking into account the redistribution of the particulate concentration, the depth of flow and water filtration on the bottom of the channel, and also created an efficient method of calculation. In this case, the two-speed flow is considered, i.e. the presence of the longitudinal and vertical components of the phase velocities is taken into account, and we also believe that the flow parameters along the flow do not change. Initial and boundary conditions are established based on theoretical and empirical formulas, which are widely used in practice. The flow in open channels is non-pressurized, occurs under the influence of gravity and is characterized by the fact that the flow has a free surface. At the initial moment of time, we consider the flow to be uniform in the longitudinal direction and all parameters are set by known theoretical and empirical formulas. At the bottom of the channel for longitudinal velocity component of the water use condition of adhesion, and for the longitudinal velocity component of solid phase condition for the shift and believe the known concentrations of solid particles, and vertical components of velocity the phases of the filtering conditions (for water), and hydraulic size (for solid particles). On the free surface, we consider that there are no solid particles, and for the longitudinal components of the phase velocities we neglect the force of air friction, and for the vertical components of the phase velocities we use the condition of non-uniformity of the free surface in time. On the basis of the developed mathematical model and the created method of calculation, the changes of the main parameters in the depth of the flow and in time are determined.

RESEARCH ON THE EFFECT OF THE INITIAL SPEED OF THE MIXTURE ON THE PROCESS OF LOADING

The work is devoted to the study of the influence of the initial velocity of the loose mixture on the loading process of the vibrating sieve. The regularities of layer thickness, longitudinal and transverse components of velocity, density of loose mixture and specific load on the entire area of a vibrating sieve are established. When the initial velocity is less than velocity of the mixture movement on the sieve is the thickness of the layer has become over the entire surface area, the surface density of the mixture decreases, and the longitudinal velocity component increases with length. The transverse velocity component contributes to the rapid redistribution of the mixture from the congested central area to the unloaded lateral ones. When the initial velocity is equal to the velocity of the mixture movement on the sieve, the thickness of the layer and the surface density of the mixture are constant on the surface area, the longitudinal velocity component is constant along the length and has an initial velocity profile along the width of the sieve, which is aligned with the length. The transverse velocity component decreased and the specific loading deviations increased. When the initial velocity is greater than the velocity of the mixture movement on the sieve, the thickness of the layer decreases, the surface density of the mixture increases, and the longitudinal velocity component decreases with length. The transverse velocity component is almost absent, the specific loading is uneven throughout the sieve area. Thus, the value of the initial velocity affects all the characteristics of the loose mixture, and the nature of changing some of them turns to the opposite. When the mixture is unevenly fed across the width at the inlet of the sieve, the increase of the initial velocity increases the uneven distribution of the specific load over the area of the work surface. The regularities of distribution of the specific load of the sieve are decisive in the design of feeders and distributors of loose mixtures, as well as in calculation of separation modes.

Radiative instability of a barotropic jet flow in a stratified rotating atmosphere

The problem of the stability of a jet flow with a piecewise linear velocity profile in a stratified rotating atmosphere is considered. The linearized system of equations for perturbations is reduced to a single equation with respect to the amplitude of the longitudinal velocity component containing the turning points. In terms of Airy functions, an asymptotic solution of the equation is constructed that is valid for small values of the Rossby number. It is shown that the flow becomes unstable due to radiation of inertial-gravitational waves. An analytical expression is obtained for the growth rate of perturbations.

Spectral analogy between temperature and velocity fluctuations in a turbulent boundary layer

Experiments were carried out in the turbulent boundary layer on a slightly heated plate in order to establish, mainly for the larger scales of motion, any analogy that may exist between the temperature and velocity fluctuations. With this goal in mind, the spectra and cospectra of the temperature and velocity fluctuations were measured. In particular, the cospectra were obtained by the ‘fluctuation-diagram method’. It soon became evident that the temperature spectrum, except very close to the wall, differs strongly from the spectrum of the longitudinal velocity component. At least for the lower frequency spectral range, which includes about 80% of the total variance, the experimental results support an analogy between the temperature spectrum and a new type of spectrum consisting of the sum of the spectra of the three velocity components weighted by their relative energy. This analogy was established throughout most of the boundary layer.

Conditional sampling and other measurements in a plane turbulent wake

A series of hot-wire measurements has been carried out in a plane wake to investigate the structure of the turbulence boundary and the relation of its instantaneous position to the behaviour in the core of the flow. The principal measured quantities are as follows: mean velocity profile; intermittency factor; burst rate; mean of the longitudinal component of velocity conditioned upon various specified interface positions; autocorrelation of the intermittency signal; probability densities a t the half-intermittency point for the time between bursts and the duration of a burst; probability density for the longitudinal velocity component and its time derivative at various points across the wake; probability density a t the half-intermittency point for the same quantities in the turbulent and irrotational zones separately. In addition, the profile of the second moment of the probability density for the time between bursts has been obtained indirectly and part of the theory of Phillips (1955) has been shown to be applicable in the intermittent region.The present measurements appear to indicate that the turbulence boundary in the wake resembles that in other plane flows more closely than has been supposed hitherto. The theory of normally distributed random noise was found to explain many of the observed statistical properties of the turbulence boundary.

Experimental evidence of waves in the sublayer

Two-dimensional frequency-wave-number spectra [Fcy ](kx, ω) and [Fcy ](kz, ω) of the longitudinal velocity component are presented for the sublayer in fully developed turbulent pipe flow, at Reynolds numbers between 10600 and 46400. All of these sublayer spectra apparently scale by introducing dimensionless quantities based on a chara cteristic length scale ν/UTand a characteristic time scale ν/UT2.Representative convection velocities have been obtained from the [Fcy ](kxω) spectra. The characteristic convection velocity in the sublayer is independent of wave-number and is the same at all positions in the layercx≃ 8·0UT. This result has led to the conclusion that sublayer turbulence is wave-like.Existing visualization data seem to indicate that the sublayer waves are also relatively periodic at least at low values of Reynolds number. Characteristic dimensions of the sublayer waves are λ+x≃ 630, and λz+= 135. Results of the visualization studies of Fage & Townend (1932) and of Runstadler, Kline & Reynolds (1963) and Klineet al.(1967) do not appear to conflict with a wave model for the sublayer.All of the existing measurements of the sublayer have been for relatively low Reynolds numbers. Some of the present results for positions just outside the sublayer suggest that at Reynolds numbers greater than 30000, the structure and properties will change substantially from those observed to date. In particular the streaky structure which is commonly regarded as being characteristic of the sublayer will probably not be detected at sufficiently high Reynolds numbers.