Martin Morris

Aerodynamic applications of pressure sensitive paint

A pressure measurement technique based on a photoluminescent coating is being developed and used for aerodynamic applications. Visible light excites probe molecules in the paint and their luminescence is related to the static pressure. Details of the illumination, luminescence detection, and data reduction for this technique are presented. These include key issues such as temperature effects, camera calibration, and model movement. Results from this technique in a variety of flowfields are given. Comparisons with pressures measured using standard wall taps show good agreement

Step response of pressure-sensitive paints

An experimental and analytical characterization of the response of three typical pressure-sensitive paint (PSP) formulations to a step change in pressure is presented. The three PSP formulations tested have all been previously used in wind-tunnel experiments and have been shown to have acceptable aerodynamic surface properties and mechanical durability. The time response of the PSP coatings is dependent on the diffusion of oxygen through the PSP binder material with typical time constants ranging from 0.05 to 2.5 s. The PSP response is best characterized by a two-term exponential decay function representing a complex first-order dynamic system. In contrast, a standard pressure transducer responds as a second-order dynamic system. The two-exponential curvefit provides a convenient way to compare the time response of different PSP formulations. A mass diffusion model of the PSP response is also presented that is capable of predicting the time response of PSP layers.

Temperature Dependence of Pressure Sensitive Paints

The photoluminescence properties of a typical pressure sensitive paint (PSP) formulation consisting of tris-(4,7-diphenylphenanthrollne)ruthenium(II) dichloride (RudpCl) dispersed in a polydimethylsiloxane (PDMS) binder were examined as a function of temperature. Thus, the temperature dependence of the luminescence intensity I em and emission decay lifetime τ em of the PSP formulation and for the photoluminescent RudpCl dye dissolved in ethanol solvent were determined for temperatures ranging from 5 to 50°C. Analysis of the experimental data indicates that under deoxygenated conditions the temperature dependence of I em and τ em for either the PSP formulation or ethanol solutions is dominated be the intrinsic temperature dependence of the nonradiative decay rate of the photoluminescent dye molecule. By contrast, for the PSP formulation at 1-atm air pressure the temperature dependence of I em and τ em is dominated by the temperature dependence of the diflusivity of oxygen in the PDMS binder. The implications of the experimental results on the design and application of PSP formulations are discussed.

Experimental investigation of terminal shock sensors for mixed-compression inlets

This paper describes experimental investigations of devices designed for the nonintrusive detection of terminal shock location in mixed-compression inlets at high supersonic flight speeds. Systems based on sensing wall pressures by an array of wall-mounted transducers were selected for detailed study. Pressure signals were processed by three different methods: (1) interpretation of instantaneous pressure distributions, (2) detection of the turbulent intensity amplification occurring at the shock, and (3) determination of the upstream limit to which a search-tone, introduced at the downstream end of the channel, can propagate. The first two of these methods were tested in real time. The third method appeared feasible for weak shocks only; at high shock strengths, propagation upstream of the source could not be detected.

An Experimental Investigation of Butterfly Valve Performance Downstream of an Elbow

Primary emphasis is given the influences of valve disk angle, valve/elbow spacing, and valve/elbow orientation on the dimensionless pressure drop, mass flow coefficient, and aerodynamic torque coefficient characteristics of the valve.

Experimental investigation of normal-shock/turbulent-boundary-layer interactions with and without mass removal

Interactions of a normal shock with a turbulent boundary layer over a flat surface were investigated with and without imposing mass removal. The approach flow was very nearly two-dimensional, with a uniform freestream Mach number of 1.48, strong enough to cause separation at the shock foot. Suction was imposed immediately upstream of the shock over a finely perforated surface, removing much of the boundary-layer flow. The time-mean wall pressure distributions and two components of the time-mean velocity vector field were determined for both cases. Mass removal distorted the original shock pattern and eliminated the separation at the shock foot while reducing the boundary-layer thicknesses and growth rates to less than half. Mass removal also introduced some undesirable effects: asymmetric sidewall boundary-layer growth in the subsonic flow and increased shock oscillation amplitudes. The removed mass flow varied strongly in the streamwise direction in a manner that indicated wide variations of the flow coefficients for the individual perforations.

Compressible flowfield characteristics of butterfly valves

The results of an experimental investigation into the flowfield characteristics of butterfly valves under compressible flow operating conditions are reported. The experimental results include Schlieren and surface flow visualizations and flowfield static pressure distributions. Two valve disk shapes have been studied in a planar, two-dimensional test section: a generic biconvex circular are profile and the midplane cross-section of a prototype butterfly valve. The results demonstrate that under certain conditions of operation the butterfly valve flowfield can be extremely complex with oblique shock waves, expansion fans, and regions of flow separation and reattachment

Aerodynamic Torque Characteristics of Butterfly Valves in Compressible Flow

The results of an experimental investigation of the aerodynamic torque characteristics of butterfly valves under compressible flow conditions are reported. Both three-dimensional prototype valves and two-dimensional planar models have been studied at choked and unchoked operating points. Other parameters investigated include the operating pressure ratio across the valve, the valve disk angle, and the disk shape

Use of pressure-sensitive paints in low-speed flows

Pressure measurements based on pressure-sensitive paint (PSP) have been shown to be useful in low speed flows. Many obstacles were addressed in making these successful measurements. The considerations for making these measurements are presented, as well as, a brief discussion of important procedures. A sample of data is presented to demonstrate the agreement between pressure-sensitive paint and traditional pressure taps.

Pressure sensitive paint: application to a sinusoidal pressure fluctuation

An experimental characterization of the frequency response of a Pressure Sensitive Paint (PSP) has been performed. The PSP response to a sinusoidal pressure field was investigated. A Fourier analysis was then used to extended the results to a general periodic pressure field. Amplitude response and phase shift as a function of frequency are presented. The techniques developed in this paper are suitable for comparing the unsteady characteristics of various PSP formulations. Additionally, the frequency response characterization may be used in dynamic compensation techniques to correct for PSP time lag.