Emilio Graff

Two-frame 3D particle tracking

A whole-field three-dimensional (3D) particle tracking velocimetry (PTV) tool for diagnostics in fluid mechanics is presented. Specifically, it is demonstrated why and when PTV is the natural choice in 3D applications compared to particle image velocimetry (PIV). Three different tracking methods are investigated, namely the nearest neighbour, the neural network and the relaxation method. In order to demonstrate the use of PTV for 3D applications, the selected tracking schemes are implemented for use with the defocusing digital particle image velocimetry (DDPIV) technique. The performance of the tracking algorithms is evaluated based on synthetic 3D information. Furthermore, the potential benefit of a merging between the PIV and PTV approaches is explored within the DDPIV framework. The results show that the relaxation tracking method is the most robust and efficient, while the combined PIV/PTV analysis brings significant improvements solely with the neural network scheme. In terms of errors, PTV is found to be more sensitive to particle reconstruction errors than the DDPIV cross-correlation analysis.

Performance Enhancement of a Vertical Tail Model with Sweeping Jet Actuators

Active Flow Control (AFC) experiments performed at the Caltech Lucas Adaptive Wall Wind Tunnel on a 12%-thick, generic vertical tail model indicated that sweeping jets emanating from the trailing edge (TE) of the vertical stabilizer significantly increased the side force coefficient for a wide range of rudder deflection angles and yaw angles at free-stream velocities approaching takeoff rotation speed. The results indicated that 2% blowing momentum coefficient (C(sub mu) increased the side force in excess of 50% at the maximum conventional rudder deflection angle in the absence of yaw. Even C(sub mu) = 0.5% increased the side force in excess of 20% under these conditions. This effort was sponsored by the NASA Environmentally Responsible Aviation (ERA) project and the successful demonstration of this flow-control application could have far reaching implications. It could lead to effective applications of AFC technologies on key aircraft control surfaces and lift enhancing devices (flaps) that would aid in reduction of fuel consumption through a decrease in size and weight of wings and control surfaces or a reduction of the noise footprint due to steeper climb and descent.

Improving Rudder Effectiveness with Sweeping Jet Actuators

The application of active flow control on a vertical tail of a typical twin engine aircraft was investigated. Sweeping jets installed into the rudder surface were used and their effect was assessed by force measurements, flow visualization and local pressure distributions. The airfoil forming the tail is a NACA 0012 with a rudder using 35% of its chord. The tests were carried out at the Lucas Wind Tunnel at the California Institute of Technology at representative Reynolds numbers of up to Re=1.5 million. Multiple flap deflections and spanwise actuator configurations were tested resulting in an increase of up to 50-70% in side force depending on the free stream velocity and momentum input.

Flow Separation Control on A Full-Scale Vertical Tail Model Using Sweeping Jet Actuators

* Aerospace Engineer, Flow Physics and Control Branch, MS 170, AIAA Senior Member † Aerospace Engineer, Flow Physics and Control Branch, MS 170, AIAA Associate Fellow ‡ AeroScience Lead, Flow Physics and Control Branch, MS 41 § R & D Engineer, Boeing Research & Technology, Mail Stop: S306-4030, AIAA Senior Member ** Research Project Manager, Graduate Aerospace Laboratories, AIAA Member †† Professor, Aerospace and Mechanical Engineering Department, AIAA Fellow Abstract

Performance Enhancement of a Full-Scale Vertical Tail Model Equipped with Active Flow Control

* R & D Engineer, Boeing Research & Technology, Mail Stop: S306-4030, AIAA Senior Member † Product Development Engineer, Boeing Commercial Airplanes, PO Box 3707, M/S 0R-MM, AIAA Senior Member ‡ Aerospace Engineer, Flow Physics and Control Branch, MS 170, AIAA Associate Fellow § Aerospace Engineer, Flow Physics and Control Branch, MS 170, AIAA Senior Member ** AeroScience Lead, Flow Physics and Control Branch, MS 41 †† Research Project Manager, Graduate Aerospace Laboratories, AIAA Member ‡‡ Professor, Aerospace and Mechanical Engineering Department, AIAA Fellow Abstract

A Mach-Zender digital holographic microscope with sub-micrometer resolution for imaging and tracking of marine micro-organisms

Digital holographic microscopy is an ideal tool for investigation of microbial motility. However, most designs do not exhibit sufficient spatial resolution for imaging bacteria. In this study we present an off-axis Mach-Zehnder design of a holographic microscope with spatial resolution of better than 800 nm and the ability to resolve bacterial samples at varying densities over a 380 μm × 380 μm × 600 μm three-dimensional field of view. Larger organisms, such as protozoa, can be resolved in detail, including cilia and flagella. The instrument design and performance are presented, including images and tracks of bacterial and protozoal mixed samples and pure cultures of six selected species. Organisms as small as 1 μm (bacterial spores) and as large as 60 μm (Paramecium bursaria) may be resolved and tracked without changes in the instrument configuration. Finally, we present a dilution series investigating the maximum cell density that can be imaged, a type of analysis that has not been presented in previous holographic microscopy studies.

Influence of common transparent materials on the accuracy of image-based velocimetry

We discuss the performance of commonly available architectural window materials with respect to the accuracy of optical measurements (e.g. metrology from images, particle image velocimetry, direct image correlation, etc). Window samples were examined for flatness/homogeneity and their performance was quantified by their effect on measurements taken by a three-dimensional velocimetry system. Optical glass performed the best, but also annealed normal and annealed low iron glasses are good, economical options. Plastic-based windows can suffer from damage by laser beams and are only an option if illumination is less important. Polycast acrylic is the best choice within this specific group.

Applications of DDPIV to Studies Associated with Road Vehicles

The quantification of experimental flows is a problem that poses several challenges, the most obvious of which is how to extract motion from an “invisible” phenomenon. In general, flows can be analyzed through a sequence of still images (Singh 1991). For example, the motion of patterns generated by dye, clouds or particles can be used to obtain such a time sequence of still images. The main problem with using a continuous-intensity pattern, generated by scalar fields (e.g., dye patterns), is that it must be somehow discretized and contain variations of intensity at all scales before mean and turbulent velocity information can be obtained (Pearlstein and Carpenter 1995). In this respect, the discrete nature of images generated by seeding particles has made particle tracking the method of choice for whole field velocimetry. Displacement and, thus, velocity information can be extracted through statistical methods and other methods such as particle tracking. The spatial resolution of this method depends on the number density of the particles.