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Research illustrates Whittaker method of error analysis for subpixel resolution of correlation peaks to set tolerance limits for optimum image sport sizes. Data demonstrate that by using the tolerances camera alignment manipulations can easily be carried out.

Results show that rotor-generated tip vortices are nonaxisymmetric in structure and no changes are observed in the strength of the vortices through all ages. Data further indicate that there is a logarithmic increase in growth of the viscous core whereas the core swirl velocity decreases logarithmically.

The increasing popularity of the aerodynamic development of laminar wings for commercial airplanes has stimulated research on a strategy to employ modern experimental and numerical methods to elucidate on the flow velocities around the wings. Laser Doppler anemometry (LDA) was found to be useful in providing local velocity data. However, special LDA systems have to be developed. Studies on LDA systems revealed two optical units suitable for in-flight velocity measurements on airplane wings.

A study was conducted to examine the influence of spacing ration on the near-wake regions behind porous disks supporting several annular elements. A platinum wire was utilized to carry out the hydrogen bubble method to conduct flow visualization studies while the mean and fluctuating velocity fields were determined using laser Doppler velocimetry. Results indicated that three dimensional large-scale motions for small spacing rations dominated the intermediate wake.

A study was conducted to examine the flow physics of laminar flow control suction surfaces using a three-component laser Doppler velocimetry system. The system supported a 5-W argon-ion laser, a transmitter box and a three-axis traverse mechanism. The Reynolds number of natural transition was determined utilizing a surface-mounted hot-film probe. Results indicated an interaction relationship between crossflow vortices and suction-induced longitudinal vortices.

An experiment was performed to measure the mean density, turbulence quantities and mean velocities of a supersonic, high-temperature exhaust plume using Rayleigh scattering system and a two-dimensional laser Doppler velocimeter. Results showed that supersonic flow is maintained only up to 15 nozzle diameters while the potential core of the supersonic jet is estimated at 6 nozzle diameters.

The empirical investigation and analysis of the dynamics of helicopter rotor wakes and blade tip vortices have created a variety of challenges for scientists. Some of these dynamics include wake instabilities, vortex/surface interaction, vortex perturbations and blade/vortex interactions. Laser Doppler velocimetry was used in quantitative measurements and flow visualization.

A study was conducted to provide a comparison between inert and reacting wakes of bluff bodies through velocity measurements. A experimental setup, which facilitates the test numerical predictions, was designed and utilized. The velocity measurements were acquired using a laser Doppler velocimeter. Results showed that the reacting wakes were characterized by the absence of vortex shedding which can be found in inert wakes.

Measurement techniques such as oil flow visualization, laser Doppler velocimetry, surface pressure, and surface hot-film skin friction are used to detect the location of three-dimensional crossflow separations. The study revealed that laser Doppler velocimeter measurements produce the most detail about the separation flowfield while directional surface hot-film provides a global measurement of separation and detailed surface topology. Pressure is also the least sensitive of the separation indicators.

The rollup region of the tip vortex from a rectangular wing of NACA 0015 profile was measured using a laser Doppler velocimetry to study the time-averaged flow structure in highly three-dimensional near-wake region. The vortex core was found to be predominantly due to axial vorticity that is concentrated at the center and approaches a zero value at the outer portion of the vortex. The length and velocity scales of the vortex were also demonstrated to originate from the near wake, with the inner part of the vortex easily reaching a universal state.

A study on the 3D separation region of a 6:1 prolate spheroid was conducted in a continuous, closed-test-section, single return, subsonic wind tunnel at the Virginia Polytechnic and State University. A specially designed miniature, 3D, fiber-optic laser Doppler velocimeter was used to measure three simultaneous, orthogonal velocity components. Results show that the total velocity vector and Reynolds stress tensor can be accurately obtained. Moreover, it was found that there are several ways for determining the separation and reattachment points on the spheroid model.

The OH planar laser-induced fluorescence (PLIF) velocimetry was utilized for computational fluid dynamics (CFD) validation based on spatially resolved and time-averaged velocity measurements. Doppler-shifted PLIF velocity measurements to combusting supersonic flow provided a quantitative, spatially complete velocity data set with excellent pixel-to-pixel spatial resolution. Furthermore, the uncertainty of the PLIF velocity measurements was dependent on OH signal level and velocity magnitude.

Three-dimensional laser Doppler velocimetry was used to measure the velocity and turbulent flow structure of a hovering rotor's tip vortex. The viscous core size was calculated at 2.5% of the blade chord right after formation and rose to 13% at one rotor revolution. The method measured turbulence quantities such as Reynolds' stress and turbulence radial and axial components.

Streaked particle imaging velocimetry and sizing (SPIVS), a nonintrusive laser-based optical probe, precisely and reliably determines the droplet size and velocity in an atomization spray. Measurements of SPIVS conform to those of the phase/Doppler particle analyzer (PDPA) technique. However, due to the sensitivity of the digital imaging system, SPIVS shows sampling bias in favor of the bigger drops. The technique is capable of droplet image pairing and time sequencing of droplet image pairs, and measuring droplet size from the recorded total light-scattering energy for each droplet streak.

A synergy of laser doppler velocimetry and multiple overheat cross-film anemometry provides direct measurements of the mean and turbulent flow properties in a supersonic turbulent flow. The measurements not only agree with the numerical predictions based on the Favre approach but are also in consonance with the algebraic turbulence models based on the Reynolds approach. The synergistic approach facilitates measurements of the Reynolds and Favre averaged turbulent shear stress for thin-layer nonreacting flows. Mean velocity and mass flux are also determined.

Three-dimensional laser Doppler anemometry facilitates the measurement of the spanwise varying velocity components within Gortler vortices (GV). A four-degree-of-freedom, least squares, sine wave curvefit provides estimates of GV wavelength and oscillation amplitudes. The disturbance along the w-direction are detectable near the wall, while the u and v disturbances can be observed higher up in the boundary layer. A 10% scatter is present for the curvefit wavelengths derived from all velocity components. Steamwise conservation of GV wavelength is suggested.

A numerical algorithm enables estimation of the particle size distribution using laser Doppler velocimetry measurements. The algorithm uses classical particle behavior through an oblique shock from a hypersonic inlet forebody. The method is easy to implement and does not require any hardware or extensive data collection. The technique is based on the fact that the particle velocity is different from the fluid velocity within a flowfield and the difference depends on the particle size distribution.

Flow visualization using laser Doppler velocimetry in the near wake of a cylindrical afterbody shows that the bleed flow displaces the primary recirculation region downstream of the base plane. The size and strength of the region reduces as the bleed flow provides most of the fluid needed for shear layer entrainment. High base pressure, absence of primary recirculation region and low turbulence levels in the near-wake flowfield enhance the benefits of base bleed.

Laser Doppler anemometer measurements on a turbulent boundary layer over a riblet surface show that the near-wall turbulence structure adjusts to a change from a smooth wall to a V-grooved riblet surface. The adjustment causes drag reduction or drag increase. The Reynold stress tensor over drag-reducing riblets is nearly similar to that on a smooth wall. For drag-augmenting conditions, on the other hand, the Reynold stresses are larger and the flow is more isotropic than on a smooth wall.

The recirculation zones for the confined and unconfined flowfields of an annular swirling jet include stable flow, vortex shedding, transition, prepenetration, penetration, vortex breakdown and attachment. The confined and unconfined flows differ in the attachment regime. The recirculation depends on the Reynolds number and swirl number. The flow structures behind an axially mounted cylindrical bluff body of the jet are studied. Laser-Doppler anemometry is used to estimate the velocity at the jet exit and downstream of the annular jet flows.

An absorption filter planar Doppler velocimetry (PDV), used on sonic and supersonic jets, obtains single-velocity-component single-shot planar images at 30 Hz by using a pulsed Nd:YAG laser as a light source. The optical splitter permitted the use of a single camera to measure velocity components. The Doppler and reference images are viewed from the same angle to eliminate the effect of the Mie scattering lobes. Modification of the absorption filters enables the use of velocimetry for both high and low speed regimes.

Autoregressive sequences help produce three-dimensional flowfields for numerical simulation of particle arrival statistics for laser Doppler anemometry (LDA) of homogeneous particle densities. Simulations of processor sampling and data acquisition help examine bias and variance of statistical estimators. The studies and examples show the flexibility and potential of this simulation method for studying LDA flow estimators. A few limitations of the simulation model are discussed.

A nonintrusive method requires near wake data to study the fluid dynamics involved in supersonic base flowfields. The method is a supersonic flow-aligned circular cylinder as the test model and yields pressure distributions, average velocities and Reynold's shear stresses for a given flowfield. The test results imply that, for a near wake flowfield, the mean static pressure pattern is nearly the same across the base.

The fully developed region of the mixing layer reveals that peak values of streamwise and spanwise turbulence intensities are similar. Decreased peak values of transverse turbulence intensity, normalized primary Reynolds shear stress and normalized turbulent kinetic energy are also obtained from the results.

A data set derived through three-component laser Doppler velocimetry in a fully developed, smooth-walled, open-channel turbulent water flow was used to examine the performance of several velocity bias correction methods. Results showed that computing mean flow characteristics in similar wall-bounced flows can easily produce relative deviations of about 10%, depending on the bias correction method used. Moreover, choosing the right bias correction scheme is essential if high-accuracy measurements are needed in cases involving low or immediate data density.

Vortex-generating tabs arranged in the form of an array have been examined experimentally using a laser Doppler anemometer in a two-stream mixing flow situation. The vortex-generating tabs are the 'delta tabs,' i.e., triangular-shaped protrusions into the flow attached to the trailing edge of the splitter plate. A velocity ratio of 2:1 (upper and lower) between the two coflowing streams was used. Three arrangements for the tabs are investigated. Case 1 has all of the tabs located on the high-speed side. The tabs are located alternatively on either side of the splitter plate for case 2, and finally, case 3 is similar to case 2, but the tab on the low-speed side is tilted upstream (i.e., similar to a delta-wing vortex generator). Mutual cancellation between streamwise vortices rotating in the opposite sense was observed in case 1, whereas in case 2 the merging of streamwise vortices rotating in the same sense had delayed the decay of the streamwise vorticity. For case 3 the upstream tilted tab appeared to have generated relatively weak streamwise vortices so that they were canceled off by the vortices generated on the high-speed side near the trailing edge. Finally, the turbulence characteristics for each case are presented and discussed.

Two-component laser Doppler velocimetry measurements were made in a planar, shock-separated free shear layer formed by the convergence of two supersonic streams past a thick plate. High-speed wall-pressure measurements were used to locate the unsteady shock wave formed by this interaction and, consequently, facilitated separation of the effects of shock motion from the turbulent fluctuations in the velocity measurements of the shear layer. Shock-induced flow separation dramatically increases the turbulent normal and shear stresses. The shock-separated shear layer displays a positive shear stress region between separation and reattachment. Reattachment produces a shift in turbulent kinetic energy from the streamwise component to the transverse component. The region of shock motion has a relatively constant width, irrespective of distance from the wall.

A planar Doppler velocimetry (PDV) system was developed and demonstrated in a small-scale facility (Mach 1.36 freejet) and then applied in a large-scale subsonic wind tunnel, where measurements were made over a delta wing at a 23-deg angle of attack. This PDV system utilized a pulsed, injection-seeded, frequency-doubled Nd:YAG laser to interrogate the flow. Back-illuminated charge-coupled device (CCD) cameras in conjunction with an iodine filter were used to record images produced by the scattered laser light, permitting the determination of the velocity at each CCD pixel. The PDV instrument also included custom software and a frequency-monitoring system composed of photodiodes, gated integrators, and a second iodine cell. With this setup, we recorded the shot-to-shot iodine-filtered and reference images and the associated laser frequency. In the freejet, mean velocities in the core were measured by PDV to within 6.4 m/s (out of ~260 m/s) of the value obtained by laser Doppler velocimetry. In the wind tunnel, freestream empty-tunnel measurements indicated bias and random errors of less than 2 and 4 m/s, respectively. The dominant source of random error arose from laser speckle, and the dominant source of bias error came from the characterization of the iodine filters. Measurements over the delta wing showed similar velocity ranges but smaller vortex cores when compared to the velocity field predicted by a computational fluid dynamics model.

A fundamental experimental investigation is described of the structure and streamwise development of a confluent boundary layer generated by the interaction of a leading-edge slat wake with the turbulent boundary layer on the main element of a multi-element airfoil model. The slat and airfoil model geometry are both fully two dimensional. The research is performed in an attempt to investigate the flow physics of confluent boundary layers and to build an archival database on the interaction of the slat wake and the main element wall layer. In addition, an attempt is made to identify clearly the role that slat wake/airfoil boundary-layer confluence has on lift production and how this occurs. Although complete laser Doppler velocimetry flow surveys were performed for a variety of slat gap and overhang settings, the focus is on two cases representing both strong and weak wake boundary-layer confluence. For those interested in performing numerical simulations, the full database is available from the authors.