Sudesh Woodiga

Global Luminescent Oil-Film Skin-Friction Meter

This paper describes a global luminescent oil-film skin-friction meter that is particularly useful in global skinfriction diagnostics for complex flows. This method is developed based on the relationship between the oil-film thickness and luminescent intensity of an oil film doped with luminescent molecules. The projected thin oil-film equation is given in the image plane, which relates skin friction with the normalized luminescent intensity. A variational formulation with a smoothness constraint on skin friction is given, and the corresponding Euler– Langrage equations are solved to obtain a snapshot solution for a relative skin-friction field. Successive snapshot solutions are superposed to reconstruct a complete relative skin-friction field, and the corresponding absolute field can be further determined by in situ calibration. This method is examined through numerical simulation and experiments.

Global skin-friction diagnostics based on surface mass-transfer visualizations

The theoretical foundations are formulated for extraction of skin-friction fields from surface mass-transfer visualizations with pressure-sensitive paint and sublimating coatings. The asymptotic form of the mass transport equation at a wall is expressed as the optical flow equation in the image plane. Then, a relative skin-friction field is obtained by solving the optical flow equation as an inverse problem via the variational method. For steady-state visualizations with pressure-sensitive paint and sublimating coatings, a relative skin-friction field can be obtained from a single normalized intensity image. Further, a superposition procedure of a snapshot solution and a variation solution associated with the unsteady effect is proposed to reconstruct an unsteady skin-friction field from a time sequence of pressure-sensitive paint visualization images. The capability of the proposed method is examined by applying it to pressure-sensitive paint visualizations in impinging nitrogen jets. This method is also...

Drainage and filling in cylindrical and rectangular containers

Abstract Drainage and filling processes in cylindrical and rectangular containers for several motion sequences are experimentally studied using a stereo videogrammetric technique. The measured quantities include the rigid body motion of the containers and the water level relative to the body coordinate system as a function of time. The experimental data are used to validate Torricellis law and determine the time constant, discharge coefficient, and water volume. In addition, the air funnel shapes in vortical sinks in a stationary cylinder are measured, and the effects of the initial water height and swirling on the drainage are addressed.

Global luminescent oil-film skin-friction meter generalized to three-dimensional geometry and applied to FAITH Hill

This paper further develops the global luminescent oil-film skin-friction meter by considering its application to a three dimensional axisymmetric wall-mounted bump subjected to subsonic turbulent boundary layer flow. The geometry gives rise to a necklace vortex and large scale separation on its lee side. An oil-film is only usable by the global luminescent oil-film skin-friction meter if it meets certain criteria. Most notably, it must be sufficiently thick to provide a good signal but not so thick that the relationship between luminescent intensity and oil-film thickness becomes nonlinear. Different regions on the model give rise to a usable oil-film at different times in an experiment. This paper proposes a technique for the selection of which solutions from a sequence of “snapshot solutions” taken during the run should be averaged for a particular region on the model. A relative skin-friction distribution resulting from the techniques proposed herein is presented for each of four sections of the model: One down the model’s centerline, and three across the model in the spanwise direction.

Physics-Based Optical Flow Method in Global Flow Diagnostics

The physics-based optical flow method is described as a unified framework for global diagnostics of velocity and skin friction fields in complex flows. In particular, the foundations and applications of this method for satellite/spacecraft images of large-scale flow structures in atmospheres and oceans are discussed to extract velocity fields. Also, the same method is adapted for global quantitative skin friction diagnostics on a general surface based on luminescent oil visualizations. A sketch of mathematical analysis on the variational solution of the physics-based optical flow equation is given.

Mapping Skin Friction Fields in Complex Flows Using Luminescent Oil

This paper describes application of a global luminescent oil film skin friction meter to quantitative skin friction diagnostics in complex flows. This meter is developed based on the relationship between the oil film thickness and luminescent intensity of an oil film mixed with a luminescent dye. The projected thin oil film equation is given to relate the normalized luminescent intensity with skin friction. A variational formulation with a smoothness constraint on skin friction is proposed to obtain a snap shot solution from two consecutive images for a relative skin friction field. Then, a complete skin friction field is reconstructed through superposition of a sequence of snap shot solutions. The method is used to map skin friction fields in junction flows and flows over surface roughness elements, delta wings and low aspect ratio wing.

Effects of yaw and roll angles on skin friction topology on delta wings

High-resolution skin friction fields in separated flows on delta wings are measured using quantitative global skin friction diagnostics based on luminescent oil visualizations. The effects of the yaw and roll angles on the skin friction topology on delta wings are studied systematically. The topological features like separation and attachment lines and isolated singular points are identified. The conservation law given by the Poincare-Bendixson index formula for the numbers of the isolated singular points and the boundary switch points is used as a general approach to analyze the skin friction topology.