Engineering topics

Orloff, K. L.

Publications and source records attributed to Orloff, K. L..

At least 37 records · Page 2

NASA NTRS1978

Laser-velocimeter surveys of merging vortices in a wind tunnel: Complete data and analysis

The merger of two corotating vortices was studied with a laser velocimeter designed to measure the two cross-stream components of velocity. Measurements were made at several downstream distances in the vortex wake shed by two semispan wings mounted on the wind-tunnel walls. The velocity data provided wall-defined contours of crossflow velocity, stream function, and vorticity for a variety of test conditions. Downstream of the merger point, the vorticity was found to be independent of the downstream distance for radii smaller than r/b = 0.05. For larger radii, the vorticity depended on the distance from the wing. Upstream of the merger, a multicell vorticity pattern was found.

Corsiglia, V. R.↗

NASA NTRS1978

The spanwise lift distribution on a wing from flow-field velocity surveys

The application of the incompressible three-dimensional momentum integral equation to a finite wing is reviewed. The objective is to interpret the resulting equations in a way that suggests an alternate experimental method for determining the span-wise distribution of lift. Consideration is given to constraints that must be placed on the character of the vortex wake of the wing to provide the familiar relationship between lift and bound vorticity. A novel technique is then presented for obtaining, from behind the wing, the spanwise lift distribution from velocity surveys that are made over only a short distance above and below the wing trailing edge. The necessary formalism is developed to use these measured values to obtain the actual span loading by using an equivalent single horseshoe vortex model to account for the unmeasured portion of the downward (or upward) momentum. The results of a numerical simulation are presented for a typical loading distribution. The technique is then verified experimentally using laser velocimeter data for the flow field around a model wing.

Orloff, K. L.↗

NASA NTRS1978

Laser-velocimeter surveys of merging vortices in a wind tunnel

The merger of two vortices was studied with a laser velocimeter designed to measure the two cross-stream components of velocity. Measurements were made at several downstream distances in the vortex wake shed by two semispan wings mounted on the wind tunnel walls. The velocity data provided well difined contours of cross-flow velocity, stream function and vorticity. Downstream of the merger point the vorticity was shown to be independent of the downstream distance for small radii, and at larger radii was dependent on the distance from the wing rather than from the merger point. Upstream of the merger point a multicell vorticity pattern was shown.

Corsiglia, V. R.↗

NASA NTRS1977

Laser velocimeter measurements of two-bladed helicopter rotor flow fields

Data from a wind tunnel investigation of the flow fields around helicopter rotors were presented. A two component laser velocimeter was used to measure the velocity fields of two 2.1 m diameter rotors. A minicomputer-based online data system is described which monitored, reduced, and plotted the results. Tip vortices constitute the primary disturbances in the flow field, but present theories do not predict vortex positions and velocity distributions with sufficient accuracy.

Biggers, J. C.↗

NASA NTRS1977

Determining the Lift and Drag Distributions on a Three-Dimensional Airfoil from Flow-Field Velocity Surveys

The application of the incompressible momentum integral equation to a three-dimensional airfoil was reviewed to interpret the resulting equations in a way that suggests a reasonable experimental technique for determining the spanwise distributions of lift and drag. Consideration was given to constraints that must be placed on the character of the vortex wake structure shed by the wing, to provide the familiar relationship between lift and bound vorticity. It is shown that the induced drag distribution is not directly measurable, but can be obtained, via the lift distribution, approximately for a deflected wake and exactly for a planar wake. Moreover, it is shown that it is only necessary to survey a short distance above and below the wing trailing edge. Examples are presented for several typical loading distributions and the results of a numerical simulation of the suggested experiment are discussed.

Orloff, K. L.↗

NASA NTRS1977

Laser anemometer signals - Visibility characteristics and application to particle sizing

Investigations have been conducted concerning the characteristics of the visibility function as determined by the parameters of the laser anemometer system and the electromagnetic scattering properties of the particles. Experiments have been performed to evaluate the backscatter visibility of signals from a symmetric, s polarization laser anemometer as a function of the particle diameter and a parameter ratio. The results have been compared with the predictions of an analysis based on Mie's scattering theory. The analysis has also been used to evaluate the effects of the collecting aperture's size and location.

Adrian, R. J.↗

NASA NTRS1977

Measurements of helicopter rotor tip vortices

This paper presents results from a recent wind-tunnel investigation of model helicopter rotor tip vortices. Measurements were made of the vortex positions, core sizes, and velocity distributions. A laser velocimeter was used to make the measurements, and a minicomputer-based data system was used to process the data and to aid in controlling the experiment. The velocimeter, the data system, and the software developed for the minicomputer are briefly described. The rotors investigated were two-bladed, teetering rotors with diameters of 2.1 m. Two sets of blades were used, one set with zero twist and one set with -11 deg of linear twist. The vortex positions were obtained by making flow field traverses while strobing the data system at a fixed azimuth. Aging of a vortex element was also studied by following the convected element while strobing the data system at different azimuths. By this method, the effects on the vortex of a close interaction with a blade and another vortex were studied.

Biggers, J. C.↗

NASA NTRS1977

Application of laser velocimetry to aircraft wake-vortex measurements

The theory and use of a laser velocimeter that makes simultaneous measurements of vertical and longitudinal velocities while rapidly scanning a flow field laterally are described, and its direct application to trailing wake-vortex research is discussed. Pertinent measurements of aircraft wake-vortex velocity distributions obtained in a wind tunnel and water towing tank are presented. The utility of the velocimeter to quantitatively assess differences in wake velocity distributions due to wake dissipating devices and span loading changes on the wake-generating model is also demonstrated.

Ciffone, D. L.↗

NASA NTRS1976

Investigating complex aerodynamic flows with a laser velocimeter

The application of the laser velocimeter in the study of two highly complex aerodynamic flows is discussed. In the first experiment, the laser velocimeter was used with frequency tracking electronics to survey the multiple vortex wake structure behind a model of a large jet transport. The second application is to the study of the induced instantaneous inflow velocities near the blades of a model helicopter rotor; counter-type processing was used in these measurements. In each experiment, the data output channels of these processors were handled in an on-line fashion, including both velocity computations and the plotting of fully reduced data.

Orloff, K. L.↗

NASA NTRS1976

Scanning laser-velocimeter surveys and analysis of multiple vortex wakes of an aircraft

A laser velocimeter capable of rapidly scanning a flow field while simultaneously sensing two components of the velocity was used to measure the vertical and streamwise velocity structure 1.5 spans downstream in the wake of a model typical of a large subsonic transport (Boeing 747). This flow field was modeled by a superposition of axisymmetric vortices with finite cores. This theoretical model was found to agree with the measured velocities everywhere except where two vortices were in close proximity. Vortex strengths derived from the span loading on the wing as predicted by vortex-lattice theory also agree with the present measurements. The axisymmetric vortex model used herein is a useful tool for analytically investigating the vortex wakes of aircraft.

Corsiglia, V. R.↗

NASA NTRS1976

Investigating complex aerodynamic flows with a laser velocimeter

The paper discusses the application of the laser velocimeter in the study of two highly complex aerodynamic flows. In the first experiment, the laser velocimeter has been used with frequency tracking electronics to survey the multiple vortex wake structure behind a model of a large jet transport. The second application is to the study of the induced instantaneous inflow velocities near the blades of a model helicopter rotor; counter type processing was used in these measurements. In each experiment, the data output channels of these processors were handled in an on-line fashion, including both velocity computations and the plotting of fully reduced data.

Orloff, K. L.↗

NASA NTRS1976

Limitations on the use of laser velocimeter signals for particle sizing

The paper discusses the complex relationship existing between the diameter of a particle, its index of refraction, and the output signal of a fringe-type laser velocimeter, and describes a special purpose laser velocimeter for aerosol sizing that determines aerosol size distributions on the basis of Farmer's (1973) relationship between visibility and particle size. In experiments with particles of known size, this relationship is in qualitative agreement with the experimentally observed results, the main differences being that (1) the visibility does not assume a minimum value of zero, as predicted, and (2) the visibility value above which there is no ambiguity in the corresponding fringe spacing is higher than that predicted.

Orloff, K. L.↗

NASA NTRS1976

Modular high accuracy tracker for dual channel laser Doppler velocimeter

In the study described, a scanning dual-channel cross-beam laser Doppler velocimeter (developed for measuring simultaneously the two orthogonal components of flow velocity and turbulence intensity) was used to measure the instantaneous velocity characteristics of a model helicopter rotor and in a vortex wake survey experiment on a Boeing 747 aircraft model. Particular attention is given to a special purpose dual-loop frequency tracker developed to track and demodulate 10 microsecond wide pulse burst Doppler signals with a study cycle of 25% (or narrower signals at a higher duty cycle) generated by the laser Doppler velocimeter.

Fridman, J. D.↗

NASA NTRS1975

Laser velocimeter measurements of rotor blade loads and tip vortex rollup

A method for obtaining and analyzing the instantaneous velocities of helicopter rotor flow fields through use of a laser velocimeter capable of simultaneously sensing two components of velocity is described. Rotor blade aerodynamic loads may be computed from the velocity distributions near the blades. The experiment was conducted with a 2.13 m (7 ft) diameter model helicopter rotor operating in a wind tunnel. Velocity distributions are presented which document the flow field near the advancing blade. Circulation is calculated from the velocity measurements, and the radial distribution of circulation is discussed. The influence of the tip vortex from the preceding blade is apparent in this distribution. Tip vortex rollup on the advancing blade was documented by making a series of measurements at various distances behind the blade. Effects of blade drag are evident in the velocities behind the blade trailing edge.

Biggers, J. C.↗

NASA NTRS1974

Axial flow measurements in trailing vortices

A scanning laser Doppler velocimeter was used to measure the axial velocity defect in the cores of trailing vortices behind a lifting airfoil of rectangular planform. Data were obtained at several different angles of attack and downstream distances ranging from 30 to 1000 chord lengths. The test was designed to obtain continuous data from the near field into the far field while removing uncertainties associated with the interpretation of data obtained by the hydrogen bubble technique. The measured velocities of V sub x/U sub infinity are compared with those predicted. The agreement is remarkably good over the entire range of downstream distances, which supports the credibility of calculating axial velocities using the results of Moore and Saffman (1973).

Ciffone, D. L.↗

NASA NTRS1974

Far-field wake-vortex characteristics of wings

Velocity measurements have been made in the wake of wings that were being towed underwater. As the wake aged, measurements of the tangential and axial velocity profiles were made with a two-dimensional scanning laser velocimeter at downstream distances of 5 to 200 span lengths behind wings with different span loadings. The results identify two characteristic flow regions for the dependence of vortex maximum tangential velocity on downstream distance. The first, a region with little, if any, change in maximum tangential velocity, extends from wake rollup to downstream distances as great as 100 span lengths, depending on span loading and angle of attack. This is followed by a decay region in which the maximum tangential velocity decreases with downstream distance at rates nominally proportional to the inverse one-half power.

Ciffone, D. L.↗

NASA NTRS1974

Vortex measurements behind a swept wing transport model

A backscatter laser Doppler velocimeter which simultaneously senses the axial and the tangential components of the velocity has been used to measure the velocity distributions in the near wake of a swept wing semispan transport model in a wind tunnel. The model configuration included nacelles, pylons, antishock bodies, and wing flaps which could be deflected 27 deg. Typical wake vortex velocity profiles are presented for the flaps-retracted and the flaps-deployed 27 deg configurations, respectively.

Orloff, K. L.↗

NASA NTRS1974

Laser velocimeter measurements of the helicopter rotor-induced flow field

The use of a two-color laser velocimeter to measure the flow velocities in the wake of a helicopter rotor is discussed, including methods for obtaining two components of both instantaneous and time-averaged velocities. Results are presented from an experiment using a 2.13 m diameter model helicopter rotor operating at a tip speed ratio of 0.18 in a wind tunnel. The location of the tip vortex from the preceding blade was determined on the advancing side, and the diameter of the vortex core was found to be 15 percent of the blade chord (1.5 percent of the radius). The effects of the airfoil's bound vorticity were observed in the velocity distributions vry near the blade. These effects suggest that the laser velocimeter may be used to determine the aerodynamic loading (circulation) at a spanwise station on the blade. Also, the structure and boundary of the time-averaged wake were investigated.

Biggers, J. C.↗