Effect Of Nonparallelism Research Articles

On the nonparallelism effect in thin film plate–plate rheometry

The effect of nonparallelism in a plate–plate torsional geometry is investigated for confined Newtonian fluids by directly solving Reynolds equation. A nondimensionalization is proposed, and theoretical results are compared to triborheological experiments by Kavehpour and McKinley [Tribol. Lett. 17, 327–335 (2004)] in the form of a frictional Stribeck curve.

Thermal analysis and optimization of the emitter in the solar thermophotovoltaic (STPV)

A model for predicting the performance of the emitter in the solar thermophotovoltaic (STPV) system is presented in this article. The effect of non-parallelism of sun rays on concentration capability is numerically calculated, also the flow field in the emitter cavity and the temperature distribution of the emitter with different inlet conditions are compared. Numerical results show that free convection of the air inside the emitter cavity has great effect on the emitter temperature and may reduce the electricity output of the cells. At last, a new kind of selective film is put forward. Through optimizing the cut-off wavelength of a selective film, radiation loss is further reduced and system efficiency is improved.

Effect of nonparallelism of guiding air-liquid layers on the reflection dip in attenuated total reflection

The effect attributable to the nonparallelism of the guiding layer of a planar waveguide on the reflection dip of the attenuated total reflection (ATR) spectrum is investigated. It is considered that the reflected light from a nonparallel waveguide is, indeed, the superposition of a series of beams propagating in different directions. The ATR spectra are numerically calculated with various inclination values. Compared with those of the corresponding parallel ones, with the inclination of waveguides exceeding 1 microrad, the characteristics of the ATR spectra begin to differ considerably, and when the inclination reaches 10 microrad, the sensitivity of sensors based on the waveguide is reduced by 62.7% and 67.3% for the free space coupling structure and the prism coupling structure, respectively. When the inclination becomes larger than 100 microrad, the ATR phenomenon cannot be observed any longer.

Effect of flow nonparallelism on instability of the Taylor-Görtler waves in supersonic axisymmetric jets

Within the framework of the linear theory of hydrodynamic stability, the characteristics of the Taylor-Gortler waves are numerically simulated at the initial section of a supersonic axisymmetric jet taking into account the effects of flow nonparallelism and expansion. The special features of the streamwise dynamics of the growth rates of various wave components for turbulent. weakly nonisobaric, and laminar jets are studied. It is shown that the growth rates depend strongly on the quantity on which their determination is based, the position of the point where it is measured, and the flow regime. Some experimental results are discussed, and a method for determining the growth rates is proposed.

Study on the vibrational characteristics of ultrasonic transducers using tapered piezoelectric ceramic elements

Any nonuniformity in the flatness of a crystal element used in an ultrasonic transducer may lead to significant variations in transducer response. An accurate estimation of such variations could obviously be a measure of the nonuniformity involved, whatever its extent may be. Studies are reported on the effect of nonparallelism between two major plane surfaces of the crystal element on transducer response by studying the normal displacement amplitude pattern and its distribution over one of the vibrating (plane) surfaces at resonance. Measurements are carried out in air using a phase-locked laser interferometry technique where the effect of tapering in disk thickness on the transducer performance is manifested through the variation in vibrational patterns. Results of these measurements are compared with those obtained from electrical (conductance) response to highlight the importance of the former. Other comparison measurements, such as the conventional method of determination of acoustic response and pulse waveforms of the radiated signals in water, are also reported as a function of tapering in disk thickness. A correlation is discussed between results obtained from different measurements.

Linear and nonlinear stability of the Blasius boundary layer

Two new techniques for the study of the linear and nonlinear instability in growing boundary layers are presented. The first technique employs partial differential equations of parabolic type exploiting the slow change of the mean flow, disturbance velocity profiles, wavelengths, and growth rates in the streamwise direction. The second technique solves the Navier–Stokes equation for spatially evolving disturbances using buffer zones adjacent to the inflow and outflow boundaries. Results of both techniques are in excellent agreement. The linear and nonlinear development of Tollmien–Schlichting (TS) waves in the Blasius boundary layer is investigated with both techniques and with a local procedure based on a system of ordinary differential equations. The results are compared with previous work and the effects of non-parallelism and nonlinearly are clarified. The effect of nonparallelism is confirmed to be weak and, consequently, not responsible for the discrepancies between measurements and theoretical results for parallel flow. Experimental uncertainties, the adopted definition of the growth rate, and the transient initial evolution of the TS wave in vibrating-ribbon experiments probably cause the discrepancies. The effect of nonlinearity is consistent with previous weakly nonlinear theories. White nonlinear effects are small near branch I of the neutral curve, they are significant near branch II and delay or event prevent the decay of the wave.

Analysis of the linear stability of compressible boundary layers using the PSE

The application of linearized parabolic stability equations (PSE) to compressible flow is considered. The effect of mean-flow nonparallelism is found to be weak on 2D waves and strong on 3D waves. Results for a single choice of free-stream parameters that corresponds to the atmospheric conditions at 15,000 m above sea level are presented.

Effect of nonparallelism on the stability of a Bickley ? Schlichting jet

Effect of nonparallelism on the stability of a Bickley ? Schlichting jet