Effects Of Nonuniform Flow Research Articles

Systematic measurements of duct end corrections in the Greenspan viscometer

A Greenspan viscometer is a Helmholtz resonator that has been optimized for viscosity measurements in gases. It consists of two chambers connected by a duct. The model, design considerations, and performance of such a device have been described elsewhere [Gillis etal., ‘‘Acoustic Greenspan viscometer for gases,’’ submitted to Rev. Sci. Instrum.]. The model represented the effects of nonuniform flow near the ends of the duct as a complex acoustic impedance Zend, based on the numerical calculations by Mehl [J. Acoust. Soc. Am. 97, 3327 (1995) and unpublished calculations]. In this work, the ‘‘end corrections’’ were measured in a Greenspan viscometer with interchangeable ducts and a detector located in each chamber. This new design enabled a series of viscosity measurements to be performed with the same chambers and transducers, and with three different duct lengths and two duct diameters. The consistency between the experiments and the model will be presented. [Work supported by the Office of Naval Research.]

Evaluation of longitudinal dispersivity from nonuniform flow tracer tests

The importance of incorporating nonuniform flow effects in determining field-scale values of long-itudinal dispersivity from tracer tests in aquifers is illustrated. We show that under conditions of Fickian dispersive flux, where a tracer has traveled at least 10 times the longitudinal dispersivity value, nonuniform flow effects account for the typical tailing exhibited by data from radial flow and doublet (two-well) tracer tests. Approximate analytical solutions for solute transport in nonuniform flow fields based on earlier general work are presented. Specific cases evaluated include pulse and step inputs in diverging radial flow, a pulse input in converging radial flow, and doublet (two-well) tests with pulse and step inputs. The additional effect of longitudinal dispersivity increasing linearly with distance for radial flow cases is examined. Also presented is an analysis of the effect of injection borehole flushing represented by an exponentially decreasing tracer input in the converging radial flow case. The solutions are applied to four sets of field data where previous analyses did not adequately address nonuniform flow effects. Some data reanalyses yield longitudinal dispersivity values which are up to a factor of three smaller than those previously reported, indicating a previous overprediction of plume dilution. We demonstrate that an understanding of the sensitivity of the mathematical solutions to tracer input conditions, nonuniform flow effects, and scale can lead to better tracer-test design.

Application of compound compressible flow to nonuniformities in hypersonic propulsion systems

An analytical model is presented to study the propagation of the forebody boundary layer inside the engine channel of a hypersonic engine, based on a compound compressible one-dimensional streamtube method. It is shown that the compound compressible flow model can be greatly simplified in the hypersonic regime. This model is appropriate for studying the effects of nonuniform flow inside a supersonic combustion ramjet. It is found that even a small boundary layer can produce noticeable changes in freestream properties inside the inlet. In the combustor models, it is seen that freestream Mach number is generally increased, and so static pressure and temperature are decreased. It is suggested that these effects will reduce the combustion reaction rate relative to that expected in a uniform flow and will therefore reduce the total heat release and increase losses inside the engine.

Noise radiation from transverse air flow over cylinders of constant and varying diameter: An empirical predictive model

A simplified model to estimate the amplitude and frequency content of the noise radiated by constant and varying (tapered) diameter cylinders has been developed. Using the measured intensity level of Aeolian tones for several constant diameter cylinders, the incremental source strength along the cylinder has been determined as a function of Reynolds numbers. After choosing an element size consistent with the correlation length of the vortex shedding, tapered cylinders are modeled as a series of small, discrete cylinders each of constant diameter. The total sound produced by the tapered cylinder is then determined by summing the contribution of each segment over the cylinder length, properly accounting for geometry using the assumption that the sources add incoherently. The results predicted by this approach have been found to be quantitatively consistent with the data measured for tapered cylinders at several orientations. The model can also be readily extended to examine the effect of nonuniform flow on radiated noise.

The Importance of Circumferential Non-uniformities in a Passage-Averaged Quasi-Three-Dimensional Turbomachinery Design System

The purpose of this paper is to show, for both rotating and non-rotating blade rows, the importance of including circumferential non-uniform flow effects in a quasi-three-dimensional blade design system. The paper follows from previous publications on the system in which the mathematical analysis and computerized system are detailed. Results are presented for a different stack of the nozzle guide vane presented previously and for a turbine rotor. In the former case it is again found that the blade force represents a major contribution to the radial pressure gradient, while for the rotor the radial pressure gradient is dominated by centrifugal effects. In both examples the effects of circumferential non-uniformities are detailed and discussed.

Flow uniformity in rock beds

Although theories on rock bed behaviour assume uniform flow across the bed, measurements on real beds show that the flow is actually non-uniform. By experiments on a full-scale rock-bed, this paper established the cause and magnitude of non-uniform flow. The cause is pressure-variations in the plenums. The magnitude, as measured by the coefficient of variation r of the velocity profile, is typically on order r = 0.2; as measured by the peak-to-peak variation in velocity, it is as high as 125 per cent. The paper also theoretically estimates the effect of non-uniform flow on the total system performance. The effect is small provided r ⩽ 0.3, but it is substantial if r ⋍ 1.0.

Effect of Non-uniform Flow in an MHD Electrical Power Generator Channel Cross Section

Effect of Non-uniform Flow in an MHD Electrical Power Generator Channel Cross Section

Dc flow considerations for crossed-field acoustic amplifiers and other solid-state traveling-wave devices

The direct Current flow in two simple device structures used for crossed-field, traveling-wave devices is analyzed, and some properties of the flow which can affect the RF performance are studied in detail. The results show nonuniform flow to be significant only in localized regions, which can be made small by a proper choice of electrode and sample geometry. Approximate formulas are derived for estimating the important flow parameters of interest in specific applications. As an example, the effect of nonuniform flow on the acoustic amplifier is estimated. The deflection and refraction of a shear-wave acoustic beam in InSb at 77°K is found to be negligible, but the gain is reduced appreciably for large µB <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</inf> . Considerations entering into device design, such as heat sinking and the provision of an RF circuit, are also discussed with regard to an optimum choice of electrode configuration for a rectangular device.

Average Volumetric Concentration in Two-Phase Flow Systems

A general expression which can be used either for predicting the average volumetric concentration or for analyzing and interpreting experimental data is derived. The analysis takes into account both the effect of nonuniform flow and concentration profiles as well as the effect of the local relative velocity between the phases. The first effect is taken into account by a distribution parameter, whereas the latter is accounted for by the weighted average drift velocity. Both effects are analyzed and evaluated. The results predicted by the analysis are compared with experimental data obtained for various two-phase flow regimes, with various liquid-gas mixtures in adiabatic, vertical flow over a wide pressure range. Good agreement with experimental data is shown.