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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 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

An eight-month climatology of marine stratocumulus cloud fraction, albedo, and integrated liquid water

As part of the FIRE/Extended Time Observations (ETO) program, extended time observations were made at San Nicolas Island (SNI) from March to October, 1987. Hourly averages of air temperature, relative humidity, wind speed and direction, solar irradiance, and downward longwave irradiance were recorded. The radiation sensors were standard Eppley pyranometers (shortwave) and pyrgeometers (longwave). The SNI data were processed in several ways to deduce properties of the stratocumulus covered marine boundary layer (MBL). For example, from the temperature and humidity the lifting condensation level, which is an estimate of the height of the cloud bottom, can be computed. A combination of longwave irradiance statistics can be used to estimate fractional cloud cover. An analysis technique used to estimate the integrated cloud liquid water content (W) and the cloud albedo from the measured solar irradiance is also described. In this approach, the cloud transmittance is computed by dividing the irradiance measured at some time by a clear sky value obtained at the same hour on a cloudless day. From the transmittance and the zenith angle, values of cloud albedo and W are computed using the radiative transfer parameterizations of Stephens (1978). These analysis algorithms were evaluated with 17 days of simultaneous and colocated mm-wave (20.6 and 31.65 GHz) radiometer measurements of W and lidar ceilometer measurements of cloud fraction and cloudbase height made during the FIRE IFO. The algorithms are then applied to the entire data set to produce a climatology of these cloud properties for the eight month period.

Fairall, C. W.↗
NASA NTRS1990

Optical properties of marine stratocumulus clouds modified by ship track effluents

The angular distribution of scattered radiation deep within a cloud layer was measured in marine stratocumulus clouds modified by the emissions from ships. These observations, obtained at thirteen discrete wavelengths between 0.5 and 2.3 microns, were obtained as the University of Washington Convair C-131A aircraft flew through a pair of roughly parallel ship tracks off the coast of southern California on 10 July 1987. In the first of these ship tracks, the cloud droplet concentration increased from 40 to 107/cu cm (125/cu cm in the second ship track). Simultaneous to this spectacular change, the aircraft measured interstitial aerosol (Aitken nucleus) concentration that increased from 400 to 1000/cu cm and cloud liquid water content that increased from 0.03 to 0.75 g/cu m. Broadband pyranometer measurements showed that the upwelling flux density increased from 150 to 280 W/sq m. These in-situ microphysics and broadband pyranometer results, together with AVHRR satellite images obtained with the NOAA-10 satellite, are described in detail by Radke et al., (1989). Internal scattered radiation measurements at selected wavelengths obtained with the cloud absorption radiometer (King et al., 1986) for a 100 km section of marine stratocumulus clouds containing these two ship track features are presented.

King, Michael D.↗
NASA NTRS1989

Climate stability and cloud optical thickness feedbacks

An improved radiative-convective model (RCM) has been developed and used to examine the role of cirrus clouds in the optical thickness feedback mechanism. Low and middle clouds are approximately black bodies for infrared radiative transfer, and so any increase in their optical thickness primarily increases the cloud albedo. Thus, if a climate warming is accompanied by an increase in average atmospheric absolute humidity and hence in average cloud liquid water content, low and middle cloud optical thickness and albedo may increase. The result is a negative feedback on the climate change, tending to reduce the surface temperature increase. Recent research suggests that the optical thickness feedback can depend sensitively on aspects of cirrus which are not well observed or adequately incorporated in typical present-day climate models.

Somerville, Richard C. J.↗
NASA NTRS1990

Development of a phase Doppler based probe for icing cloud droplet characterization

The development and evaluation of a compact optical fiber probe (OFP) for airborne and wind tunnel icing cloud characterizations is described. This probe was based upon the proven phase Doppler technique for measuring the size and velocity of spherical drops. Direct comparisons of the size distributions from the standard PDPA with the OFP were used to confirm the reliability of the probe. After some improvements in the fiber coupling efficiency, the number density and liquid water content data agreed to within 15 percent.

Rudoff, R. C.↗
NASA NTRS1990

Model test of CCN-cloud albedo climate forcing

Cloud condensation nuclei (CCN) influence cloud albedo through their effect on the cloud droplet size distribution. A number of studies have evaluated the climatic impact of the CCN-cloud albedo feedback, but all have assumed that cloud distributions, cloud thicknesses, and cloud liquid water contents would remain constant as the climate adjusted. This assumption has been tested using the Livermore version of the National Center for Atmospheric Research Community Climate Model. The results indicate that there are no significant compensating changes in cloud properties that would counteract the 1.7 percent global albedo increase resulting from a fourfold increase in marine CCN concentration. Furthermore, when ocean surface temperatures are decreased 4 C in a manner broadly consistent with the enhanced cloud albedos, an increase in cloud fraction of 3.5 percent and a reduction in cloud altitude are predicted, leading to a positive feedback from clouds that would imply a climate impact roughly double that calculated from cloud droplet size distribution change alone.

Ghan, S. J.↗
NASA NTRS1990

Estimating integrated cloud liquid water from extended time observations of solar irradiance

An analysis technique used to estimate the integrated liquid water content (LWC) from the measured solar irradiance is described. The cloud transmittance is computed by dividing the irradiance measured at some time by a clear sky value obtained at the same time on a cloudless day. From the transmittance and the zenith angle, the cloud LWC is computed using the radiative transfer parameterizations of Stephens et al., (1984). The results are compared with 17 days of mm-wave (20.6 and 31.65 GHz) radiometer measurements made during the First ISCCP Regional Experiment (FIRE) Intensive Field Observation (IFO) in July of 1987.

Fairall, C. W.↗
NASA NTRS1990

Thermodynamic structure of the stratocumulus-capped boundary layer on 5 July 1987

The National Center for Atmospheric Research (NCAR) Electra flew a single aircraft mission on July 5 in comparatively uniform stratocumulus cloud (80 to 100 percent cloud coverage). The flight pattern, a series of north-south doglegs centered at (32N, -122W), included 15 full or partial soundings to examine layer vertical structure between altitudes of 150 and 5000 m. The air below the inversion was well-mixed in moist static energy, total water, and ozone. The inversion base measured by the aircraft ranged from 920 to 938 hPa, while the thickness of the cloud layer varied between 30 and 10 hPa. Maximum cloud liquid water contents approached 0.3 g kg(-1) (as measured by the Johnson-Williams and King probes). Comparison of soundings made in the same location show a strengthening of the inversion and increasing shear at cloud top over the observation period (16:50 to 00:22 UT). Typical windspeeds below the inversion were approximately 10 m s(-1) decreasing to 6 m s(-1) 8 hPa above cloud top. A thermodynamic budget for this case is in preparation; it will provide a comparison and contrast with the more complicated July 7 case.

Austin, Philip H.↗
NASA NTRS1991

A review of ice accretion data from a model rotor icing test and comparison with theory

An experiment was conducted by the Helicopter Icing Consortium (HIC) in the NASA Lewis Icing Research Tunnel (IRT) in which a 1/6 scale fuselage model of a UH-60A Black Hawk helicopter with a generic rotor was subjected to a wide range of icing conditions. The HIC consists of members from NASA, Bell Helicopter, Boeing Helicopter, McDonnell Douglas Helicopters, Sikorsky Aircraft, and Texas A&M University. Data was taken in the form of rotor torque, internal force balance measurements, blade strain gage loading, and two dimensional ice shape tracings. A review of the ice shape data is performed with special attention given to repeatability and correctness of trends in terms of radial variation, rotational speed, icing time, temperature, liquid water content, and volumetric median droplet size. Moreover, an indepth comparison between the experimental data and the analysis of NASA's ice accretion code LEWICE is given. Finally, conclusions are drawn as to the quality of the ice accretion data and the predictability of the data base as a whole. Recommendations are also given for improving data taking technique as well as potential future work.

Britton, Randall K.↗
NASA NTRS1991

Results of a sub-scale model rotor icing test

A heavily instrumented sub-scale model of a helicopter main rotor was tested in the NASA Lewis Research Center Icing Research Tunnel (IRT) in September and November 1989. The four-bladed main rotor had a diameter of 1.83 m (6.00 ft) and the 0.124 m (4.9 in) chord rotor blades were specially fabricated for this experiment. The instrumented rotor was mounted on a Sikorsky Aircraft Powered Force Model, which enclosed a rotor balance and other measurement systems. The model rotor was exposed to a range of icing conditions that included variations in temperature, liquid water content, and median droplet diameter, and was operated over ranges of advance ratio, shaft angle, tip Mach number (rotor speed) and weight coefficient to determine the effect of these parameters on ice accretion. In addition to strain gage and balance data, the test was documented with still, video, and high speed photography, ice profile tracings, and ice molds. The sensitivity of the model rotor to the test parameters, is given, and the result to theoretical predictions are compared. Test data quality was excellent, and ice accretion prediction methods and rotor performance prediction methods (using published icing lift and drag relationships) reproduced the performance trends observed in the test. Adjustments to the correlation coefficients to improve the level of correlation are suggested.

Flemming, Robert J.↗
NASA NTRS1991

Prediction of ice shapes and their effect on airfoil performance

Calculations of ice shapes and the resulting drag increases are presented for experimental data on a NACA 0012 airfoil. They were made with a combination of LEWICE and interactive boundary-layer codes for a wide range of conditions which include air speed and temperature, the droplet size and liquid water content of the cloud, and the angle of attack of the airfoil. In all cases, the calculated results account for the drag increase due to ice accretion and, in general, show good agreement.

Shin, Jaiwon↗
NASA NTRS1991

Model rotor icing tests in the NASA Lewis icing research tunnel

Tests of a lightly instrumented two-bladed teetering rotor and a heavily instrumented sub-scale articulated main rotor were conducted in the NASA Lewis Research Center Icing Research Tunnel (IRT) in August 1988 and September and November 1989. The first was an OH-58 tail rotor which had a diameter of 1.575 m and a blade chord of 0.133 m, and was mounted on a NASA designed test rig. The second, a four bladed articulated rotor, had a diameter of 1.83 m with 0.124 m chord blades specially fabricated for the experiment. This rotor was mounted on a Sikorsky Aircraft Powered Force Model, which enclosed a rotor balance and other measurement systems. The models were exposed to variations in temperature, liquid water content, and medium droplet diameter, and were operated over ranges of advance ratio, shaft angle, tip Mach number (rotor speed), and weight coefficient to determine the effect of these parameters on ice accretion. In addition to strain gage and balance data, the test was documented with still, video, and high speed photography, ice profile tracing, and ice molds. Presented here are the sensitivity of the model rotors to the test parameters and a comparison of the results to theoretical predictions.

Flemming, Robert J.↗
NASA NTRS1990

Icing tests of a model main rotor

A NASA-sponsored consortium conducted an experimental program to investigate the characteristics of a model rotor under icing conditions. This project resulted in the first U.S. test of a heavily instrumented model rotor conducted in the controlled environment of a refrigerated wind tunnel, the NASA Lewis Icing Research Tunnel. The tunnel entry used a powered force model with a 1.83-m-diameter main rotor, with 0.124-m-chord main rotor blades fabricated specially for this experiment. Test conditions included a range of liquid water content and median volume droplet diameters that fell within the FAA and DOD icing envelopes. The test data show the effects of icing on rotor lift, rotor torque, blade loads, and vibration. Ice shapes and ice dimensions were taken, and molds were made of three ice shapes. High-speed movies were taken to document ice shedding. The results have been compared with analytical accretion predictions.

Bond, Thomas H.↗
NASA NTRS1991

A review of ice accretion data from a model rotor icing test and comparison with theory

An experiment was conducted by the Helicopter Icing Consortium (HIC) in the NASA Lewis Icing Research Tunnel (IRT) in which a 1/6 scale fuselage model of a UH-60A Black Hawk helicopter with a generic rotor was subjected to a wide range of icing conditions. The HIC consists of members from NASA, Bell Helicopter, Boeing Helicopter, McDonnell Douglas Helicopters, Sikorsky Aircraft, and Texas A&M University. Data was taken in the form of rotor torque, internal force balance measurements, blade strain gage loading, and two dimensional ice shape tracings. A review of the ice shape data is performed with special attention given to repeatability and correctness of trends in terms of radial variation, rotational speed, icing time, temperature, liquid water content, and volumetric median droplet size. Moreover, an indepth comparison between the experimental data and the analysis of NASA's ice accretion code LEWICE is given. Finally, conclusions are shown as to the quality of the ice accretion data and the predictability of the data base as a whole. Recommendations are also given for improving data taking technique as well as potential future work.

Britton, Randall K.↗
NASA NTRS1991

Results of a sub-scale model rotor icing test

A heavily instrumented sub-scale model of a helicopter main rotor was tested in the NASA Lewis Research Center Icing Research Tunnel (IRT) in September and November 1989. The four-bladed main rotor had a diameter of 1.83 m (6.00 ft) and the 0.124 m (4.9 in) chord rotor blades were specially fabricated for this experiment. The instrumented rotor was mounted on a Sikorsky Aircraft Powered Force Model, which enclosed a rotor balance and other measurement systems. The model rotor was exposed to a range of icing conditions that included variations in temperature, liquid water content, and median droplet diameter, and was operated over ranges of advance ratio, shaft angle, tip Mach number (rotor speed) and weight coefficient to determine the effect of these parameters on ice accretion. In addition to strain gage and balance data, the test was documented with still, video, and high speed photography, ice profile tracings, and ice molds. The sensitivity of the model rotor to the test parameters is given, and the result to theoretical predictions are compared. Test data quality was excellent, and ice accretion prediction methods and rotor performance prediction methods (using published icing lift and drag relationships) reproduced the performance trends observed in the test. Adjustments to the correlation coefficients to improve the level of correlation are suggested.

Flemming, Robert J.↗
NASA NTRS1991

Prediction of ice shapes and their effect on airfoil performance

Calculations of ice shapes and the resulting drag increases are presented for experimental data on an NACA 0012 airfoil. They were made with a combination of LEWICE and interactive boundary-layer codes for a wide range of conditions which include airspeed and temperature, the droplet size and liquid water content of the cloud, and the angle of attack of the airfoil. In all cases the calculated results account for the drag increase due to ice accretion and, in general, show good agreement with data.

Shin, Jaiwon↗
NASA NTRS1991

The science benefits of and the antenna requirements for microwave remote sensing from geostationary orbit

The primary objective of the Large Space Antenna (LSA) Science Panel was to evaluate the science benefits that can be realized with a 25-meter class antenna in a microwave/millimeter wave remote sensing system in geostationary orbit. The panel concluded that a 25-meter or larger antenna in geostationary orbit can serve significant passive remote sensing needs in the 10 to 60 GHz frequency range, including measurements of precipitation, water vapor, atmospheric temperature profile, ocean surface wind speed, oceanic cloud liquid water content, and snow cover. In addition, cloud base height, atmospheric wind profile, and ocean currents can potentially be measured using active sensors with the 25-meter antenna. Other environmental parameters, particularly those that do not require high temporal resolution, are better served by low Earth orbit based sensors.

Stutzman, Warren L.↗
NASA NTRS1991

Model rotor icing tests in the NASA. Lewis Icing Research Tunnel

Tests of a lightly instrumented two bladed teetering rotor and a heavily instrumented subscale articulated main rotor were conducted in the NASA Lewis Icing Research Tunnel (IRT). The first was an OH-58 tail rotor which had a diameter of 1.575 m and a blade chord of 0.133 m, and was mounted on a NASA designed test rig. The second, a four bladed articulated rotor, had a diameter of 1.83 m with 0.124 m chord blades specifically fabricated for the experiment. This rotor was mounted on a Sikorsky Aircraft Powered Force Model, which enclosed a rotor balance and other measurement systems. The models were exposed to variations in temperature, liquid water content, and medium droplet diameter, and were operated over ranges of advance ratio, shaft angle, tip Mach number (rotor speed), and weight coefficient to determine the effect of these parameters on ice accretion. In addition to strain gage and balance data, the test was documented with still, video, and high speed photography, ice profile tracing, and ice molds. The sensitivity is presented of the model rotors to the test parameter and a comparison of the results to theoretical predictions.

Flemming, Robert J.↗
NASA NTRS1992

Experimental study of performance degradation of a rotating system in the NASA Lewis RC icing tunnel

The Helicopter Icing Consortium (HIC) conducted one of the first U.S. tests of a heavily instrumented model in the controlled environment of a refrigerated tunnel. In the Icing Research Tunnel (IRT) at NASA LeRC, ice was accreted on the main rotor blade of the BMTR-1 Sikorsky model helicopter under a variety of environmental conditions, such that liquid water content (LWC) and volume mean droplet diameter (VMD) ranges reflected the Federal Aviation Agency and Department of Defence icing condition envelopes. This report gives the correlated results of the data provided by NASA LeRC. The method of statistical analysis is discussed. Lift, thrust, and torque coefficients are presented as a function of icing time, as correlated with changes in ambient temperature, LWC, and VMD. The physical significance of these forces is discussed.

Korkan, Kenneth↗