High concentrations of particulate matter in air lead to deposition at the sealing radius of self-sealing valves involving direct intake from the environment. Dust deposition at and near this radius causes an increase in leakage flow when the valve is closed. In this paper, the mechanism which results in dust deposition in such valves is investigated and a new valve design which reduces leakage flow is developed and experimentally assessed. ANSYS Fluent 15.0 is used to numerically model the laminar flow assuming axisymmetry. Particle paths are predicted using Discrete Phase Modeling (DPM) as a post-processing step. Experimentally, dust deposition, mass flow at the operating pressure differential, and leakage flow rate are measured. The numerical and experimental results are utilized together to gain insight into the particles’ behavior. One of the key outcomes of this work is a post-processing technique which allows the numerical and experimental particle deposition results to be quantitatively compared. This supports the utlity of the numerical approach as locations of high concentrations of particle impacts in the numerical simulations are associated with locations of dense dust deposition in the experiments. High concentrations of particles at and near the sealing radius are observed to lead to increased leakage flow. Therefore, the impact of high concentrations of particles in this region is to be avoided. Utilizing this insight, the valve geometry is modified to reduce the amount of dust deposited in the region of the sealing radius. In the modified design, leakage flow is decreased by up to 93%, with a maximum of 2.1% reduction in flow rate margin relative to valve specifications.

Experimental study was carried out to investigate the Reynolds number effects on surface jet characteristics. The surface jet was produced using orifice nozzle with offset height ratio of 2. Six different Reynolds numbers ranging from 2300 to 11900 were investigated. Potential core region of the jet decreased with Reynolds number up to the Reynolds number of 5500. Reattachment point was sensitive to Reynolds number within the range of the present study. The maximum velocity decay and jet spread were nearly independent of Reynolds number. The streamwise mean velocity, streamwise turbulence intensity and Reynolds shear stress distribution along surface-normal direction were affected by the free surface and showed Reynolds number independency at the Reynolds numbers beyond 5500.

With the availability of high-frame-rate (HFR) PIV systems, it is possible to capture time series of particle images at rates which can exceed the necessary frequency to temporally resolve essential flow. In this case, some of the recorded frames can be skipped, in order to obtain an adequate time step between two images, leading to favorable values for pixel displacement. In this paper a technique for decreasing pixel locking in complex flows based on an adaptive time step processing procedure is proposed. If PIV data are taken at much higher frequency than needed, the processing can be repeated for multiple time steps, ensuring the optimal pixel displacement for every interrogation spot. A smaller time step is used for large velocities and larger time steps are used in the areas of low velocity. To illustrate this technique, a sample data set was acquired of the flow on the suction side and the region just downstream of a NACA 0015 hydrofoil at a high angle of attack (16 degrees), ensuring a wide range of velocities within the PIV field of view. The experiments were performed in the University of New Hampshire High-Speed Cavitation Tunnel – HiCaT , at a comparatively low speed (2 m/s) in order to increase the range of possible time steps for post processing. HFR PIV data were obtained at 1800 frames per second for a field of view of approximately 100 mm × 100 mm. The data were processed multiple times, each time skipping between 0 and 19 frames, resulting in time steps between 1 to 20 times of the original time step between two images. As expected, there is a significant difference between the results for mean velocities with different time step processing, most notably in the region of the suction side of the foil. The RMS velocity fields also show a similar trend. In order to obtain a more accurate representation of the mean flow, the data for each interrogation spot were combined based on the pixel displacement values. The resulting velocity field was compared to that obtained with single-time-step PIV. A “map” was created showing what time step was selected for each interrogation spot. Suggestions were made on what time steps should be selected for the post processing in order to decrease the post processing computational time. A discussion was provided on the feasibility of using the technique for instantaneous velocity fields. Using ATS PIV may be beneficial in flows where both large and small velocities are of importance, e.g., flows with separation.

Solid particle laden flows are very common in many industries including oil and gas and mining. Repetitive impacts of the solid particles entrained in fluid flow can cause erosion damage in industrial equipment. Among the numerous factors which are known to affect the solid particle erosion rate, the particle impact speed and angle are the most important. It is widely accepted that the erosion rate of material is dependent on the particle speed by a power law V n , where typically n = 2–3. Therefore, accurate measurements of abrasive particle impact speed and angle are very important in solid particle erosion modeling. In this study, utilizing a Particle Image Velocimetry (PIV) system, particle impact conditions were measured in a direct impinging jet geometry. The measurements were conducted with two different test rigs, for both air-sand and liquid-sand flows. In air-sand testing, two types of solid particles, glass beads and sharp sand particles, were used. The measurements in air-sand tests were carried out using particles with various sizes (75, 150, and 500 μm). Also, submerged testing measurements were performed with 300 μm sand particles. In the test conditions, the Stokes number was relatively high ( St = 3000 for air/sand flow, St = 27 for water/sand flow), and abrasive particles were not closely following the fluid streamlines. Therefore, a Particle Tracking Velocimetry (PTV) technique was employed to measure the particle impact speed and its angle with the target surface very near the impact. Furthermore, Computational Fluid Dynamics (CFD) simulations were performed, and the CFD results were compared with the experimental data. It was found that the CFD results are in very good agreement with experimental data.

In this work, ultra-high speed imaging of conical liquid sheets allows for non-invasive measurements of both global and local features of a swirling conical liquid sheet. The breakup of the swirling conical liquid sheet is visualized and the interface tracked between the conical liquid sheet and the ambient air. The applied experimental technique and the image processing technique capture planar images that are capable of tracking the dynamic behavior of the conical liquid sheet. Cone angle is shown to increase up to a critical Weber Number. The film length is obtained by identifying singular points in the signal response of the radial fluctuations. The results of the proper orthogonal modes indicate the existence of traveling waves on the interface of the swirling conical liquid sheet. Wavelength measurements of the traveling waves are comparable with linear instability analysis.

A single-camera color PIV system based on the combination of a color-coded illumination and a color high-speed video camera has been developed. The system realizes flow velocity vector fields in multiple layers in the depth direction for a relatively wide volume. The working principle belongs to smoke-imaging PIV since particle per pixel is larger than unity in the digital image plane, which is different from the case of color 3-D PTV. The accuracy of the present color PIV depends on how the integral equation of color-signal overlapping among three wavelengths (R,G,B) is solved as inverse analysis. We propose in this paper a method to reasonably solve the equation, which removes color contamination in RGB sensors, and decomposes the color-illuminated smoke images into the smoke distributions inside individual layers. The first half of the paper deals with linear backward analysis for the color de-contamination to establish triple-layer velocimetry by a single-view imaging of smoke. Based on the success, we present in the second half an extended system that realizes simultaneous six-layer color PIV to which three intermediate colors are additionally illuminated into the measurement volume.

Bubbles injected into a turbulent boundary layer have a significant potential to reduce frictional shear stress, but this drag reduction technique has not been optimized yet because of its low and unstable performance. If monitoring and controlling of advective bubbles beneath ships are realized, these provide insight for improving the performance. In this paper, we performed experiments using a model ship with 4 m in length in a towing tank with 80 m in distance. The model ship is fully made of acrylic resin and mounts shear stress sensors and ultrasonic measurement system. The shear stress and bubble information, such as a void fraction and a thickness of liquid film above the bubbles, are obtained at three locations arranged at the front, the middle and the rear of the ship bottom plane. By analyzing these data, it is confirmed that the drag reduction occurs when a thin liquid film exists.

Nonstationary analysis of flow field is required to detect the source of aerodynamic noise, in order to accomplish the reduction of aerodynamic noise in life environment, including low-frequency noise, which may be harmful for human health. Pressure sensitive paint (PSP) is a quantitative pressure visualization technique on solid surfaces based on oxygen quenching of luminescent molecule. Polymer-type PSP composed of PtTFPP, a luminescent molecule with high oxygen quenching probability, and poly(TMSP), a glassy polymer with high oxygen permeability, has high pressure sensitivity for low-speed flow field. However, the pressure sensitivity of the polymer-type PSP for nonstationary pressure change has not been examined enough. In this study, we investigate the time response of the poly(TMSP)-based PSP, to evaluate the feasibility of the polymer-type PSP as a measurement tool for nonstationary low-speed flows, when the frequency of pressure fluctuation is relatively low. Because response time of polymer-type PSP is proportional to the square of the thickness of the PSP layer, we prepare thinner-layer PSP to increase the response speed by reducing the amount of polymer. The polymer-type PSP is applied to measurement of nonstationary pressure distribution around a circular cylinder in low-speed flow, and compare the amplitude spectra of PSP and that of pressure probe, which are obtained by FFT analysis. As a result it is clarified that the sensitivity of the PSP for pressure variation lower than 100Hz is as high as that for stationary pressure. For pressure variation higher than 100Hz the sensitivity decreases as the frequency of pressure variation increases, but pressure variation with the amplitude of about 300Pa can be detected by the poly(TMSP)-based PSP even if the frequency is as high as 850Hz. Furthermore we have visualized the distribution of the integrated intensity of the PSP amplitude spectrum around the peak, to visualize the area with large pressure variation on the cylinder surface.

Effects of free surface on development of turbulent boundary layer and wake fields were investigated. By measuring flow field around a surface piercing cylinder in various advance speed conditions in a towing tank, free surface effects were identified. A towed underwater Stereoscopic Particle Image Velocimetry (SPIV) system was used to measure the flow field under free surface. The cross section of the test model was water plane shape of the Wigley hull, of which longitudinal length and width were 1.0 m and 100 mm, respectively. With sharp bow shape and slender cross section, flow separation was not expected in two-dimensional flow. Flow fields near the free-surface and in deep location that two-dimensional flow field was expected were measured and compared to identify free-surface effects. Some planes perpendicular to longitudinal direction near the model surface and behind the model were selected to track development of turbulent boundary layer. Froude numbers of the test conditions were from 0.126 to 0.40 and corresponding Reynolds numbers were from 395,000 to 1,250,000. In the lowest Froude number condition, free-surface wave was hardly observed and only free surface effects without surface wave could be identified while violent free-surface behavior due to wave-induced separation dominated the flow fields in the highest Froude number condition. From the instantaneous velocity fields, Time-mean velocity, turbulence kinetic energy, and flow structure derived by proper orthogonal decomposition (POD) were analyzed. As the free-surface effect, development of retarded wake, free-surface waves, and wave-induced separation were mainly observed.

As a refrigerant used for a refrigeration cycle, carbon dioxide (CO 2 ) is regarded. In the case that CO 2 is used as a refrigerant, a gas-liquid two-phase flow ejector is very important. The gas-liquid two-phase flow ejector consists of a driving flow nozzle, a suction chamber, a mixing section and a diffuser. It is important for optimally designing the driving flow nozzle of the two-phase flow ejector to make clear the acceleration characteristics of the high speed gas-liquid two-phase flow. However, there is only a few study examples to evaluate the acceleration performance reasonably. Therefore, the purpose of this study is to measure the acceleration characteristics and temperature distribution in the CO 2 gas-liquid two-phase flow nozzle of the CO 2 two-phase flow ejector by experiment. In the experiment, CO 2 is blown down through the convergent-divergent nozzle and is discharged into the atmosphere. Visualization of the nozzle flow has been carried out by Particle Image Velocimetry (PIV). Temperature measurement has been carried out by thermocouples. Obtained velocity distribution of gas-liquid two-phase flow nozzle have been considered as the droplets velocity. By the experiment, these velocity distributions in parts of the nozzle and these temperature distributions in the nozzle are obtained. Therefore, the flow acceleration in the nozzle divergent part is clarified by the experimental work.

The problem of extracting static pressure fields on and away from flow boundaries in complex flows, is considered. Given the correct velocity field in steady incompressible flow, an assumption of constant or known stagnation pressure allows finding the static pressure. This gives an upper bound on static pressure, and is in fact close to the real answer. The technique developed here is to start with the measured, ensemble-averaged 3-component velocity field in a periodic flow. The static pressure field computed from this velocity field in incompressible flow can be used along with the velocity field as the starting guess of a solution in a Navier-Stokes solver. The method is applied to the bottom surface near the sharp edge of a rotating rotor blade in the reverse flow domain encountered at high advance ratio in a wind tunnel. The drop in stagnation pressure along given streamlines even through the sharp-edge vortex, is shown to be very small, so that the effect on the static pressure estimate is minor. The pressure field successfully explains some features that could not otherwise be explained.

Innovative optical techniques based on nano-biophotonics such as surface plasmon resonance (SPR) imaging and R-G-B natural fringe mapping techniques are developed to characterize the transport and optical properties of nanofluids in situ, real-time, and full field manner. Recent results regarding the characterization of nanofluids are summarized and future research directions are presented. 47 nm Al 2 O 3 nanoparticles are dispersed in water with various concentrations. Al 2 O 3 nanofluids droplets are placed on substrates and evaporated in room temperature. In-situ visualization of evaporation-induced self-assembly is conducted to detect concentration, effective refractive index, and different self-assembled pattern including cavity with various nanofluids concentrations and surface hydrophobbicities with SPR and fringe mapping. During the evaporation, time-dependent and near-field nanoparticle concentrations are determined by correlating the SPR reflectance intensities with the effective refractive index (ERI) of the nanofluids. With increasing the concentrations of nanofluids, the existence of hidden complex cavities inside a self-assembled nanocrystalline structure or final dryout pattern is discovered in real-time. R-G-B natural fringe mapping allowed the reconstruction of the 3D cavity formation and crystallization processes quantitatively. The formation of the complex inner structure was found to be attributable to multiple cavity inceptions and their competing growth during the aquatic evaporation. Furthermore, the effect of surface hydrophobicity is examined in the formation of hidden complex cavities, taking place on three different substrates bearing different levels of hydrophobicity; namely, cover glass (CG), gold thin film (Au), and polystyrene dish (PS). These surface plamson resonance imaging and natural fringe mapping techniques are expected to provide a breakthrough in micro-nanoscale thermal fluids phenomena and nano-biochemical sensing when coupled with localized surface Plasmon and metamaterials techniques.

Single phase friction factor and pressure drop behavior of smooth and microfin tubes are studied experimentally. The vertical test section was working as a counter flow double tube heat exchanger with water flowing in the inner smooth and microfin tubes having varying inner diameters and cooling water flowing in the annulus. Pressure drop of water due to cooling in upward flow in inner tubes is determined by experiments. Inner tube mass flow rate was between 0.023 kg/s to 0.100 kg/s while test section inlet temperatures were 40°C and 60°C. Effect of Reynolds number on pressure drop is also investigated and Blasius type friction factor correlations are developed for both smooth and microfin tubes.

A novel image processing algorithm has been designed in MATLAB to analyze digital images of spherical bubbles which are backlit. The algorithm possess a series of steps to determine which bubbles are in focus, remove out of focus bubbles and record measurements of bubble size and location. Specifically, the algorithm relies on self-adaptive user determined thresholds, gradient detection, correlation determination, and multiple confirmation strategies. The results are capable of handling variations in bubble appearance due to inconsistent background and overlapping. This paper describes the details of the algorithm and its use in recording bubble measurements from images of varying bubble size and bubble number density. Results from the algorithm as compared with bubble measurements from the same image sets determined via the manual line drawing method.

Aircraft icing has been recognized as the most significant weather hazard that impacts aviation safety. A thin sheet of ice on lifting or control surfaces of an aircraft can adversely affect its flight performance by increasing drag and decreasing lift and thrust. The uncontrolled shedding of ice built up on surfaces may severely damage critical components. The occurrence of ice accretion is also a big challenge in terms of economic impact. The presence of ice can not only cause flight delays, but also reduce flight profits by increasing fuel consumptions and additional cost for de-icing operations. A better understanding of the physical mechanisms of water movement and the ice formation process on aircraft surfaces is very important and critical in ensuring safe and efficient operation of aircraft in cold weather. Generally there are two types of ice that can be deposited during flight: glaze ice and rime ice, which occur is dependent on weather conditions. Glaze ice is formed with high liquid water content (LWC) and large droplet size at temperatures just below the freezing point, and it has a smooth, clear and dense appearance. Rime ice forms with lower LWC and smaller droplet size at temperatures around or below −12 C°. It is a mixture of tiny ice particles, containing many micro bubbles and cracks, and it has a white rough appearance. These two types of ice may have significantly different effects on flight performance. However, most of the current de-icing approaches and practices do not consider this and operators potentially perform a lot of unnecessary actions. In this study, attenuation measurement of ultrasonic waves is performed to investigate the feasibility of characterization of ice types. Analysis investigates frequency dependent attenuation properties that are potentially closely related to ice acoustic properties and hence the micro-structure.

Cooling with mist flow can achieve higher heat transfer rates to meet the cooling requirements in recent industry applications. The mist flow was produced by introducing the dispersed water droplets in the air stream, and was used for cooling a heated surface in a vertical square duct with the hydraulic diameter of 4 cm. Digital image analysis method was developed to obtain the size of the droplets ranging from 20 to 110μm. The digital images were segmented using the optimal threshold gray level for droplets sizing. Droplet size variation subjected to a single-side heated wall with constant heat flux was investigated. Infrared thermography was applied to obtain the surface temperature distribution during the cooling test. The air-water mist flow gave much lower surface temperature compared to the air cooling, and the mean droplet diameter decreased as it flowed over the heated surface.

Understanding the mechanisms for multiphase flow within the subsurface is critical to the planning and execution of a multitude of energy related projects including, enhanced oil recovery, geologic carbon sequestration, geothermal energy extraction, and gas production from tight shale reservoirs. This paper provides a brief review of the use of X-ray computed tomography (CT) scanning to visualize multiphase flows within geologically relevant rock cores, and then provides recent examples of multiphase flow at the National Energy Technology Laboratory. With modern CT scanning techniques we show how it is possible to visualize dynamic flooding of cores with fluids, as well as calculate changes in the saturation within the porous matrix from image analysis of the scans.

This study focuses on the interaction of a turbulent channel flow at Re τ =2310 over a flat, compliant boundary made of PDMS (Polydimethylsiloxane). Two noninvasive optical techniques, namely tomographic PIV (TPIV) and Mach-Zehnder Interferometry (MZI), are integrated to perform simultaneous measurements of the 3D flow field and the corresponding surface deformation. The measurements are performed in a refractive index-matched facility, where the working fluid is aqueous solution of sodium iodide (NaI). The TPIV measurement volume is 30×10×10 mm 3 in the streamwise, wall-normal and spanwise directions, respectively. The MZI phase evaluation and unwrapping algorithms have been developed, calibrated and implemented. Preliminary results show qualitative correlation between wall deformation and flow structures near the wall.

Aerated-liquid atomization, also called “effervescent atomization”, is a technique that has a wide range of applications such as gas turbine combustors, internal combustion engines, furnaces and burners, and pharmaceutical sprays. We report on an experimental study conducted to investigate the two-phase flow in an Effervescent atomizer. A novel aerator tube base was implemented and tested. It is observed that the novel configuration suppresses the separation bubble at the trailing edge and results in more uniform and smaller bubbles compared to the standard flat base aerator. It has been found that the more uniform and smaller bubbles are generated as the mixing chamber length is reduced. It is concluded that by using a conical base aerator and by reducing the mixing chamber length, the spray steadiness and the atomization process can be significantly improved.

The presented work is focused on developing closure models for simulation of multiphase flow using multi-fluid models. In the two-fluid model, pseudo turbulent terms appear in both the heat transfer term in the energy equation and the mass transfer term in the species equation. These terms are often neglected due to lack of information, but recent studies show that they can indeed be significant in the simulation of the inter particle phenomena. In the present work, we experimentally investigate the importance of pseudo turbulent term in passive scalar transport. A simultaneous stereo particle image velocimetry and planar laser induced fluorescence (SPIV/PLIF) measurement of the field data for a liquid-solid flow is presented in this study. The results of this measurement are used to validate data from Particle Resolved DNS (PR-DNS) that in turn is used to develop the aforementioned closure models. In this work, results for a single sphere are presented for Reynolds number ranging from 50 to 150. In addition, results for arrays of spheres representing volume fractions of 0.1 and 0.2 are presented for the same range of Reynolds number.