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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
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Infrared-sensor cells used for measuring partial pressures of CO(2) and other breathable gases modified to prevent entry of liquid water into sensory optical paths of cells. Hydrophobic membrane prevents drops of water entrained in flow from entering optical path from lamp to infrared detectors.
We present computations of the emission-line spectra produced when hot gas cools nonuniformly. During inhomogeneous cooling, soft X-ray/extreme ultraviolet radiation from 10(exp 5) to 10(exp 7) K gas photoionizes coexisting clouds that have already cooled to 10(exp 4) K. Thus, strong emission lines emerge from both the high-ionization cooling gas and embedded low-ionization knots. This mechanism, which ought to operate naturally within the sonic radii of cooling flows, can generate optical emission-line spectra similar to those observed at the centers of many clusters of galaxies thought to contain such flows. We have computed the X-ray, ultraviolet (UV), optical, and infrared (IR) emission-line fluxes expected under a variety of intracluster conditions so that the self-irradiation hypothesis can be compared thoroughly with observations. If this picture is found to be adequate, the models can also be used to measure mass flow rates and inflow velocities in the vicinities of cooling-flow nebulae and to constrain the column densities and covering factors of condensed material at the centers of these clusters.
This project, as described in the following report, involved design and fabrication of fiber optic sensors for the detection and measurement of dynamic fluid density variations. These devices are created using UV (ultraviolet) ablation and generally modified transverse holographic fiber grating techniques. The resulting phase gratings created on or immediately underneath the flat portion of D-shaped optical waveguides are characterized as evanescent field sensing devices. The primary applications include the sensor portion of a real-time localized or distributed measurement system for hydrodynamic flow, fluid density measurements, and phase change phenomena. Several design modifications were implemented in an attempt to accomplish the tasks specified in our original proposal. In addition, we have established key collaborative relationships with numerous people and institutions.
Recent developments in X-ray and hard X-ray imaging detector, high-intensity sources, hard X-ray imaging optics, calibration, and detection technologies are discussed. Particular attention is given to a high-MTF X-ray image intensifier, application of monolithic CdZnTe linear solid state ionization detectors for X-ray imaging, magnetic response of high-Tc superconductors to X-ray radiation and detection of X-rays, laboratory soft X-ray source with foil target, detection of explosive materials using nuclear radiation, energy response of astronomical CCD X-ray detectors, calibration techniques for high-flux X-ray detectors, fabrication of grazing-incidence optics using flow-polishing techniques, and numerical simulations for capillary-based X-ray optics. (No individual items are abstracted in this volume)
This paper summarizes a variety of optically based flow-visualization techniques used for high-speed research by the Configuration Aerodynamics Wind-Tunnel Test Team of the High-Speed Research Program during its tenure. The work of other national experts is included for completeness. Details of each technique with applications and status in various national wind tunnels are given.
The aero-optical effects associated with propagating a laser beam through both an aircraft turbulent boundary layer and artificially generated shear layers are examined. The data present comparisons from observed optical performance with those inferred from aerodynamic measurements of unsteady density and correlation lengths within the same random flow fields. Using optical instrumentation with tens of microsecond temporal resolution through a finite aperture, optical performance degradation was determined and contrasted with the infinite aperture time averaged aerodynamic measurement. In addition, the optical data were artificially clipped to compare to theoretical scaling calculations. Optical instrumentation consisted of a custom Q switched Nd:Yag double pulsed laser, and a holographic camera which recorded the random flow field in a double pass, double pulse mode. Aerodynamic parameters were measured using hot film anemometer probes and a five hole pressure probe. Each technique is described with its associated theoretical basis for comparison. The effects of finite aperture and spatial and temporal frequencies of the random flow are considered.
The scope of investigations conducted with coaxial interacting supersonic jet flows covers (1) acoustic measurements in both the far noise field and near noise field, (2) surveys of mean flow properties and fluctuating pressures, optical visualization of interacting jet flows, the associated flow and shock structure changes and the noise field, (3) the effects of different geometrical parameters of the coaxial nozzles, and (4) thrust measurements. It is shown that the flow interaction between two suitable controlled interacting coaxial supersonic axisymmetric jet flows results in substantial noise reduction based on equivalent thrust considerations. This flow interaction technique appears to be potentially an attractive approach for suppression of noise from supersonic jet exhausts.
The development of large space infrared optical systems, such as the Next Generation Space Telescope (NGST), has increased requirements for measurement accuracy in the optical properties of materials. Many materials used as optical components in infrared optical systems, have strong temperature dependence in their optical properties. Unfortunately, data on the temperature dependence of most of these materials is sparse. In this paper, we provide a description of the capabilities existing in the Optics Branch at the Goddard Space Flight Center that enable the characterization of the refractive index and absorption coefficient changes and other optical properties in infrared materials at cryogenic temperatures. Details of the experimental apparatus, which include continuous flow liquid helium optical cryostat, and a Fourier Transform Infrared (FTIR) spectrometer are discussed.
Microwave and optical measurements of decay of neutral metastable and charged species in flowing He afterglow
An experimental and numerical investigation of the thermochemical state of arcjet flows is currently being conducted at NASA Ames Research Center. The experimental approach relies on the use of laser- and emission-spectroscopic diagnostic techniques in three regions of the flow. A fiber optic sensor is used to record spectrally resolved emission signals from the electrode package region, where the flow is most likely to be in thermochemical equilibrium. A second emission diagnostic measurement is made in the shock layer formed over a blunt-body test article placed in the stream, and a CCD camera is used to simultaneously record spectral emission from several measurement locations along the stagnation streamline. Downstream of the nozzle exit, but upstream of the test article, Laser-Induced Fluorescence (LIF) of atomic nitrogen is used to assess the nonequilibrium distribution of flow enthalpy in the free stream. Results from the measurements are compared with predictions from a two-temperature, axisymmetric flow model that solves the nozzle and shock-layer flows.
The rotational relaxation of the He2(3p(3pi g)) state is examined by optically pumping a flowing helium afterglow with a tuneable dye laser. The population of the J = 8 rotational state is enhanced by optically saturating the R sub 7 component of the transition connecting this state with the metastable He2(2s (3 Sigma u +)) molecular state. From the lifetime and yield of the Q sub 7 component, the rate coefficient for the rotational relaxation via the forbidden delta J = 1 channel is determined to be of the order of 2 x 10 to the minus 11th power cm3/sec. It is found that this represents about half of the total rate of rotational relaxation in this state.
The Space Infrared Telescope Facility (SIRTF) Infrared Array Camera (IRAC) uses two dichroic beamsplitters, four bandpass filters, and four detector arrays to acquire images in four channels at wavelengths between 3 and 10 micron. Accurate knowledge of the pass bands is necessary because, in order to meet the science objectives, IRAC is required to do 2% relative photometry in each band relative to the other bands. We report the in-band and out-of-band polarized transmittance and reflectance of these optical elements measured near the instrument operating temperature of 1.4 K. Details of the experimental apparatus, which include a continuous flow liquid helium optical cryostat and a Fourier transform infrared (FTIR) spectrometer are discussed.
The number of optical techniques that may potentially be used during a given wind tunnel test is continually growing. These include parameter sensitive paints that are sensitive to temperature or pressure, several different types of off-body and on-body flow visualization techniques, optical angle-of-attack (AoA), optical measurement of model deformation, optical techniques for determining density or velocity, and spectroscopic techniques for determining various flow field parameters. Often in the past the various optical techniques were developed independently of each other, with little or no consideration for other techniques that might also be used during a given test. Recently two optical techniques have been increasingly requested for production measurements in NASA wind tunnels. These are the video photogrammetric (or videogrammetric) technique for measuring model deformation known as the video model deformation (VMD) technique, and the parameter sensitive paints for making global pressure and temperature measurements. Considerations for, and initial attempts at, simultaneous measurements with the pressure sensitive paint (PSP) and the videogrammetric techniques have been implemented. Temperature sensitive paint (TSP) has been found to be useful for boundary-layer transition detection since turbulent boundary layers convect heat at higher rates than laminar boundary layers of comparable thickness. Transition is marked by a characteristic surface temperature change wherever there is a difference between model and flow temperatures. Recently, additional capabilities have been implemented in the target-tracking videogrammetric measurement system. These capabilities have permitted practical simultaneous measurements using parameter sensitive paint and video model deformation measurements that led to the first successful unified test with TSP for transition detection in a large production wind tunnel.
A spectroscopic Doppler velocimetry technique has been developed for measuring two transverse components of velocity and hence streamwise vorticity in free jet flows. The nonintrusive optical measurement system uses Mie scattering from a 200 mW green continuous-wave laser interacting with dust and other tracer particulates naturally present in the air flow to measure the velocities. Scattered light is collected in two opposing directions to provide measurements of two orthogonal velocity components. An air-spaced Fabry-Perot interferometer is used for spectral analysis to determine the optical frequency shift between the incident laser light and the Mie scattered light. This frequency shift is directly proportional to the velocity component in the direction of the bisector of the incident and scattered light wave propagation vectors. Data were acquired for jet Mach numbers of 1.73 and 0.99 using a convergent 1.27-cm diameter round nozzle fitted with a single triangular "delta-tab". The velocity components and the streamwise vorticity calculated from the measurements are presented. The results demonstrate the ability of this novel optical system to obtain velocity and vorticity data without any artificial seeding and using a low power laser system.
The objectives are to obtain temperature, density and velocity profile measurements in the expansion region of low Reynolds number nozzles through the use of optical diagnostics. An LIF system will be used to probe the expansion of a microwave-heated expansion in the Center vacuum facility. The experimental measurements made in this program will be compared to numerical predictions obtained by Drs. Charles Merkle and Lyle Long.
This video supplements a report examining optical techniques for studying sonic and supersonic injection into MACH-3 flow The study used an injection-seeded, frequency doubled ND:YAG pulsed laser to illuminate a transverse section of the injectant plume. Rayleigh scattered light was passed through an iodine absorption cell to suppress stray laser light and was imaged onto a cooled CCD camera. The scattering was based on condensation of water vapor in the injectant flow. High speed shadowgraph flow visualization images were obtained with several video camera systems. Roof and floor static pressure data are presented several ways for the three configurations of injection designs with and without helium and/or air injection into Mach 3 flow.
Researchers are working on many konts to make possible high speed, automated classification and quantification of constituent materials in numerous environments. NASA's Marshall Space Flight Center has implemented a system for rocket engine flow fields/plumes; the Optical Plume Anomaly Detection (OPAD) system was designed to utilize emission and absorption spectroscopy for monitoring molecular and atomic particulates in gas plasma. An accompanying suite of tools and analytical package designed to utilize information collected by OPAD is known as the Engine Diagnostic Filtering System (EDIFIS). The current combination of these systems identifies atomic and molecular species and quantifies mass loss rates in H2/O2 rocket plumes. Additionally, efforts are being advanced to hardware encode components of the EDIFIS in order to address real-time operational requirements for health monitoring and management. This paper addresses the OPAD with its tool suite, and discusses what is considered a natural progression: a concept for migrating OPAD towards detection of high energy particles, including neutrons and gamma rays. The integration of these tools and capabilities will provide NASA with a systematic approach to monitor space vehicle internal and external environment.
In this paper we present an evaluation of critical requirements of organometallic chemical vapor deposition (OMCVD) at elevated pressure for a channel flow reactor in a microgravity environment. The objective of using high pressure is to maintain single-phase surface composition for materials that have high thermal decomposition pressure at their optimum growth temperature. Access to microgravity is needed to maintain conditions of laminar flow, which is essential for process analysis. Based on ground based observations we present an optimized reactor design for OMCVD at high pressure and reduced gravity. Also, we discuss non-intrusive real-time optical monitoring of flow dynamics coupled to homogeneous gas phase reactions, transport and surface processes. While suborbital flights may suffice for studies of initial stages of heteroepitaxy experiments in space are essential for a complete evaluation of steady-state growth.