Sharp-edged Nozzle Research Articles

Design Parameter Influence on Losses and Downstream Flow Field Uniformity in Supersonic ORC Radial-Inflow Turbine Stators

The design of organic Rankine cycle (ORC) turbines often requires dealing with transonic flows due to the cycle efficiency requirements and the matching of the temperature profiles with heat sources and sinks, as well as the nature of organic fluids, often featuring high molecular weight. Consequently, the use of convergent–divergent turbine stators has been widely established as a solution in the published literature for use in both axial- and radial-inflow machines. With respect to the latter layout in particular, the available design guidelines are still limited. The present work shows the results of an investigation into a series of ORC radial-inflow convergent–divergent nozzles that differ with respect to the vane count and the designed metal angle of the outlet. These stators were designed by fitting the divergent portion of a sharp-edged minimum-length nozzle, designed by means of the method of characteristics (MoC) adapted to dense gases, into a radial-inflow turbine stator. The geometries were analysed by means of steady-state RANS CFD calculations, and the results were used to assess the influence of the design parameters on the nozzle losses and downstream flow field uniformity, showing that conflicting trends exist between optimum stator efficiency and optimum downstream flow field uniformity.

Experimental study on instability of round nanofluid jets at low velocity

The effects of nano-alumina additives on the instability of round water jets were experimentally studied. The flow visualization inside and near the exit of two transparent nozzles was obtained by high-speed shadow imaging. A spectrum analysis method was applied to determine the surface wavelengths by performing fast Fourier transform on the image grayscale standard deviation data. According to the flow structure inside the sharp-edged nozzle, an integrated model for wavelength prediction was constructed based on the boundary layer instability theory. The effects of the nanoparticle additives on the jet instability were mainly caused by viscosity enhancement and cavitation promotion. The effects were divided into three categories according to the cavitation state in the nozzle. Firstly, for the no-cavitation flow, the nanoparticles exerted a frequency-reduction effect owing to the viscosity increase. Secondly, for the partial cavitation state, the nanoparticles had an increasing-frequency effect owing to the internal cavitation enhancement. Thirdly, for supercavitation or high-speed flow, the dominant frequency no longer changed, whereas the nanoparticles increased the jet instability owing to the enhancements in the external cavitation and aerodynamic force.

Large-scale motion of submerged offset jets issuing from sharp-edged rectangular nozzles

The mean flow, turbulence characteristics, and dynamics of large-scale vortices are investigated for an offset jet issuing from different nozzle expansion ratios using a four-receiver acoustic Doppler velocimeter. The jet was discharged from sharp-edged rectangular nozzles with expansion ratios of 0.24, 0.49, 0.75, and 1.00 at Reynolds number of 5.3 × 104. The decay rate of the maximum mean velocity decreased with increasing expansion ratio due to suppressed lateral entrainment of ambient fluid. The acoustic Doppler velocimeter proved capable of providing high-quality data to investigate the energy spectrum and turbulent structures embedded in the flow. Large-scale vortices dominated the recirculation region compared to the reattachment and developing regions of the jet. Increasing the expansion ratio resulted in larger order of magnitude of the vortices within the recirculation region. The turbulent structures stretched in the lateral direction in regions where smaller-sized structures existed in the streamwise direction and vice versa.

Effect of Nanoparticles on Cavitation in a Round Liquid Jet

Nanofluid has drawngreatattentionas a new efficientenergy carrier for improving heat-transfer and combustionperformance. However, universalconsensus has not been reached on the mechanism of nanoparticlesinfluencing atomization and combustion. In this paper, the focus was thecavitation of Al2O3-H2O nanofluids inside and outside a nozzle with circular cross section. Comprehensive analyses of flow morphology were carried out based on a highspeed-macro shadow imaging system. The effects of nanoparticles on the initial development of round jet, incipient cavitation and supercavitation inside sharp-edge nozzle, and jet cavitationoutside round-edge nozzle were discussed. Results showed that: nanoparticles accelerated the formation of cavitation inside the nozzle, and reduced the critical supercavitation pressure. Meanwhile, they promoted the formation and persistence of bubbles in liquid jet. These bubbles generated near the KH-instability wave peaks below the nozzle. Compared with that of basic fluid, the wavelocationof nanofluid jet was closer to the nozzle exit. In conclusion, the addition of nanoparticlespromoted the cavitation inside and outside the nozzle.Itcan be attributed tothe following changes: nanoparticles increased the original adsorption of air, reduced the tensile strength of liquid, speeded up the disturbances of jet, and played the role of heterogeneous nucleation points.

Experimental study on splash phenomena of liquid jet impinging on a vertical wall

In this study, the splash phenomena of a plain orifice jet impinging on a vertical wall were examined. Experiments were carried out by changing the jet speed (i.e., inlet pressure) and the distance of a vertical wall with rounded and sharp-edged nozzles of different diameters, and the splashed fraction was measured by weighing the mass drained on the vertical wall. In addition, the breakup of the liquid jet and the flow patterns resulting from the jet impinging on the vertical wall were visualized.By increasing the velocity of a liquid jet emerging from a rounded nozzle, the Rayleigh, first wind-induced, and second wind-induced regimes could be observed in order. For the cavitating jet, the jet velocity became significantly larger than the volume flow rate divided by the nozzle area. Nevertheless, the trends of jet breakup as well as the splashed fraction results between the rounded and sharp-edged nozzles were similar for the same jet velocity. The splashed fraction reached its maximum value when small droplets resulted from the secondary breakup of large fragments started impinging on the vertical wall. In addition, the jet velocity at which the maximum splashed fraction attained decreased with increasing distance of the vertical wall from the nozzle exit. These experimental results were explained qualitatively in terms of the conditions of the liquid jet, breakup regime, drop impact, and splashing phenomena.

Determination of Maximum Surface Heat Flux during Jet Impingement Surface Quenching with a Sharp Edge Nozzle

The maximum surface heat flux is determined during jet impingement quenching of hot vertical stainless steel surface of 800 ± 10 °C initial temperature. Water jet through a sharp edge nozzle of 24 ± 1 °C temperature is injected on a vertical test surface of 0.25 mm thickness. The investigation is made up for stagnation point to 24 mm downstream location above and below of the stagnation point. Water flow is regulated to maintain the jet Reynolds number in the range of 5000–24,000. It has been observed that maximum surface heat flux is highest for the stagnation point and reduces monotonically for the downstream spatial locations. The decrease in maximum surface heat flux is higher for the locations above the stagnation point as compared to the locations below the stagnation point. However, for the entire measured spatial locations the maximum surface heat flux increases with the rise in jet diameter and coolant flow rate. The proposed correlation for the maximum surface heat flux predicts experimental data within an error band of ±15%.

Thermal-Hydraulics Program in Support of Canadian SCWR Concept Development

The thermal-hydraulics program in support of the development of the Canadian supercritical water-cooled reactor (SCWR) concept has undergone several phases. It focused on key parameters such as heat transfer, critical flow, and stability of fluids at supercritical pressures. Heat-transfer experiments were performed with tubes, annuli, and bundles in water, carbon dioxide (CO2), or refrigerant flows. Data from these experiments have led to enhancement in understanding of the phenomena, improved prediction methods, and verified analytical tools. In addition, these experiments facilitated the investigation of separate effects on heat transfer (such as geometry, diameter, spacing device, and transient). Chocking flow characteristics were studied experimentally with sharp-edged nozzles of two different sizes of opening. Experimental data have been applied in improving the critical-flow correlation in support of accident analyses. A one-dimensional (1D) analytical model for instability phenomena has been developed and assessed against the latest experimental data for quantifying the prediction capability and applicability.

Effect of nozzle-exit conditions on the near-field characteristics of a transverse liquid jet in a subsonic uniform cross airflow

Several tapered- and sharp-edge nozzles with different exit diameters were used to investigate their effect on the near-field characteristics of a liquid jet injected transversely into a subsonic uniform cross airflow including a jet’s structure, column trajectory, and its breakup length. The experimental results demonstrated that at a low range of jet velocity, the axial turbulence intensity of a liquid jet issuing from a sharp-edge nozzle is greater than that of a tapered-edge nozzle. This resulted in a more irregular surface of the liquid column injected from a sharp-edge nozzle. However, the presence of hydraulic flip in the case of a sharp-edge nozzle at high jet velocity caused a reduction in the axial turbulence intensity of the injected liquid jet which has a smoother surface. Prior to the occurrence of hydraulic flip, the column trajectory of a liquid jet issuing from a tapered-edge nozzle is similar to that of a sharp-edge nozzle. However, the jet issuing from the latter penetrates farther than the former under hydraulic flip conditions. The presence of hydraulic flip increases the breakup length of a liquid jet. Furthermore, the present experiments allowed estimating the discharge coefficient of each nozzle by comparing with the mathematical correlations developed in our previous studies for predicting the column trajectory and breakup length of a transverse liquid jet. This allowed extending the applicability of these correlations to account for the effect of nozzle’s exit conditions on the near-field characteristics of a transverse liquid jet.

Size-Selective Sampling Performance of Six Low-Volume "Total" Suspended Particulate (TSP) Inlets.

Several low-volume inlets (flow rates ≤16.7 liters per minute (Lpm)) are commercially available as components of low-cost, portable ambient particulate matter samplers. Because the inlets themselves do not contain internal fractionators, they are often assumed to representatively sample "total" mass concentrations from the ambient air, independent of aerodynamic particle size and wind speed. To date, none of these so-called "TSP" inlets have been rigorously tested under controlled conditions. To determine their actual size-selective performance under conditions of expected use, wind tunnel tests of six commonly used omnidirectional, low-volume inlets were conducted using solid, polydisperse aerosols at wind speeds of 2, 8, and 24 km/hr. With the exception of axially-oriented, isokinetic sharp-edge nozzles operating at 5 and 10 Lpm, all low-volume inlets showed some degree of non-ideal sampling performance as a function of aerodynamic particle size and wind speed. Depending upon wind speed and assumed ambient particle size distribution, total mass concentration measurements were estimated to be negatively biased by as much as 66%. As expected from particle inertial considerations, inlet efficiency tended to degrade with increasing wind speed and particle size, although some exceptions were noted. The implications of each inlet's non-ideal behavior are discussed with regards to expected total mass concentration measurement during ambient sampling and the ability to obtain representative sampling for size ranges of interest, such as PM2.5 and PM10. Overall test results will aid in low-volume inlet selection and with proper interpretation of results obtained with their ambient field use.

The predominant effect of stroke length on velocity profiles at the exit of axisymmetric synthetic jet actuators

This paper addresses the effect of stroke length on velocity profiles at the exit of axisymmetric synthetic jet actuators. An actuator with a “short-orifice” nozzle geometry was studied (the length of the sharp-edged orifice nozzle being always shorter than the stroke length). The investigation was carried out using hot-wire experiments and numerical approaches in the range of the Reynolds number from 400 to 5600 and a dimensionless stroke length from 1.5 to 86 (i.e. the Stokes number was from 16 to 102). To quantify the velocity profiles at the actuator exit, the ratio of the two characteristic velocities was used. The former one was evaluated as the time- and spatially-averaged orifice velocity and the latter as the time-mean centerline velocity. It was found that this average-to-centerline velocity ratio depends mainly on the dimensionless stroke length, with a minor dependence on the Reynolds number. An approximation function of this predominant relationship has been proposed. The results of both experimental and numerical approaches are in reasonable agreement showing variation of average-to-centerline velocity ratio in the range of 0.7–1.3.

Comparison of synthetic jet actuators based on sharp-edged and round-edged nozzles

Axisymmetric synthetic jet actuators based on a loudspeaker and on two types of flanged nozzles were tested and compared experimentally. The first type of the nozzle was a sharp-edged circular hole. The second one had a special design with fillets at inner and outer nozzle exit and with a small step in the middle of the nozzle. The function of the step was to prevent the flow reattachment during the extrusion stroke. The actuators with the two types of nozzles were operated at resonance and were compared first qualitatively using a simple phase locked flow visualization. Then the hot-wire anemometer was used to measure velocity distributions along nozzle axis and velocity profiles at the nozzle exit. Comparison of the nozzles was based on evaluation of the characteristic velocity and integral quantities (volumetric, momentum, and kinetic energy fluxes). It was found out that these quantities, which were evaluated at the nozzle exit, differ substantially for both nozzles. On the other hand the velocity flow field in farther distances from the nozzle exit area did not exhibit such prominent differences.

Numerical analysis of cavitation cloud shedding in a submerged water jet

Focused on the unsteady behavior of high-speed water jets with intensive cavitation a numerical analysis is performed by applying a practical compressible mixture flow bubble cavitation model with a simplified estimation of bubble radius. The mean flow of two-phase mixture is calculated by unsteady Reynolds averaged Navier-Stokes (URANS) for compressible flow and the intensity of cavitation in a local field is evaluated by the volume fraction of gas bubbles whose radius is estimated with a simplified Rayleigh-Plesset equation according to pressure variation of the mean flow field. High-speed submerged water jet issuing from a sheathed sharp-edge orifice nozzle is treated. The periodically shedding of cavitation clouds is captured in a certain reliability compared to experiment data of visualization observation and the capability to capture the unsteadily shedding of cavitation clouds is demonstrated. The results demonstrate that cavitation takes place near the entrance of nozzle throat and cavitation cloud expands consequentially while flowing downstream. Developed bubble clouds break up near the nozzle exit and shed downstream periodically along the shear layer. Under the effect of cavitation bubbles the decay of core velocity is delayed compared to the case of no-cavitation jet.

CFD simulation of nozzle characteristics in a gas aggregation cluster source

Computational fluid dynamics (CFD) simulation for the sharp-edged nozzle was made using the OpenFOAM source code. Jet dynamics characteristics for the gas stream from a sharped-edged nozzle are then simulated under two-dimensional and axisymmetric steady state condition. Gas and particle velocities in a jet are obtained under different input and boundary conditions to provide an insight into the jet characteristics. For the range of downstream distances considered, the results indicate that a jet is characterized by an initial rapid decay of the axial velocity at the jet center while the cross-sectional flow evolves toward a top-hat profile downstream. Numerical simulation of the free-jet expansion from six types of nozzles indicated that the flow fields had significant differences in the early stages of the expansion. The effects of nozzle geometry on the nanoparticles were investigated. Simulation results indicated that the geometry of nozzle affected the cluster penetration efficiency and beam diameter. The extent to which to the Brownian diffusion can affect the particle extraction from nozzle is investigated. Simulations have shown that the Brownian motion perturbs the clusters from the trajectories dictated by the carrier gas and increases the rate of cluster deposition on the nozzle.

Numerical Simulation of Unsteady Cavitation in a High-speed Water Jet

Abstract Concerning the numerical simulation of high-speed water jet with intensive cavitation this paper presents a practical compressible mixture flow method by coupling a simplified estimation of bubble cavitation and a compressible mixture flow computation. The mean flow of two-phase mixture is calculated by RANS for compressible fluidU he intensit. T y of cavitation in a local field is evaluated by the volume fraction of gas phase varying with the mean flow, and the effect of cavitation on the flow turbulence is considered by applying a ion to density correctthe evaluation of eddy viscosity. High-speed submerged water jets issuing from a sheathed sharp-edge orifice nozzle are treated when the cavitation number, σ = 0.1, and the computation result is compared with experimental data The result reveals that cavitation occurs initially at the entrance of orifice and bubble cloud develops gradually while flowing downstream along the shear layer. Developed bubble cloudbreaks up and then sheds downstream periodically near the sheath exit. The pattern of cavitation cloud shedding evaluated by simulation agrees experimental one, and the possibility to capture the unsteadily shedding of cavitation clouds is demonstrated. The decay of core velocity in cavitating jetis delayed greatly compared to that in no-activation jet, and the effect of the nozzle sheath is demonstrated.

Stress intensity factor calculation in sharp and beveled edge nozzle corners

This paper presents the work performed for the development of Stress Intensity Factor compendia for defects in nozzle corners. For that purpose, a large set Finite Element modeling were performed in order to cover the geometries, the defect sizes, the loading situations … encountered by large nuclear components. Then, based on that set of Finite Element modeling, an approximate solution relying on a fit of the stress field along the bisector line of the nozzle corner is proposed. This solution allows determining accurately the mean and maximum Stress Intensity Factor along the crack front for pressure loading and at the maximum of cold thermal shock loading. It is validated through a comparison to existing solutions or Finite Element modeling results.

An experimental investigation on mixing enhancements in non-circular sharp-edged nozzles using the entropy production concept

An experimental study on mixing enhancement in free jets, issuing from sharp-edged nozzles of different geometry, is performed by using particle image velocimetry. The attention is focused on the jet near-field and interaction zones (0 < X/D < 18, where X is the axial coordinate and D the diameter of the equivalent circular jet). The mixing efficiency is evaluated and quantified using the definition of entropy production derived from the velocity field. The effect of Reynolds number is also discussed by performing measurements at Re = 8000 and Re = 35,000. The results are compared to circular nozzle data to evaluate the change in mixing efficiency among axisymmetric and non-symmetric nozzles. While the effect of Reynolds number on mixing is small, at least for the values tested here, the change in geometry is rather crucial. In terms of entropy production, the rectangular and elliptical nozzles show higher mixing for X/D< 7, whereas the other ones attain the best results for larger distances. This behaviour is basically related to the axis-switching phenomenon observed in elongated jets. Different variables are tested and compared as possible velocity and length scales to derive a meaningful non-dimensional entropy production.

Effect of Nozzle Geometry on the Rewetting of Hot Surface During Jet Impingement Cooling

An investigation has been carried out to investigate the effect of nozzle geometry on hot horizontal surface rewetting during water jet impingement cooling. The test surface of 800 ± 10°C initial surface temperature is cooled by water jet of 22 ± 1°C temperature. The water flow is varied to maintain the jet Reynolds number in a range of 5,000 to 24,000. The rewetting phenomena with sharp-edged and tube-type nozzles are compared on the basis of rewetting temperature, wetting delay, rewetting velocity, and maximum surface heat flux. The rewetting performance with tube-type nozzle is better than the sharp-edged nozzle particularly for the downstream spatial locations; however, maximum surface heat flux at the stagnation region is higher with the sharp-edged nozzle.

Particle image velocimetry investigation on mixing enhancement of non-circular sharp edge nozzles

An experimental study using Particle Image Velocimetry (PIV) on free jets issuing from different orifice plate (OP) nozzles is reported. Mean velocity, turbulence intensity and higher order profiles relevant for large and small scale mixing are considered in the near field and interaction zone (0<X/D<20). This is done to determine mixing enhancement due to rectangular, squared, elliptic and triangular nozzles in comparison to circular nozzle results in two orthogonal planes. The effect of Reynolds number on the differences among the nozzle shapes is also considered by performing measurements just after laminar–turbulent transition (Re=8000) and in the fully turbulent regime (Re=35,000). The results at low Reynolds number show two classes of jets, i.e. at one side, those closer to axial-symmetric conditions, as circular, square and triangular jets, whereas on the other side those with elongated nozzles as rectangular and elliptic. The reason for the different behavior of the latter is connected to the phenomenon of axis-switching which allows a rearrangement of turbulence over the different velocity components and directions. However, for the highest Reynolds number investigated, all nozzles show similar behavior especially in the jet far field (X/D>10), thus suggesting a significant Reynolds number dependence of the results.

Determination of rewetting on hot horizontal surface with water jet impingement through a sharp edge nozzle

The rewetting phenomenon was experimentally investigated for the hot horizontal stainless steel surface of 0.25 mm thickness and 800 ± 10 °C initial surface temperature. The round water jet of 2.5 mm diameter at 22 ± 1 °C temperature was injected through a sharp edge nozzle. The investigation was done for the stagnation point to 12 mm (≈5d) radial distance and jet Reynolds number varied in the range of 5000–24,000. The rewetting phenomena during the transient cooling was accessed on the basis of rewetting temperature, wetting delay, wetting speed and maximum surface heat flux.It has been observed that with rise in jet Reynolds number, the rewetting performance increased for the entire measured spatial locations. However, for downstream region the surface rewetting has been delayed and occurred at the reduced surface temperature as compared to the stagnation region. The maximum surface heat flux is the highest at the stagnation point and in a range of 2.1–2.45 MW/m2. The correlation developed for the wetting front speed predicts 85 percent of experimental data within an error band of ±20 percent and the correlation for maximum surface heat flux predicts 90 percent of experimental data within an error band of ±10 percent.

Particle image velocimetry measurements in curved turbulent jets produced from a slot diffuser

An experimental investigation was undertaken to study the characteristics of curved turbulent water jets produced from a vertical slot diffuser with sharp protrusions at the exit plane. The experiments were performed at two different flow rates for which the Reynolds number based on slot width and average velocity were 2050 and 4100. A high resolution particle image velocimetry system was used to perform detailed velocity measurements which were post-processed to obtain the mean velocities, Reynolds stresses and turbulence kinetic energy. The decay of the centerline mean velocity and jet half-width were also obtained to evaluate the mixing characteristics of the present slot configuration vis-à-vis results reported in previous studies. It was observed that the mixing characteristics of the slot configuration investigated in this study are superior to most of the sharp-edged nozzle configurations and curved jets studied in the past. The effects of streamline curvature on the Reynolds stresses in the convex and concave regions were also examined. The results clearly demonstrated that streamline curvature significantly enhanced the level of the streamwise turbulence intensity in the convex region more than in the concave region. On the contrary, the Reynolds shear stress and transverse turbulence intensity are much larger in the concave region than in the convex region. These results, together with the distributions of the Reynolds stress ratios across the jet, provide clear indications that turbulence models that assume local equilibrium and isotropy will not be able to accurately reproduce the flow characteristics of curved turbulent jets.