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Niobium superconductive radio frequency cavities (SRF cavities) are commonly employed in linear accelerator; very pure, clean, and smooth internal walls are required to make the cavity working properly and with a high Q factor. Typically, to achieve a suitable surface quality the SRF cavities are subjected to a surface treatment called Buffered Chemical Polish (BCP), the latter uses a strong concentrated acids mixture flowing through the cavity to chemically etch a thin niobium layer (∼250 μm). A viable way to understand and optimize the BCP process is by using computational fluid dynamic (CFD); however, the experimental validation of the numerical and physical models is required to confidently use CFD results. The aim of our work is to investigate the fluid dynamics of the BCP process by using the Particle Image Velocimetry (PIV) and the refractive index matching (RIM) techniques, and to provide data to validate CFD simulations. The paper describes and briefly analyse the experimental setup and the preliminary results achieved so far.

A joint measurement campaign has been performed by the MARS project partners NUAA, CNRS (Poitiers) and DLR. The objective was to apply advanced measurement techniques to the actuator types which turned out to be most promising in the previous investigations. The selected devices were synthetic jet actuators from NUAA and plasma actuators from CNRS. Both actuator types were investigated in a backward facing step (BFS) geometry. Additional measurements took place using the synthetic jet actuator in a NACA-0015 profile from NUAA. For the measurements, a tomographic PIV and a long-distance microscopic stereo PIV measurement system—both capable to provide time-resolved data—have been set up by DLR in the one meter wind tunnel (1MG) at DLR Gottingen. The successful completion of this intercontinental experimental cooperation provides results which are a valuable data base for comparison with and validation of numerical methods.

This paper describes a set of measurements taken at the Caltech Lucas Wind Tunnel, along with Computational Fluid Dynamic analyses, on a wing-body configuration. The configuration is designed to produce regions of separation in the juncture where the wing meets the body. Detailed near- and off-body stereo PIV measurements in the juncture flow are compared with predictions from computational methods based on the Reynolds Average Navier Stokes formulation. The results from the experimental measurements will become part of a database of high fidelity measurements, to be used for calibration of turbulence models and validation of emerging computational techniques.

Dual-plane stereoscopic particle image velocimetry (PIV) is capable of quantifying the flow field in terms of three-component (3C) flow vectors and 3C vorticity vectors simultaneously. Here, we present a test rig to carry out the 20 kHz dual-plane stereo PIV measurements on a premixed swirling flame by using a two-legged burst-mode laser. Other than the traditional methods employing the laser polarization direction and the two-color separation methods, two same-color laser sheets with a 100 ns delay were adopted to separate the imaging processes for the two pairs of cameras using the image straddling method. Each laser sheet with the same wavelength of 532 nm has a pulse cyclic frequency of 20 kHz within each burst generated by the high-repetition-rate burst-mode laser. 3C velocity vectors of a swirling flame were obtained based on the sequential particle images for each laser sheet. In spite of non-perfect simultaneous flow measurements on the two spatially separated laser sheets, the velocity error caused by the 100 ns delay on top of a 50 μs duration, which was used for the velocity vector calculation, is negligible. This short-delay separation method significantly simplifies the experimental setup for dual-plane stereo PIV measurements, especially for low-speed flows.

Prosthetic heart valves can be associated to mechanical loading of blood, potentially linked to complications (hemolysis and thrombogenicity) which can be clinically relevant. In order to test such devices in pulsatile mode, pulse duplicators (PDs) have been designed and built according to different concepts. This study was carried out to compare anemometric measurements made on the same prosthetic device, with two widely used PDs.The valve (a 27-mm bileaflet valve) was mounted in the aortic section of the PD. The Sheffield University PD and the RWTH Aachen PD were selected as physical models of the circulation. These two PDs differ mainly in the vertical vs horizontal realization, and in the ventricular section, which in the RWTH PD allows for storage of potential energy in the elastic walls of the ventricle. A glassblown aorta, realized according to the geometric data of the same anatomical district in healthy individuals, was positioned downstream of the valve, obtaining 1:1 geometric similarity conditions. A NaI-glycerol-water solution of suitable kinematic viscosity and, at the same time, the proper refractive index, was selected. The flow field downstream of the valve was measured by means of the stereo-PIV (Particle Image Velocimetry) technique, capable of providing the complete 3D velocity field as well as the entire Reynolds stress tensor. The measurements were carried out at the plane intersecting the valve axis.A three-jet profile was clearly found in the plane crossing the leaflets, with both PDs. The extent of the typical recirculation zone in the Valsalva sinus was much larger in the RWTH PD, on account of the different duration of the swirling motion in the ventricular chamber, caused by the elasticity of the ventricle and its geometry.The comparison of the hemodynamical behaviour of the same bileaflet valve tested in two PDs demonstrated the role of the mock loop in affecting the valve performance.

A stereo PIV system for investigating complex highly turbulent flows, typical for gas flows in aircraft engines and gas turbines, is developed, and the values obtained for the velocity are compared with the results measured using a laser Doppler anemometer. The features of the use of the PIV system for measurements in three-dimensional highly turbulent flows with high velocity gradients are investigated.

Stereoscopic PIV was used to measure the three-component velocity distribution around a live fish. At the same time, shadow images of the fish were captured by additional cameras in order to reconstruct the three-dimensional shape of the fish. The side jet shed against the swept tail during turning was evident in the results. The height of the jet was approximately equal to the height of the tail fin, and a vortex ring was observed around the side jet. Based on the circulation and diameter of the vortex ring, the impulse and time-averaged force in terms of the side jet were estimated.

It is assumed that cerebral homodynamics is an important factor for the cerebrovascular disorders such as subarachnoid hemorrhage. Since a blood vessel has bend and bifurcation with pulsatile blood flow, the flow structure becomes complex and in the three-dimensions. In order to obtain the information on velocity components at an orbital location and time, the stereo PIV technique is applied to measure and visualize flow in the realistic cerebral aneurysm model, which is based on the medical image data. Because it is difficult to place the calibration plate, the paper presents the calibration method such that laser beams create calibration points. As a result, the flow structure along the aneurysm is observed successfully.

It is assumed that cerebral homodynamics is an important factor for the cerebrovascular disorders such as subarachnoid hemorrhage. Since a blood vessel has bend and bifurcation, the flow structure is in the three-dimensions. The Stereo PIV is a suitable method for measurement of complicated flow phenomena. The Stereo PIV uses a plate in a measurement domain for calibration. However, if the domain is complicated, it is difficult to place such an object. In this research, we have presented a noninvasive calibration method using a calibration point created by laser beams.

Unsteady three-dimensional flow phenomena must be investigated and well understood to be able to design devices to control such complex flow phenomena in order to achieve the desired behavior of the flow and to assess their performance, even in harsh industrial environments. Experimental investigations for flow control research require measurement techniques capable to resolve the flow field with high spatial and temporal resolution to be able to perceive the relevant phenomena. Particle Image Velocimetry (PIV), providing access to the unsteady flow velocity field, is a measurement technique which is readily available commercially today. This explains why PIV is widely used for flow control research. A number of standard configurations exist, which, with increasing complexity, allow capturing flow velocity data instantaneously in geometrical arrangements extending from planes to volumes and in temporal arrangements extending from snapshots to temporarily well resolved data. With increasing complexity these PIV systems require advancing expertise of the user and growing investment costs. Using typical problems of flow control research, three different standard PIV systems will be characterized briefly. It is possible to upgrade a PIV system from a simple planar to a “high end” tomographic PIV system over a period of time, if sufficient PIV expertise can be built up and budget for additional investments becomes available.

This paper describes an experimental study on the propagation of premixed flames through a flow with well-defined turbulence characteristics. In this study, multi-plane OH planar laser-induced fluorescence (OH-PLIF) and stereoscopic particle image velocimetry (SPIV) were applied simultaneously at 10 kHz to measure the local three-dimensional displacement velocity of unstabilized, freely propagating flames passing through a premixed flow of methane and air. The dual-plane OH-PLIF data was used to track both reaction zone location and flame-normal orientation, while SPIV was used to track the three-component velocity field. The vectorial difference of the two produces a direct, time-resolved measurement of the local 3D displacement velocity of the flame. The use of unstabilized, freely propagating flames eliminates spatiotemporal dependence of local 3D displacement velocity associated with burner- or aerodynamically-stabilized test flames. Statistics of local 3D displacement velocities are presented. These show values ranging from slightly negative up to approximately eight times the laminar flame speed. Instantaneous flame-normal orientation with respect to the direction of local fluid velocity is identified as one parameter affecting instantaneous displacement velocities.

The present experimental work investigates the near surface flow structure and aerodynamic characteristics of X-45 type non-slender delta wing planform using dye visualization, Stereoscopic Particle Image Velocimetry (stereo-PIV) and aerodynamic load measurements. The instantaneous images are acquired on the plan-view plane within 5o ≤ a ≤ 20o to calculate the time-averaged flow data. In order to compare flow structures with other non-slender wing planforms such as delta and lambda, previously presented dye visualization and stereo-PIV results are also provided. It can be concluded that vortical flow with a pair of well-defined LEVs over X-45 develop at very low angles of attack, and form close to the wing surface similar to delta and lambda planforms. The stall occurs at an angle of attack a = 32o, whereas stalling is evident at relatively lower angles of attack for simple delta wing., Mevcut deneysel çalışma ile X-45 tipi delta kanat modeli üzerinde oluşan yakın yüzey akış yapısı ve aerodinamik karakteristikleri, boya görüntüleme, üç boyutlu Stereoskopik Parçacık Görüntüleme Tekniği (stereo PIV) ve aerodinamik kuvvet ölçümleri kullanılarak araştırılmıştır. Anlık görüntüler ile üst görünüş düzleminde zaman ortalama akış verileri 5o ≤ α ≤ 20ohücum açılarında elde edilmiştir. Delta ve Lamda tipi diğer düşük süpürme açılarına sahip delta kanat modelleri ile akış yapılarını karşılaştırmak için önceki sunulan boya görüntüleri ve steroPIV sonuçları kullanılmıştır. Düşük hücum açılarında X-45 tipi delta kanat modeli üzerinde iyi tanımlanmış ön uç yanal girdaplar delta ve lamda modellerine benzer kanat yüzeyinde oluşmaktadır. X-45 tipi delta kanat modelinde ölü akış yapısı α = 32ode oluşmaktayken basit delta kanat ve lamda modellerinde daha düşük hücum açılarında meydana gelmektedir

International audience; The present paper addresses an experimental investigation of the dynamic and the control of a longitudinal vortex emanating from the front pillar of a dihedral bluff body corresponding to a simplified geometry of an automotive vehicle. The control system is based on a thin rectangular slot located along the lateral edge of the windscreen and provides steady suction or blowing normal to the lateral face of the geometry. Qualitative results obtained with dye visualizations and Schlieren photos provide an overview of the impact of the control on the topology of the vortex flow. Quantitative Stereo-PIV measurements and unsteady forces measurements are used to characterize the interaction between the control and the longitudinal vortex. Controls that change significantly the topology of the vortex core and reduce aerodynamic drag are identified.

The performance of three implementations of pinhole-based camera models for use in common light-sheet imaging arrangements is investigated on the background of application to particle image velocimetry (PIV) and Doppler global velocimetry (DGV). Calibration data obtained from translated planar calibration targets was found to yield camera attitude within 0.1° on four different test cases with object distance varying as little as 2% depending on the choice of camera model. Camera calibration using data from a single image of coplanar points is considered a viable alternative to manual triangulation of camera positions but is restricted to off-normal viewing directions.

Two different experiments have been carried out by means of multi-plane and stereo PIV in order to analyze the structures of late transitional boundary layer flows. To achieve a better understanding of the characteristics and structures of “natural” transition scenarios, measurements in different complex initiated transitional boundary layer flows on a wing glove of a 2-D airfoil of the Tech. Univ. of Berlin have been performed. Additionally, artificially-generated turbulent spots in a laminar flat-plate boundary layer have been investigated in detail. Instantaneous velocity vector fields measured in different planes parallel to the wall and special statistical approaches applied to the vector fields of turbulent spots, yield valuable information about the structures leading to the breakdown process and governing the turbulent mixing of the boundary layer flow.

Flow structure behind the backward facing step in a narrow channel was studied in details. The step height was 25% of the channel width. The structure of the region just behind the step forming the back-flow region is studied in details using stereo PIV technique. Time-mean 3D structures behind the step are evaluated and shown in the paper. (© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

A unique, highly modular and flexible underwater system for stereoscopic particle image velocimetry (PIV) measurements has been designed, manufactured and tested. The instrument is intended for planar three-dimensional velocity measurements in large facilities such as water tow tanks and tunnels. The performance of the system is assessed in four major stereoscopic configurations. Errors under 2% for the in-plane components and 4% for the out-of-plane components are found. The system is tested in the INSEAN large circulating water channel where the measurement of the flow around a model ship oriented at a moderate yaw angle is performed and puts into evidence the main features of the flow.

Active and passive approaches to control the velocity and concentration of a high speed round particle-laden jet are investigated experimentally using a stereo PIV system. Active control of the flow field and the particles’ velocity and concentration fields, via the addition of swirl to the carrier jet, has shown to have a significant effect in altering both phases. Control is also affected by placing passive pins at the jet exit plane, which results in alteration of the velocity in planes across and normal to the pins. Furthermore, the mixing is increased and the spreading rate is modified. Depending on the number of pins used and their azimuthal location, their interaction with the carrier jet flow lead to the modification of the cross-flow shape of the jet and the direction of the flow.Copyright © 2003 by ASME