Analysis Of Random Fluctuations Research Articles

Turbulence and Secondary Flows in an Axial Flow Fan With Variable Pitch Blades

This paper analyzes the structure of turbulence and secondary flows at the exit of an axial flow fan with variable pitch blades. The influence of changing the blades’ pitch angle over the turbulent structures is assessed by means of turbulence intensity values and integral length scales, obtained by using hot-wire anemometry for several test conditions. Since total unsteadiness is composed of both periodic and random unsteadiness, it is necessary to filter deterministic unsteadiness from the raw velocity traces in order to obtain turbulence data. Consequently, coherent flow structures were decoupled and thus, levels of turbulence—rms values of random fluctuations—were determined using a filtering procedure that removes all the contributions stemming from the rotational frequency, the blade passing frequency, and its harmonics. The results, shown in terms of phase-averaged distributions in the relative frame of reference, revealed valuable information about the transport of the turbulent structures in the unsteady, deterministic flow patterns. The anisotropic turbulence generated at the shear layers of the blade wakes was identified as a major mechanism of turbulence generation, and significant links between the blade pitch angle and the wake turbulent intensity were established. In addition, the autocorrelation analysis of random fluctuations was also used to estimate integral length scales—larger eddy sizes—of turbulence, providing useful data for computational fluid dynamics applications based on large eddy simulation algorithms. Finally, contours of radial vorticity and helicity gave a detailed picture of the vortical characteristics of the flow patterns, and the definition of secondary flow as the deviation of the streamwise component from the inviscid kinematics was introduced to determine the efficiency of the blade design in the energy exchange of the rotor.

Measurement and Modeling of Pacific AC Intertie Response to Random Load Switching

In recent years spectral analysis of system response to random load changes has become a standard engineering tool at the Bonneville Power Administration. Analysis of random fluctuations in power on the Pacific AC Intertie has provided information about the influence of system operating conditions upon the effectiveness of Pacific HVDC Intertie modulation, and about dynamic behavior of the western power system generally. This technique has also been used to estimate the required size for a superconducting electromagnetic storage device which will provide backup to HVDC Modulation, and has detected a major system mode 6 months before it was first observed in a transient disturbance

Topology of Linear Neutron Kinetics

In the theory and interpretation of pulsed neutron measurements and in the analysis of random fluctuations in a nuclear fission reactor it is often helpful to study the kinetic behavior of the time-dependent, space-independent model of the multiplying assembly. For this purpose the neutron kinetics may be formulated as an integral equation as opposed to the more conventional set of first-order differential equations. This has some advantages in that the kernel functions of the Volterra-type integral equation have immediate physical significance, the integral equation is logically related to the topological representation of the fission process, numerical computation of resolvent kernels is usually more efficient than forward integration, and extension of the theory to non-stationary reactor kinetics and non-linear reactor topology is obvious. On the basis of a theory presented, the computation of reactor frequency and transient responses is carried out automatically on a digital computer. Step, pulse, ramp, sine, and arbitrary time-responses can be studied for fixed, circulating fuel, and boiling-water reactors. Some solutions of the integral equation are given for linear variations in reactivity. (auth)