Visualisation and quantitative analysis of the near nozzle formation and structure of a high pressure water jet in air and water

[EN] High pressure water jets (HPWJ) with Reynolds numbers in the scale of 104 are visualised by high speed photography in air and water. Moreover, suitable measurement techniques are tested and verified by quantitative analysis of the emerging jet to identify the influence of the surrounding fluid on the HPWJ. The HPWJ process known from industrial applications can be adapted to the field of rock drilling. In this specific case, the HPWJ is used to cut and destroy rock in deep geothermal reservoirs. The process is known as jet drilling. Although there have been research activities in this field, the process itself is not well understood so far and practical applications are rare. Therefore, the aim of our work is the visualisation of the process to increase the knowledge of waterjet and rock interactions. High speed photography in terms of shadowgraph experiments is used for visualisation. Moreover, an estimation of the fluid velocity on the boundary of the HPWJ in air is performed. For this, the shadowgraph images are evaluated with the double-frame technique well known with particle image velocimetry (PIV). Analysis of both the structure and the velocity distribution of the HPWJ in water is done by combined PIV and laser induced fluorescence (LIF) analysis with fluorescent dye.This work is being funded through the “FH-Struktur2016” venue for universities of applied sciences by the ministry for innovation, science and research of the state of Nordrhein-Westfalen, Germany (AZ: 322-8.03.04.02).Jasper, S.; Hussong, J.; Lindken, R. (2017). Visualisation and quantitative analysis of the near nozzle formation and structure of a high pressure water jet in air and water. En Ilass Europe. 28th european conference on Liquid Atomization and Spray Systems. Editorial Universitat Politècnica de València. 947-953. https://doi.org/10.4995/ILASS2017.2017.4736OCS94795

Nanoparticle image velocimetry at topologically structured surfaces

Nanoparticle image velocimetry ͑nano-PIV͒, based on total internal reflection fluorescent microscopy, is very useful to investigate fluid flows within ϳ100 nm from a surface; but so far it has only been applied to flow over smooth surfaces. Here we show that it can also be applied to flow over a topologically structured surface, provided that the surface structures can be carefully configured not to disrupt the evanescent-wave illumination. We apply nano-PIV to quantify the flow velocity distribution over a polydimethylsiloxane surface, with a periodic gratinglike structure ͑with 215 nm height and 2 m period͒ fabricated using our customized multilevel lithography method. The measured tracer displacement data are in good agreement with the computed theoretical values. These results demonstrate new possibilities to study the interactions between fluid flow and topologically structured surfaces

Analysis of tracer particle characteristics for micro PIV in wall-bounded gas flows

The investigation of the gas flow in a working fuel cell by means of optical measurement techniques like micro Particle-Image Velocimetry (µPIV) requires the generation of suitable tracer particles. In this work the analysis of tracer particle characteristics is described which serves as a means to identify suitable particles for wall-bounded gas flows. Several materials and different types of particle generators were examined to check for obtainable particle size distributions and particle concentrations. A simple experiment was designed to investigate the capability of the generated particles to adequately follow the flow. An optically transparent micro-channel with a 90° elbow was manufactured and the µPIV measurement technique is applied. Firstly, the gas-flow seeded with tracer particles is investigated within this 90° elbow micro-channel. Secondly, to check whether the measured flow structure in this previous case matches with the real flow, the same flow conditions are investigated using water as working fluid with solid tracer particles taking into account Re-ynolds number similarity. Thirdly, CFD-calculations using the same reference parameters as in the experimental investiga-tions were performed to quantify the deviation of the particle traces from the real flow streamlines. The results show ethy-lene glycol to be a suitable tracer material since the obtained tracer particles are optically detectable without severe image post-processing and since this material can be easily transformed into an aerosol with suitable concentrations and particle size distributions. The application of the µPIV technique on such a gaseous particle laden flow provided promising results concerning the intended application of this technique to operating fuel cells

µPIV measurement of the 3D velocity distribution of Taylor droplets moving in a square horizontal channel

Abstract: This paper presents a µPIV measurement of the 3D2C velocity distribution of Taylor droplets moving in a square horizontal microchannel at Cac= 0.005 and Rec= 0.051. We reconstruct the third velocity component and present an accuracy assessment of the reconstruction based on a volume flow balance of the 3D3C velocity field. The velocity field allows the investigation of the 3D flow features such as stagnation regions and the shear rate distribution. The maximum shear rate is located at the entrances and exits of the wall films and at the corner flow (gutter) bypassing the Taylor droplet. The regions of high strain correspond to the cap positions of the Taylor droplets. An experimental data set allows visualization of the streamlines of the velocity distribution on the interface of a Taylor droplet and to directly relate it to the main and secondary vortices of the droplet phase velocity field. The measurement data are provided as a digital resource for the validation of numerical simulation or further assessment. Graphic abstract: [Figure not available: see fulltext.]Fluid Mechanic

Reconstruction of the 3D pressure field and energy dissipation of a Taylor droplet from a μ PIV measurement

In this study, we reconstruct the 3D pressure field and derive the 3D contributions of the energy dissipation from a 3D3C velocity field measurement of Taylor droplets moving in a horizontal microchannel (Ca c= 0.0050 , Re c= 0.0519 , Bo = 0.0043 , λ=ηdηc=2.625). We divide the pressure field in a wall-proximate part and a core-flow to describe the phenomenology. At the wall, the pressure decreases expectedly in downstream direction. In contrast, we find a reversed pressure gradient in the core of the flow that drives the bypass flow of continuous phase through the corners (gutters) and causes the Taylor droplet’s relative velocity between the faster droplet flow and the slower mean flow. Based on the pressure field, we quantify the driving pressure gradient of the bypass flow and verify a simple estimation method: the geometry of the gutter entrances delivers a Laplace pressure difference. As a direct measure for the viscous dissipation, we calculate the 3D distribution of work done on the flow elements, that is necessary to maintain the stationarity of the Taylor flow. The spatial integration of this distribution provides the overall dissipated energy and allows to identify and quantify different contributions from the individual fluid phases, from the wall-proximate layer and from the flow redirection due to presence of the droplet interface. For the first time, we provide deep insight into the 3D pressure field and the distribution of the energy dissipation in the Taylor flow based on experimentally acquired 3D3C velocity data. We provide the 3D pressure field of and the 3D distribution of work as supplementary material to enable a benchmark for CFD and numerical simulations. Graphical abstract: [Figure not available: see fulltext.]Fluid Mechanic

Nanoparticle image velocimetry at topologically structured surfaces

Nanoparticle image velocimetry (nano-PIV), based on total internal reflection fluorescent microscopy, is very useful to investigate fluid flows within ∼100 nm from a surface; but so far it has only been applied to flow over smooth surfaces. Here we show that it can also be applied to flow over a topologically structured surface, provided that the surface structures can be carefully configured not to disrupt the evanescent-wave illumination. We apply nano-PIV to quantify the flow velocity distribution over a polydimethylsiloxane surface, with a periodic gratinglike structure (with 215 nm height and 2 μm period) fabricated using our customized multilevel lithography method. The measured tracer displacement data are in good agreement with the computed theoretical values. These results demonstrate new possibilities to study the interactions between fluid flow and topologically structured surfaces

Optimization of multiplane ?PIV for wall shear stress and wall topography characterization

Multiplane ?PIV can be utilized to determine the wall shear stress and wall topology from the measured flow over a structured surface. A theoretical model was developed to predict the measurement error for the surface topography and shear stress, based on a theoretical analysis of the precision in PIV measurements. The main parameters that affect the accuracy of the measurement are identified. The effect of different parameter settings is studied by means of Monte Carlo simulations, and the results are compared with an experimental test case. The results are used to determine the recommended parameter settings for this measurement approach.Process and EnergyAerospace Engineerin