Experiments in Fluids最新文献

{"title":"PIV-based fast pressure reconstruction and noise prediction of tandem cylinder configuration","authors":"Langsheng Chen,&nbsp;Qingqing Ye","doi":"10.1007/s00348-024-03833-w","DOIUrl":"10.1007/s00348-024-03833-w","url":null,"abstract":"<div><p>The present work proposes a fast and optimized experimental approach for pressure reconstruction and far-field noise prediction for flow past tandem cylinders based on time-resolved particle image velocimetry (PIV). The low-order reconstruction of the velocity fields based on proper orthogonal decomposition (POD) is applied, which effectively mitigates the incoherent measurement noise by selecting the low-order modes representing the dominant coherent structures. The preprocessing of velocity fields significantly improves the accuracy of both field and surface pressure fluctuations estimated by solving the Poisson equation. The time-marching enhancement algorithm uses the pressure field from the preceding snapshot as the initial guess in the iterative process, which accelerates convergence and reduces the computational cost for solving the Poisson equation of the PIV database with a large ensemble size. The estimated surface pressure fluctuations are used to predict the far-field noise through Curle’s analogy with the correction based on the spanwise correlation length. Comparisons are performed with reference signals, yielding good agreement on both pressure and noise spectra.</p></div>","PeriodicalId":554,"journal":{"name":"Experiments in Fluids","volume":"65 6","pages":""},"PeriodicalIF":2.3,"publicationDate":"2024-06-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141415514","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"PIV analysis of wake characteristics of slanted-back Ahmed bodies: effect of leading-edge shape","authors":"Amir Sagharichi,&nbsp;Mark Francis Tachie","doi":"10.1007/s00348-024-03834-9","DOIUrl":"10.1007/s00348-024-03834-9","url":null,"abstract":"<div><p>This study experimentally investigates turbulent flow separation around a slanted-back Ahmed body with different leading edge configurations [rounded (RL) and square (SL)] using the particle image velocimetry technique. The Reynolds number (based on freestream velocity and body height) is <span>({text{Re}}_{text{H}})</span> = 0.17 × 10⁵. Spatiotemporal flow characteristics, including mean flow, vorticity flux, two-point correlation, reverse flow area, frequency spectra, and proper orthogonal decomposition, are analyzed to elucidate the effects of leading edge shape on separated shear layer interactions over the roof, slanted surface, and the wake region. The results show that rounding the leading edge of the Ahmed body leads to the formation of smaller coherent structures with lower shedding frequency over the roof. While, the structures are still smaller over the slanted surface and the wake region of the RL body, the shedding frequency surpasses that of the SL ones. The results also show evidence of the identical shedding frequency over the roof, slanted surface, and wake region of the RL body. Detailed analyses, including convective velocities of vortices over the roof, slanted surface, and in the wake region, vary significantly between SL and RL cases, indicating distinct shedding mechanisms influenced by leading edge geometry.</p></div>","PeriodicalId":554,"journal":{"name":"Experiments in Fluids","volume":"65 6","pages":""},"PeriodicalIF":2.3,"publicationDate":"2024-06-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141395454","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Optimization of SLIPI–polarization ratio imaging for droplets sizing in dense sprays","authors":"S. Garcia,&nbsp;M. Stiti,&nbsp;P. Doublet,&nbsp;C. Lempereur,&nbsp;M. Orain,&nbsp;E. Berrocal","doi":"10.1007/s00348-024-03830-z","DOIUrl":"10.1007/s00348-024-03830-z","url":null,"abstract":"<div><p>In this article, structured laser illumination planar imaging and polarization ratio techniques are successfully combined to size droplets in various optically dense sprays. The polarization ratio approach is based on the acquisition of the perpendicular and parallel polarized components of Lorenz–Mie scattered light, for which the ratio is proportional to the surface mean diameter, <i>D</i>₂₁. One of the main advantages of this technique, compared to some other laser imaging techniques for particle sizing, is that no fluorescent dye is required. This makes the technique suitable for characterizing sprays under evaporation conditions, such as combustion or spray drying applications. In addition, the SLIPI technique aims at suppressing the detection of multiple light scattering and at extracting the desirable single-light scattering signal. To test the reliability of this novel approach, an industrial hollow-cone nozzle is used, injecting at 50 bar water mixed with Glycerol (in the range of 0–60%). The first aim of this work is to study the experimental parameters that influence the reliability of the technique, such as the polarization orientation of the incident light, the refractive index of the injected liquid and the variation of the droplet size distribution. Using Phase Doppler Anemometry, the results show that a linear calibration is obtained for droplets ranging between 10 and 70 μm, when the incident illumination has a polarization set to 10° and 20°. In addition, this article demonstrates the feasibility of the technique for the measurement of liquids having a refractive index reaching 1.41. In the last stage of this work, after rotating the nozzle every 5°, a 3D tomographic reconstruction of <i>D</i>₂₁ is performed. This demonstrates the robustness and efficiency of the technique for droplet sizing in 3D, under challenging conditions.</p></div>","PeriodicalId":554,"journal":{"name":"Experiments in Fluids","volume":"65 6","pages":""},"PeriodicalIF":2.3,"publicationDate":"2024-06-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s00348-024-03830-z.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141404841","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Experimental study of dynamic wetting behavior through curved microchannels with automated image analysis","authors":"Huijie Zhang,&nbsp;Anja Lippert,&nbsp;Ronny Leonhardt,&nbsp;Tobias Tolle,&nbsp;Luise Nagel,&nbsp;Mathis Fricke,&nbsp;Tomislav Marić","doi":"10.1007/s00348-024-03828-7","DOIUrl":"10.1007/s00348-024-03828-7","url":null,"abstract":"<div><p>Preventing fluid penetration poses a challenging reliability concern in the context of power electronics, which is usually caused by unforeseen microfractures along the sealing joints. A better and more reliable product design heavily depends on the understanding of the dynamic wetting processes happening inside these complex microfractures, i.e. microchannels. A novel automated image processing procedure is proposed in this work for analyzing the moving interface and the dynamic contact angle in microchannels. In particular, the developed method is advantageous for experiments involving non-transparent samples, where extracting the fluid interface geometry poses a significant challenge. The developed method is validated with theoretical values and manual measurements and exhibits high accuracy. The implementation is made publicly available. The developed method is validated and applied to experimental investigations of forced wetting with two working fluids (water and 50 wt% glycerin/water mixture) in four distinct microchannels characterized by different dimensions and curvature. The comparison between the experimental results and molecular kinetic theory (MKT) reveals that the dynamic wetting behavior can be described well by MKT, even in highly curved microchannels. The dynamic wetting behavior shows a strong dependency on the channel geometry and curvature.</p></div>","PeriodicalId":554,"journal":{"name":"Experiments in Fluids","volume":"65 6","pages":""},"PeriodicalIF":2.3,"publicationDate":"2024-06-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141549036","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Deep learning-based image segmentation for instantaneous flame front extraction","authors":"Ruben M. Strässle,&nbsp;Filippo Faldella,&nbsp;Ulrich Doll","doi":"10.1007/s00348-024-03814-z","DOIUrl":"10.1007/s00348-024-03814-z","url":null,"abstract":"<div><p>This paper delves into the methodology employed in examining lean premixed turbulent flame fronts extracted from Planar Laser Induced Fluorescence (PLIF) images at elevated pressures. In such flow regimes, the PLIF signal suffers from significant collisional quenching, typically resulting in image data with low signal-to-noise ratio (SNR). This poses severe difficulties for conventional flame front extraction algorithms based on intensity gradients and requires intense user intervention to yield acceptable results. In this work, we propose Convolutional Neural Network (CNN)-based Deep Learning (DL) models as an alternative to problem specific conventional methods. The pretrained DL models were fine-tuned, employing data augmentation, on a small annotated dataset including a variety of conditions between SNR <span>(approx)</span> 1.6 to 2.6 and subsequently evaluated. All DL models significantly outperformed the best-scoring conventional implementation both quantitatively and visually, while having similar inference times. IoU-scores and Recall values were found to be up to a factor <span>(approx)</span> 1.2 and <span>(approx)</span> 2.5 higher, respectively, with <span>(approx)</span> 1.15 times improved Precision. Small-scale structures were captured much better with fewer erroneous predictions, becoming particularly pronounced for the lower SNR data investigated. Moreover, by applying artificially modeled noise, it was shown that the range of image conditions in terms of SNR that can be reliably processed extends well beyond the images included in the training data, and satisfactory segmentation performances were found for SNR as low as <span>(approx)</span> 1.1. The presented DL-based flame front detection algorithm marks a methodology with significantly increased detection performance, while a similar computational effort for inference is achieved and the need for user-based parameter tuning is eliminated. It enables a very accurate extraction of instantaneous flame fronts in large image datasets where supervised processing is infeasible, unlocking unprecedented possibilities for the study of flame dynamics and instability mechanisms at industry-relevant conditions.</p></div>","PeriodicalId":554,"journal":{"name":"Experiments in Fluids","volume":"65 6","pages":""},"PeriodicalIF":2.3,"publicationDate":"2024-06-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s00348-024-03814-z.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141258259","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Liquid film flow rate from measurements of disturbance wave characteristics for applications in thin film flow","authors":"Jason Chan,&nbsp;Roman W. Morse,&nbsp;Maggie A. Meissner,&nbsp;Kristofer M. Dressler,&nbsp;Evan T. Hurlburt,&nbsp;Gregory F. Nellis,&nbsp;Arganthaël Berson","doi":"10.1007/s00348-024-03832-x","DOIUrl":"10.1007/s00348-024-03832-x","url":null,"abstract":"<div><p>This paper discusses the extension of an optical liquid film thickness measurement technique to characterize liquid film flow rate in wavy thin liquid film flow. The technique, based on laser refractometry, is used to measure wave height, shape, frequency, and velocity. A two-zone model to process the measured wave characteristics is used to estimate the liquid film flow rate. The method is validated in a falling film facility where easy optical access allows comparisons of the wave velocity measurements with high-speed videos and where the calculated liquid film mass flow rate can be compared with actual measurements. The paper provides a framework for analyzing time-resolved film thickness data using multizone models in more complex liquid film flows, such as in two-phase annular flow.</p></div>","PeriodicalId":554,"journal":{"name":"Experiments in Fluids","volume":"65 6","pages":""},"PeriodicalIF":2.3,"publicationDate":"2024-06-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141258320","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Shape/penetration analysis and comparisons of isolated spray plumes in a multi-hole Diesel spray","authors":"Lokesh Mopuri,&nbsp;Viljam Grahn,&nbsp;David Sedarsky,&nbsp;Jari Hyvönen","doi":"10.1007/s00348-024-03829-6","DOIUrl":"10.1007/s00348-024-03829-6","url":null,"abstract":"<div><p>Fuel injection systems significantly impact the combustion process and play a key role in reducing harmful exhaust emissions in internal combustion engines. For dual-fuel (DF) engines operating in gas mode, ignition of the main fuel is typically controlled by directly injected liquid pilot fuel. Liquid pilot fuel’s initial penetration and total mass considerably impact exhaust emissions and combustion stability. We investigated the spray morphology of a multi-hole diesel fuel injector within a constant-volume spray chamber using high-speed shadowgraphy and Mie-scattering measurements. Two methodologies were employed. The first one utilized a nozzle equipped with a thimble structure to isolate a single plume. The second methodology known as plume-blocking, involved sealing the orifices of the multi-hole nozzle to generate a single-spray plume. Our findings revealed that the plume-blocking approach demonstrated greater penetration than the thimble-equipped nozzle. The rapid penetration of this method may restrict its applicability to single-spray studies. Sprays generated from this partially sealed nozzle exhibited noticeable disparities compared to an unblocked nozzle, whereas a nozzle equipped with a thimble produced similar outcomes to the standard nozzle. The orifices when sealed, modify the flow distribution within the sac volume, which consequently affects the spray characteristics. In summary, this research provides insights into the impacts of various plume isolation methods on spray morphology, thereby enhancing the understanding of spray behaviour in transient conditions by comparing plume variations and disturbances under various fuel pressure and ambient conditions.</p></div>","PeriodicalId":554,"journal":{"name":"Experiments in Fluids","volume":"65 6","pages":""},"PeriodicalIF":2.3,"publicationDate":"2024-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s00348-024-03829-6.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141193923","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Infrared thermography techniques for boundary layer state visualisation","authors":"William Davis,&nbsp;Nicholas R. Atkins","doi":"10.1007/s00348-024-03827-8","DOIUrl":"10.1007/s00348-024-03827-8","url":null,"abstract":"<div><p>The rapid decarbonisation of the power generation and aviation sectors will require a move away from incremental development, exposing designers and researchers to the risk of unexpected results from uncertainty in boundary layer state. This problem already exists for parts developed with fully turbulent assumptions, but in novel design spaces the risk increases for both real components, where previous knowledge of similar designs may be inapplicable, and particularly in experimental testing of scaled models, where reducing Reynolds number can result in a drastic change in flow topology that skews the conclusions of a test. Computational methods struggle to reliably predict boundary layer state so experimental techniques for diagnosing boundary layer state are needed. Infrared thermography (IR) is a non-invasive technique that offers simple, fast visualisation of boundary layer state with no additional instrumentation. IR is relatively uncommon in the literature and there is minimal information available on the best practices for its use. This paper aims to encourage the adoption of IR as a diagnostic tool by demonstrating routes for optimisation and pointing out pitfalls to avoid. A low-order model is developed and used to predict how the signal-to-noise ratio (SNR) of an IR visualisation changes depending on the thermal design of the test piece. It is shown that in low-speed flows with active heating from the surface the SNR is maximised through a suitable choice of surface insulation, while in high-speed flows, where passive temperature differences are used, there is a crossover between heat transfer and recovery temperature effects that results in an SNR of zero, an effect that can arise in both steady-state and transient experiments. Experimental validation of the 1D model in both flow regimes is shown alongside two case studies on the use of IR in sub-scale testing where uncertainty in boundary layer state results in critical differences from the full-scale flow.</p></div>","PeriodicalId":554,"journal":{"name":"Experiments in Fluids","volume":"65 6","pages":""},"PeriodicalIF":2.3,"publicationDate":"2024-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s00348-024-03827-8.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141194221","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Assessment of particle image velocimetry applied to high-speed organic vapor flows","authors":"T. Michelis,&nbsp;A. J. Head,&nbsp;M. Majer,&nbsp;P. Colonna,&nbsp;C. De Servi","doi":"10.1007/s00348-024-03822-z","DOIUrl":"10.1007/s00348-024-03822-z","url":null,"abstract":"<div><p>Compressible flows of fluids whose thermophysical properties are related by complex equations are quantitatively and can be qualitatively different from high-speed flows of ideal gases. Nonideal compressible fluid dynamics (NICFD) is concerned with these fluid flows, which are relevant in many processes and power and propulsion systems. Typically, NICFD effects occur if the fluid is an organic compound and its vapor state is close to the vapor–liquid critical point, at high-reduced temperature and pressure (even supercritical). Current design and analysis of devices operating in the nonideal compressible regime demand for validated simulation software, characterized in terms of uncertainty. Moreover, experiments are needed to further validate related theory. Experimental data are limited as generating and measuring these flows is challenging given their high pressure or temperature or both. In addition, flows of organic compounds can be flammable, can thermally decompose, and sealing may demand for special materials. Recently, more research has been devoted to the measurement of these flows using both intrusive and less intrusive techniques relying on optical access and lasers. The transparency and refractive properties of these dense vapors pose additional problems. The ORCHID (organic Rankine cycle hybrid integrated device) at the Aerospace Propulsion and Power Laboratory of Delft University of Technology is a closed-loop facility, used to generate a continuous nonideal supersonic flow of siloxane MM with the vapor at 4<span>({{textrm{bar}}})</span> and 220 °C at the inlet of the test section. Within this work, we have employed particle image velocimetry for the first time to obtain the velocity field in a de Laval nozzle in such flows. Measured velocity fields (expanded uncertainty within 1.1% of the maximum velocity) have been compared with those resulting from a CFD simulation. The comparison between experimental and simulated data is satisfactory, with deviation ranging from 0.1 to 10 % from the throat to the outlet, respectively. This discrepancy is attributed to hardware limitations, which will be overcome in the future experiments. The feasibility of PIV with uncontrolled but fixed seeding density to measure high-speed vapors of organic vapors has been demonstrated, and future experimental campaigns will target flows for which nonideal effects are more pronounced, other paradigmatic configurations, and improvements to the measurement techniques.</p></div>","PeriodicalId":554,"journal":{"name":"Experiments in Fluids","volume":"65 6","pages":""},"PeriodicalIF":2.3,"publicationDate":"2024-05-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s00348-024-03822-z.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141193859","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Aerodynamics of a dart-shaped projectile at low Reynolds number","authors":"Amit A. Pawar,&nbsp;Kumar Sanat Ranjan,&nbsp;Arnab Roy,&nbsp;Sandeep Saha","doi":"10.1007/s00348-024-03824-x","DOIUrl":"10.1007/s00348-024-03824-x","url":null,"abstract":"<div><p>A sports dart pierces the dartboard because it possesses a remarkable aerodynamic property of ‘self-correcting’ its attitude in flight. This property arises from its aerodynamic design with a long heavy Barrel and large cruciform wings known as flights. We characterize the aerodynamics of dart-shaped projectiles at typical flight Reynolds numbers between 14500 and 20500 using wind tunnel experiments and numerical simulations. Force measurement tests from wind tunnel experiments yield the lift, drag, and pitching moment coefficients over a range of angles of attack; the experimental estimates are in quantitative agreement with those obtained from numerical simulations. Examining the surface pressure distribution, streamlines, and wall shear–stress distribution, along with the skin friction lines obtained from numerical simulations, reveals that the aerodynamics of the dart is governed by an interaction between the Barrel vortex (BV) shed by the cone–cylinder body and the wing leading edge vortex (WLV) over the horizontal flights influenced by solid impediment offered by the vertical flights. Smoke flow visualization images corroborate the vortex–vortex and vortex–wall interactions over the flights found in the numerical simulations. A complex interplay of vortex structures is observed, which depends on the angle of attack. The WLV develops an elliptic instability while exhibiting a partial merger with the Barrel vortex in the presence of secondary vorticity generated by the walls amidst the rapid weakening of the WLV. We conclude that the role of aerodynamics is largely pitch stabilization by means of aerodynamic moment and the normal force generation.</p></div>","PeriodicalId":554,"journal":{"name":"Experiments in Fluids","volume":"65 6","pages":""},"PeriodicalIF":2.3,"publicationDate":"2024-05-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141194020","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}