Weber Number Tests in the NASA Icing Research Tunnel

King, Michael C.; Bachalo, W. D.; Bell, Dwayne; King-Steen, Laura-Cheri

doi:10.2514/6.2018-3184

Cited by 3 publications

(1 citation statement)

References 7 publications

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“…Additional numbers are included into the state vector to enable further examination of the results even if they are not explicitly required for solving the differential equations: The Biot number Bi to emphasize applicability of the shell model versus the lumped model approach, the Weber number We to observe limitations for droplet break up [18] in further research focusing on the layout of a wind tunnel specifically designed for SLD [19].…”

Section: Temperaturementioning

confidence: 99%

Kinetic and thermal simulation of water droplets in icing wind tunnels

et al. 2021

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Within the certification process of aircraft, tests under specific icing conditions are required. For such safety relevant tests—which are performed under defined and repeatable test conditions—specially equipped Icing Wind Tunnels (IWT) are required. In such IWTs, supercooled water droplets are created with the aid of a spray system injecting pre-tempered water droplets of specific diameters into the free stream air flow. Especially tests with a droplet size up to 2mm (Supercooled Large Droplets - SLDs) are of great importance. SLDs are difficult to generate under laboratory conditions in IWT since usually the available droplet flight time from the injection location to the impact position on the test object is insufficient to reliably cool down a droplet at least to freezing temperature. To investigate the limitations associated with the application of SLD, the current work provides a method to allow detailed insight into the behavior of droplets on the path from the injection spray nozzle to the test section. In this work a state space model of a single droplet is derived that combines the kinetic aspects, thermal properties as well as the governing differential equations for motion, convective heat transfer at the droplet surface and heat conduction inside the droplet. Beside the states for the droplet’s position and velocity in space, the state space vector comprises various fluid and thermodynamic parameters. The droplet-internal temperature distribution is modelled by a discrete one-dimensional spherical shell model that also incorporates the aggregate phase (freezing mass fraction) at each shell node. This approach allows, therefore, the simulation of potential droplet phase change processes (freezing/melting) as well. With the model at hand, the influence of various boundary conditions (initial droplet temperature, flow field, ambient air temperature, etc.) can be determined and evaluated. As a result, concrete measures to achieve a desired operating condition (e.g. droplet temperature at the test object) for various model assumptions can be derived. In addition, the simulation model facilitates the prediction of the droplet diameter threshold for ensuring a supercooled state upon the impact on the test object. The governing theoretical influences are described, and various simulation results for representative test conditions that occur at the Rail-Tec-Arsenal (RTA) in Vienna are presented.

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Section: Temperaturementioning

confidence: 99%

Kinetic and thermal simulation of water droplets in icing wind tunnels

et al. 2021

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Phase Doppler Interferometry for Efficient Cloud Drop Size Distribution, Number Density, and LWC Measurements

Bachalo¹

2023

SAE Technical Paper Series

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<div class="section abstract"><div class="htmlview paragraph">Threats to aviation safety as a result of super-cooled large drops (SLD) has been addressed by the FAA rules change (14 CFR Part 25) with the additional icing certification requirement. SLD clouds often consist of bi-modal drop size spectra leading to significant problems in simulating and characterizing these conditions in situ and in icing wind tunnels. Legacy instrumentation for measuring drop size distributions and liquid water content are challenged under these conditions. The large size range measurement problem is addressed with the development of the Phase Doppler Interferometer, Flight Probe Dual-Range (PDI FPDR). The method is described in this report along with the measurement capabilities including the dynamic measurement range and overall working size range. The PDI instrument bases drop size measurements on the light wavelength as the measurement length scale. The light wavelength is a much more robust scale, especially as compared to the light scattering intensity. Methods for accurately characterizing the sample volume in situ based on measured drop velocity and transit time are reviewed, given the importance of this parameter for merging results and measuring LWC. Droplet coincidence in the sample volume can be problematic so this condition is treated with an innovative signal parsing approach. Measurement examples acquired in the NASA IRT are provided. Measurements of LWC showed good agreement with the Artium Particle Imaging (PI) instrument but diverged from the tunnel calibration results for larger MVD values.</div></div>

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High Resolution Cloud Particle Imaging Incorporating State-of-the-Art Digital Cameras with Pulsed LED Illumination

Bachalo¹

2023

SAE Technical Paper Series

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<div class="section abstract"><div class="htmlview paragraph">Super-cooled large drops present serious threats to aviation safety and as a result, the problem has been addressed by the FAA with the additional icing certification requirement. SLD clouds often consist of bi-modal drop size spectra leading to great challenges when it comes to simulating and characterizing these conditions in situ and in icing wind tunnels. Legacy instrumentation for measuring drop size distributions and liquid water content has been challenged under these conditions. In this report, a high-resolution particle imaging instrument is described; this instrument addresses the need for measuring drop size distributions and liquid water content over a wide range of drop sizes (10 to 2500 μm or larger). A high-throughput megapixel digital camera is used to record shadow images of the particles. High-quality illumination of the particle field is provided with high-power LED illumination with driving electronics designed to provide pulse durations as short as 25ns with sufficient fluence. Image processing software has been developed to enable automated setup of the instrument, image acquisition and processing, and efficient storage of the particle images. Calibration methods regarding the dependence of the depth-of-field to drop size were developed to enable sampling statistics bias corrections due to variations in the sample volume. Measurements acquired in the NASA Icing Research Tunnel (IRT) are provided as an example of the measurement capabilities of the newly developed instruments.</div></div>

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Weber Number Tests in the NASA Icing Research Tunnel

Cited by 3 publications

References 7 publications

Kinetic and thermal simulation of water droplets in icing wind tunnels

Kinetic and thermal simulation of water droplets in icing wind tunnels

Phase Doppler Interferometry for Efficient Cloud Drop Size Distribution, Number Density, and LWC Measurements

High Resolution Cloud Particle Imaging Incorporating State-of-the-Art Digital Cameras with Pulsed LED Illumination

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