scholarly journals Theoretical and Experimental Characterization of the Ultrafast Aircraft Thermometer: Reduction of Aerodynamic Disturbances and Signal Processing

2005 ◽  
Vol 22 (7) ◽  
pp. 988-1003 ◽  
Author(s):  
Bogdan Rosa ◽  
Konrad Bajer ◽  
Krzysztof E. Haman ◽  
Tomasz Szoplik
Keyword(s):  
Boundary Layer ◽  
Electronic System ◽  
Reynolds Numbers ◽  
Aerodynamic Noise ◽  
Sensing Element ◽  
Cloud Droplets ◽  
Strong Shear ◽  
System Temperature ◽  
The Impact

Abstract The ultrafast aircraft thermometer, built for measuring temperature in clouds at flight speeds up to 100 m s−1, employs a 2.5-μm-thick platinum-coated tungsten wire as a sensing element. When temperature increases, the wire resistance increases. The changes are amplified by an electronic system. Temperature measurements made in a wind tunnel and during flights show noise that is related to the von Kármán vortex street generated behind the shield that protects the sensing element against the impact of cloud droplets. To reduce both the level of turbulence and the amount of water collected on the shield, suction is applied through the slits in its sides. The effect of suction on the flow field is twofold. First, at the Reynolds numbers that the thermometer is operated suction eliminates aerodynamic disturbances. Second, suction diverts the inner part of the boundary layer into the slit. This inner part is a region of strong shear and, therefore, a region where intensive viscous heating takes place. When the suction is on much of the air that is heated in the boundary layer in the front part of the shield is removed through the slits and never reaches the sensor. To study the role of the shield with suction and confirm its chosen shape, two-dimensional (2D) direct numerical simulations (DNSs) are performed of the airflow and of the trajectories of droplets of various sizes and initial positions. The influence on the temperature distribution of the irreversible dissipation of energy due to air viscosity is also examined. This is found to have a small but measurable effect. The effects associated with sampling and processing of the analog signal obtained from the sensing wire are discussed. The results herein quantitatively explain the nature of the measured aerodynamic noise.

scholarly journals Characterization of a boreal convective boundary layer and its impact on atmospheric chemistry during HUMPPA-COPEC-2010

2012 ◽  
Vol 12 (19) ◽  
pp. 9335-9353 ◽  
Author(s):  
H. G. Ouwersloot ◽  
J. Vilà-Guerau de Arellano ◽  
A. C. Nölscher ◽  
M. C. Krol ◽  
L. N. Ganzeveld ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Atmospheric Chemistry ◽  
Convective Boundary Layer ◽  
Large Scale ◽  
Spatial Scales ◽  
Potential Temperature ◽  
Chemical Species ◽  
Convective Boundary ◽  
The Impact

Abstract. We studied the atmospheric boundary layer (ABL) dynamics and the impact on atmospheric chemistry during the HUMPPA-COPEC-2010 campaign. We used vertical profiles of potential temperature and specific moisture, obtained from 132 radio soundings, to determine the main boundary layer characteristics during the campaign. We propose a classification according to several main ABL prototypes. Further, we performed a case study of a single day, focusing on the convective boundary layer, to analyse the influence of the dynamics on the chemical evolution of the ABL. We used a mixed layer model, initialized and constrained by observations. In particular, we investigated the role of large scale atmospheric dynamics (subsidence and advection) on the ABL development and the evolution of chemical species concentrations. We find that, if the large scale forcings are taken into account, the ABL dynamics are represented satisfactorily. Subsequently, we studied the impact of mixing with a residual layer aloft during the morning transition on atmospheric chemistry. The time evolution of NOx and O3 concentrations, including morning peaks, can be explained and accurately simulated by incorporating the transition of the ABL dynamics from night to day. We demonstrate the importance of the ABL height evolution for the representation of atmospheric chemistry. Our findings underscore the need to couple the dynamics and chemistry at different spatial scales (from turbulence to mesoscale) in chemistry-transport models and in the interpretation of observational data.

scholarly journals Observation of the Diurnal Cycle in the Low Troposphere of West Africa

2008 ◽  
Vol 136 (9) ◽  
pp. 3477-3500 ◽  
Author(s):  
Marie Lothon ◽  
Frédérique Saïd ◽  
Fabienne Lohou ◽  
Bernard Campistron
Keyword(s):  
Boundary Layer ◽  
Water Vapor ◽  
West Africa ◽  
Planetary Boundary Layer ◽  
Diurnal Cycle ◽  
Dry Season ◽  
Nocturnal Jet ◽  
The Impact ◽  
Made In

Abstract The authors give an overview of the diurnal cycle of the low troposphere during 2006 at two different sites, Niamey (Niger) and Nangatchori (Benin). This study is partly based on the first observations of UHF wind profilers ever made in West Africa in the context of the African Monsoon Multidisciplinary Analysis (AMMA) project. Also used are the radiosoundings made in Niamey and ground station observations at Nangatchori, which allow for the study of the impact of the dynamics on the water vapor cycle and the turbulence observed at the ground. Profiler measurements revealed a very consistent year-round nocturnal low-level jet maximal around 0500 UTC and centered at 400-m above the ground, with wind speed around 15 m s−1. This jet comes either from the northeast during the dry season or from the southwest during the wet season, in relation with the position of the intertropical discontinuity. The radiosoundings made in Niamey highlight both the role of the nocturnal jet in bringing water vapor from the south during the night when the intertropical discontinuity has reached the vicinity of the considered area at the end of the dry season and the role of the daytime planetary boundary layer in mixing this water vapor within a larger depth of the troposphere. The planetary boundary layer processes play a large role in the diurnal cycle of the position of the intertropical discontinuity itself. The observations of turbulence made at the ground in Nangatchori showed that the best signature of the nocturnal jet close to surface can be seen in the turbulent kinetic energy and skewness of the air vertical velocity, rather than on the mean wind itself. They reveal the downward transport of momentum from the jet core aloft to the surface.

scholarly journals The role of urban boundary layer investigated by high resolution models and ground based observations in Rome area: a step for understanding parameterizations potentialities

2013 ◽  
Vol 6 (3) ◽  
pp. 5297-5344
Author(s):  
E. Pichelli ◽  
R. Ferretti ◽  
M. Cacciani ◽  
A. M. Siani ◽  
V. Ciardini ◽  
...  
Keyword(s):  
Boundary Layer ◽  
High Resolution ◽  
Urban Areas ◽  
Prediction Models ◽  
Weather Prediction ◽  
Sonic Anemometer ◽  
Lower Atmosphere ◽  
Area Of Interest ◽  
The Impact

Abstract. The urban forcing on thermo-dynamical conditions can largely influences local evolution of the atmospheric boundary layer. Urban heat storage can produce noteworthy mesoscale perturbations of the lower atmosphere. The new generations of high-resolution numerical weather prediction models (NWP) is nowadays largely applied also to urban areas. It is therefore critical to reproduce correctly the urban forcing which turns in variations of wind, temperature and water vapor content of the planetary boundary layer (PBL). WRF-ARW, a new model generation, has been used to reproduce the circulation in the urban area of Rome. A sensitivity study is performed using different PBL and surface schemes. The significant role of the surface forcing in the PBL evolution has been verified by comparing model results with observations coming from many instruments (LiDAR, SODAR, sonic anemometer and surface stations). The crucial role of a correct urban representation has been demonstrated by testing the impact of different urban canopy models (UCM) on the forecast. Only one of three meteorological events studied will be presented, chosen as statistically relevant for the area of interest. The WRF-ARW model shows a tendency to overestimate vertical transmission of horizontal momentum from upper levels to low atmosphere, that is partially corrected by local PBL scheme coupled with an advanced UCM. Depending on background meteorological scenario, WRF-ARW shows an opposite behavior in correctly representing canopy layer and upper levels when local and non local PBL are compared. Moreover a tendency of the model in largely underestimating vertical motions has been verified.

The Role of Reynolds Number Effect and Tip Leakage in Compressor Geometry Scaling at Low Turbulent Reynolds Numbers

2020 ◽  
Vol 142 (3) ◽  
Author(s):  
Markus Diehl ◽  
Christoph Schreiber ◽  
Jürg Schiffmann
Keyword(s):  
Reynolds Number ◽  
Surface Friction ◽  
Reynolds Numbers ◽  
Small Scale ◽  
Tip Leakage ◽  
Reynolds Number Effect ◽  
Geometric Scaling ◽  
Compressor Performance ◽  
The Impact

Abstract In compressor design, a convenient way to save time is to scale an existing geometry to required specifications, rather than developing a new design. The approach works well when scaling compressors of similar size at high Reynolds numbers but becomes more complex when applied to small-scale machines. Besides the well-understood increase in surface friction due to increased relative surface roughness, two other main problems specific to small-scale turbomachinery can be specified: (1) the Reynolds number effect, describing the non-linear dependency of surface friction on Reynolds number and (2) increased relative tip clearance resulting from manufacturing limitations. This paper investigates the role of both effects in a geometric scaling process, as used by a designer. The work is based on numerical models derived from an experimentally validated geometry. First, the effects of geometric scaling on compressor performance are assessed analytically. Second, prediction capabilities of reduced-order models from the public domain are assessed. In addition to design point assessment, often found in other publications, the models are tested at off-design. Third, the impact of tip leakage on compressor performance and its Reynolds number dependency is assessed. Here, geometries of different scale and with different tip clearances are investigated numerically. Fourth, a detailed investigation regarding tip leakage driving mechanisms is carried out and design recommendations to improve small-scale compressor performance are provided.

Aerodynamic Loading Distribution Effects on Off-Design Performance of Highly Loaded LP Turbine Cascades Under Steady and Unsteady Incoming Flows

2016 ◽  
Author(s):  
Marco Berrino ◽  
Daniele Simoni ◽  
Marina Ubaldi ◽  
Pietro Zunino ◽  
Francesco Bertini
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Incidence Angle ◽  
Reynolds Numbers ◽  
Angle Variation ◽  
Aerodynamic Loading ◽  
Profile Losses ◽  
Unsteady Inflow ◽  
The Impact ◽  
Highly Loaded

The present work is part of a continuous cooperation between GE AvioAero and the University of Genova aimed at understanding the detailed flow physics of efficient highly loaded LPT blades for aeroengine applications. In this paper the effects of the aerodynamic loading distribution on the performances of three different cascades with the same Zweifel number have been experimentally investigated under steady and unsteady incoming flow conditions. Measurements have been carried out for several Reynolds numbers (in the range 70000<Re<300000) with an incidence angle variation of ±9°, in order to cover the typical realistic LP aeroengine turbine working range on design and off-design conditions. Profile aerodynamic loadings and total pressure loss coefficients have been evaluated for the different cases. Efficiency data clearly highlight that at nominal incidence an aft loaded cascade provides the lowest profile losses when the boundary layer is attached to the wall, as it occurs in the unsteady case or at high Reynolds numbers. Only at the lowest Reynolds number in the steady case, a front loaded profile is preferable since it helps to prevent a laminar boundary layer separation. Moreover, the aft loaded profile has also shown a better robustness to incidence angle variation, both for the steady and the unsteady inflow conditions. Indeed, the growth of profile losses with incidence is weaker for the aft loaded cascade with respect to the front and the mid loaded ones. However, irrespective of the loading distribution the loss trend vs incidence angle has been found to be completely different between the steady and the unsteady operations. Results in the paper give a clear overview of the impact of the loading distribution on profile losses as a function of Reynolds number, as well as a detailed view of the influence due to the loading characteristics on incidence robustness under the realistic unsteady inflow case.

scholarly journals Probing the Response of Tropical Deep Convection to Aerosol Perturbations Using Idealized Cloud-Resolving Simulations with Parameterized Large-Scale Dynamics

2019 ◽  
Vol 76 (9) ◽  
pp. 2885-2897
Author(s):  
Usama M. Anber ◽  
Shuguang Wang ◽  
Pierre Gentine ◽  
Michael P. Jensen
Keyword(s):  
Boundary Layer ◽  
Large Scale ◽  
Diabatic Heating ◽  
Deep Convection ◽  
Cloud Droplets ◽  
Aerosol Loading ◽  
Microphysical Properties ◽  
Tropical Deep Convection ◽  
Gross Moist Stability ◽  
The Impact

Abstract A framework is introduced to investigate the indirect effect of aerosol loading on tropical deep convection using three-dimensional limited-domain idealized cloud-system-resolving model simulations coupled with large-scale dynamics over fixed sea surface temperature. The large-scale circulation is parameterized using the spectral weak temperature gradient (WTG) approximation that utilizes the dominant balance between adiabatic cooling and diabatic heating in the tropics. The aerosol loading effect is examined by varying the number of cloud condensation nuclei (CCN) available to form cloud droplets in the two-moment bulk microphysics scheme over a wide range of environments from 30 to 5000 cm−3. The radiative heating is held at a constant prescribed rate in order to isolate the microphysical effects. Analyses are performed over the period after equilibrium is achieved between convection and the large-scale environment. Mean precipitation is found to decrease modestly and monotonically when the aerosol number concentration increases as convection gets weaker, despite the increase in cloud liquid water in the warm-rain region and ice crystals aloft. This reduction is traced down to the reduction in surface enthalpy fluxes as an energy source to the atmospheric column induced by the coupling of the large-scale motion, though the gross moist stability remains constant. Increasing CCN concentration leads to 1) a cooler free troposphere because of a reduction in the diabatic heating and 2) a warmer boundary layer because of suppressed evaporative cooling. This dipole temperature structure is associated with anomalously descending large-scale vertical motion above the boundary layer and ascending motion at lower levels. Sensitivity tests suggest that changes in convection and mean precipitation are unlikely to be caused by the impact of aerosols on cloud droplets and microphysical properties but rather by accounting for the feedback from convective adjustment with the large-scale dynamics. Furthermore, a simple scaling argument is derived based on the vertically integrated moist static energy budget, which enables estimation of changes in precipitation given known changes in surfaces enthalpy fluxes and the constant gross moist stability. The impact on cloud hydrometeors and microphysical properties is also examined, and it is consistent with the macrophysical picture.

scholarly journals Study on the role of Black Carbon aerosols in cloud droplets during the dissipation of a fog.

2021 ◽  
Author(s):  
Lea Al Asmar ◽  
Luc Musson-Genon ◽  
Eric Dupont ◽  
Karine Sartelet
Keyword(s):  
Black Carbon ◽  
Volume Fraction ◽  
Solar Heating ◽  
Urban Atmosphere ◽  
Radiative Properties ◽  
Solar Irradiation ◽  
Liquid Content ◽  
Cloud Droplets ◽  
The Impact

&lt;p&gt;&lt;span&gt;Cloud condensation nuclei (CCN) are the subset of aerosol particles able to form cloud droplets.&lt;/span&gt;&lt;span&gt; CNN activation is influenced by the size distribution, chemical composition and number of particles. They consequently impact the cloud microstructure,&lt;/span&gt;&lt;span&gt; which affects the radiative properties of clouds, atmospheric circulation and thermodynamics, as well as radiative budgets. By influencing&lt;/span&gt;&lt;span&gt; the single scattering albedos of clouds, some particles lead to an increase of the solar irradiation absorption and solar heating in the cloud layers. A good example of these absorbing particles is those made of black carbon (&lt;/span&gt;&lt;span&gt;BC), which is emitted during the combustion of various types of fuel and non-exhaust traffic-related processes. &lt;/span&gt;&lt;span&gt;The present study deals with the role of BC in a solar radiative scheme and its interaction with clouds during a well-documented case of a fog that evolves into a low stratus cloud. To do so, the solar scheme of the computational fluid dynamic model &lt;/span&gt;&lt;span&gt;&lt;em&gt;Code Saturne&lt;/em&gt;&lt;/span&gt;&lt;span&gt; is used for the estimation of fluxes and heating rates in the atmosphere&lt;/span&gt;&lt;span&gt;&lt;em&gt;.&lt;/em&gt;&lt;/span&gt;&lt;span&gt; It is based on &lt;/span&gt;&lt;span&gt;the two-stream parameterization with calculations done in the ultraviolet-visible (UV-Vis) and solar infrared (SIR) bands. &lt;/span&gt;&lt;/p&gt;&lt;p&gt;&lt;span&gt;A special attention is given on the impact of BC on the dissipation of the fog. As expected, &lt;/span&gt;&lt;span&gt;the introduction of BC in cloud droplets accentuates the heating in the layers at the top of the cloud where water liquid content is maximum. In the SIR band, there is an increase of approximatively 80 %. In the UV-Vis band, where absorption of solar irradiance by ozone is minor, the heating rate is now 10 times higher. The contribution of the UV-Vis band becomes more important. The augmentation of solar heating leads to a reduction of the liquid water content and, consecutively, to a faster dissipation of the fog and the stratus. Therefore, direct surface fluxes are also increased.&lt;/span&gt;&lt;/p&gt;&lt;p&gt;&lt;span&gt;When increasing the volume fraction of black carbon in cloud droplets, the water liquid content is furthermore reduced leading to a faster dissipation of the fog. However, this impact is small, because the fog is formed in the morning. At this time, the cooling rate due to thermal radiation is higher than the solar heating at the top of the cloud. We expect the impact of black carbon in cloud droplets&lt;/span&gt;&lt;span&gt; to be higher for more persistent clouds or for a fog in the boundary layer of the urban atmosphere, where the fraction of BC in particles is higher.&lt;/span&gt;&lt;/p&gt;

Pressure fluctuations produced by forward steps immersed in a turbulent boundary layer

2014 ◽  
Vol 756 ◽  
pp. 384-421 ◽  
Author(s):  
Manuj Awasthi ◽  
William J. Devenport ◽  
Stewart A. L. Glegg ◽  
Jonathan B. Forest
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Pressure Fluctuations ◽  
Field Measurements ◽  
Reynolds Numbers ◽  
Step Height ◽  
Stream Velocity ◽  
Step Size ◽  
High Reynolds ◽  
The Impact

AbstractExperiments have been performed on the disturbance of a high-Reynolds-number turbulent boundary layer by three forward steps with sizes close to 3.8, 15 and 60 % of the boundary layer thickness. Particular attention is focused on the impact of the steps on the fluctuating surface pressure field. Measurements were made from 5 boundary layer thicknesses upstream to 22 boundary layer thicknesses downstream of the step, a distance equivalent to over 600 step heights for the smallest step size. Flow speeds of 30 and $\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}60\ \mathrm{m}\ {\mathrm{s}}^{-1}$ were studied, corresponding to boundary layer momentum thickness Reynolds numbers of 15 500 and 26 600 and step size Reynolds numbers from 6640 to 213 000. The steps produce a disturbance to the boundary layer pressure spectrum that scales on step size and decays remarkably slowly with distance downstream. When normalized on step height and free-stream velocity, the disturbance is self-similar and appears to develop almost independently of the enveloping boundary layer. The disturbance is still clearly visible at 150 step heights downstream of the mid-size step. Pressure correlations show the disturbance to be characterized by organized quasiperiodic motions that become visible well downstream of reattachment. The coherence and scale of these motions, as seen in the wall pressure correlations, scales on the step height and thus their visibility relative to the boundary layer grows rapidly as the step size is increased.

scholarly journals The role of urban boundary layer investigated with high-resolution models and ground-based observations in Rome area: a step towards understanding parameterization potentialities

2014 ◽  
Vol 7 (1) ◽  
pp. 315-332 ◽  
Author(s):  
E. Pichelli ◽  
R. Ferretti ◽  
M. Cacciani ◽  
A. M. Siani ◽  
V. Ciardini ◽  
...  
Keyword(s):  
Boundary Layer ◽  
High Resolution ◽  
Urban Areas ◽  
Prediction Models ◽  
Weather Prediction ◽  
Sonic Anemometer ◽  
Lower Atmosphere ◽  
Area Of Interest ◽  
The Impact

Abstract. The urban forcing on thermodynamical conditions can greatly influence the local evolution of the atmospheric boundary layer. Heat stored in an urban environment can produce noteworthy mesoscale perturbations of the lower atmosphere. The new generation of high-resolution numerical weather prediction models (NWP) is nowadays often applied also to urban areas. An accurate representation of cities is key role because of the cities' influence on wind, temperature and water vapor content of the planetary boundary layer (PBL). The Advanced Weather Research and Forecasting model WRF (ARW) has been used to reproduce the circulation in the urban area of Rome. A sensitivity study is performed using different PBL and surface schemes. The significant role of the surface forcing in the PBL evolution has been investigated by comparing model results with observations coming from many instruments (lidar, sodar, sonic anemometer and surface stations). The impact of different urban canopy models (UCMs) on the forecast has also been investigated. One meteorological event will be presented, chosen as statistically relevant for the area of interest. The WRF-ARW model shows a tendency to overestimate the vertical transport of horizontal momentum from upper levels to low atmosphere if strong large-scale forcing occurs. This overestimation is partially corrected by a local PBL scheme coupled with an advanced UCM. Moreover, a general underestimation of vertical motions has been verified.

scholarly journals Winds from Cataclysmic Variables

1997 ◽  
Vol 163 ◽  
pp. 465-474
Author(s):  
J. E. Drew
Keyword(s):  
Boundary Layer ◽  
Mass Loss ◽  
Radiation Pressure ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Cataclysmic Variables ◽  
Recent Developments ◽  
Orbital Phase ◽  
The Impact

AbstractThe winds associated with high states of non-magnetic (diskaccreting) cataclysmic variables are described and discussed. A quick summary of the basic phenomenology is given, and followed by a presentation of some of the more important recent developments in our understanding. The near-ubiquity of orbital-phase linked variability of the UV resonance lines (generally thought of as mainly wind-produced) is noted and its implications are considered. The impact of the much lower-thanexpected boundary layer luminosity upon mass loss rate determinations is also discussed. Current work on the role of radiation pressure (mediated by line opacity) is placed in context.

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