Laser Doppler Velocimetry Research Articles

Turbulence statistics estimation across a step change in roughness via interpretable network-based modelling

Abstract This study proposes a data-driven methodology to complement existing time-series measurement tools for turbulent flows. Specifically, a cluster-based transition network model is employed for the estimation of velocity time traces and their corresponding statistics. The method is tested on a laboratory-modelled turbulent boundary layer over a step change in surface roughness, where velocity time series are recorded for training and validation purposes via Laser Doppler Anemometry. Results show that our approach can estimate velocity and momentum flux statistics within experimental uncertainty over a rough surface through an unsupervised approach, and across the step change in roughness through a semi-supervised variant. The friction velocity across the domain is also estimated with 10\% relative error compared to the measured value. The proposed methodology is interpretable robust against the main methodological parameters. A reliable data-driven framework is hence provided that can be integrated within existing laboratory setups to supplement or partially replace measurement systems, as well as to reduce wind tunnel running times.

Self-mixing thinly sliced ruby laser for laser Doppler velocimetry with high optical sensitivity

In self-mixing laser Doppler velocimetry (LDV), the motion of a moving target is observed by using intensity-modulated laser light detected by a simple photodetector. Here, the self-mixing laser output modulation takes place, reflecting the pronounced effective loss modulation index, which is proportional to the fluorescence-to-photon lifetime ratio. The fluorescence lifetime of a ruby laser is extremely long, so if a ruby crystal can be used as a laser light source for a self-mixing LDV system, high-sensitivity LDV measurements can be performed with it. We describe a method for velocimetry of moving targets using self-mixing LDV in which a CW oscillating ruby laser is the light source. The oscillation mechanism of the thin-slice ruby laser with a large fluorescence-to-photon lifetime ratio, which is suitable for LDV measurements, is clarified and the results of highly sensitive LDV measurements are presented, featuring nonlinear dynamics observed associated with the self-mixing velocimetry experiment. The measurement accuracy is clarified by measuring the rotating disc with various conditions using self-mixing LDV.

Experimental Design Validation of a Swirl-Stabilized Burner With Fluidically Variable Swirl Number

Abstract Swirling flows are commonly used for flame stabilization in gas turbine combustors, which are hence equipped with suitable swirler units. In these units the air rotation, quantified by the swirl number, is fixed through the geometry and represents a parameter significantly affecting flame stability and dynamics. The possibility of a continuous swirl variation, on the other hand, would be advantageous for the assessment and control of thermoacoustic instabilities. This is especially true for fuel-flexible applications, for which different swirl numbers are needed to stabilize flames arising from the combustion of different fuels. Most swirl-varying systems rely on mechanical adjustments. In this work, instead, a novel swirl-stabilized burner is investigated experimentally, which is based exclusively on fluidic actuation. For the experimental assessment of the resulting flow field, the axial and azimuthal velocity components are determined through laser Doppler anemometry (LDA) measurements. The measurements are performed in a volume downstream of the burner's mixing tube. The data are processed and computed into swirl-numbers in order to quantify the degree of swirl as a function of the fluidic actuation. The characteristics of two different burner geometries are investigated, with and without a central cone within the swirler, respectively. The configuration with the cone is found to generate higher swirl over the investigated operational range. For this configuration, the technically relevant operating range is determined in which the swirl number can be continuously set from zero to around 0.9. Our experimental results show that fluidic actuation is a viable way to continuously change the swirl number, and that the achievable swirl range is quantitatively comparable to that of state-of-the-art swirl-stabilized burners.

Dual-frequency laser Doppler velocimetry based on long short-term memory

Dual-frequency laser Doppler velocimetry based on long short-term memory

Spatial and frequency identification of the dynamic properties of thin plates with the Frequency-Adapted Virtual Fields Method

Vibroacoustic inverse methods use the measured response of a vibrating structure to identify a structural parameter or a dynamic load. Two inverse methods are considered, the Force Analysis Technique (FAT) and the Virtual Fields Method (VFM). The Corrected Force Analysis Technique (CFAT) is a variant of FAT that corrects its singularity. This correction allows the method to be applied in the high-frequency domain, when the number of measurement points per flexural wavelength becomes small. In this study, the proposed novelty is the development of a Frequency-Adapted VFM (FA VFM) to the case of a Love–Kirchhoff plate. Thanks to this method, the VFM can now be applied to identify the equivalent bending stiffness and structural damping of a thin plate when the number of measurement points per wavelength is small. The method has previously been developed for an Euler–Bernoulli beam. An experimental identification of the complex bending stiffness of an locally damped aluminium plate using Laser Doppler Velocimetry (LDV) data and the developed method is performed. The experimental study shows for the first time that the FA VFM can be used to map the equivalent bending stiffness and structural damping as a function of position on a plate and identify these parameters as a function of frequency over a large frequency band. The results of the Frequency-Adapted VFM are compared with those of CFAT and the classical VFM approach. FA VFM results are more accurate than those of classical VFM and similar to those of CFAT.

Wind tunnel measurements of cross-ventilation flow in a realistic building geometry: Influence of building partitions and wind direction

Wind tunnel measurements have widely been used for validation of computational fluid dynamics simulations of natural ventilation airflows. However, the majority of such measurements employed simple generic single-zone buildings, while there is a lack of studies on realistic buildings including flow-critical geometrical features (e.g. internal partitions). To assess the effect of internal partitions at different incident flow angles (α = 0° and α = 30°), wind tunnel measurements of velocities in and around a cross-ventilated realistic residential building (with and without internal partition) were performed. Measurements were conducted at a geometric scale 1:40, using laser Doppler anemometry. Results indicate a large impact of the internal partition on indoor airflow distribution and resulting ventilation flow rates. For instance, for α = 0°, on the partitioned building side, regions of velocity increase (from ∼0 m/s to ∼80% of the outdoor reference velocity, Uref), but also regions of velocity decrease (from ∼50% of Uref to ∼0 m/s) were observed. The ventilation flow rate through the windows at the partitioned side decreased by 23% and 32%, respectively. For the partitioned building, a change from α = 0° to α = 30° resulted in regions of velocity increase from 0 m/s to ∼60% of Uref.

Assessment of the gate rudder system on the cavitation and underwater radiated noise characteristics of a containership

Predictions of model tests and numerical studies (Sasaki et al., 2016), both at model- and full-scale, as well as results of the recent sea trials, have demonstrated that the Gate Rudder System (GRS), a novel energy-saving device, increases propulsive efficiency and reduces fuel consumption of a ship. Despite detailed investigations into the impact of the GRS on powering performance and manoeuvring, studies on its effect on cavitation phenomena and underwater radiated noise (URN) are limited. In this study, the effects of the GRS on cavitation and URN were investigated experimentally and compared to a conventional rudder system (CRS). Cavitation observations and URN measurements were conducted on sister ships -one with the CRS, SAKURA, and the other with the GRS, SHIGENOBU- at Istanbul Technical University Cavitation Tunnel (ITUKAT). A wooden ship model was built to be used in resistance and propulsion tests and then truncated due to the cavitation tunnel's test section length limitation of 5.5 m. Numerical studies were performed for both the original and truncated models at model- and full-scale to assess their wake characteristics. The nominal wake distributions along the CRS and GRS propeller planes were measured using a Laser Doppler Velocimetry (LDV) system. The test results supported the findings of the sea trials, showing that the GRS significantly reduces URN levels by up to 10 dB at high-frequencies, compared to the CRS, due to its effect on propeller loading and cavitation phenomenon.

Swirl-induced hysteresis in a sudden expansion flow

Swirling sudden expansion flows are complex flow fields containing several coherent structures that depend on the swirl number and can exhibit hysteresis behavior between increasing and subsequently decreasing swirl levels. While these flows have extensively been studied in simple geometries, results involving special designed nozzles are scarce. Therefore, this paper aims to provide insights into a more complex geometry, specifically a two-step conical expansion with a converging outlet. Experimental data is acquired for changing swirl numbers at a Reynolds number in the range of 35, 000. Stereoscopic Particle Image Velocimetry is employed to characterize downstream flow structures, while Laser Doppler Velocimetry is used to characterize upstream structures and to determine the inlet swirl number. Several distinct flow patterns are found as a function of the swirl number and the identified flow patterns include, in order of increasing swirl, a Closed Jet Flow, an Open Jet Flow (OJF), and a Coandã Jet Flow (CoJF). A central positive axial velocity is noted for both OJF and CoJF downstream of the expansion due to the converging outlet geometry. At higher swirl numbers, Vortex Breakdown moves upstream into the nozzle until a negative axial velocity is noted in the inlet tube. For these higher swirl numbers, no hysteresis is observed in the inlet tube between increasing and subsequently decreasing swirl. However, downstream of the nozzle, it is observed that the CoJF detaches at a lower swirl number than the swirl number required for attachment, indicating a hysteresis effect between in- and decreasing swirl.

Analysis of droplet motion in cavity zone of rotating packed bed

Droplet motion in outer cavity zone of rotating packed bed is a complex phenomenon that requires analysis of liquid and gas flow to clarify influences of factors such as rotation speed, liquid flow rate, or gas flow rate. In this study, hydrodynamics is described using laser Doppler velocimetry and high-resolution visualization for droplet motion characterization. The results reveal that droplet motion initially depends on the peripheral velocity of the packing, while further from the packing, it loses kinetic energy mainly due to the drag force caused by the surrounding gas. Two-way coupling is investigated as both phases interact with each other. Rankine vortex theory is applied to simulate gas flow in the outer cavity zone. A model, based on Newton’s second law, is developed to predict droplet dynamics, including impingement velocity, trajectory length, and total residence time. Validation of the model shows that it can predict the liquid velocity in the outer cavity zone accurately. Upon impingement of droplets on the casing, part of the liquid rebounds as secondary droplets into the cavity, where they circulate with the gas flow. Overall, this study provides insights into droplet dynamics in the rotating packed bed and offers a basis for optimizing process efficiency and design in various applications, including chemical processing and environmental engineering.

Laser Doppler Anemometry of a Dispersed Mixture of Two Liquids with Similar Densities

Laser Doppler Anemometry of a Dispersed Mixture of Two Liquids with Similar Densities

Laser Doppler Anemometry of Cavitating Hydrofoil in a Slit

Laser Doppler Anemometry of Cavitating Hydrofoil in a Slit

Laser Doppler velocimetry based on multi-core fiber

Fiber laser doppler velocimetry has the advantages of high measurement accuracy, wide measurement range and non-contact measurement. Usually, fiber optic bundles are used in traditional measurement systems. Multi-core fiber (MCF) is a new structure of optical fiber with multiple cores in the same cladding and a uniform core layout. Compared to traditional fiber bundles, multi-core fibers have advantages in integration and volume. Therefore, by taking advantage of the special spatial arrangement of cores and compact structure of MCF, we investigate the laser doppler velocimetry system. The main work includes:1. Simulation and analysis of double-beam interference fringes based on MCF; 2. Construct a laser doppler velocimetry system based on MCF, and verify the feasibility of the experimental system. Our method provides an effective solution for fiber laser doppler velocimetry.

A multiblock (MIB) finite element method for accurate and efficient blood flow simulation

We present an efficient and accurate immersed boundary (IB) finite element (FE) method for internal flow problems with complex geometries (e.g. blood flow in the vascular system). In this study, we use a voxelized flow domain (discretized with hexahedral and tetrahedral elements) instead of a box domain, which is frequently used in IB methods. We highlight the applicability and efficiency of the proposed method in generating the flow domain mesh and removing unnecessary portions of the domain, compared to the standard IB methods that rely on a full Cartesian mesh. Our approach is attractive for internal flow problems that use IB methods. The proposed method accurately satisfies the boundary conditions on the immersed object using velocity and pressure correction procedures. The velocity correction applies implicitly such that the velocity on the immersed boundary (Lagrangian points) interpolated from the corrected velocity values computed on the mesh nodes (Eulerian nodes) accurately satisfies the prescribed velocity boundary conditions. The proposed method utilizes the well-established incremental pressure correction scheme (IPCS) FE solver, and the boundary condition-enforced IB (BCE-IB) method to numerically solve the transient, incompressible Navier-Stokes (NS) flow equations. We verify the accuracy of our numerical method using the analytical solution for the Poiseuille flow in a cylinder, and the available experimental data (laser Doppler velocimetry) for the flow in a three-dimensional 90° angle tube bend. We further examine the accuracy and applicability of the proposed method by considering flow within complex geometries, such as blood flow in aneurysmal vessels and the aorta, flow configurations that would otherwise be difficult to solve by most IB methods. Our method offers high accuracy, as demonstrated by the verification examples, and high applicability, as demonstrated through the solution of blood flow within complex geometry. The proposed method is efficient, since it is as fast as the traditional finite element method used to solve the Navier–Stokes flow equations, with a small overhead (not more than 5%) due to the numerical solution of a linear system formulated for the IB method.

Analysis of the limits of applicability of photomultiplier as part of a laser Doppler anemometer

This paper considers the use of laser Doppler anemometry methods for non-contact measurement of the velocity of a moving medium in various phase states. It notes the specifi city of conditions of application of laser Doppler anemometers, in that in a number of cases there are restrictions on the use of photomultipliers. In order to find an alternative to the classic photomultiplier of a laser Doppler anemometer, three types of photomultipliers were investigated: classic electric vacuum; silicon avalanche multipixel; with microchannel plate. Physical experiments were conducted to measure the velocity of aero- and hydrodynamic fl ows by laser Doppler anemometer with photomultipliers of three types. The velocities of a rotating glass disk, aerodynamic fl ow in a channel of rectangular cross-section, and aerosol flow, as well as hydrodynamic flooded jet, were measured. The obtained experimental data were analyzed according to the criteria for assessing the quality (efficiency) of operation and finding the limits of applicability of the specified photomultipliers. Based on the physical properties of the studied photomultipliers, their efficiency indicators in various experiments are explained. The boundaries of the effective use of these photomultipliers in a wide class of physical experiments are determined. The results obtained are important for researchers involved in the study of aero- and hydrodynamic flows, where accurate and reliable measurements of flow velocity are required. The choice of an optimal photomultiplier tube for the laser anemometer allows increasing the accuracy and ease of obtaining experimental data and reducing the cost of the final equipment.

Behavior of hydrofoil cavitation in a slit channel

The paper presents the results of a cavitation in a slit channel study and offers an analytical description of cavity development. Special emphasis was placed on examining partial cavitation near a NACA 0012 hydrofoil (NACA – the National Advisory Committee for Aeronautics) inside slit channels of different geometries. Experimental investigation was carried out via high-speed imaging and the laser Doppler anemometry (LDA) method. The experimental data showed that the local flow velocity in hydrofoil leading edge area increased abruptly under arising cavitation. In addition, occurrence of cavitation raised flow velocity pulsation by 20%. In the case of a shorter channel, cavity growth occurred at higher cavitation numbers than for a longer channel. The cavity growth velocity was higher for a shorter channel. We showed that the tendency of partial cavitation development in the slit channel can be described as follows: L/C ∼ σ−1, where L is the cavity length; C is the hydrofoil chord; σ is the cavitation number; and parameter A changes as the slit channel length is varied. Comparison of cavitation development near hydrofoil at different attack angles α inside the slit channel with a three-dimensional (3D) cavitation tunnel was conducted. Cavitation in the slit channel occurred at lower σ/2α values compared to 3D cavitation flow around the hydrofoil. To directly compare lengths of the attached cavities arising in slit channels and 3D cavitation tunnels, an additional parameter is proposed, taking into account friction of the slit channel: K = λ·l/D. This parameter allowed us to quantitatively compare the characteristics of cavitating hydrofoils in slit channels and 3D tunnels. The paper provides the governing criteria of the cavitation in the slit channel. Our results propose the physical foundations for the development of cavities in the slit channel.

Deposition of Human-Serum-Albumin-Functionalized Spheroidal Particles on Abiotic Surfaces: Reference Kinetic Results for Bioparticles.

Human serum albumin (HSA) corona formation on polymer microparticles of a spheroidal shape was studied using dynamic light scattering and Laser Doppler Velocimetry (LDV). Physicochemical characteristics of the albumin comprising the zeta potential and the isoelectric point were determined as a function of pH for various ionic strengths. Analogous characteristics of the polymer particles were analyzed. The adsorption of albumin on the particles was in situ monitored by LDV. The stability of the HSA-functionalized particle suspensions under various pHs and their electrokinetic properties were also determined. The deposition kinetics of the particles on mica, silica and gold sensors were investigated by optical microscopy, AFM and quartz microbalance (QCM) under diffusion and flow conditions. The obtained results were interpreted in terms of the random sequential adsorption model that allowed to estimate the range of applicability of QCM for determining the deposition kinetics of viruses and bacteria at abiotic surfaces.

Applications of RIM-Based Flow Visualization in Fluid-Solid Interaction Problems: A Review of Formulations and Prospects

Over the past three decades, optical visualization measurements based on the Refractive Index Match (RIM) method have played a significant role in the experimental studies of fluid-solid interaction. The RIM method, which coordinates the refractive indices of the liquid and solid materials in the experiment, dramatically reduces the observation error due to optical refraction. However, the existing literature on RIM has not systematically reviewed the various applications of this technique. This review aims to fill this gap by providing a comprehensive overview of the RIM technique, examining its role in material selection for fluid-solid interaction studies, and scrutinizing its applications across various engineering disciplines. The paper begins with a brief introduction to the RIM technique and then turns to material selection and its various applications in fluid-solid interaction. It also enumerates and analyzes specific RIM-based optical measurement techniques such as Laser Doppler Velocimetry (LDA), Particle Tracking Velocimetry (PTV), and Particle Image Velocimetry (PIV) from various research perspectives in previous studies. In addition, it summarizes RIM formulations categorized by different applications in liquid-solid interaction fields. RIM-based measurement techniques generally offer intuitive, non-intrusive, cost-effective, and convenient advantages over traditional methods. The paper also critically evaluates the strengths and limitations of different materials used in RIM experiments and suggests directions for future research, emphasizing the need to develop environmentally friendly and cost-effective RIM materials.

Characteristics of the jet shear layer of a round elevated jet in crossflow

The present research aims at an experimental study to investigate the effect of velocity ratio (R) on the evolution of elevated round jet issued from a stack having an aspect ratio (AR) of 9.0 in a uniform crossflow at a Reynolds number of 2000. The experiments are conducted in a low-speed, recirculating water tunnel. Laser Doppler Velocimetry (LDV) is employed to characterize the water tunnel. Particle Image Velocimetry (PIV) is used to measure the flow field, and the dye visualization technique is utilized to capture the accompanying instantaneous flow structures. Depending on the velocity ratio (R = 0.16 - 1.5), distinct jet shear layer (JSL) structures are observed in the symmetric plane (XY), confirmed by both the flow visualization and PIV data. These structures include clockwise vortices, anticlockwise vortices, swing-induced mushroom vortices, and jet-like vortices. For R<0.5, entrainment of a substantial amount of jet fluid into the stack-wake region (downwash) has been observed. At R=0.5, the streak image captured in the wall parallel plane reveals the ring-like vortices that appear to wrap around the jet core while upright vortices are detected downstream on the lee side of the jet. Additionally, variations in average velocity and turbulent fluctuations in the near field, contingent on different velocity ratios, are discussed.

2D3C Measurement Of Velocity, Pressure And Temperature Fields In A Intake Flow Of An Air Turbine By Filtered Rayleigh Sattering (FRS) And Validation With LDV And PIV

A Filtered Rayleigh Scattering Technique is implemented in two different experimental setups and compared to the established velocity measurement techniques Laser Doppler Anemometry (LDA) and Particle Image Velocimetry (PIV). The Frequency Scanning Filtered Rayleigh Scattering Method employed uses an imagefiber bundle which allows for the simultaneous observation of the flow situation from six independent perspectives, utilizing only one sCMOS camera. A testrig with a nominal diameter of 80 mm was implemented by ILA R&amp;D GmbH. Here measurements with straight pipe flow and a swirl generator were realised, as well as comparisions with LDA. A second experiment utilized Cranfields University’s Complex Intake Facility (CCITF), enabling the simulation of the flow field for an engine intake as observed behind an S-Duct diffuser. The diameter in the measuring plane was 160 mm. Measurements up to a mach number of 0.4 were performed and compared with HighSpeed Stereo-PIV (S-PIV) measurements. Good agreement was achieved in respect to both the absolute magnitude of the velocity measurements as well as to the resolution of complex flow structures. The developed FRS multi-view Setup is able to simultaneously determine the 3D velocity components, the pressure and the temperature on a measurement plane with high resolution and without seeding. After calibration the FRS system yields the pressure and temperature within 3 percent respectively 0.8 percent of the reference values. The measured velocity was within 1-2 m/s of the reference.

A Novel Cost-Effective Approach To Flow Visualization Using Particle Streak Angles

Comprehending the complexity of pipe flow dynamics is important for a variety of sectors, including environmental, industrial, and engineering research. Conventional techniques such as Particle Image Velocimetry (PIV) and Laser Doppler Velocimetry (LDV) have long been the heart of these kinds of investigations, but they are often quite expensive and complex. Our research offers a novel, affordable visualization method that aims to transform the way we examine and interpret flow dynamics in response to these challenges. Our method is developed to utilize a low-cost camera system with a simple laser setup to investigate fluid dynamics inside pipes. By introducing particles into the flow and manipulating the camera shutter speed in real-time under the laser, we created streaks capable of displaying complex flow patterns. We gathered precise information about streak angles using rigorous image processing, providing clarity in our insights into the flow dynamics of the particulate pipe flow. Notably, our strategy eliminates the need for expensive and sophisticated equipment while providing researchers and practitioners with a simple yet reliable alternative. The potential for improving our knowledge of pipe flow dynamics is shown by preliminary studies that demonstrate how well it captures dynamic flow characteristics. Our technique, which is easy to use and effective, promises fresh insights into fluid dynamics and opens up new avenues for pipe flow analysis, making it suitable for a broad spectrum of users.