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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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At least 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
NASA NTRS2004

Velocity and Temperature Measurement in Supersonic Free Jets Using Spectrally Resolved Rayleigh Scattering

The flow fields of unheated, supersonic free jets from convergent and convergent-divergent nozzles operating at M = 0.99, 1.4, and 1.6 were measured using spectrally resolved Rayleigh scattering technique. The axial component of velocity and temperature data as well as density data obtained from a previous experiment are presented in a systematic way with the goal of producing a database useful for validating computational fluid dynamics codes. The Rayleigh scattering process from air molecules provides a fundamental means of measuring flow properties in a non-intrusive, particle free manner. In the spectrally resolved application, laser light scattered by the air molecules is collected and analyzed using a Fabry-Perot interferometer (FPI). The difference between the incident laser frequency and the peak of the Rayleigh spectrum provides a measure of gas velocity. The temperature is measured from the spectral broadening caused by the random thermal motion and density is measured from the total light intensity. The present point measurement technique uses a CW laser, a scanning FPI and photon counting electronics. The 1 mm long probe volume is moved from point to point to survey the flow fields. Additional arrangements were made to remove particles from the main as well as the entrained flow and to isolate FPI from the high sound and vibration levels produced by the supersonic jets. In general, velocity is measured within +/- 10 m/s accuracy and temperature within +/- 10 K accuracy.

Panda, J.↗
NASA NTRS1982

Dynamic gas temperature measurement system

The development of an advanced measuring system which measures the rapidly varying gas temperature at the exit of an aircraft jet engine combustor during ground based testing of hot section components was identified. Sensor guidelines, technical approach/program schedule, and the accomplishments are reviewed. The environment of a present generation combustor is shown. The method uses two beadless junctions type-B thermocouples to measure heat transfer coefficient in situ. Heat conduction effects are shown by a finite element model of the thermocouple.

Elmore, D.↗
DOE OSTI2024

One-dimensional temperature measurement of supersonic jet flow by resonantly ionized photoemission thermometry of molecular nitrogen

As the field of fluid dynamics progresses, the demand for sophisticated diagnostic methods to accurately assess flow conditions rises. In this work, resonantly ionized photoemission thermometry (RIPT) has been used to directly target and ionize diatomic nitrogen (N 2 ) to measure one-dimensional (1D) temperature profiles in a supersonic jet flow. This technique can be considered non-intrusive as the premise uses resonantly enhanced multiphoton ionization (REMPI) to target molecular nitrogen. This resonance excites N 2 into absorption bands of the P, Q, and R rotational branches of N 2 ( b 1 Π u ). The ideal (3 + 1) REMPI scheme excites from the ground state and ionizes N 2 ( b 1 Π u ← X 1 Σ g + ) where de-excitation results in photoemission from the first negative band of ionized N 2 + ( B 2 Σ u + → X 2 Σ g + ) as nitrogen returns to the ground state. The resulting emission can be observed using an intensified camera, thus permitting inference of the rotational temperature of ground-state molecular nitrogen. A linearly regressive Boltzmann distribution is applied based on previous calibration data for this technique to quantify the temperature along the ionized line. This work applies this technique to a pure N 2 supersonic jet in cross-flow and counter-flow orientations to demonstrate N 2 RIPT’s applications in a supersonic flow. Temperature variations are observed at different locations downstream of the exit in cross-flow, and axisymmetric in counter-flow, to generate profiles characterizing the flow dynamics. Due to the collisional effects resulting from the number density of N 2 at higher pressures, a (3 + 2) REMPI scheme is observed throughout this text.

Clark, Aleksander (ORCID:0009000855600042)↗
NASA NTRS1973

Temperature measurements in sliding elastohydrodynamic point contacts

Techniques using the infrared radiation emitted by a sliding elastohydrodynamic (EHD) point contact to measure oil film and surface temperature are discussed. Temperature distributions in the EHD contact are presented for a naphthenic mineral oil at 1.04 GN/sq m (150,000 psi) Hertz pressure and several sliding velocities. Film temperatures as high as 360 C are reported at locations near the points of minimum film thickness in the contact side lobes.

Turchina, V.↗
NASA NTRS2005

Should We Believe Atmospheric Temperatures Measured by Entry Accelerometers Traveling at "Slow" Near-Sonic Speeds?

Mars Pathfinder's Accelerometer instrument measured an unexpected and large temperature inversion between 10 and 20 kilometer altitude. Other instruments have failed to detect similar temperature inversions. I test whether this inversion is real or not by examining what changes have to be made to the assumptions in the accelerometer data processing to obtain a more "expected" temperature profile. Changes in derived temperature of up to 30K, or 15%, are necessary, which correspond to changes in derived density of up to 25% and changes in derived pressure of up to 10%. If the drag coefficient is changed to satisfy this, then instead of decreasing from 1.6 to 1.4 from 20 kilometers to 10 kilometers, the drag coefficient must increase from 1.6 to 1.8 instead. If winds are invoked, then speeds of 60 meters per second are necessary, four times greater than those predicted. Refinements to the equation of hydrostatic equilibrium modify the temperature profile by an order of magnitude less than the desired amount. Unrealistically large instrument drifts of 0.5-1.0 meters per square second are needed to adjust the temperature profile as desired. However, rotational contributions to the accelerations may have the necessary magnitude and direction to make this correction. Determining whether this hypothesis is true will require further study of the rigid body equations of motion, with detailed knowledge of the positions of all six accelerometers. The paradox concerning this inversion is not yet resolved. It is important to resolve it because the paradox has some startling implications. At one extreme, are temperature profiles derived from accelerometers inherently inaccurate by 20K or more? At the other extreme, are RS temperature profiles inaccurate by this same amount?

Withers, Paul↗
NASA NTRS1968

Ultrasonic temperature measuring device

Pulse echo ultrasonic system automatically determines the temperature in the core of a nuclear rocket engine by measuring the transit time of an acoustic pulse in a wire sensor. The measurement is based on the fact that the speed of sound in the sensor material is a function of temperature.

Carnevale, E. H.↗
NASA NTRS1984

A sensitive optical pyrometer for shock-temperature measurements

A new optical system was used to determine temperatures above 2400 K in shocked materials by measuring the spectral radiance of sub-microsecond pulses of light emitted from initially transparent solid samples in the visible and near infrared (450 to 900 nm). The high sensitivity of this optical pyrometer is attributed to the small number of channels, large aperture (0.03 steradian), the large bandwidth per channel (40 nm), and large photodiode detection area (0.2 sq cm). Improved calibration techniques reduce systematic errors encountered in previous shock-temperature experiments.

Boslough, M. B.↗
NASA NTRS1968

Detection of effect of deposits on optical windows of pyrometer measurements

Temperatures measurements in an enclosed test chamber are more accurate when the reflectivity of the inner coated surface is compared to the outer clean surface of an optical window. Temperature readings are corrected by correlating the reflectivity of the deposits with their effect on the temperature measurement.

Cipolone, P.↗
NASA NTRS1987

Temperature measurement in a compressible flow field using laser-induced iodine fluorescence

The thermometric capability of a two-line fluorescence technique using iodine seed molecules in air is investigated analytically and verified experimentally in a known steady compressible flow field. Temperatures ranging from 165 to 295 K were measured in the flowfield using two iodine transitions accessed with a 30-GHz dye-laser scan near 543 nm. The effect of pressure broadening on temperature measurement is evaluated.

Fletcher, D. G.↗
NASA NTRS1987

Comparison of measured temperatures, thermal stresses and creep residues with predictions on a built-up titanium structure

Temperature, thermal stresses, and residual creep stresses were studied by comparing laboratory values measured on a built-up titanium structure with values calculated from finite-element models. Several such models were used to examine the relationship between computational thermal stresses and thermal stresses measured on a built-up structure. Element suitability, element density, and computational temperature discrepancies were studied to determine their impact on measured and calculated thermal stress. The optimum number of elements is established from a balance between element density and suitable safety margins, such that the answer is acceptably safe yet is economical from a computational viewpoint. It is noted that situations exist where relatively small excursions of calculated temperatures from measured values result in far more than proportional increases in thermal stress values. Measured residual stresses due to creep significantly exceeded the values computed by the piecewise linear elastic strain analogy approach. The most important element in the computation is the correct definition of the creep law. Computational methodology advances in predicting residual stresses due to creep require significantly more viscoelastic material characterization.

Jenkins, Jerald M.↗
DOE OSTI2022

Internal 2-D Surface Temperature Measurements for Large Complex Geometries

For 2D-temperature monitoring applications, a variant of EIT (Electrical Impedance Tomography) is evaluated computationally in this work. Literature examples of poor sensor performance in the center of the 2D domains away from the side electrodes motivated this study which seeks to overcome some of the previously noted shortcomings. In particular, the use of ‘sensing skins’ with novel tailored baseline conductivities were examined using the EIDORS package for EIT. It was found that the best approach for detecting a hot spot depends on several factors such as the current injection (stimulation) patterns, the measurement patterns, and the reconstruction algorithms. For a well-performing combination of these factors, tailored baseline conductivities were assessed and compared to the baseline uniform conductivity. It was discovered that for some EIT applications, a tailored distribution needs to be smooth and that sudden changes in the conductivity gradients should be avoided. Still, the benefits in terms of improved EIT performance were small for conditions for which the EIT measurements had been ‘optimized’ for the uniform baseline case. Within the limited scope of this study, only two specific cases showed benefits from tailored distributions. For one case, a smooth tailored distribution with increased baseline conductivity in the center provided a better separation of two centrally located hot spots. For another case, a smooth tailored distribution with reduced conductivity in the center provided better estimates of the magnitudes of two hot spots near the center of the sensing skin.

47 OTHER INSTRUMENTATION↗
NASA NTRS1990

Response of Venus exospheric temperature measured by neutral mass spectrometer to solar EUV flux measured by Langmuir probe on the Pioneer Venus orbiter

The photoelectron current from the Pioneer Venus Langmuir probe has provided measurements of the total flux of solar EUV photons at Venus since 1979. The neutral oxygen scale height measured by the orbiter neutral mass spectrometer has permitted the exospheric temperature to be derived during the same mission. In this paper, the EUV observations are used to examine the response of exospheric temperature to changes in solar activity, primarily those related to solar rotation. It is found that the dayside exospheric temperature quite faithfully tracks variations in the EUV flux. Comparison is also made with the earth-based solar activity index F10.7 adjusted to the position of Venus. This index varied from 142 to 249 flux units during the period of measurements. The exospheric temperature is better correlated with EUV flux than with the 10.7-cm solar radio flux.

Mahajan, K. K.↗