Showing papers by "James W. Gregory published in 2010"

Development of a Two Layer Dual-Luminophore Pressure Sensitive Paint for Unsteady Pressure Measurements

Abstract: This paper describes the development of a two layer dual-luminophore pressure sensitive paint. In the bottom layer, a reference probe is sealed in Dupont Chroma Clear, which is oxygen impermeable, serving as a reference channel for the correction of temperature or illumination effects. The top layer is a typical formulation of porous polymer/ceramic paint with short response time, which is suitable for unsteady applications. Several options of luminophores are available for both the reference channel and the pressure-sensitive channel; a number of different combinations have been evaluated, among which the best combination was chosen for temperature correction. The thickness of the porous polymer/ceramic paint layer was found to be important since it is directly related to the signal attenuation of the reference channel. The optimum thickness was determined based on optical analysis and modeling. A demonstration of this new DL-PSP was performed in the 6”×22” transonic wind tunnel at The Ohio State University with the optimum paint configuration.

Investigation of Side-View Mirror Flow-Induced Vibration Phenomena

Abstract: The primary objective of this research is to develop an understanding of the flow mechanisms which induce side-view mirror vibrations The unsteady nature of the flow over side-view mirrors causes unsteady aerodynamic load distributions and flow-induced vibrations on the mirror assembly These vibrations generate blurred rear-view images and higher noise levels, affecting the safety and comfort of the passengers Geometrical design features of side-view mirrors exacerbate the flow-induced vibration levels of the mirror assembly significantly This work quantifies the impact of these design features on the vibration amplitude; develops a methodology for testing mirror vibrations in a small, low-speed wind tunnel using only the mirror of interest; and delves into the interactions between the bluff body mirror geometry and its wake Two similar side-view mirror designs, a baseline design and a turn-signal design, were investigated The baseline mirror has a sharp-edged corner near the trailing edge, while the turn-signal design has an edge with an increased radius of curvature for the tip profile A laser-based vibration measurement technique was developed and used to quantify vibration levels Flow visualization, Particle Image Velocimetry (PIV), Constant Temperature Anemometry (CTA), and Surface Stress Sensitive Film (S3 F) techniques were used to understand the separation characteristics over the mirrors since the time-dependent changes in separation location directly affect the unsteady loading on the mirror The flow over the turn signal mirror with larger tip radius has larger excursions in the separation location, a wider wake, increased unsteadiness, and higher vibration levels Results at the high Reynolds numbers for these test conditions indicate the absence of a discrete vortex shedding frequency However, vortical structures in the wake are correlated with unsteady movement of the separation locationCopyright © 2010 by ASME

Comparison of Unsteady Pressure-Sensitive Paint Measurement Techniques

Abstract: The current work focuses on the development and application of fast-responding polymer/ceramic pressure-sensitive paint (PSP) as an advanced surface pressure measurement technique for unsteady flow fields in large-scale wind tunnels. Three different experimental methods for acquiring quality PSP data are discussed: phase-averaging, realtime data acquisition using a high-speed camera, and single-shot lifetime. The three techniques are all demonstrated on a benchmark test case, resolving the unsteady surface pressure distribution on a hemispherical dome tested in the United States Air Force Research Laboratory’s Trisonic Gasdynamics Facility. The hemispherical dome was tested at a freestream Mach number of 0.6 with a total pressure of 1500 psf, where the Reynolds number was 2.4x10. At this flow condition, a predominant shear layer oscillated at 400 Hz over the test model, causing pressure fluctuations on the aft portion of the model. An assessment of the three techniques is presented, with the strengths and disadvantages for each technique evaluated through example.