Experiments in Fluids最新文献

{"title":"FIEVel: a Fast and InExpensive Velocimeter based on an optical mouse sensor","authors":"Robert Hunt,&nbsp;Eli Silver,&nbsp;Daniel M. Harris","doi":"10.1007/s00348-025-04027-8","DOIUrl":"10.1007/s00348-025-04027-8","url":null,"abstract":"<div><p>Fluid velocimetry is fundamental to a breadth of applications spanning academia and industry; however, velocimetry at high temporal resolution is often prohibitively costly. Here, we introduce a Fast and InExpensive Velocimeter (FIEVel) based on an optical mouse sensor. At its core, the optical mouse sensor consists of a small pixel array that acquires image data at high rates, with onboard hardware to compute and output motion in two orthogonal axes directly. We adapt this widely available integrated circuit to image illuminated particles in the bulk of a fluid as in standard particle image velocimetry (PIV). We demonstrate that FIEVel is capable of resolving two components of pointwise velocity (0d2c) nonintrusively in the bulk of a flowing fluid at rates up to 6.4 kHz, at orders of magnitude lower cost than traditional velocimetry devices. We demonstrate and validate the velocimeter across a range of flows, operating conditions, and illumination strategies. As a sample application, we measure the temporal spectrum of a grid-generated turbulent flow and show excellent agreement with traditional particle image velocimetry using a high-speed camera.</p></div>","PeriodicalId":554,"journal":{"name":"Experiments in Fluids","volume":"66 6","pages":""},"PeriodicalIF":2.3,"publicationDate":"2025-05-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s00348-025-04027-8.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144140175","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":"Application of BOS velocimetry to full-scale helicopter flight tests","authors":"Johannes N. Braukmann,&nbsp;C. Christian Wolf,&nbsp;Anthony D. Gardner","doi":"10.1007/s00348-025-04043-8","DOIUrl":"10.1007/s00348-025-04043-8","url":null,"abstract":"<div><p>Time-resolved background-oriented schlieren (BOS) data are used to calculate the two-dimensional velocity field in the wake of free-flying full-scale helicopters in ground effect. The calculation is performed based on the density gradient pattern of the helicopter engine exhaust gas passing the BOS field of view. A classical BOS evaluation allows the visualization of density gradients such as vortices and the exhaust plume. The result is the BOS displacement field. Applying the two-dimensional divergence to these data results in a pattern that is constant in shape across multiple BOS images, but convects downstream with the outwash velocity of the helicopter. Quantitative two-dimensional velocity fields are calculated using the divergence of the BOS shift as input to a second, time-resolved evaluation. Choosing an appropriate strategy for preparing and evaluating the data is critical to a reliable velocity estimation. Another important aspect is to distinguish between reliable velocity data and erroneous results in areas of reduced signal intensity due to a lack of thermal structures. The velocity data obtained are compared with an analytical outwash model and constant temperature anemometry data acquired simultaneously with the BOS images. The data show good quantitative agreement in areas of sufficient thermal structures within the field of view. This demonstrates the feasibility of BOS velocimetry to investigate large flow fields in full-scale helicopter flight tests.</p></div>","PeriodicalId":554,"journal":{"name":"Experiments in Fluids","volume":"66 6","pages":""},"PeriodicalIF":2.3,"publicationDate":"2025-05-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s00348-025-04043-8.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144131495","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 characterization of a rotor to dynamic collective pitch inputs in hover","authors":"Patrick Mortimer,&nbsp;Jayant Sirohi","doi":"10.1007/s00348-025-04037-6","DOIUrl":"10.1007/s00348-025-04037-6","url":null,"abstract":"<div><p>Experiments were performed on a two-meter-diameter, four-bladed rotor to extract the coefficients of a dynamic inflow model. The frequency response of rotor-induced velocity to rotor thrust was found by introducing stepped-sine collective pitch inputs at frequencies of 0.2 per revolution to 0.7 per revolution, where the rotor rotational frequency was 14 Hz. The induced velocity field was measured using phase-resolved, two-dimensional, three-component particle image velocimetry (PIV) over a large region of interest (0.84 m<span>(times)</span>0.77 m) in a radial slice of the rotor flow field. The rotor thrust was measured using a hub-mounted load cell. Limited by the frame rate of the cameras, PIV was performed using an under-sampling technique in which one image pair was captured during each rotor revolution, and the time history was recreated from the phase-resolved measurements. The thrust amplitude was found to increase with input frequency, reaching 27.4% of the steady thrust at the highest input frequency. The induced velocity amplitude followed the opposite trend, decreasing to 2.0% of the steady value at the highest input frequency. Dynamic inflow states were extracted and fit to a first-order transfer function. The gain and corner frequency of the transfer function were found to be <span>(K = 34.7pm 1.52)</span> dB and <span>(b = 4.08pm 0.19)</span> rad/s, respectively, which followed a similar trend to computational studies reported in the literature.</p></div>","PeriodicalId":554,"journal":{"name":"Experiments in Fluids","volume":"66 6","pages":""},"PeriodicalIF":2.3,"publicationDate":"2025-05-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144125870","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":"Time-averaged density tomography of non-axisymmetric jets with a rotating nozzle and telecentric, single-camera BOS","authors":"Fernando Zigunov","doi":"10.1007/s00348-025-04052-7","DOIUrl":"10.1007/s00348-025-04052-7","url":null,"abstract":"<div><p>In this article, a method for density tomography using a telecentric BOS setup coupled with a motorized, rotating nozzle will be described. The telecentric optics allow for the disentanglement of the ray path integral and density gradient operators through Leibniz’s integral rule because the rays seen by a telecentric setup are parallel in the Schlieren domain. This enables the usage of a fast gradient inversion solver based on the rotating parallel ray integral method, previously developed by the author, to solve for the ray-integrated density fields in two dimensions for each view individually, producing a set of ray-integrated density measurements similar to a set of images captured by a regular absorption or emission-based computed tomography setup. By leveraging well-known computed tomography algorithms, such as the inverse Radon transform, a tomographic reconstruction of the average density field is quickly found only requiring a simple 2D camera calibration. A demonstration experiment setup is used to test the technique, where a low-speed hot jet produced by different nozzle shapes is measured. The 3D density fields are then converted to temperature fields and the temperatures are compared to a reference measurement with a thermocouple scanner. The strong agreement between the two measurements creates confidence that this technique can be deployed to produce quantitative measurements of the density fields in complex flows, which can be combined with 3D PIV measurements to obtain the four time-averaged thermodynamic fields in compressible jet flows.</p></div>","PeriodicalId":554,"journal":{"name":"Experiments in Fluids","volume":"66 6","pages":""},"PeriodicalIF":2.3,"publicationDate":"2025-05-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s00348-025-04052-7.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144125869","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":"In vitro modeling of fluid dynamics in the left and right coronary arteries during rest and exercise conditions","authors":"Seyyed Mahmoud Mousavi,&nbsp;Gianluca Zitti,&nbsp;Maurizio Brocchini","doi":"10.1007/s00348-025-04036-7","DOIUrl":"10.1007/s00348-025-04036-7","url":null,"abstract":"<div><p>Accurate understanding and simulation of coronary artery perfusion are crucial for assessing the heart function under varying cardiac workloads. This is particularly important given that sudden cardiac death (SCD) events have been observed during intense physical activity, not only in individuals with congenital coronary anomalies but also in healthy individuals. In response, we developed a novel in vitro laboratory setup to study the fluid dynamics of the left (LCA) and right (RCA) coronary arteries, using an anatomically accurate model of a healthy human aortic root and ascending aorta under different workloads. A key achievement is the simultaneous measurement of pressure in the left ventricle (LV), aorta (Ao), LCA, and RCA, along with flow rates in both coronary arteries. This is the first study to provide high-resolution, simultaneous in vitro data on pressure and flow values in coronary arteries under both rest and exercise conditions. During rest, the aortic pressure waveform decreases linearly, while during exercise, it displays a secondary diastolic peak. This distinctive aortic pressure feature during exercise is reflected in the coronary fluid dynamics, highlighting differences in the mechanisms of rest and exercise conditions. The RCA pressure closely mirrors the aortic pressure under all conditions, but the LCA pressure shows a secondary diastolic peak during exercise, phase-shifted by <span>(sim 0.2T)</span> from the cardiac cycle. This peak arises from a backward propagating pressure wave from its distal part, generated by myocardium contraction loads. Our findings highlight the amplified interaction of incident and reflected waves during exercise, making LCA perfusion highly sensitive to wave dynamics.</p></div>","PeriodicalId":554,"journal":{"name":"Experiments in Fluids","volume":"66 6","pages":""},"PeriodicalIF":2.3,"publicationDate":"2025-05-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s00348-025-04036-7.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144125497","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":"Kinematic decomposition of volumetric particle tracking velocimetry data","authors":"Michael R. Fenelon,&nbsp;Yang Zhang,&nbsp;Peter J. Schmid,&nbsp;Louis N. Cattafesta III","doi":"10.1007/s00348-025-04035-8","DOIUrl":"10.1007/s00348-025-04035-8","url":null,"abstract":"<div><p>This paper describes a comprehensive kinematic decomposition of unstructured Lagrangian data from volumetric particle tracking velocimetry measurements. The method uses particle location data at an arbitrary time <i>t</i> and calculates linear affine mappings at a later time <span>(t+{text{d}}t)</span>. The transformation produces the full velocity gradient tensor, which can then be further analyzed to identify the four types of fluid motion (i.e., translation, rotation, dilatation, and shear) without using spatial derivatives. The methodology provides insights into the underlying kinematics and facilitates the identification of coherent structures using, for example, the <i>Q</i>-criterion, within the flow without resorting to numerical differentiation or data assimilation methods. The method is first validated using analytical solutions and direct numerical simulations and then applied to experimental subsonic jet measurements. The method’s accuracy is discussed, and leading-order error sources are presented. </p></div>","PeriodicalId":554,"journal":{"name":"Experiments in Fluids","volume":"66 6","pages":""},"PeriodicalIF":2.3,"publicationDate":"2025-05-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144117725","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":"A hybrid PIV/PSV approach for a large dynamic velocity range","authors":"Dapeng Zhang,&nbsp;Wu Zhou,&nbsp;Cameron Tropea,&nbsp;Haoqin Huang,&nbsp;Xiangrui Dong,&nbsp;Tianyi Cai,&nbsp;Xiaoshu Cai","doi":"10.1007/s00348-025-04040-x","DOIUrl":"10.1007/s00348-025-04040-x","url":null,"abstract":"<div><p>Particle image velocimetry (PIV), particle tracking velocimetry (PTV) and particle streak velocimetry (PSV) are well-established image-based measurement techniques for flow velocity fields; the main difference among the techniques lies in the timing sequence, i.e., the choice of illumination/exposure times and the time between image frames. These are chosen with respect to the expected range of seeding particle movement in time and the desired temporal resolution of flow fluctuations. Difficulties arise when very large differences in velocity occur within a single planar field of view, such that any single timing sequence is inappropriate for certain regions of the observed field. If for instance, the illumination time is adjusted to suit a PIV measurement at low velocities, high velocities in other flow regions will result in streaks. One question to be addressed is therefore, to what extent PIV processing algorithms can properly cope with streaks, which are possibly truncated in either of the consecutive images? In this context, the notion of ‘truncation bias’ will be introduced and evaluated. The present study investigates the possibility of combining image processing algorithms of PIV and PSV in a hybrid manner, while using a single timing sequence for image recording. After image recording, the images are segmented into regions according to which processing algorithm is most appropriate—PIV or PSV—and the respective algorithm is applied to each of the segments. This is followed by a recombination of the computed velocity field from each segment to obtain a result for the total field of view. The performance of this hybrid approach will be evaluated by generating and processing synthetic input data from a direct numerical simulation of a transitional boundary layer. An example laboratory flow is then used to demonstrate the hybrid technique in practice.</p></div>","PeriodicalId":554,"journal":{"name":"Experiments in Fluids","volume":"66 6","pages":""},"PeriodicalIF":2.3,"publicationDate":"2025-05-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144108509","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":"Full-domain POD modes from PIV asynchronous patches","authors":"Iacopo Tirelli,&nbsp;Adrian Grille Guerra,&nbsp;Andrea Ianiro,&nbsp;Andrea Sciacchitano,&nbsp;Fulvio Scarano,&nbsp;Stefano Discetti","doi":"10.1007/s00348-025-04029-6","DOIUrl":"10.1007/s00348-025-04029-6","url":null,"abstract":"<div><p>A method is proposed to obtain full-domain spatial modes based on proper orthogonal decomposition (POD) of particle image velocimetry (PIV) measurements taken at different (overlapping) spatial locations. This situation occurs when large domains are covered by multiple non-simultaneous measurements and yet the large-scale flow field organization is to be captured. The proposed methodology leverages the definition of POD spatial modes as eigenvectors of the spatial correlation matrix, where local measurements, even when not obtained simultaneously, provide each a portion of the latter, which is then analyzed to synthesize the full-domain spatial modes. The measurement domain coverage is found to require regions overlapping by <b>50–75%</b> to yield a smooth distribution of the modes. The procedure identifies structures twice as large as each measurement patch. The technique, referred to as <i>Patch POD</i>, is applied to planar PIV data of a submerged jet flow where the effect of patching is simulated by splitting the original PIV data. Patch POD is then extended to <b><i>3D</i></b> robotic measurement around a wall-mounted cube. The results show that the patching technique enables global modal analysis over a domain covered with a multitude of non-simultaneous measurements.</p></div>","PeriodicalId":554,"journal":{"name":"Experiments in Fluids","volume":"66 6","pages":""},"PeriodicalIF":2.3,"publicationDate":"2025-05-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s00348-025-04029-6.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143938172","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":"Dynamics of vortex interaction and entrainment characteristics in inclined elliptic jets using sparse track-enhanced volumetric measurements","authors":"Xin Zeng,&nbsp;Hao Qu,&nbsp;Chuangxin He,&nbsp;Yingzheng Liu,&nbsp;Lian Gan","doi":"10.1007/s00348-025-04038-5","DOIUrl":"10.1007/s00348-025-04038-5","url":null,"abstract":"<div><p>This work is a further discussion about elliptical jet flows (Zeng et al. in Exp Fluids 64:142, 2023) by exploring how variations in nozzle shape enhance flow control efficiency. The study examines the dynamic evolution of vortex interactions and their positive effects on the entrainment of inclined elliptical jets (with inclination angles of 30° in both the major and minor planes) compared to non-inclined elliptical jets. Experiments were conducted at an aspect ratio (AR) of 2 and a Reynolds number of approximately 3000. Time-resolved tomographic particle image velocimetry (Tomo-PIV) and three-dimensional Lagrangian particle tracking (3D LPT) measurements were employed to capture the flow dynamics in detail. The Eulerian velocity field datasets obtained from Tomo-PIV are enhanced using high-precision tracks from 3D LPT measurements, improving the accuracy of velocity field reconstruction. Statistical analyses indicate that inclined elliptical jets exhibit greater mass entrainment characteristics and higher momentum flux compared to non-inclined elliptical jets. The power spectral densities (PSDs) and time-domain spectral proper orthogonal decomposition (td-SPOD) results reveal that for the major-plane inclined-A nozzle, both the leading and trailing vortex rings share the same dominant frequency of St = 0.28, suggesting that vortex pairing and merging in the 30° inclined-A jet may be a periodic process. After vortex merging at approximately <i>Y</i>/<i>D</i>_<i>e</i> ≈ 3.5, the first axis-switching is completed, indicating that axial switching is suppressed in the major-plane inclined-A elliptical jet compared to the non-inclined case. In contrast, for the minor-plane inclined-B jet, the dominant frequencies of the leading and trailing vortex rings are St = 0.28 and St = 0.61, respectively. In some instances, two consecutive large-scale vortex rings corresponding to SPOD mode (3,4) do not merge downstream; instead, they develop independently and eventually break down separately. At the axis-switching plane (<i>Y</i>/<i>D</i>_<i>e</i> = 2.5), during both the merging and axis-switching processes of vortex rings in the two inclined nozzles, a significant number of streamwise vortex structures are generated. This phenomenon substantially contributes to an increased mean entrainment rate, further enhancing the mixing characteristics of inclined elliptical jets.</p><h3>Graphical Abstract</h3>\u0000<div><figure><div><div><picture><source><img></source></picture></div></div></figure></div></div>","PeriodicalId":554,"journal":{"name":"Experiments in Fluids","volume":"66 6","pages":""},"PeriodicalIF":2.3,"publicationDate":"2025-05-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143938173","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":"Data-driven spatiotemporal analysis of cloud cavitation by means of spectral proper orthogonal decomposition","authors":"Grigorios Hatzissawidis,&nbsp;Moritz Sieber,&nbsp;Kilian Oberleithner,&nbsp;Peter F. Pelz","doi":"10.1007/s00348-024-03949-z","DOIUrl":"10.1007/s00348-024-03949-z","url":null,"abstract":"<div><p>The global dynamics of cloud cavitation are not always obvious; cloud cavitation may exhibit chaotic, multimodal and intermittent behaviour, where dominant flow structures are hidden to the naked eye. To address this, spectral proper orthogonal decomposition (SPOD) is applied, a method that can continuously transition between proper orthogonal decomposition (POD) and discrete Fourier transformation (DFT)/dynamic mode decomposition (DMD). This provides the opportunity to break down the complex dynamics of interacting and transient processes into interpretable modal bases. Experiments were conducted in a high-speed cavitation tunnel using a two-dimensional NACA 0015 hydrofoil at a fixed Reynolds number of <span>(8 times 10^5)</span> and an incidence of <span>(12^circ)</span> for varying cavitation numbers. The cavitation was recorded using a synchronised dual-camera set-up with simultaneously captured pressure signals. Shockwave-driven and re-entrant flow-driven cloud shedding is identified, as well as the transition regime in between, exhibiting more complex behaviour. The transition from shockwave-driven to re-entrant flow-driven cloud cavitation is smooth, with shockwaves becoming more dominant as the cavitation number decreases. SPOD modes allow for a frequency and amplitude variation, which successfully decomposes the data into the dominant modes, whereas classical modal decomposition methods such as POD and DMD do not provide interpretable decompositions. SPOD grants access to a transient analysis of the data via the SPOD time coefficients. We validate the SPOD results using space–time plots and power spectral density (PSD) of the pressure signals, being in good agreement with the SPOD spatial modes and time coefficients. The complex time coefficients give access to instantaneous mode frequencies and allow calculating a standard deviation of the frequency modulation of the modes. The findings provide a deep insight into the spatial and temporal behaviour of cloud cavitation and support the understanding of its physics.</p></div>","PeriodicalId":554,"journal":{"name":"Experiments in Fluids","volume":"66 5","pages":""},"PeriodicalIF":2.3,"publicationDate":"2025-05-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s00348-024-03949-z.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143918995","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}