Ventilated Flow Between Corotating Disks With Large Obstructions in a Fixed Cylindrical Enclosure (Data Bank Contribution)

1994 ◽  
Vol 116 (4) ◽  
pp. 828-834 ◽  
Author(s):  
D. Gor ◽  
J. A. C. Humphrey ◽  
R. Greif
Keyword(s):  
Angular Velocity ◽  
Velocity Component ◽  
Data Bank ◽  
Laser Doppler Velocimeter ◽  
Blockage Ratio ◽  
Time Resolved ◽  
Disk Rotation ◽  
Ventilation Condition ◽  
The Mean ◽  
Flow Case

Time-resolved laser-Doppler velocimeter measurements of the circumferential velocity component were obtained for the flow between the center pair of four disks of common radius R2 corotating at angular velocity Ω in a fixed, cylindrical enclosure. Mean and rms profiles of this velocity component were obtained for two disk rotation speeds (300 and 3600 rpm), two relatively thick tapered obstructions (long and short) placed radially inward midway between each pair of disks, and three ventilation conditions (unventilated, blowing, and sucking) resulting from an imposed inter-disk radial throughflow. The profiles were determined at four circumferential locations downstream of the respective obstructions; radially along the midplane, and axially at selected radial locations. The profiles for the unventilated flow case show that the circumferential component of motion signficantly accelerates near the hub, in the region between the tip of the obstruction and the rotating hub. Elsewhere, this component of motion is significantly decelerated. The presence of ventilation, whether directed radially outward or inward, significantly affects the flow field only in the region immediately around the hub, and far downstream of the obstruction where it increases both the mean and rms velocities. Analysis of the time records suggests that the observed increases in the rms values are due to the circumferentially periodic nature of the radial ventilation condition. These observations are, for the most part, independent of the disk speed of rotation and the length of the obstructions. A comparison of present unventilated flow results with the corresponding results of Usry et al. (1993), who used much thinner obstructions, reveals the extent to which increasing the obstruction blockage ratio induces larger levels of flow unsteadiness.

Unsteady Flow in the Obstructed Space Between Disks Corotating in a Cylindrical Enclosure

1993 ◽  
Vol 115 (4) ◽  
pp. 620-626 ◽  
Author(s):  
W. R. Usry ◽  
J. A. C. Humphrey ◽  
R. Greif
Keyword(s):  
Velocity Component ◽  
Large Scale ◽  
Radial Direction ◽  
Laser Doppler Velocimeter ◽  
Time Resolved ◽  
Characteristic Frequencies ◽  
Velocity Deficit ◽  
Secondary Motion ◽  
Flow Oscillations ◽  
The Mean

Time-resolved measurements of the circumferential velocity component were obtained with a laser-Doppler velocimeter in the space between the center pair of four disks corotating in air in an axisymmetric cylindrical enclosure. The separate influences on the flow of two obstructions of similar shapes but having different lengths were investigated. The results show that both obstructions significantly alter the mean and rms distributions of velocity in quantitatively different but qualitatively similar ways. Both obstructions also alter the characteristic frequencies of flow oscillations associated with large scale motions present in the flow, apparently of the type that arise in unobstructed configurations. The measurements suggest that an obstruction can induce bimodal states of motion over frequency ranges that depend on the obstruction’s length. The presence of an obstruction increases the strength of the cross-stream secondary motion in the inter-disk space by redirecting fluid moving in the circumferential direction towards the radial direction. While this reduced the magnitude of the velocity deficit in the obstruction wake, for the cases investigated the flow did not recover within one revolution from the effects of either obstruction.

Ventilated Flow in the Unobstructed Space Between Corotating Disks in a Cylindrical Enclosure

1993 ◽  
Vol 115 (3) ◽  
pp. 398-407 ◽  
Author(s):  
D. Gor ◽  
J. A. C. Humphrey ◽  
R. Greif
Keyword(s):  
Flow Characteristics ◽  
Laser Doppler Velocimeter ◽  
Radial Coordinate ◽  
Time Resolved ◽  
Fundamental Interest ◽  
Axial Coordinate ◽  
Disk Storage ◽  
Ventilation Condition ◽  
Potential Impact ◽  
Improved Design

An experimental investigation has been performed for the ventilated flow of air in the unobstructed space between the center pair of four disks corotating in a fixed cylindrical enclosure. This configuration is of fundamental interest and considerable practical utility in the computer industry. Time-resolved and time-averaged measurements of the circumferential velocity component were obtained using a laser-Doppler velocimeter in back-scatter mode. The data were collected along the radial coordinate direction on the midplane between the disks (Z = 0) and along the axial coordinate at two radial locations (R = 0.71 and 0.86). Three values of the Reynolds number (Re = 2.73 × 103, 2.22 × 104, and 2.66 × 105) were investigated for a limited but significant range of the Rossby number (|Ro| < 0.85), including air sucked radially inward (Ro < 0) and air blown radially outward (Ro > 0). The experimental data present a challenging target for numerical procedures purporting to predict this class of flows. In agreement with earlier preliminary calculations performed by Humphrey et al. (1992), the imposition of a radial ventilation condition in the experiments is observed to have a pronounced effect on the inter-disk flow characteristics. However, the predicted results were found to depend strongly on the boundary conditions imposed and present measurements show the importance of knowing these accurately. These and related findings are discussed with special consideration given to their potential impact on the improved design of ventilated disk storage systems.

scholarly journals Time-Resolved Reflectance Spectroscopy Applied to the Nondestructive Monitoring of the Internal Optical Properties in Apples

2001 ◽  
Vol 55 (10) ◽  
pp. 1368-1374 ◽  
Author(s):  
Rinaldo Cubeddu ◽  
Cosimo D'Andrea ◽  
Antonio Pifferi ◽  
Paola Taroni ◽  
Alessandro Torricelli ◽  
...  
Keyword(s):  
Optical Properties ◽  
Industrial Applications ◽  
Nondestructive Monitoring ◽  
Nondestructive Measurement ◽  
Time Resolved ◽  
Mean Values ◽  
Scattering Coefficients ◽  
Scattering Spectra ◽  
The Mean ◽  
Temporal Dispersion

Time-resolved reflectance has been used for the nondestructive measurement of optical properties in apples. The technique is based on the detection of the temporal dispersion of a short laser pulse injected into the probed medium. The time distribution of re-emitted photons interpreted with a solution of the diffusion equation yields the mean values of the absorption and reduced scattering coefficients of the medium. The proposed technique proved useful for the measurement of the absorption and scattering spectra of different varieties of apples, revealing the spectral shape of chlorophyll. No major variations were observed in the experimental data when the fruit was peeled, showing that the optical properties measured were those of the pulp. With this technique the change in chlorophyll absorption during storage and ripening could be followed. Finally, a compact prototype working at few selected wavelengths was designed and constructed, demonstrating potentialities of the technique for industrial applications.

scholarly journals III. Researches in physical astronomy

1831 ◽  
Vol 121 ◽  
pp. 17-66
Keyword(s):  
Angular Velocity ◽  
Major Axis ◽  
The Body ◽  
Fixed Plane ◽  
Resisting Medium ◽  
Axis Of Rotation ◽  
Geographical Latitude ◽  
The Mean ◽  
The Stability ◽  
Revolving Body

In last April I had the honour of presenting to the Society a paper containing expressions for the variations of the elliptic constants in the theory of the motions of the planets. The stability of the solar system is established by means of these expressions, if the planets move in a space absolutely devoid of any resistance*, for it results from their form that however far the ap­proximation be carried, the eccentricity, the major axis, and the tangent of the inclination of the orbit to a fixed plane, contain only periodic inequalities, each of the three other constants, namely, the longitude of the node, the longitude of the perihelion, and the longitude of the epoch, contains a term which varies with the time, and hence the line of apsides and the line of nodes revolve continually in space. The stability of the system may therefore be inferred, which would not be the case if the eccentricity, the major axis, or the tangent of the inclination of the orbit to a fixed plane contained a term varying with the time, however slowly. The problem of the precession of the equinoxes admits of a similar solution; of the six constants which determine the position of the revolving body, and the axis of instantaneous rotation at any moment, three have only periodic inequalities, while each of the other three has a term which varies with the time. From the manner in which these constants enter into the results, the equilibrium of the system may be inferred to be stable, as in the former case. Of the constants in the latter problem, the mean angular velocity of rotation may be considered analogous to the mean motion of a planet, or its major axis ; the geographical longitude, and the cosine of the geographical latitude of the pole of the axis of instantaneous rotation, to the longitude of the perihelion and the eccentricity; the longitude of the first point of Aries and the obliquity of the ecliptic, to the longitude of the node and the inclination of the orbit to a fixed plane; and the longitude of a given line in the body revolving, passing through its centre of gravity, to the longitude of the epoch. By the stability of the system I mean that the pole of the axis of rotation has always nearly the same geographical latitude, and that the angular velocity of rotation, and the obliquity of the ecliptic vary within small limits, and periodically. These questions are considered in the paper I now have the honour of submitting to the Society. It remains to investigate the effect which is produced by the action of a resisting medium; in this case the latitude of the pole of the axis of rotation, the obliquity of the ecliptic, and the angular velocity of rotation might vary considerably, although slowly, and the climates undergo a con­siderable change.

scholarly journals VERTICAL VARIATION OP UNDERTOW IN THE SURF ZONE

1988 ◽  
Vol 1 (21) ◽  
pp. 33 ◽  
Author(s):  
Akio Okayasu ◽  
Tomoya Shibayama ◽  
Kiyoshi Horikawa
Keyword(s):  
Laboratory Experiments ◽  
Eddy Viscosity ◽  
Surf Zone ◽  
Viscosity Coefficient ◽  
Laser Doppler Velocimeter ◽  
Vertical Variation ◽  
Two Component ◽  
The Mean ◽  
Eddy Viscosity Coefficient ◽  
The Vertical Distribution

In order to establish a model of the vertical distribution of the undertow, laboratory experiments were performed on uniform slopes of 1/20 and 1/30. The turbulent velocity in the surf zone including the area close to the bottom was measured by using a two-component laser doppler velocimeter. The distributions of the mean Reynolds stress and the mean eddy viscosity coefficient were calculated. Based on the experimental results, a model to predict the vertical profile of the undertow was presented.

scholarly journals Pulse Radiolysis Studies of Collisional Deexcitation of Ne(3P1) by H2

2015 ◽  
Vol 19 (1) ◽  
pp. 75-78
Author(s):  
Deba Bahadur Khadka
Keyword(s):  
Optical Absorption ◽  
Absorption Spectroscopy ◽  
Cross Sections ◽  
Pulse Radiolysis ◽  
Science And Technology ◽  
Optical Absorption Spectroscopy ◽  
Time Resolved ◽  
Collisional Energy ◽  
The Mean ◽  
Collisional Deexcitation

The cross sections for the deexcitation of Ne(3P1) by H2 have been measured as a function of the mean collisional energy in the range of 17.3-37.9 meV or in the temperature range from 134 K to 293 K using a pulse radiolysis method as combined with time-resolved optical absorption spectroscopy. The deexcitation cross sections are in the range of 2.1- 5.6 Å2 for Ne(3P1) and nearly constant or increase slightly with increasing the collisional energy.Journal of Institute of Science and Technology, 2014, 19(1): 75-78

scholarly journals Investigation of Changes of the Kinematic Parameters of Antarctic Tectonic Plate Using Data Observations of Permanent GNSS Stations

2017 ◽  
Vol 103 (1) ◽  
pp. 119-135 ◽  
Author(s):  
Kornylii Tretyak ◽  
Al-Alusi Forat ◽  
Yurii Holubinka
Keyword(s):  
Angular Velocity ◽  
Kinematic Parameters ◽  
Antarctic Region ◽  
Tectonic Plate ◽  
Euler Pole ◽  
The Mean ◽  
Using Data ◽  
Gnss Permanent Stations ◽  
The Antarctic

Abstract The paper describes a modified algorithm of determination of the Euler pole coordinates and angular velocity of the tectonic plate, considering the continuous and uneven distribution of daily measurements of GNSS permanent stations. Using developed algorithm were determined the mean position of Euler pole and angular velocity of Antarctic tectonic plate and their annual changes. As the input data, we used the results of observations, collected on 28 permanent stations of the Antarctic region, within the period from 1996 to 2014.

Influences of Turbulence Boundary Conditions on RANS and URANS Simulations for an Inter-Turbine Duct

2020 ◽  
Author(s):  
Alessio Firrito ◽  
Yannick Bousquet ◽  
Nicolas Binder ◽  
Ludovic Pintat
Keyword(s):  
Flow Field ◽  
Boundary Conditions ◽  
Mean Flow ◽  
Time Resolved ◽  
Flow Solution ◽  
Low Pressure Turbine ◽  
Outlet Flow ◽  
Architecture Evolution ◽  
The Mean ◽  
Turbulence Length

Abstract In recent years, lot of turbine research is focused on the study and optimization of inter-turbine ducts, an aero-engine component for which the design is becoming more challenging due to the turbofan architecture evolution. Starting from the early design phase, the knowledge of the component performance and outlet flow pattern is crucial in the design of the low pressure turbine. To improve prediction, multi-row unsteady simulations are deployed. Unfortunately, some questions arise in the use of these simulations, among others the knowledge of the turbulent boundary conditions and the contribution of the unsteady simulations to the flow solution. In this paper steady and time resolved RANS simulations of a turning inter-turbine duct are investigated. Particularly, two questions are addressed. The first one is the influence of the turbulent quantities boundary conditions in the case of a k–ω Wilcox turbulence model in the flow field solution. The second one is the contribution of the unsteadiness to the mean flow prediction. It will be shown that the mean flow depends on inlet turbulence only if the turbulence length scale is relatively high; otherwise the flow field is almost turbulence-invariant. For the unsteady simulations, unsteadiness modifies the mean flow solution only with low inlet turbulence.

Turbulent Boundary Layers Subjected to Multiple Strains

1999 ◽  
Vol 121 (3) ◽  
pp. 526-532 ◽  
Author(s):  
Andreas C. Schwarz ◽  
Michael W. Plesniak ◽  
S. N. B. Murthy
Keyword(s):  
Shear Stress ◽  
Pressure Gradient ◽  
Boundary Layers ◽  
Reynolds Shear Stress ◽  
Turbulent Boundary Layers ◽  
Laser Doppler Velocimeter ◽  
Strain Rates ◽  
The Mean ◽  
Convex Curvature ◽  
Multiple Strain Rates

Turbomachinery flows can be extremely difficult to predict, due to a multitude of effects, including interacting strain rates, compressibility, and rotation. The primary objective of this investigation was to study the influence of multiple strain rates (favorable streamwise pressure gradient combined with radial pressure gradient due to convex curvature) on the structure of the turbulent boundary layer. The emphasis was on the initial region of curvature, which is relevant to the leading edge of a stator vane, for example. In order to gain better insight into the dynamics of complex turbulent boundary layers, detailed velocity measurements were made in a low-speed water tunnel using a two-component laser Doppler velocimeter. The mean and fluctuating velocity profiles showed that the influence of the strong favorable pressure augmented the stabilizing effects of convex curvature. The trends exhibited by the primary Reynolds shear stress followed those of the mean turbulent bursting frequency, i.e., a decrease in the bursting frequency coincided with a reduction of the peak Reynolds shear stress. It was found that the effects of these two strain rates were not superposable, or additive in any simple manner. Thus, the dynamics of the large energy-containing eddies and their interaction with the turbulence production mechanisms must be considered for modeling turbulent flows with multiple strain rates.

Electrically evoked isokinetic plantar flexor torque in males

1987 ◽  
Vol 63 (4) ◽  
pp. 1499-1503 ◽  
Author(s):  
D. O. Thomas ◽  
M. J. White ◽  
G. Sagar ◽  
C. T. Davies
Keyword(s):  
Angular Velocity ◽  
Muscle Activation ◽  
Triceps Surae ◽  
Plantar Flexor ◽  
Velocity Data ◽  
Exponential Equation ◽  
Isometric Torque ◽  
The Mean ◽  
Electrical Stimuli ◽  
Male Subjects

The involuntary angle-specific isokinetic plantar flexor torques of seven male subjects aged 18–21 yr were measured using a Cybex II dynamometer (Lumex) modified by the addition of a strain-gauge load cell to improve the dynamic response of the instrument. Supramaximal electrical stimuli were used to evoke a maximal tetanic response from the triceps surae and ensure constant muscle activation at each angular velocity studied. Angle-specific torques were measured over a range (0.5–5.0 rad/s) of preset velocities, torque decreasing in a nonlinear manner with increasing angular velocity. The torque-velocity data was adequately described by an exponential equation of the form: V = a(e-1/b - e-Po/b) where V = velocity (rad/s), P = torque (N.m), Po = isometric torque (N.m), and a and b are constants. The mean intrasubject coefficient of variation of torque over the range of velocities studies was 7.9 +/- 1.88% (SD).

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