John P. Sullivan

A review of pressure-sensitive paint for high-speed and unsteady aerodynamics

Abstract The current paper describes the development of pressure-sensitive paint (PSP) technology as an advanced measurement technique for unsteady flow fields and short-duration wind tunnels. Newly developed paint formulations have step response times approaching 1 μs, making them suitable for a wide range of unsteady testing. Developments in binder technology are discussed, which have resulted in new binder formulations such as anodized aluminium, thin-layer chromatography plate, polymer/ceramic, and poly(TMSP) PSP. The current paper also details modeling work done to describe the gas diffusion properties within the paint binder and understand the limitations of the paint response characteristics. Various dynamic calibration techniques for PSP are discussed, along with summaries of typical response times. A review of unsteady and high-speed PSP applications is presented, including experiments with shock tubes, hypersonic tunnels, unsteady delta wing aerodynamics, fluidic oscillator flows, Hartmann tube oscillations, acoustics, and turbomachinery. Flowfields with fundamental frequencies as high as 21 kHz have been successfully measured with porous PSP formulations.

Increased muscle sympathetic nerve activity acutely alters conduit artery shear rate patterns

Escalating evidence indicates that disturbed flow patterns, characterized by the presence of retrograde and oscillatory shear stress, induce a proatherogenic endothelial cell phenotype; however, the mechanisms underlying oscillatory shear profiles in peripheral conduit arteries are not fully understood. We tested the hypothesis that acute elevations in muscle sympathetic nerve activity (MSNA) are accompanied by increases in conduit artery retrograde and oscillatory shear. Fourteen healthy men (25 +/- 1 yr) performed three sympathoexcitatory maneuvers: graded lower body negative pressure (LBNP) from 0 to -40 Torr, cold pressor test (CPT), and 35% maximal voluntary contraction handgrip followed by postexercise ischemia (PEI). MSNA (microneurography; peroneal nerve), arterial blood pressure (finger photoplethysmography), and brachial artery velocity and diameter (duplex Doppler ultrasound) in the contralateral arm were recorded continuously. All maneuvers elicited significant increases in MSNA total activity from baseline (P < 0.05). Retrograde shear (-3.96 +/- 1.2 baseline vs. -8.15 +/- 1.8 s(-1), -40 LBNP, P < 0.05) and oscillatory shear index (0.09 +/- 0.02 baseline vs. 0.20 +/- 0.02 arbitrary units, -40 LBNP, P < 0.05) were progressively augmented during graded LBNP. In contrast, during CPT and PEI, in which MSNA and blood pressure were concomitantly increased (P < 0.05), minimal or no changes in retrograde and oscillatory shear were noted. These data suggest that acute elevations in MSNA are associated with an increase in conduit artery retrograde and oscillatory shear, an effect that may be influenced by concurrent increases in arterial blood pressure. Future studies should examine the complex interaction between MSNA, arterial blood pressure, and other potential modulatory factors of shear rate patterns.

Numerical and experimental study of gas flows in 2D and 3D microchannels

In the experiments conducted at Purdue, the air flow in rectangular cross-section microchannels was investigated using pressure sensitive paint. The high resolution pressure measurements were obtained for inlet-to-outlet pressure ratios from 1.76 to 20 with the outlet Knudsen numbers in the range from 0.003 to 0.4 based on the hydraulic diameter of 151.7 ?m and the length-to-height ratio of about 50. In the slip flow regime, the air flow was simulated by the 2D and 3D Navier?Stokes equations with no-slip and slip boundary conditions. For various pressure ratios, the entrance flow development, compressibility and rarefaction effects were observed in both experiments and numerical simulations. It was found that the accurate modeling of gas flows in finite-length channels requires the inlet and outlet reservoirs to be included in computations. Effects of entrance geometry on the friction factor were studied for 3D cases. In both experiments and numerical modeling, significant pressure drop was found starting at the inlet chamber. The numerical modeling also predicted an apparent temperature drop at the channel exit.

Direct measurement of large-strain deformation fields by particle tracking

A hybrid particle image velocimetry/particle tracking velocimetry (PIV/PTV) method is described for direct measurement of large-strain deformation fields using plane-strain machining as the model system. PIV/PTV is shown to accurately measure displacements and velocities with a spatial resolution of ~1/10th of a pixel, which is an order of magnitude improvement over a comparable PIV-based method. For the configuration studied here, this translates to about ~400 nm in terms of displacement and ~80 ?m s?1 in terms of velocity. Furthermore, the method is shown to be able to capture steep gradients in velocity, which are typical of deformation zones in machining. This enables accurate estimation of associated strain rates. Implications of the technique for measuring large-strain fields in deformation processes and indentation tests, and velocity gradients due to friction at sliding interfaces, are briefly discussed.

Numerical Inverse Heat Transfer Analysis for Temperature-Sensitive-Paint Measurements in Hypersonic Tunnels

This paper describes a numerical inverse method used in temperature-sensitive-paint measurements for quantitative global heat flux diagnostics in hypersonic tunnels. An iterative algorithm is developed to solve the one-dimensional inverse heat transfer problem for unsteady heat flux into a polymer layer (temperature-sensitive paint) on a semi-infinite base, where the temperature dependencies of the thermal properties of materials are taken intoaccount.Surfaceheat fluxdistributionsonconemodelsarecalculatedbyusingthisalgorithmfromtemperaturesensitive-paint images acquired in hypersonic wind tunnel testing. Nomenclature a = thermal diffusivity c = specific heat I = luminescent intensity k = thermal conductivity L = polymer thickness qs = surface heat flux qs� 1D� = surface heat flux obtained by using the onedimensional method T = temperature Tin = initial temperature t = time x, z = coordinates on surface y = coordinate in normal direction to surface

Experimental Testing and Numerical Simulations of Shrouded Plug-Nozzle Flowfields

The static tests of Purdue experimental shrouded plug nozzle which is a sub-scale model of the Gulfstream concept without the bypass exhaust stream is the focus of current computational and experimental effort. The static tests brought to light unsteady characteristics related shock/shock and shock/boundary layer interactions. Through a series of steady and unsteady axisymmetric computations the flow structure and physics were studied and the computational results were found to be in good agreement with experimental observations. Primarily flow structures, flow regimes and static pressure distributions were computationally studied and analyzed in conjunction with the experiments.

Variable-Frequency Fluidic Oscillator Driven by a Piezoelectric Bender

A new actuator for aerodynamic flow control applications is described and evaluated in this paper: the piezo-fluidic oscillator. This actuator is a fluidic device based on wall attachment of a fluid jet and modulated by piezoelectric devices. The piezo-fluidic oscillator successfully decouples the operating frequency from the flow characteristics of the device. The frequency is specified by an input electrical signal that is independent of pressure, making this actuator ideal for closed-loop flow control applications. The oscillator exhibits high bandwidth (up to 1.2 kHz), modulation rates up to 100%, and a velocity range reaching sonic conditions. Furthermore, the bistable actuator may be operated in a steady state, with momentum flux in one of two desired directions for flow vectoring purposes. The piezo-fluidic oscillator may be used in flow control applications in which synthetic jets or plasma actuators cannot provide enough momentum for control authority. This paper details the design and characterization of the piezo-fluidic oscillator. The dynamic response characteristics are evaluated with flow visualization and hot-film probe measurements on the output.

Temperature Field in Severe Plastic Deformation at Small Strain Rates

The temperature and strain rate fields in severe plastic deformation (SPD) are measured using infra-red thermography and Particle Image Velocimetry (PIV), respectively. Plane strain machining is used as the method of SPD to impose controlled strains and strain rates. For metals such as titanium, the temperature rise is small at small strain rates and SPD occurs at near-ambient temperature. The possibility of exploring dynamic recovery/recrystallization phenomena using the Zener-Hollomon parameter in this SPD framework is briefly discussed.

Numerical and Experimental Study of Gas Flows in 2D and 3D Microchannels

In the experiments conducted at Purdue, the air flow in rectangular cross-section microchannels was investigated using the pressure sensitive paints. The high resolution pressure measurements were obtained for inlet-to-outlet pressure ratios from 1.76 to 20 with the outlet Knudsen numbers in the range from 0.002 to 0.06 based on hydraulic diameter of 157.9 micron and the length-to-height ratio of about 50. In the slip flow regime, air flow was simulated by the 2D and 3D Navier-Stokes equations with no-slip and slip boundary conditions. For various pressure ratios, the entrance flow development, compressibility and rarefaction effects were observed in both experiments and numerical simulations. It was found that accurate modeling of gas flows infinite-length channels requires that inlet and outlet reservoirs to be included in computations. Effects of entrance geometry on the friction factor were studied for 3D cases. In both experiments and numerical modelings, significant pressure drop was found starting at the inlet chamber. The numerical modeling also predicted an apparent temperature drop especially at the channel exit.© 2007 ASME