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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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NASA NTRS2019

Convective Entrainment Rates Estimated from Aura CO and CloudSat/CALIPSO Observations and Comparison with GEOS-5

Entrainment rate (λ) in convective parameterizations remains a sensitive parameter with much uncertainty in model simulations. This study estimates λ using carbon monoxide (CO) measurements jointly from the Microwave Limb Sounder (MLS) and Tropospheric Emission Spectrometer (TES) onboard the Aura satellite, associated with deep convective cases identified by CloudSat and CALIPSO observations. CO is treated as a conserved quantity over convective transport time scales and a simple entraining-plume model is used to derive entrainment rates. The relationships of the observational estimates of λ as a function of convective height, environmental relative humidity and convective available potential energy (CAPE) derived from Atmospheric Infrared Sounder (AIRS) data are compared with those from Goddard Earth Observing System Model (GEOS-5) simulations. Bulk statistics of λ show that the values of λ are predominately below 20% km(exp-1) for deep convection and the occurrence frequency of any λ decreases with increasing λ. Composite λ values are generally lower in the tropics compared to northern mid-latitudes in both observations and the GEOS-5 model. A decrease of λ with increasing convective height is found in both observations and model simulations. We also find that λ tends to decrease with increasing CAPE in the observation-based λ’s and plume-based GEOS-5 λ’s, although the model given λ’s have a non-monotonic relation with CAPE. The observed λ’s have a weak relation with lower-to-mid tropospheric RH, while both GEOS-5 plume-based and given λ increases with increasing RH.

Ryan E Stanfield↗
NASA NTRS2022

Dilution of Boundary Layer Cloud Condensation Nucleus Concentrations by Free Tropospheric Entrainment During Marine Cold Air Outbreaks

Recent aircraft measurements over the northwest Atlantic enable an investigation of how entrainment from the free troposphere (FT) impacts cloud condensation nucleus (CCN) concentrations in the marine boundary layer (MBL) during cold-air outbreaks (CAOs), motivated by the role of CCN in mediating transitions from closed to open-cell regimes. Observations compiled over eight flights indicate predominantly far lesser CCN concentrations in the FT than in the MBL. For one flight, a fetch-dependent MBL-mean CCN budget is compiled from estimates of sea-surface fluxes, entrainment of FT air, and hydrometeor collision-coalescence, based on in-situ and remote-sensing measurements. Results indicate a dominant role of FT entrainment in reducing MBL CCN concentrations, consistent with satellite-observed trends in droplet number concentration upwind of CAO cloud-regime transitions over the northwest Atlantic. Relatively scant CCN may widely be associated with FT dry intrusions, and should accelerate cloud-regime transitions where underlying MBL air is CCN-rich, thereby reducing regional albedo.

Boundary Layer Cloud Condensation Nucleus Concentr↗
NASA NTRS1972

Analysis of an entrainment model of the jet in a crossflow

A theoretical model has been proposed for the problem of a round jet in an incompressible cross-flow. The method of matched asymptotic expansions has been applied to this problem. For the solution to the flow problem in the inner region, the re-entrant wake flow model was used with the re-entrant flow representing the fluid entrained by the jet. Higher order corrections are obtained in terms of this basic solution. The perturbation terms in the outer region was found to be a line distribution of doublets and sources. The line distribution of sources represents the combined effect of the entrainment and the displacement.

Chang, H. S.↗
NASA NTRS1978

Prediction of nearfield jet entrainment by an interactive mixing/afterburning model

The development of a computational model (BOAT) for calculating nearfield jet entrainment, and its application to the prediction of nozzle boattail pressures, is discussed. BOAT accounts for the detailed turbulence and thermochemical processes occurring in the nearfield shear layers of jet engine (and rocket) exhaust plumes while interfacing with the inviscid exhaust and external flowfield regions in an overlaid, interactive manner. The ability of the model to analyze simple free shear flows is assessed by detailed comparisons with fundamental laboratory data. The overlaid methodology and the entrainment correction employed to yield the effective plume boundary conditions are assessed via application of BOAT in conjunction with the codes comprising the NASA/LRC patched viscous/inviscid model for determining nozzle boattail drag for subsonic/transonic external flows. Comparisons between the predictions and data on underexpanded laboratory cold air jets are presented.

Dash, S. M.↗
NASA NTRS1978

A computational model for the prediction of jet entrainment in the vicinity of nozzle boattails (the BOAT code)

The development of a computational model (BOAT) for calculating nearfield jet entrainment, and its incorporation in an existing methodology for the prediction of nozzle boattail pressures, is discussed. The model accounts for the detailed turbulence and thermochemical processes occurring in the mixing layer formed between a jet exhaust and surrounding external stream while interfacing with the inviscid exhaust and external flowfield regions in an overlaid, interactive manner. The ability of the BOAT model to analyze simple free shear flows is assessed by comparisons with fundamental laboratory data. The overlaid procedure for incorporating variable pressures into BOAT and the entrainment correction employed to yield an effective plume boundary for the inviscid external flow are demonstrated. This is accomplished via application of BOAT in conjunction with the codes comprising the NASA/LRC patched viscous/inviscid methodology for determining nozzle boattail drag for subsonic/transonic external flows.

Dash, S. M.↗
NASA NTRS1981

Entrainment and thrust augmentation in pulsatile ejector flows

This study comprised direct thrust measurements, flow visualization by use of a spark shadowgraph technique, and mean and fluctuating velocity measurements with a pitot tube and linearized constant temperature hot-wire anemometry respectively. A gain in thrust of as much as 10 to 15% was observed for the pulsatile ejector flow as compared to the steady flow configuration. From the velocity profile measurements, it is concluded that this enhanced augmentation for pulsatile flow as compared to a nonpulsatile one was accomplished by a corresponding increased entrainment by the primary jet flow. It is also concluded that the augmentation and total entrainment by a constant area ejector critically depends upon the inlet geometry of the ejector. Experiments were performed to evaluate the influence of primary jet to ejector area ratio, ejector length, and presence of a diffuser on pulsatile ejector performance.

Sarohia, V.↗
NASA NTRS1984

Problems with the process partitioning theory of stratocumulus entrainment

Three different approaches to partitioning were proposed. Ball (1960), Lilly (1968), and Deardorff et al. (1969, 1974) considered the sign of the net buoyancy flux at each level. If the net flux is positive, it is counted as TKE producing; otherwise, it is counted as TKE consuming. This approach can be called Eulerian partitioning. The second approach can be called process partitioning. It is assumed that the various processes acting in concert each produce and consume the same energy as if they acted independently (Manins and Turner, 1978). The total rates of TKE production and consumption are obtained by summing the effects of all the forcing processes. The third approach is Lagrangian partitioning. Each air parcel is considered as either producing or consuming TKE, according to the sign of the product of its density and vertical velocity anomalies. Stage and Businger (1981a,b) have applied process partitioning to the cloud topped mixed layer. One of the most important processes influencing entrainment into such a layer is cloud top radiative cooling. The production and consumption due to entrainment and radiative cooling are thus closely related. Model results are sensitive to the choice of formulation.

Randall, D. A.↗
NASA NTRS1985

Entrainment region phenomena for a large plane shear layer

The subatmospheric test section of the present free shear layer facility allows the entrainment air to be introduced with a negligible disturbance level. The very low frequency oscillations, which are prominently observed in the entrainment stream and which are present throughout the shear layer, are attributed to an inherent instability in the transition from a boundary layer to a free shear layer state. The basic features of the disturbance field are documented herein.

Ali, S. K.↗
NASA NTRS1989

A parameterization of the depth of the entrainment zone

A theory of the parameterization of the entrainment zone depth has been developed based on conservation of energy. This theory suggests that the normalized entrainment zone depth is proportional to the inverse square root of the Richardson number. A comparison of this theory with atmospheric observations indicates excellent agreement. It does not adequately predict the laboratory data, although it improves on parcel theory, which is based on a momentum balance.

Boers, Reinout↗
NASA NTRS1989

Ozone conservation and entrainment in cumulus congestus

This study demonstrates that ozone mixing ratio is conserved during moist convection and can be used as a tracer for cloud entrainment studies. The approach is to apply mixing line analysis to pairs of liquid water potential temperature, total water mixing ratio, O3 and pseudo-equivalent potential temperature derived from aircraft penetrations of growing cumulus congestus. Conclusions about entrainment from the mixing diagrams employing O3 agree with those using thermodynamic quantities. Any disagreement uncovered deficiencies in the water substance measurement technique.

Pearson, R., Jr.↗
NASA NTRS1989

Saltation thresholds and entrainment of fine particles at Earth and Martian pressures

An open circuit wind tunnel designed to operate in a large vacuum chamber was built at NASA-Ames to investigate saltation threshold, flux, deflation rates, and other aeolian phenomena on the planet Mars. The vacuum chamber will operate at pressures as low as 4 mbar, and the tunnel operates at windspeeds as high as 150 m/sec. Either air or CO2 can be used as a working fluid. It was found that, to a first order approximation, the same dynamic pressure was required at Martian pressure to entrain or saltate particles as was required on Earth, although wind and particle speed are considerably higher at Martian pressure. A 2nd wind tunnel, designed to operate aboard the NASA KC-135 0-g aircraft to obtain information on the effect of gravity on saltation threshold and the interparticle force at 0-g, is also described and test data presented. Some of the experiments are summarized and various aspects of low pressure aeolian entrainment for particles 12 to 100 micron in diameter are discussed, some of them unique to low pressure testing and some common in Earth pressure particle transport testing. The facility, the modes of operation, and the materials used are described.

Leach, Rodman↗
NASA NTRS1993

Breaking Kelvin-Helmholtz waves and cloud-top entrainment as revealed by K-band Doppler radar

Radars have occasionally detected breaking Kelvin-Helmholtz (KH) waves under clear-air conditions in the atmospheric boundary layer and in the free troposphere. However, very few direct measurements of such waves within clouds have previously been reported and those have not clearly documented wave breaking. In this article, we present some of the most detailed and striking radar observations to date of breaking KH waves within clouds and at cloud top and discuss their relevance to the issue of cloud-top entrainment, which is believed to be important in convective and stratiform clouds. Aircraft observations reported by Stith suggest that vortex-like circulations near cloud top are an entrainment mechanism in cumuliform clouds. Laboratory and modeling studies have examined possibility that KH instability may be responsible for mixing at cloud top, but direct observations have not yet been presented. Preliminary analyses shown here may help fill this gap. The data presented in this paper were obtained during two field projects in 1991 that included observations from the NOAA Wave Propagation Laboratory's K-band Doppler radar (wavelength = 8.7 mm) and special rawinsonde ascents. The sensitivity (-30 dBZ at 10 km range), fine spatial resolution (375-m pulse length and 0.5 degrees beamwidth), velocity measurement precision (5-10 cm s-1), scanning capability, and relative immunity to ground clutter make it sensitive to non-precipitating and weakly precipitating clouds, and make it an excellent instrument to study gravity waves in clouds. In particular, the narrow beam width and short pulse length create scattering volumes that are cylinders 37.5 m long and 45 m (90 m) in diameter at 5 km (10 km) range. These characteristics allow the radar to resolve the detailed structure in breaking KH waves such as have been seen in photographic cloud images.

Martner, Brooks E.↗
NASA NTRS1998

A Quantitative Investigation of Entrainment and Detrainment in Numerically Simulated Convective Clouds: Model Development - Pt. 1

A method is developed which uses numerical tracers to make accurate diagnoses of entraimnent and detrainment rates and of the properties of the entrained and detrained air in numerically simulated clouds. The numerical advection scheme is modified to make it nondispersive, as required by the use of the tracers. Tests of the new method are made, and an appropriate definition of clouds is selected. Distributions of mixing fractions in the model consistently show maximums at the end points, for nearly undilute environmental air or nearly undilute cloud air, with a uniform distribution between. The cumulonimbus clouds simulated here entrain air that had been substantially changed by the clouds, and detrained air that is not necessarily representative of the cloud air at the same level.

Cohen, Charles↗
NASA NTRS2000

Dry Air Entrainment into Hurricane Earl

Hurricane Earl formed in the Gulf of Mexico in September 1998. It quickly was upgraded from a tropical disturbance to tropical storm status and then to a hurricane. Earl possessed hybrid (tropical and extratropical) characteristics throughout its lifetime. The system maintained and erratic track, which led to wide variability in the operational track forecasts. It eventually made landfall on the Florida panhandle on 2 September and raced northeastward. During August and September 1998, NASA conducted the third Convection and Moisture Experiment (CAMEX-3). The experiment was focused on studying hurricanes with an emphasis toward developing a better understanding of their intensification and motion. Earl provides a unique opportunity to utilize high spatial and temporal resolution data collected from the DC-8 and high altitude ER-2 NASA platforms, which flew over Earl as it made landfall. These data can also be put into broader view provided by other instruments from the Geosychronous Operational Environmental Satellites (GOES) and the Tropical Rainfall Measuring Mission (TRMM) satellites. Hurricane Earl was affected by entrainment of dry air from the northwest. Hurricane Isis was intensifying and approaching the Mexican Pacific coast with its associated outflow potentially affecting the inflow into Earl as the storm neared Florida. In addition, a longwave synoptic trough circulation was present over the eastern U.S. Either or both of these could be responsible for the dry air into the system. This paper will focus on identifying the source of the dry by using upper-level wind and moisture fields derived from the GOES 6.7 um water vapor imagery. We will attempt to relate the large-scale observations to those from the NASA aircraft. An infrared instrument onboard the ER-2 also has a similar wavelength and may be able to confirm some of the GOES findings. In addition, a microwave radiometer with 4 channels focused on measuring precipitation and its associated ice scattering was also aboard the ER-2. The microwave observations will allow the authors to relate the entrainment to precipitation changes near the flight path of the aircraft.

Guillory, Anthony R.↗
NASA NTRS1999

Entrainment of Upper Level Dry Air Into Hurricane Earl

Hurricane Earl formed in the Gulf of Mexico in September 1998. It quickly was upgraded from a tropical disturbance to tropical storm status and then to a hurricane. Earl possessed hybrid (tropical and extratropical) characteristics throughout its lifetime. The system maintained and erratic track, which led to wide variability in the operational track forecasts. It eventually made landfall on the Florida panhandle on 2 September and raced northeastward. During August and September 1998, NASA conducted the third Convection and Moisture Experiment (CAMEX-3). The experiment was focused on studying hurricanes with an emphasis toward developing a better understanding of their intensification and motion. Earl provides a unique opportunity to utilize high spatial and temporal resolution data collected from the DC-8 and high altitude ER-2 NASA platforms, which flew over Earl as it made landfall. These data can also be put into broader view provided by other instruments from the Geosynchronous Operational Environmental Satellites (GOES) and the Tropical Rainfall Measuring Mission (TRMM) satellites. Hurricane Earl was affected by entrainment of dry air from the northwest. Hurricane Isis was intensifying and approaching the Mexican Pacific coast with its associated outflow potentially affecting the inflow into Earl as the storm neared Florida. In addition, a longwave synoptic trough circulation was present over the eastern U.S. Either or both of these could be responsible for the dry air into the system. This paper will focus on identifying the source of the dry by using upper-level wind and moisture fields derived from the GOES 6.7 um water vapor imagery. We will attempt to relate the large-scale observations to those from the NASA aircraft. An infrared instrument onboard the ER-2 also has a similar wavelength and may be able to confirm some of the GOES findings. In addition, a microwave radiometer with 4 channels focused on measuring precipitation and its associated ice scattering was also aboard the ER-2. The microwave observations will allow the authors to relate the entrainment to precipitation changes near the flight path of the aircraft.

Guillory, Anthony R.↗
NASA NTRS2012

A FIRE-ACE/SHEBA Case Study of Mixed-Phase Arctic Boundary Layer Clouds: Entrainment Rate Limitations on Rapid Primary Ice Nucleation Processes

Observations of long-lived mixed-phase Arctic boundary layer clouds on 7 May 1998 during the First International Satellite Cloud Climatology Project (ISCCP) Regional Experiment (FIRE)Arctic Cloud Experiment (ACE)Surface Heat Budget of the Arctic Ocean (SHEBA) campaign provide a unique opportunity to test understanding of cloud ice formation. Under the microphysically simple conditions observed (apparently negligible ice aggregation, sublimation, and multiplication), the only expected source of new ice crystals is activation of heterogeneous ice nuclei (IN) and the only sink is sedimentation. Large-eddy simulations with size-resolved microphysics are initialized with IN number concentration N(sub IN) measured above cloud top, but details of IN activation behavior are unknown. If activated rapidly (in deposition, condensation, or immersion modes), as commonly assumed, IN are depleted from the well-mixed boundary layer within minutes. Quasi-equilibrium ice number concentration N(sub i) is then limited to a small fraction of overlying N(sub IN) that is determined by the cloud-top entrainment rate w(sub e) divided by the number-weighted ice fall speed at the surface v(sub f). Because w(sub c)< 1 cm/s and v(sub f)> 10 cm/s, N(sub i)/N(sub IN)<< 1. Such conditions may be common for this cloud type, which has implications for modeling IN diagnostically, interpreting measurements, and quantifying sensitivity to increasing N(sub IN) (when w(sub e)/v(sub f)< 1, entrainment rate limitations serve to buffer cloud system response). To reproduce observed ice crystal size distributions and cloud radar reflectivities with rapidly consumed IN in this case, the measured above-cloud N(sub IN) must be multiplied by approximately 30. However, results are sensitive to assumed ice crystal properties not constrained by measurements. In addition, simulations do not reproduce the pronounced mesoscale heterogeneity in radar reflectivity that is observed.

Fridlin, Ann↗
NASA NTRS2022

Light in Ecological Settings: Entrainment, Circadian Disruption, and Interventions

Light is the predominant signal for the human circadian clock to synchronize to the solar 24-h day through an active process called entrainment. Modern light profiles are characterized by exposure to both natural daylight and artificial lighting. A mismatch between these self-selected light profiles and the solar day-night alternation can disrupt the circadian system, resulting in acute and chronic effects for health and safety. In this chapter, we describe (i) how entrainment works in the real world, illustrating the major role of light for this process; (ii) ways in which the circadian system can be disrupted by (external) factors such as irregular sleep, shift work, daylight saving time, and longitudinal position in a time zone; and (iii) how field studies have used light interventions to reduce direct and indirect effects of circadian disruption in ecological settings.

light interventions↗