Bulletin of the American Physical Society
77th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 24–26, 2024; Salt Lake City, Utah
Session X23: Experimental Techniques: Aerodynamics / High Speed Flows |
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Chair: Jimmy Philip, University of Melbourne Room: 251 A |
Tuesday, November 26, 2024 8:00AM - 8:13AM |
X23.00001: Spatio-temporal measurements of wall friction using three-dimensional photoelasticity Agastya Balantrapu, Dhiraj Kumar Singh, Eric R Pardyjak, Alexander Tschinkel Accurate measurements of wall shear stress in turbulent, low-speed, incompressible flows remain a challenge as it requires a non-intrusive tangential force sensor that can respond swiftly, is ultra-sensitive and noise free. We are proposing a novel method, employing a three-dimensional photo-elastic material, to spatio-temporally measure the wall shear stress under a high Reynolds number turbulent boundary layer. We fabricate a low modulus of elasticity, stress-free photo elastic sheet, using epoxy resin (SQ-2001) and hardener (SQ-3154) that can discriminate the tangential stresses from normal forces via an optical fringe pattern. The experimental setup consists of white light, an optical arrangement of a polarizer and analyzer, and a Single Lens Reflex camera. The shear stress information is extracted using a neural network-based approach to fringe patterns. The estimated Young’s modulus of elasticity of the sheet with dimensions 20 cm x 20 cm x 0.1 cm is 0.05Mpa. The temporal response the photoelastic sheet, measured using an acoustic transducer, had a 20 microsecond delay with a 5 milli-Newton sensitivity. |
Tuesday, November 26, 2024 8:13AM - 8:26AM |
X23.00002: Acquiring accurate measurements of instantaneous wall-shear stresses in wall-turbulent air flows in wind tunnel applications Xiaonan Chen, Joe O'Connor, Andrew Wynn, Sylvain Laizet, Kevin Wilson, Richard D Whalley Accurately measuring the instantaneous wall-shear stress in wall-bounded turbulent air flows is notoriously difficult. While conventional flush-mounted hot-film sensors can be calibrated by standard methods to acquire the mean wall-shear stress, the instantaneous fluctuations of wall-shear are significantly underestimated as heat from the hot-film probe is transferred into the sensor substrate. To address this issue, a new technique using non-linear regression (NLR) is used to calibrate a hot-film sensor to enable accurate measurements of instantaneous wall-shear stresses in turbulent boundary layers. During the NLR calibration process, the first four moments of wall-shear stress are acquired from either Laser Doppler Velocity (LDV), by linear fitting the velocity profile from within the viscous sublayer, or from Direct Numerical Simulation (DNS) data. As a result, the instantaneous wall-shear stress measured by the hot-film sensor matches excellently with the wall-shear stress measured by LDV placed directly above the sensor. Further investigation on different Reynolds numbers showed that the second-order moment is directly proportional to the first-order moment of the wall-shear stress, while the third-order and fourth-order moments are approximately constant over the Reynolds number range investigated. Inspired by this result, it was possible to calibrate the hot-film to accurately measure the instantaneous wall-shear stress with only the first-order moment of wall-shear stress. |
Tuesday, November 26, 2024 8:26AM - 8:39AM |
X23.00003: Towards Emulating Geophysical Boundary Layers with Variable Density Experiments Nick Conlin, Marcus Hultmark Boundary layer flows in geophysical settings are often modulated by buoyancy. Vertical temperature gradients in the Atmospheric Boundary Layer (ABL) can invigorate or sap the energy of turbulent motions, resulting in a change in mean profile, turbulence intensity, and turbulence structure. These modifications to the ABL have implications for weather/climate forecasting, wind energy, and pollutant dispersion. Replicating geophysical boundary layers in laboratory experiments is challenging as high Reynolds numbers and non-vanishing Richardson numbers are required. This talk will discuss the development of an experimental facility specialized for studying geophysical boundary layers, the Princeton SuperTank. |
Tuesday, November 26, 2024 8:39AM - 8:52AM |
X23.00004: Unsteady Flow-Field Measurements with a Five-Hole Probe Rhett Cook, Jonathan W Naughton, Pourya Nikoueeyan Multi-hole probes have provided reliable flow-field measurements for many years. However, the use of these probes has been primarily limited to mean measurements due to the attenuation and lag that is experienced by the pressure signals passing from the ports on the probe tip to the transducers making the pressure measurement. In this work, the capability to reconstruct the unsteady pressure from the pressures measured through the tubing systems has been coupled with a traditional static five-hole probe characterization to allow for unsteady flow-field measurements. Prior to testing, the dynamic response of each pressure port is dynamically characterized via an in-situ technique. Unsteady pressure measurements are then acquired for multiple planes at varying axial distances from the jet exit. Through this approach, it has been determined that the five-hole probe is capable of collecting unsteady measurements that resolve frequencies up to 900 Hz, and provide the statistical quantities of the flow-field that would be expected in an axisymmetric jet. To evaluate the quality of the measurements, the five-hole probe measurements are compared to those using hot-wire anemometry. |
Tuesday, November 26, 2024 8:52AM - 9:05AM |
X23.00005: Low cost camera array for large-scale, slow-flow wind tunnel visualization Theresa B Oehmke, Peter Okereke Quantitative flow visualization for large scale environments often include costly equipment with relatively small fields of view compared to the experimental measurement volume. To avoid the tedious task of moving a single camera to different locations or the expensive purchase of multiple cameras, we are presenting a nine-camera Raspberry Pi array that is able to capture bubbles moving through a 18 m3 volume in a slow-flow turbulent atmospheric boundary layer wind tunnel at the University of New Hampshire. This low-cost visualization method has allowed us to track bubbles moving through an increased measurement volume, compared to a traditional high-speed camera with a much smaller measurement volume. |
Tuesday, November 26, 2024 9:05AM - 9:18AM |
X23.00006: Abstract Withdrawn
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Tuesday, November 26, 2024 9:18AM - 9:31AM |
X23.00007: Abstract Withdrawn
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Tuesday, November 26, 2024 9:31AM - 9:44AM |
X23.00008: Measurement of surface pressure and distributed strain on an IC3X model in a Mach 5 flow using PSP and fiber-optic sensors Brianna L Blocher, Tori N Schulz, Jayant Sirohi, Noel T Clemens This presentation will discuss an experimental study of the mean strain induced by aerodynamic loads on a slender axisymmetric model in a Mach 5 flow. The experimental measurements include pressure-sensitive paint (PSP), temperature-sensitive paint (TSP), and fiber-optic sensors to obtain surface pressure, surface temperature, and strain distribution of the structure, respectively. Two vehicle models, based on the outer-mold line of the IC3X vehicle, are tested at 0-degree and 6-degree angles of attack in the UT Austin Mach 5 wind tunnel. The models are 3D-printed and designed to have varying degrees of elasticity under the aerodynamic loads expected during testing. The PSP and TSP images are obtained at a steady state flow period of the wind tunnel and averaged over approximately one second. The TSP is used to correct the PSP for temperature effects. The data are mapped to a 3D reconstruction of the model built from single camera spatial calibration and MATLAB's Computer Vision Toolbox. The lift distribution and pitching moment are calculated using the pressure distribution on the vehicle model. |
Tuesday, November 26, 2024 9:44AM - 9:57AM |
X23.00009: Reconstructing a Turbulent Compressible Jet From Multi-Camera BOS Measurements Using Data Assimilation Joseph P Molnar, Samuel J Grauer We present a neural data assimilation (DA) method for 4D background-oriented schlieren (BOS) tomography that can accurately reconstruct density, velocity, and pressure fields. Scale-resolving simulations of turbulent mixing in a compressible flow are computationally costly. A RANS or LES approach is often used to lower the cost, but limitations of the turbulence model can lead to large errors. BOS measurements of compressible mixing, paired with DA, have the potential to produce high-fidelity datasets to study the mixing system, validate computational models, and perform data-driven modeling. In single-camera BOS, a camera records images of a pattern positioned behind the flow; a reference image and image distorted by refraction are processed by a computer vision algorithm to estimate the 2D deflection field. BOS tomography (usually) involves multiple cameras and backgrounds, and synchronous images are used to reconstruct the density field, which involves a series of ill-posed problems that require regularization. DA algorithms produce better estimates than tomography algorithms by including the governing equations in the reconstruction. We apply this treatment to synthetic measurements of a Mach 0.9 turbulent jet using the compressible Navier–Stokes equations. |
Tuesday, November 26, 2024 9:57AM - 10:10AM |
X23.00010: Shock wave interaction with breakable cylinders of different cross-section Mohammmad Sazedur Rahman, Alexander Sweis, Peter Vorobieff Understanding shock wave interaction with solid objects range is necessary for a range of applications in aerospace, defense, and geophysics. Our experimental study seeks a better understanding of the physics and relevant timescales, as well as collects quantitative information that will be used for numerical code validation. Shock waves at three different Mach numbers are generated in a horizontal shock tube. Solid objects (cylinders) with three different cross sections and three different lengths were fabricated by additive manufacturing process for this experiment. These solid objects were mounted in a sample holder, placed inside the shock tube, and subjected to the arrival of planar shock waves. Four high speed pressure transducers were used to record pressure readings as the shock wave propagated through the shock tube. High-speed Kronos and Phantom cameras were used to record the interaction between shock wave and test samples. Interactions of the shock with cylinders appear to depend significantly on the cylinder cross-section. Additionally, we report significant shock reflection even for configurations where the cylinders occupy a modest cross-sectional area in the shock tube. |
Tuesday, November 26, 2024 10:10AM - 10:23AM |
X23.00011: Shock Wave Interactions with Soda Lime Glass Peter Vorobieff, Carolina Gabriela Shaheen, Alexander Sweis The aim of our study is to understand the nature of fracture and fragmentation occurring in soda lime glass when impacted by a shock wave. The work is motivated by the need to understand and mitigate the severe impacts blast waves cause to infrastructure. Case studies in which blast waves are generated in conflict zones, as a result of meteorite impacts, and due to industrial failures are discussed. Shock wave experiments performed utilize a high-speed camera that captures the nature of fracture patterns and failure mechanisms. Additionally, pressure data collected throughout the shock tube provides insights regarding the shock wave propagation and reflection. Shock wave interactions with soda lime glass were examined at Mach numbers 1.2, 1.45, and 1.7 to observe correlations between shock intensity and resulting fragmentation and fracture. Contextual information regarding continuum mechanics is imperative in this study as it pertains to the theoretical framework resulting from experimental observations. Principles of continuum mechanics can be employed to develop mathematical models for computational simulations. Comparing experimental results provided in this study to computational results improves the model’s accuracy and validity. |
Tuesday, November 26, 2024 10:23AM - 10:36AM |
X23.00012: Transcritical injection: modeling and experiment Peter Vorobieff, Mohamed Abuhegazy, Robert Frederick, David Lineberry, Noah Barrineau Transcritical injection presents a challenging problem for numerical modelers because there are multiple physical mechanisms relevant for the interaction of a transcritical jet with crossflow. Along with mechanical jet breakup, heat transfer, interfacial mixing and phase transition also play roles which are not fully understood. We present our progress in developing an experimental framework for a study with the main objective to provide quantitative information about the behavior of the jet that will be used to design and validate a computationally efficient and physically faithful numerical model of the process. The experimental framework will produce benchmarks of increasing complexity, starting with a jet in crossflow without transcritical effects, to make sure that different relevant physics are faithfully modeled. |
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