Flow Characteristics of Rectangular Liquid Jets Injected Into Low Subsonic Crossflow

Perpendicular injection of liquid jets into gaseous crossflow is well-known as an effective way to obtain good mixing between liquid fuel and air crossflow. Mostly, injectors with circular holes were used as the standard method of fuel spraying. However, recently a great attention to injectors with non-circular holes has emerged that aims to improve the quality of fuel mixing and consequently combustion efficiency. In the present work, rectangular injectors with different aspect ratios varying from 1 to 4 were experimentally studied. Using a wind tunnel with maximum air velocity of 42 m/s, tests were performed for a wide range of flow conditions including liquid-to-air momentum ratios of 10, 20, 30 and 40. Backlight shadowgraphy and high speed photography were employed to capture the instantaneous physics of the liquid jets discharged into gaseous crossflow. The flow physics of the rectangular liquid jets were investigated by means of flow visualizations. Different regimes of flow breakup including capillary, arcade, bag and multimode were observed for rectangular jets. Moreover, a new technique was used to calculate the trajectory of the liquid jets. It was shown the nozzle’s shape has no significant effect on jet trajectory. Also, the momentum ratio was found to has a profound effect on jet trajectory.

Experimental Investigation of Turbulent Cavitating Flows in a Small Venturi Nozzle

The cavitating flows created in a small Venturi tube with throat cross section 4 × 15.34 mm2 are investigated based on ultra-fast x-ray imaging. The instantaneous velocities of the liquid and vapor are measured simultaneously by tracking seeding particles and vapor structures respectively while the vapor volume fraction is derived from the different x-ray attenuation. Wavelet decomposition with appropriate thresholds is used to separate seeding particles from vapor structures, so that image cross-correlations could be applied on the two phases separately. This study presents data on mean velocity and void ratio field, statistical turbulent quantities in three different cavitation levels with the same reference velocity. A type of cavitation associated with a weak but persistent re-entrant jet is described. The comparison between the cavitation and the noncavitating flow shows that the averaged flow field is significantly altered by the presence of cavitation and the vapor formation near the throat area is observed to suppress velocity fluctuations.

Visualizing Test on the Distribution Rule of Coarse Particles in a Double Blade Pump

As a typical fluid mechanics problem, pump blockage has always been a hot research topic. The obtaining of the distribution of coarse particles in the solid-liquid two-phase flow pump is the basis of improving its non-blocking performance. High-speed photography technique is applied to do visualizing test and research on the distribution of coarse particles in a double blade pump. The effects of particle concentration, particle density and particle diameter on the distribution of coarse particles in the solid-liquid two-phase flow pump at different phases are studied. Besides, the variation of hydraulic performance of the double blade pump under different parameters is also analyzed. The results show that the particles in the impeller mainly located in the vicinity of the blade pressure surface, and the distribution of the particles in each section of the volute is quite different. The great difference in particle density can result in obviously uneven distribution of particles. With the increase of particle diameter, particle density and particle concentration, the pump head and efficiency both decrease while the shaft power increase on the contrary. This research results can also provide a basis for the optimization design of solid-liquid two-phase flow pumps.

Numerical Simulation of Deposition Phenomena on High-Pressure Turbine Vane Using UPACS

We performed numerical simulation to understand deposition phenomena on high-pressure turbine vane. Several deposition models were compared and the OSU model showed good adaptation to any flow field and material, so it was implemented on UPACS. After the implementation, the simulations of deposition phenomenon in several cases of the flow field were conducted. From the results, particles adhere on the leading edge and the trailing edge side of the pressure surface. Also, the calculation of the total pressure loss coefficient was conducted after computing the flow field after deposition. The total pressure loss coefficient increased after deposition and it was revealed that the deposition deteriorates aerodynamic performance.

Cavitation in Co-Rotating Tip Vortices

This work documents flow characterization and cavitation inception of a co-rotating vortex pair shed from a single fin with a rounded tip at zero angle of attack. The fin was outfitted with a removable tip fabricated using a rapid prototype method. The co-rotating vortices result from surface discontinuities on the removable tip, near a hard wax fairing used to cover the tip attachment bolt. The vortices are shed at different locations along the chord. Flow visualization by oil paint and developed cavitation, and SPIV of the near-wake, indicate that a strong vortex is shed at the trailing edge, while a weaker vortex is shed at 82% chord. Horizontal wandering of the vortices is uncorrelated. Vertical wandering of the vortices is characterized by opposing oscillations about their mutual center. Acoustic cavitation inception in the water tunnel environment is discerned at an index 13% greater than visual detection of cavitation, and occurs within one chord of the trailing edge. The influence of the co-rotating vortex system on cavitation inception must be determined from comparison with measurements of a solitary vortex generated by analogous geometry.

Is Radioactive Tank Waste a Bingham Fluid?

Slurries and sludges across the United States Department of Energy (DOE) complex rank among the most rheologically interesting. Their composition is heterogeneous, spanning a very broad range of particle sizes, densities, and interparticle forces. All exhibit shear thinning, some have yield stresses, and many are thixotropic. Despite the variety, these complex fluids are often represented using the historic Bingham fluid model, which fits higher shear rate data to a simple straight line. The intercept provides a yield stress, which has been a key design parameter in construction of large-scale waste processing facilities. However, many radioactive wastes are simply not Bingham fluids, and this representation extrapolates poorly across low to intermediate shear rates that are characteristic of typical processing conditions. Indeed, processing shear rates as high as 200 1/s, which has been a typical minimum shear rate used in fitting the Bingham fluid model, are seldom encountered in nuclear waste processing. Therefore, more realistic rheological models are necessary to accurately predict waste processing performance. Pacific Northwest National Laboratory (PNNL) recently re-evaluated the rheology of reconstituted Hanford REDOX (reduction-oxidation) process sludge waste against a wide variety of rheological models including the Bingham, Cross, Cross with yield stress, Carreau, biviscous, Herschel-Bulkley (which includes a power law dependence), Casson, and Gay models. They found that all of the models provided a closer fit than the Bingham model and that the biviscous model and Cross with yield stress model were convincing. However, reconstituted Hanford REDOX sludge waste is but one type of DOE waste and a direct contrast, and comparison of these three models against undiluted, unmixed tank waste (actual not simulant) has not been performed previously. Therefore, the purpose of this paper is to evaluate the rheology of actual tank waste with these more accurate rheological models. In this paper, we evaluate select rheological data for slurry samples from Hanford’s AZ-101, AZ-102, and SY-101 waste tanks. In each of these cases, we find that Cross’ model with yield stress and the biviscous model significantly outperform the Bingham fluid model. Furthermore, the AZ-101 data also shows that the shear stress peak at startup significantly exceeds the Bingham yield stress, which is commonly observed in the initial moments of rheological measurements on simulants. Remarkably, Cross’ model may empirically accommodate an initial spike in shear stress at modest shear rates. These are important observations because computational and analytical fluid dynamics simulations rely on rheological constitutive models for accurately and conservatively predicting waste processing performance. These findings suggest the need for better rheological modeling of and validation against radioactive waste.

Effects of Liquid Viscosity on Laser-Induced Shock Dynamics

We experimentally study the effects of viscosity on laser-induced shockwave in glycerol-water solution. A shockwave is generated through rapid expansion of plasma, which is induced by focusing a 6 ns pulse laser (532 nm) of energy fixed at 1.66 ± 0.22 mJ into 80, 90, 100 wt% glycerol-water solution. The shockwave propagation is recorded by an ultra-high-speed camera taken at 100 Mfps together with a pulse laser stroboscope. The photographs are used to determine the shock front position as a function of time, which allows for calculating the shock pressure according to the stiffened-gas type Rankine-Hugoniot relation. It turns out that the initial plasma pressure is reduced by having higher glycerol concentration (i.e., higher viscosity); therefore, wave steepening effect is deemphasized, resulting in a smaller decay rate.

Implicit Large-Eddy Simulation of Transition and Turbulence Decay

Accurate predictions with quantifiable uncertainties are essential to many practical turbulent flow applications exhibiting extreme geometrical complexity and broad ranges of length and time scales. Under-resolved computer simulations are typically unavoidable in such applications, and implicit large-eddy simulation (ILES) often becomes the effective strategy. We focus on ILES initialized with well-characterized 2563 homogeneous isotropic turbulence datasets generated with direct numerical simulation (DNS). ILES is based on the LANL xRAGE code, and solutions are examined as function of resolution for 643, 1283, 2563, and 5123 grids. The ILES performance of new directionally-unsplit high-order numerical hydrodynamics algorithms in xRAGE is examined. Compared to the initial 2563 DNS, we find longer inertial subranges and higher turbulence Re for directional-split 2563 & 5123 xRAGE — attributed to having linked DNS (Navier-Stokes based) solutions to nominally inviscid (higher Re) Euler based ILES solutions. Alternatively — for fixed resolution, we find that significantly higher simulated turbulence Re can be achieved with unsplit (vs. split) discretizations.

Effect of Pipe Inclination on Solids Distribution in Partially Stratified Slurry Flow

Partially stratified flows like flows of sand-water slurries exhibit non-uniform distribution of solids (expressed as a vertical profile of local volumetric concentration) in a pipe cross section. The solids distribution in such flows is sensitive to pipe inclination. The more stratified the flow is the more sensitive its concentration profile is to the pipe slope. In general, the distribution tends to become more uniform (less stratified) if the inclination angle increases from zero (horizontal pipe) to positive values (ascending pipe) up to 90 degree (vertical pipe). In a pipe inclined to negative angles (descending pipe) the development is different. The flow tends to stratify more if it changes from horizontal flow to descending flow down to the angle of about −35 degree. If the angle further decreases towards −90 degree, then the flow becomes less stratified reaching uniform distribution at the vertical position. This also means that the same flow exhibits a very different degree of stratification in ascending and descending pipes inclined to the same (mild) slope say between ±10 and ±40 degree. The rather complex development of the solids distribution with the variation of the inclination of pipe is insufficiently documented experimentally and described theoretically in predictive models for a concentration profile in partially stratified flow. In order to extend the existing limited data set with experimental data for partially stratified flow of medium sand slurry, we have carried out a laboratory experiment with the slurry of narrow graded fraction of sand with the mean grain size of 0.55 mm in our test loop with an invert U-tube inclinable to arbitrary angle between 0 and 90 degree. A pipe of the loop has an internal diameter of 100 mm. Both legs of the U-tube have a measuring section over which differential pressures are measured. Radiometric devices mounted to both measuring sections sense concentration profiles across a pipe cross section. Furthermore, the discharge of slurry is measured in the test loop. In the paper, experimental results are presented for various inclination angles with a small step between 0 and ±45 degree and a development in the shape of the concentration profiles with the changing inclination angle is analyzed. For the analysis, it is critical to distinguish between suspended load and contact load in the flow as the two loads tend to react differently to the flow inclination. The measured concentration profiles and pressure drops are compared with predictions by the layered model adapted for taking the flow inclination into account.

Capillary Impregnation of Viscous Fluids in a Multi-Layered Porous Medium

Capillary impregnation of viscous fluids in porous media is useful in diagnostics, design of lab-on-chip devices and enhanced oil recovery. The impregnation of a wetting fluid in a homogeneous porous medium follows Washburn’s diffusive law. The diffusive dynamics predicts that, with the increase in permeability, the rate of spontaneous imbibition of a wetting fluid also increases. As most of the naturally occurring porous media are composed of hydrodynamically interacting layers having different properties, the impregnation in a heterogeneous porous medium is significantly different from a homogeneous porous medium. A Washburn like model has been developed in the past to predict the imbibition behavior in the layers for a hydrodynamically interacting three layered porous medium filled with a non-viscous resident phase. It was observed that the relative placement of the layers impacts the imbibition phenomena significantly. In this work, we develop a quasi one-dimensional lubrication approximation to predict the imbibition dynamics in a hydrodynamically interacting multi-layered porous medium. The generalized model shows that the arrangement of layers strongly affects the saturation of wetting phase in the porous medium, which is crucial for oil recovery and in microfluidic applications.