Bulletin of the American Physical Society
75th Annual Meeting of the Division of Fluid Dynamics
Volume 67, Number 19
Sunday–Tuesday, November 20–22, 2022; Indiana Convention Center, Indianapolis, Indiana.
Session G22: Turbulence: Flow Measurements Developments |
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Chair: Qi Wang, San Diego State University Room: 208 |
Sunday, November 20, 2022 3:00PM - 3:13PM |
G22.00001: Measurement of the velocity–pressure-gradient tensor of a turbulent shear layer flow impinging on a cavity trailing corner using time-resolved tomographic PIV Jose R Moreto, Xiaofeng Liu We measure the three-dimensional pressure-related turbulence terms i.e., the velocity–pressure-gradient tensor, which can be decomposed into the pressure–rate-of-strain, and the pressure diffusion tensors based on 35,163 realizations obtained by time-resolved tomographic PIV. The measurements were performed at the impinging area of a turbulent shear layer flow over a cavity at a Reynolds number of 4.0×104 with a sample rate of 4500Hz. The interrogation volume used was 32×32×32 voxels with a 75% overlap resulting in a vector spacing of 0.21mm. The 3D instantaneous pressure distribution was obtained by the rotating parallel ray omnidirectional integration method. The quality of the measured pressure is assessed by checking the curl-free property of the pressure gradient, as well as the zero-sum property of the inter-component energy transfer represented by the summation of the normal pressure-strain terms, i.e., R11+R22+R33=0. The continuity equation is used to assess the quality of the velocity measurement. The overall balance of the Reynolds stress transport equation is also examined. This is the first time that the 3D pressure-related turbulence transport terms around the cavity trailing corner is fully characterized, following the work of Liu and Katz (2018) based on planar-PIV. |
Sunday, November 20, 2022 3:13PM - 3:26PM |
G22.00002: Intermittency determination in the near-field region of a transitional jet by LDV Yi Qiao, K O Homan The intermittency factor is an important parameter for describing the intermittent behaviors in the flow field of turbulent flows or flows near the transition to turbulence. Many methods have been developed to calculate this parameter using different detector functions and threshold value selection. However, for most methods the determination of the threshold value is very subjective. A recent proposal identifies a method for determining a single threshold value and has been demonstrated in a boundary layer flow with Hot-wire Anemometer (HWA) velocity signals. This method remains to be validated in other type of flows using Laser Doppler Velocimetry (LDV) and Particle Image Velocimetry (PIV) data. |
Sunday, November 20, 2022 3:26PM - 3:39PM |
G22.00003: An eigen-ensemble algorithm for localization of scalar sources in turbulent environments Qi Wang, Tamer A Zaki Identifying the location and intensity of a passive scalar source from remote measurements in a turbulent flow is a challenging inverse problem. We introduce a new algorithm that can be realized using simulation data or physical measurements, and that makes use of prior tests and new sensor data to provide accurate predictions of the source parameters. We start with a set of trial sources to estimate the right and left singular vectors of the impulse-response system, namely the eigen-sources and corresponding eigen-measurements. Once we have new sensor data, we project them onto the eigen-measurements and use the results to synthesize the true source in terms of a superposition of the eigen-sources, appropriately weighted by the corresponding singular values. Since the eigen-sources converge for long time horizons, and are related to statistical properties of the scalar fields, the difficulty of identifying the sources from noisy measurements can be related to the statistics of the scalar field. Results that demonstrate the accuracy of the source reconstruction and the associated uncertainties will be discussed in the context of canonical turbulent channel flow at $Re_{\tau} = 180$. |
Sunday, November 20, 2022 3:39PM - 3:52PM |
G22.00004: Improving spatial resolution of underwater wall pressure fluctuation measurements using pinholes in a fully developed turbulent channel flow Jane H Kim, David R Dowling The current measurement method of pressure fluctuations on the surface beneath a turbulent flow typically results in poor spatial resolution because no transducers simultaneously satisfy the requirements for size and sensitivity. Mounting the transducers behind a pinhole is known to be a viable solution in airborne experiments but have not yet been shown to be effective underwater. For these investigations, underwater wall pressure fluctuations were measured in a fully developed turbulent channel flow (channel half height = 3.5 mm, with 1:14 aspect ratio) with pressure transducers mounted behind a 0.5mm, 1mm-, and 2mm diameter pinholes. To prevent air-bubble blockage, the pinholes were filled with liquids with varying viscosities (water at 1 cSt, and silicone oils at 1000 and 10,000 cSt). The effect of varying the viscosities of liquids filling the pinhole on the wall pressure fluctuation frequency spectra were evaluated for flow speeds from 1.5 to 7 m/s, resulting in Karman numbers from several hundred to more than a thousand. While the results show that pinhole-mounting may be a viable method of improving spatial resolution of underwater wall pressure fluctuations, further parameter studies are warranted. |
Sunday, November 20, 2022 3:52PM - 4:05PM |
G22.00005: Criterion for temporal up-sampling limits of advection-based techniques for PIV data Maegan Vocke, Ralf Kapulla, Christopher R Morton, Robert J Martinuzzi Experimental investigations for turbulent shear flows are challenging due to the interaction of widespread spatiotemporal scales. Particle image velocimetry (PIV) can yield spatially resolved flow measurements, but recording equipment often lack sufficient temporal sampling rates. The inadequate resolution of smaller temporal scales poses further difficulties for studying turbulent motion. This work investigates the ability of linear and non-linear advection-based flow reconstruction techniques to increase the temporal resolution of under-sampled turbulent flows. A modified semi-Lagrangian technique is used to obtain the instantaneous fluid trajectories through forward and backward integration of PIV spatiotemporal data. The estimates for the PIV data are then fused using a temporal weighting scheme to yield velocity fields at intermediate times. The performance of the method is benchmarked against the DNS of a plane jet, demonstrating that spectral information can be estimated up to two orders of magnitude beyond the Nyquist limit. The uncertainty and up-sampling threshold of the technique is investigated for PIV data of a turbulent round jet. An a priori criterion for the recovery of spectral content is proposed based on the spatiotemporal resolution of the measurements. |
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