Abstract
This article lists the principles of fire risk assessment and management of electrical installations, provides the main terms used in this subject area, and their meanings. The article also ...talks about factors affecting the magnitude of fire risk (risk-forming factors). Special attention is paid to the human factor. Formulas for probabilistic assessment of fire risks of electrical installations and an algorithm for assessing the fire hazard of electrical installations, as well as a scheme of the algorithm for calculating individual fire risk are given.
This document explains in its first part the design procedure adopted to design the contoured sidewalls of a swept-wing airfoil section mounted in a wind tunnel in order to satisfy the infinite ...swept-wing approximation. In the second part, the experimental set-up is described as well as the first results of the experimental campaign. The sidewalls are shown to play their role properly and satisfactorily provide the infinite swept-wing conditions required for subsequent investigations of the most important vortex receptivity mechanisms responsible for excitation of crossflow and Tollmien-Schlichting instability modes in the airfoil boundary layer.
The paper is devoted to experimental investigation of receptivity of a Blasius boundary layer over a concave wall to surface non-uniformities. This receptivity mechanism is responsible for excitation ...of either unsteady or steady Görtler vortices by surface vibrations and roughness. As the result of this study quantitative receptivity characteristics are obtained, including the coefficients of the corresponding localized receptivity mechanism. These coefficients are obtained in Fourier space and are independent of the particular shape of the surface non-uniformities.
The linear receptivity of a swept-wing three-dimensional boundary layer is studied
experimentally and theoretically. Cross-flow instability normal modes are excited by
means of surface vibration or ...roughness perturbations. The resulting disturbances are
investigated, and the normal modes are linked to the source perturbations. Experiments
are performed under controlled disturbance conditions with a time-harmonic
source that is localized in the spanwise direction. A localized surface vibration is
used to excite wave trains consisting of cross-flow instability waves. Normal oblique
modes (harmonic in time and space) are obtained by Fourier decomposition of
the wave trains. This provides the spatial variation of the normal modes and, in
particular, the initial amplitudes and phases of the modes at the source location.
The shape of the surface vibrator is measured and used to determine the complex
receptivity coefficients for the normal modes (i.e. for various spanwise wavenumbers,
wave propagation angles, and disturbance frequencies – including zero frequency).
The experimental receptivity coefficients are independent of the specific shape of
the surface non-uniformities and can be directly compared with calculations. The
theoretical work is based on a linear approximation to the disturbance source – valid
for small forcing amplitudes. Like earlier studies on roughness-induced receptivity, the
basic flow is locally assumed to satisfy the parallel-flow approximation. The modal
response for the cross-flow instability is determined from the residue associated with
the least-stable eigenmode. A detailed quantitative comparison between the experimental and theoretical
receptivity characteristics is carried out. Good agreement is found for the
roughness–vibrational receptivity coefficients of the swept-wing boundary layer (especially for the
most-unstable cross-flow modes) over a range of disturbance frequencies and spanwise
wavenumbers. The theory correctly predicts the initial spectra for the travelling
and stationary cross-flow instabilities excited by the surface vibrations and surface
roughness, respectively. The good agreement between theory and experiment suggests
that the linear receptivity theory can be used effectively in engineering methods for
transition prediction. The experimental data can also be used for validation of other
theoretical approaches to the problem.
The study is devoted to experimental investigation of processes of excitation of non-stationary Görtler vortices in a boundary layer on a concave wall by vortices convected in free stream. In the ...present set of experiments, performed at controlled disturbance conditions, several cases of possible receptivity mechanisms have been considered: (i) scattering of 2D freestream vortices on localized 3D surface non-uniformities, (ii) scattering of 3D freestream vortices on localized 2D surface non-uniformities, (iii) scattering of 2D freestream vortices on uncontrolled 3D base-flow non-uniformities and (iv) scattering of 3D freestream vortices on natural 2D base-flow non-uniformities. Cases (i) and (ii) represent localized types of the vortex-receptivity mechanisms, while cases (iii) and (iv) correspond to distributed type of vortex-receptivity mechanisms. Accurate measurements are carried out in a broad range of experimental parameters. It is found that in cases (i), (ii), and (iii) no generation of measurable Görtler vortices is observed. However, the interaction of 3D convected vorticity with the growing boundary layer (case (iv)) does lead to excitation of rather intensive Görtler vortices. In this case the distributed receptivity mechanism is able to change significantly the growth rates of the exciting unsteady Görtler vortices. The corresponding receptivity coefficients are evaluated.
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