Slotted Disk Research Articles

Visual study on wakes behind solid and slotted axisymmetric bluff bodies

A flow visualization study was conducted for various configurations of solid and slotted axisymmetric bluff bodies. The geometries also included those of solid and ribbon parachute canopy models. The structures of the unsteady near wake patterns were surveyed and compared. In addition, the effect of rapid model acceleration and deceleration on the wake was visualized. This article presents, although somewhat qualitatively, analysis of results from photographs and videotapes and an overview of various pertinent phenomena observed. CLEAR understanding of the wake flow behind a parachute is critical for the safe operation of parachutes. Though detailed knowledge of the wake structure is essential to predict, such phenomena as the wake recontact problem,1 analysis of the entire wake region at once appears to be inaccessible. For example, the wakes of axisymmetric bluff bodies are found to be fully three dimensional even for the simplest form of axisymmetric geometry. The flowfield imme- diately downstream of a ribbon parachute is particularly complex because of irregular merging of high speed jets through multiple narrow gaps. Moreover, the detailed study of the flowfield during a full-scale drop test appears to be a nearly inaccessible task at present. Flow visualizations in carefully designed laboratory environments, on the other hand, can not only provide excellent clues to the complex flowfield but also guide quantitative measurements and com- putation and analysis of the flowfield. It is also to be noted that some modern flow visualization techniques have started to provide detailed quantitative information with advance- ment of applied optics and image processings, as seen in Ref. 2. In the past, low-speed flow visualizations have been con- ducted to simulate complex high Reynolds number airflows in aircraft flight conditions, and somewhat surprisingly to some, the results compared well with flight test data.3 This means that many vortex-dominated flows are not as dependent on the differences in viscous effects. Naturally, additional com- pressibility effects must not be overlooked, and interpretation of flow visualizations in unsteady flowfields requires extra caution, as is often pointed out (see, for example, Gad-el- Hak4). In the present experimental investigation, the wake regions of the axisymmetric bluff bodies were observed using various flow visualization techniques in both air and water. Configurations studied included a circular disk, solid parachute model, slotted disk, and a ribbon parachute model. Flow visualization was also conducted to study the effect of rapid model acceleration and deceleration. Minnesota. The test section was 1.5m long and the cross section measured 1.37 x 0.97m. Freestream velocity up to 23 m/s can be obtained, though flow visualization was con- ducted at a substantially lower velocity, as noted in the figures in terms of the Reynolds numbers based on the model diame- ter. The tunnel flow condition5 was found adequate for the present study. The models to be described in the Results section were either sting-mounted or supported by thin wire along the centerline of the test section. The streamlined particle injector was fabricated and placed upstream of the model, and fine oil fog generated by a Rosco Model 1500 smoke/fog generator was introduced into the test section. The visualization in the empty test section as a control revealed no unsteadiness in the freestream nor any adverse effect of the injector. The diameter of particles, which are nontoxic accord- ing to the manufacturer, measured 2 jum on the average. Illumination was provided by an argon ion laser passed through a set of cylindrical lenses and front surface mirrors to produce a thin sheet of light aligned with the centerline of the model. The experiment in water was carried out in a towing tank at the St. Anthony Falls Hydraulic Laboratory, measuring 39 x 61 cm in cross section and 15.2m in length. In some tests, the tank was partitioned into a shorter segment for ease of operation. Normally, the model was towed in a stationary fluid. The towing carriage was driven by a variable speed a.c. motor. A 35-mm camera or a video camera and the lighting

Investigations of photopolymerization by means of intermittent illumination

An apparatus is described for intermittent illumination of the sample in a DSC-2C (Perkin-Elmer) modified with some additional optical equipment. A slotted disk is used as a light chopper. This is driven by a computer-controlled stepping motor. The various frequencies needed for investigations of this kind are derived from a computer quartz-controlled clock frequency by means of software. The operator dialogue is achieved through the Perkin-Elmer Data Station to simplify the use of the equipment.

Tree Line Seal for Continuous Mechanical Harvesting of Fruit

LOSS of fruit during collection has been identified as a problem with a number of continuously moving mechanical fruit harvesters. This article describes a system for reducing a major portion this loss that occurring in the vicinity of the tree trunks. The system utilizes a bank of slotted discs which rotate as the machine moves forward, effectively covering the area between and slightly behind tree limbs or trunks.

A photodetector-synchronized rapid scanning spectrometer with a rotating grating directly driven by a synchronous motor.

A new type of rapid scanning spectrometer was constructed for use in analytical atomic spectroscopy. The sine-bar and its driving system are disabled and the grating is driven directly by a synchronous motor. The wavelength synchronization is made by counting the photopulses generated by the combination of a small tungsten lamp, a phototransistor and a slotted aluminium disc which is attached to the shaft of the rotating grating. In an on-line and real-time mode, a variety of measurements can be achieved by a dedicated microcomputer. The basic analytical performance was evaluated and some applications are demonstrated.

Laser Tools for Diesel Engine Diagnosis

Two portable laser instruments are described which allow the engineer to simply ‘stand and point’ laser beams at a target surface in order to obtain a measurement of time-resolved vibration velocity. The first supplements the accelerometer and measures normal surface velocity but offers the advantage of non-contact measurement. Its use is demonstrated in detecting reduced nozzle pressures in fuel injectors. The second instrument is a laser torsional vibrometer which measures torsional oscillations of rotating machinery parts and in particular crankshaft oscillation. Comparisons are made with the more standard technique which utilizes a slotted disc. The new instrument provides advantages of non-contact measurement, insensitivity to shaft radial motion and the ability to measure oscillations of shafts of arbitrary cross-section.

Rotational kymography. Technique for automated analysis of cine left ventriculograms.

A new device provides an automatic photographic record of left ventricular contraction and expansion. A radially slotted disk is interposed between the moving cine left ventriculogram and a disk of photographic film. By rotating either the slotted disk or the film, a kymographic record of regional wall motion is obtained. Unlike more complex computer programs, the speed as well as the magnitude of contraction can be determined.

Some characteristics of pulsed nozzle beams

Some characteristic properties of pulsed nozzle beams produced with an automobile fuel injector were observed. A commercial fuel injector was modified to produce a beam pulse of a regular square shape. The beam pulse of 5 ms is again chopped by a slotted disk chopper to make a shorter burst at an arbitrary portion of the original pulse. Rotation of the disk chopper and actuation of the injector are synchronized by a microcomputer. Time-of-flight measurements were performed using beams of 15.6-μs width formed in this way. Beam fluxes were measured with a flow-through detector. The maximum beam fluxes and terminal speed ratios obtained for several gases in this work are comparable to the values published by other workers. Recoils of beam molecules from the skimmer and its vicinity significantly affect the quality of the pulsed beams.

Velocity dependence of the cross section for associative ionisation of Ne atoms by laser-excited He (31P) atoms

The velocity dependence of the associative ionisation cross section sigma AI of Ne atoms by He(31P) atoms of very short lifetime is measured in the relative velocity range 1450< nu r<3150 m s-1 (0.035<Er<0.17 eV) in a crossed-beam experiment using a slotted disc velocity selector. The 31P level is obtained by laser excitation of the metastable 21S level with an efficiency close to 100%. The authors observe that sigma aI( nu r) decreases monotonically with the increasing relative velocity of the reactants. By comparison with cross sections calculated in the framework of the classical impact parameter method, it appears that the direct process would be responsible for HeNe+ ion production, while the exchange process is dominant in the total ion production.

Low energy neutral outflux from the PLT tokamak

A time-of-flight system has been developed to measure the energy spectrum of neutral deuterium atoms emitted from the PLT tokamak plasma in the energy range 20–1000 eV. D 0 neutrals are mechanically chopped by a rotating slotted stainless steel disc. The gated neutrals impinge on a Cu-Be disc and eject secondary electrons which are collected and amplified by an electron multiplier; hence quantitative D 0 fluxes can be determined. The time evolution of the D 0 outflux emission spectra, dΓ/dEdΩ, has been measured for low density, ohmically heated PLT discharges. Our data, which covers the energy range 28–1000 eV, represent the first measurements of tokamak neutral outflux below 100 eV. For D 0 energies above 200 eV, we find that dΓ/dE dΩ vs. Particle energy monotonically decreases, typically in an exponential fashion. Early in a discharge dΓ/dEdΩ is weighted towards low energy. The measured plasma ion edge temperature increases with time, and concurrent with this rise the total particle flux falls by a factor of 25. Throughout these ohmically heated discharges the charge-exchange power loss away from the limiter is a small fraction, less than 2%, of the ohmic heating power; the charge-exchange particle loss away from the limiter is relatively unimportant in particle balance; and the bulk of the particle emission is typically at energies below 200 eV.

A new capacitive speed transducer

The theory and fabrication of a new capacitive transducer suitable for accurate measurement and control of angular speed is described. The transducer lends itself to an essentially contactless method of speed measurement, in which only a thin slotted metal disc need be attached to the rotating member. The slotted disc, which rotates in the gap of a parallel plate air capacitor alters, through its shielding action, the capacitance of the latter in a cyclic manner at a rate proportional to the angular speed. The variation of this capacitance is sensed with the aid of a unity-ratio transformer bridge set-up and the output of the bridge is amplified, demodulated and filtered, giving rise to a nearly sinusoidal signal whose frequency is a measure of the angular speed.

Drag and Pressure Distribution on a Family of Porous, Slotted Disks

form of the resistance coefficient for porous, rigid screens of infinite extent. The second part examines the flow through and around a porous, rigid body of finite extent. This body will be located in an infinite flowfield, and will be rigid and incapable of significant distortion under the aerodynamic loading. Experimental results for tests on porous, circular disks will be given in Part II. Furthermore, it will be argued and demonstrated in Part II that a macroscopic examination of the flowfield neglects an important phenomenon which relates to the microscopic flow structure behind the adjacent small elements within the porous body. References 6-8 and 10 all relate to various macroscopic treatments.

Delay times in the sputtering of atoms from alkali-halide crystals during low-energy electron bombardment

Delay times in the sputtering of atoms from RbI, RbBr and NaCl by 540 eV electrons were investigated. This was done by simultaneously using the correlation technique and a slotted disc velocity selector. We observed delays in thermally ejected alkali and halogen atoms. These times were found to be independent of target temperature and are ascribed to lifetimes of excitons. Non-thermal halogen atoms are always sputtered without any delay.

Distant synchrony and the one-way velocity of light

A number of physical processes and experimental procedures are listed which appear to be inexplicable in the context of the conventionality thesis of Reichenbach and Grunbaum. Distant synchrony can be produced by procedures based on the free displacement or rotation of elastic solids. Results are expected to agree with Einstein's definition of distant synchrony (by means of light signals, assuming isotropy). The one-way velocity of light can be measured using a rotating shaft, slotted disks, and one stationary clock.

A carbon reaction studied by crossed molecular beamsa)

The chemiluminescent reaction C2+NO→CN(B 2Σ+) +CO+2.89 eV has been studied in a crossed molecular beam configuration. The carbon beam was obtained from a graphite sublimation source operating at 2550° K. The beam (principally C, C2, C3) was pulsed by a rotating slotted disk before it crossed the NO beam. Electronically excited molecules formed in reaction, CN(B 2Σ+), were detected as they rapidly decayed to the ground state. Photon time-of-arrival measurements identified the reactant as C2. The vibrational energy disposal within CN(B 2Σ+) was derived from wavelength resolved measurements. Reaction energetics and the signal intensity indicated the companion product, CO(X1Σ). This study indicates that energy deposition into vibrational degrees of CN(B 2Σ+) disagrees mildly with ’’prior expectation’’ (Levine, Bernstein, and co-workers). The reaction probably proceeds on a potential energy surface that correlates to C2(X′ 3Πu)+NO(X 2Π).

A Mechanically Controlled Variable Rate Leaching Device

AbstractTwenty‐four leaching tubes attached to 60‐ml plastic syringes are mounted on the periphery of three vertically aligned slotted discs 45 cm in diameter. The plungers are withdrawn at a controlled rate by a variable speed screw jack that separates the two lower discs holding the plungers and syringe barrels, respectively. Leaching time can be varied from 15 min to 12 hours or more. The final volume of extract is determined by weighing the syringes. Precision of ammonium acetate CEC and extractable cations by this procedure with 2.5 g of soil and 50‐ml extract matches that of a comparable manual method using vacuum extraction with 5 g soil and 100 ml of extract. This apparatus has also cut required operator time in half.

Product magnetic defection slotted disk velocity analysis molecular beam kinetics: Li+CH3NO2, CCl4, and CH3I

Recoil velocity spectra of LiNO2, LiCl, and LiI reactively scattered from crossed thermal beams of Li and CH3NO2, CCl4, or CH3I have been measured by positioning a combination of an inhomogeneous electromagnet (to deflect aside nonreactively scattered Li atoms) and a slotted disk velocity analyzer between the beam collision zone and surface ionization detector. Transformation of these data into the center-of-mass (CM) coordinate system provides contour maps of the differential reaction cross sections. The CM product angular distributions from the three reactions are quite different: Li+CH3I favors backward scattering (i.e., a reversal in Li atom direction during the reaction) although the CM distribution is poorly resolved due to unfavorable kinematics; Li+CCl4 favors sideways scattering; and Li+CH3NO2 favors forward scattering. The product recoil energy distributions are quite similar for all three reactions and indicate potential energy surfaces with substantial repulsion between the products. These results are discussed in relation to previous work on related reactions and interpreted in terms of the electronic structure of ion-pair intermediates.

Product magnetic deflection slotted disk velocity analysis molecular beams kinetics: Li+SnCl4, PCl3, and SF6

Recoil velocity spectra of the diamagnetic Li-containing products reactively scattered from crossed thermal beams of Li and SnCl4, PCl3, or SF6 have been measured by positioning a combination of an inhomogeneous deflecting electromagnetic and slotted disk velocity analyzer between the collision zone and detector. Transformation of these data into the center-of-mass coordinate system provides contour maps of the differential reaction cross sections. Although data on Li+SF6 are very noisy, they are consistent with a long-lived collision complex and energy equipartitioning in a loose transition state (LTS) mechanism. At some scattering angles, two peaks are observed in the measured product recoil spectra for both Li+SnCl4 and Li+PCl3. For Li+SnCl4, indirect kinematic arguments suggest that this bimodal structure is due to LiSnCl3+Cl and LiCl+SnCl3 product channels proceeding via an LTS mechanism. For Li+PCl3, this bimodal structure is attributed to production of LiCl+PCl2 products via an LTS and a direct mechanism. These results are discussed in relation to previous work on these systems and interpreted in terms of the electronic structure of the ion-pair intermediates.

Product magnetic deflection slotted disk velocity analysis molecular beams kinetics: Li+Cl2, Br2, and ICl

An inhomogeneous deflecting magnet and slotted disk velocity analyzer combination has been used to deflect aside nonreactively scattered Li atoms and thereby measure velocity distributions of LiBr and LiCl reactively scattered from crossed thermal beams of Li and Br2 or Cl2. Transformation of these data into the center-of-mass coordinate system provides contour maps of the differential reactive cross sections which indicate that the Li+Br2 and the Li+Cl2 reactions have the following features in common: (a) The reaction mechanisms are direct; (b) The product angular distributions are broad although foward scattering is preferred (i.e., LiX scattered in the direction of the Li velocity); (c) Small product recoil energies are most probable but the product recoil energy distributions have a long tail. There is a strong coupling of the product recoil angle and energy distributions for Li+Cl2→LiCl+Cl with forward scattering favoring higher product recoil energy; however, this coupling phenomenon is weak or nonexistent for the Li+Br2→LiBr+Br reaction. Semiquantitative observations are also presented for the Li+ICl reaction. These results are discussed in relation to previous experimental and theoretical work on the reactions of alkali atoms with halogen molecules.

On the nature of idling noise of circular saw blades

An experimental investigation of the effects of important saw blade geometric and kinematic parameters on idling circular saw noise was conducted. Blade tip speed was determined t0 be the dominant factor in the noise production. The sound power generated was found to vary approximately as the 5·3 power of the tip velocity. Variations in blade geometry, which included the number of teeth, the blade thickness, and the tooth-gullet shape, produce effects in the radiated sound of the order of 6 dB for the blades tested. It is shown that slotted disks may be used to provide a closely controlled simulation of the saw blade noise produced aerodynamically. Results suggest that the sources are likely to be compact and are dominated by the unsteady forces acting on the tooth surfaces resulting from the interaction 0f the tooth and the incident unsteady flow in the wake of the preceding tooth.

Atom-surface scattering with velocity-selected H and D atomic beams from LiF and NaF (001)

Hydrogen and deuterium atoms with an energy between 20 and 140 meV have been scattered from LiF and NaF (001) cleavage planes in UHV. The atomic beam was nearly monoenergetic by use of a slotted disk type velocity selector with a velocity resolution of Δvv=12% (FWHM). The scattering showed diffraction with a pronounced specular beam. The energies of several bound surface states have been determined by analysis of selective adsorption minima. These energies together with relative intensities of diffracted beams and specular intensity versus incident energy measurements may be represented by an interaction potential of Morse-type with additional terms which are periodic parallel to the surface. The parameters of the Morse-potential have been found to be: depth D=17.8 meV and reciprocal range κ=1.04Å−1 for H1/LiF (001) and D = 17.9 meV, k = 1.15 Å−1 for H1/NaF (001); the additional periodic terms have relative strength β10=0.04 and β11≈β102 in the case of H 1/LiF, but β11≈β10=0.03 in the case of H1/NaF. From the observed influence of surface temperature on the position of selective adsorption minima the coefficient of thermal expansion of the topmost surface layer turns out to be approximately twice the bulk value.