James P. Hubner

Heat-Transfer Measurements in Hypersonic Flow Using Luminescent Coating Techniques

Thedevelopmentandapplicationofhigh-speedimagingandluminescentcoatingtechniquestomeasurefull-e eld surface heat-transfer rates in short-duration hypersonic e ow is presented. Tests were performed on an indented cone model at the 48-in. shock tunnel and the LENS I tunnel facilities at Calspan— University of Buffalo Research Center. Nominal test conditions ranged between Mach numbers of 9.5 and 11.1 and Reynolds numbers of 1:4 £ 10 5 and 3 £ 10 5 m ii 1 with run times of less than 10 ms. Processed submillisecond images show the threedimensional, time-dependent development of the embedded separated e ow and shock/boundary-layer interaction into a steady axisymmetric structure bounded by regions of laminar e ow. Conversion from processed image data to full-e eld heat-transfer measurements were performed using both an in situ calibration with thin-e lm platinum heat-transfer gauges as well as an a priori temperature calibration and transient heat-transfer theory. In situ calibrations displayed excellent correlation with surface-mounted gauges, whereas a priori calibrations showed a larger susceptibility to bias errors.

Temperature- and Pressure-Sensitive Paint Measurements in Short-Duration Hypersonic Flow

Surface temperatures and pressures were measured on an elliptic cone lifting body in a hypersonic e owe eld using thin-e lm (» 5πm) temperature- and pressure-sensitive paints (TSPs and PSPs ). The tests were conducted in the 48-inch hypersonic shock tunnel (48-inch HST) at Calspan‐University of Buffalo Research Center and were part of a more comprehensive experimental study examining the three-dimensional characteristics of laminar, transitional, and turbulent e ow over the model. Measurement opportunity in the 48-inch HST was limited by the short duration of steady freestream conditions of the driven gas; image acquisition times were » 3 ms. Images of the coatings applied to the broad side of the symmetric elliptic cone were calibrated with in situ static pressure and surface-e lm temperature measurements. The TSP results illustrate the higher heat transfer rates and change in boundary-layer transition over the model surface caused by the nose geometry, and the PSP results show a mild pressure gradient over the interrogated surface region. Submillisecond TSP acquisition using a high-speed imager demonstrated the feasibility of measuring the surface temperature rise.

Characterization of a new luminescent photoelastic coating

The luminescent photoelastic coating (LPC) technique measures the full-field shear strain and its principal direction on the surface of complex three-dimensional components. The measured optical strain response is also dependent on the coating thickness. Achieving uniform coating thickness is difficult, and thus requires thickness correction for accurate quantitative strain measurements. The original formulations of LPC employed a dual-layer coating containing luminescent dyes to transmit both strain and thickness information. This paper will document (theory and experiment) a new strategy: a single-layer coating that incorporates both a luminescent dye and an absorption dye. Dependent on the concentration of the absorption and luminescent dyes, the solution is sprayed onto the object of interest to a minimum threshold thickness that corresponds to a predefined penetration depth. Advantages of the single-layer coating are the elimination of thickness dependency, the elimination of compliance and adhesion issues between multiple layers, simpler data acquisition and post-processing methods, and easier and faster coating preparation and application.

Luminescent photoelastic coatings

In this paper we describe a new technique to measure the surface strain field on complex three-dimensional structural components under static load. It is cost-efficient to implement and suitable to be integrated in the product design cycle in conjunction with finite element analysis tools. The technique employs novel luminescent photoelastic coatings and digital imaging to map the in-plane strain field. The coatings consist of a binder, generally polymeric in nature, and luminescent dyes that are applied to the surface of a test part using conventional aerosol techniques. When excited with circular polarized ultraviolet or blue illumination, the corresponding emission intensity from the coating is measured via a digital camera. The relative change in emission magnitude and phase as measured after passing through an analyzing polarizer is related to the in-plane shear strain and its corresponding principal direction. Several basic test results are presented and discussed, showing quantitative, repeatable, and high spatial resolution measurements.

Controlling Pre-tension of Silicone Membranes on Micro Air Vehicle Flexible Wings

This work is concerned with a new method to apply uniform and known pre-tension silicone membranes intended for micro air vehicles. Pre-tension has an immense effect on the static and dynamic response of membrane wings and controls the overall deflections. Two different frame geometries were fabricated to attach silicone film at various temperatures to control the pre-tension. The intent is to thermally expand the silicone membrane allowing the film to stretch, attach the frame, and cool to room temperature to develop tension. Stresses and strains are provided for membrane attachment at various temperatures. The results are plotted to predict pre-tension for the given frame geometries.

Full-field strain measurement using a luminescent coating

In this paper we describe an optical-based technique, called strain sensitive skin (S3), for measuring in-plane strain data on structural members under static load. The technique employs a coating consisting of a luminescent dye and polymer binder that is applied to the surface of a test part via conventional aerosol techniques. Proper illumination stimulates the dye, which in turn emits higher wavelength luminescence. The excitation and emission intensities have different wavelengths; therefore, enabling optical filtering to separate the two signals. The optical strain response is intensity based. A network of randomized microcracks within the binder scatters the waveguided luminescence from the excited dye molecules. The amount of scattered luminescence is related to the changes in the microcrack openings and orientations via mechanical strain. Various calibration tests show the optical strain response to be proportional to the sum of in-plane principal strains. With this new experimental testing tool, full-field high-resolution strain measurements can be acquired. The optical strain response of this new sensor is minimally dependent on viewing and lighting directions, rendering the technique viable to imaging and determining strain fields for three-dimensional complex geometries.

Force and Deformation Measurement on Low Aspect Ratio Membrane Airfoils

This paper investigates the effects of pre-strain and cell aspect ratio on free trailing edge, aspect ratio two, membrane wings at low Reynolds number (Re ~ 50,000). At these conditions, the membrane visually vibrates. Of particular interest is the comparison of the membrane wing aerodynamic performance to rigid models fabricated in the shape of the time-averaged membrane deformation. Three pre-strain levels, 1%, 2% and 4%, were applied to flat membranous wings with one, two and three cells. Force and deformation measurements were performed in a low speed wind tunnel. From digital image correlation results, the rigid, time-averaged deformation wings were fabricated using three-dimensional printing. The aerodynamic loads for the printed wings were acquired at the same test conditions as membranous wings to extract the dynamic and static benefits of flexibility. In general, the membrane wings outperformed the printed wings at both pre-stall and stall conditions. Nomenclature AR = Aspect ratio AOA or uf061 = Angle of attack b = Membrane cell span c = Length of chord c = Membrane cell chord CL = Lift coefficient CL,α = Lift curve slope CD = Drag coefficient CD,o = Minimum drag coefficient CM = Pitching moment coefficient f = Frequency L/D = Lift-to-drag ratio q = Dynamic pressure Re = Reynolds number t = Membrane thickness uf050 = Dimensionless aeroelastic parameter 1 Graduate Research Assistant, AIAA Student Member 2 Undergraduate Research Assistant 3 Associate Professor, AIAA Associate Fellow 4 Graduate Research Assistant, AIAA Student Member 5 Associate Professor, AIAA Associate Fellow 6 Professor, AIAA Member 51st AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition 07 10 January 2013, Grapevine (Dallas/Ft. Worth Region), Texas AIAA 2013-0682 Copyright

Effects of Membrane Vibration on the Flow Field Surrounding Flat-Plate Membrane Airfoils

This investigation examines the fluid-structure interaction between flexible membrane airfoils and their surrounding flow field for the purpose of physically interpreting aerodynamic performance benefits attributed to certain membrane airfoil configurations in low Reynolds number (< 100,000) flight regimes. Specifically, this research effort identifies airfoil membrane vibration onset through quantifiable characteristics and presents simultaneous time-resolved hotwire anemometry and laser vibrometry to measure membrane vibration and flow field oscillation velocities, respectively. Evaluations were executed with a series of test articles consisting of rigid, flat plate airfoils containing a single, variably-sized membrane cell located at the test article’s spanwise centerline. Results demonstrate that membrane vibration onset criteria involving direct assessment of membrane oscillation velocity via laser vibrometry more closely and consistently match visual assessment of vibration onset than do onset criteria involving flow field oscillation velocity measured via hotwire anemometry. At low freestream velocities, membrane vibration does not significantly affect the surrounding flow and vibration onset cannot be consistently identified via flow field assessment. Comparison of total membrane vibration energy at varying test conditions proves to be the most consistently accurate and quantifiable indicator of vibration onset.

Flow and Structure Measurements of a Passively Compliant Wing

This paper discusses an experimental effort to study the fluid-structure interactions of flexible membrane wings at low Reynolds number by synchronized acquisition of Particle Image Velocimetry and Digital Image Correlation. The compliant wings are battenreinforced flat plates with multi-cell, scalloped membrane sections similar to some micro air vehicle designs. The data analyzed in this paper consists of time-resolved, two-component flow measurements over the model/membrane surface as well as in the near wake and 3D membrane displacement measurements. The flow over a baseline rigid flat plate is included to compare time-averaged flow properties and investigate how the membrane wings alter the flow. Membrane wing models of varying pre-tension were also investigated utilizing the digital image correlation technique to better understand the frequency response and flexibility effects of the compliant wings. The time-dependent dynamics of velocity and membrane vibrations indicate that membrane fluctuations have a strong influence on the surrounding flow, affecting the shear layer emanating from the wings’ leading edge and the development of the flow in the wake of the airfoil. Spectral and correlation analysis show quantitative evidence of membrane vibrations driving the flow over the wing and into its wake.

Principal Component Analysis of Dual-luminophore Pressure/Temperature Sensitive Paints

Multi-luminophore pressure/temperature sensitive paints are investigated using principal component analysis of the spectral emission from the coatings. Two formulations are investigated. The first consists of Ru (4,7-diphenylphenanthroline) dichloride (Ruphen) and Coumarin-7 luminophores. The second coating contains Pt(II) meso-tetrakis (pentafluorophenyl) porphine (PtTFPP) and diethyloxadicarbocyanine iodide (DOCI). The principal component analysis revealed that the Ruphen/Coumarin-7 coating requires three fundamental spectra or modes to adequately model the coating emission characteristics. The PtTFPP/DOCI coating was modeled adequately with only two modes. Analysis of the PtTFFP/DOCI coating also revealed that a temperature independent calibration of the pressure sensing function could be developed. The requirement for a wind-off reference image was also eliminated.