Nozzle Edge Research Articles

The effect of wave characteristics on rivulet formation in heated liquid films

Formation of rivulets on the surface of non-isothermal water film falling vertically over the heaters with different sizes and boundary conditions was studied experimentally. The distances between rivulets were measured depending on Reynolds number, heat flux density and film path (a distance between the lower edge of a film-former nozzle and the measurement point of film flow characteristics). The breakdown of solitary waves at liquid film heating was revealed. Four zones of film path influence on rivulet formation were distinguished.

Large-Scale Vortical Motion and Pressure Fluctuation in Noise-Controlled, Swirl-Stabilized Combustor

To clarify the mechanisms of combustion oscillation, combustion noise and their suppression by secondary fuel injection, simultaneous measurements of stereoscopic particle image velocimetry (SPIV) and pressure fluctuation in combustion chamber were conducted on several planes of a swirl-stabilized turbulent premixed flame for no control case and noise-controlled case by continuous secondary fuel injection. Velocities measured by SPIV were averaged in 8 phases of the pressure fluctuation and streamlines were obtained from the phase-averaged velocities. For no control case, large-scale vortical structures are generated in regions around the axial centerline of the combustor and outer edge of the swirl nozzle in the phase of low pressure. With increasing pressure, they move near the contour surface of mean progress variable c = 0.5 which have been obtained in the previous study. These large-scale vortical motions induce fluctuation of flame front and enhance entropy term in the acoustic sound source. The secondary fuel injection suppresses the velocity fluctuation in the inner recirculation zone, resulting in reduction of combustion noise. These results show that control of the large-scale vortical motion is important for reduction of combustion noise.

Numerical Analyses of Exhaust and Refill Processes of aLaser Pulse Jet

The exhaust-refill processes in a laser pulse jet with a conical nozzle are simulated using computational fluid dynamics to clarify the analytically unpredictable decreasing tendency of a momentum-coupling coefficient with an increasing nozzle apex angle. Because the exhaust-refill processes result from an adiabatically expanding blast wave after laser heating, a valid explosion source based on a measurement is used to drive the blast wave instead of a laser-absorption process. Results of computations show that processes that occur until the shock front of a blast wave reaches the nozzle exit are similar, irrespective of the nozzle apex angle. However, after the blast wave leaves the nozzle edge, the behavior of the rarefaction wave induced behind the shock wave depends greatly on the nozzle apex angle. In the case of small apex angles, successive refilling mechanisms with a vortex are activated by the prominently evolved rarefaction wave. In contrast, in the case of large apex angles, this mechanism disappears, due to the moderate evolution of the rarefaction wave. This difference creates a tendency of the momentum-coupling coefficient to decrease with the apex angle.

Numerical analysis of free surface instabilities in the IFMIF lithium target

The International Fusion Materials Irradiation Facility (IFMIF) uses a high speed (10–20 m/s) lithium (Li)-jet flow as a target for two 40 MeV/125 mA deuteron beams. The major function of the Li target is to provide a stable Li jet for the production of an intense neutron flux. Different hydrodynamic instability mechanisms are possible in the Li-jet flow. The main objective of this study is to provide a detailed numerical analysis of instabilities in the Li-jet flow caused by separation of the flow near the nozzle outlet. Experimental observations have shown that the change of the nozzle geometry at the outlet or nozzle edge defects causes the flow separation and occurrence of longitudinal periodic structures on the free surface. Target surface fluctuations of large magnitude can lead to the penetration of the deuteron beam in the target structure and cause the local overheating of the back plate. This work is focused on the validation the CFD code Star-CD and choice of the suitable simulation technique for further calculations of lithium target flow. Two simulation methods, Large Eddy Simulation (LES) and Reynolds Averaged Navier–Stokes method using the Shear Stress Transport (SST) turbulence model have been validated against the experimental data. Two experimental cases with two different kinds of instability sources were used to test the suitability of turbulence models to predict waves generated near the nozzle edge. While in the first case the instability source is a stationary located obstacle at the nozzle edge, in the second one the position of the instability sources is influenced from turbulent fluctuations in the boundary layer near the nozzle edge. LES has a reasonable agreement with experimental data. SST turbulence model is not able to predict the local flow separations at the nozzle edge caused by turbulence fluctuations and to reproduce instabilities of small magnitudes.

Fluctuating fluid flow and heat transfer of an obliquely impinging air jet

Heat transfer to an obliquely impinging air jet is investigated experimentally. Distributions of the mean and the fluctuating component of the surface heat transfer are reported for a jet Reynolds number of 10,000, nozzle to impingement surface distance, H/ D, from 2 to 8 and angle of impingement, α, from 30° to 90° (normal impingement). Flow velocity measurements along the impingement surface are related to heat transfer distributions. At specific locations the surface heat transfer and the local fluid velocity are measured simultaneously and coherence and phase difference information between the signals are reported. The vortical characteristic of the flow is shown to vary considerably with the angle of impingement; depending on the distance between the near nozzle edge and the impingement surface, vortices at different stages of development impact with the target surface. The influence of naturally occurring vortices in an impinging jet flow on the magnitude of heat transfer in the near wall jet is reported.

Characterization of an annular fluidized bed

The annular fluidized bed is a new technology consisting of a large central nozzle surrounded by a stationary fluidized bed. Due to the moderate primary gas fluidization of the annulus, the solids overflow at the upper edge of the central nozzle is mixed into the high upward velocity central secondary gas stream and transported into the mixing chamber. With this geometrical configuration, the process combines the advantages of the stationary fluidized bed (long solids residence time) and of the circulating fluidized bed (good heat and mass transfer). This paper presents the determination of the operating range of the system and the characterization of the solids mixing behaviour above the central nozzle in order to develop scale-up rules for the industrial application of the annular fluidized bed. The local radial solids concentration, velocity and mass flux profiles are investigated by capacitance probe measurements in a laboratory rig and a pilot plant of inside diameter 0.19 m and 0.74 m, respectively. The geometric and operating parameters varied are the diameter of the central nozzle, the gas velocity in the annulus and in the central nozzle and the pressure drop in the mixing chamber.

Control over the instability wave in terms of the two-dimensional model of a nozzle edge

The problem of generation of an instability wave leaving the edge of a half-plane that separates an immobile medium from a moving medium is considered. It is assumed that the instability wave is initiated by an acoustic wave arriving from the moving medium. The possibility of suppressing the instability wave by another acoustic wave incident from the nonflowing medium is considered. It is shown that the suppression is always possible by adjusting the amplitude and phase of the control perturbation to the parameters of the instability wave.

Instability wave control in a subsonic round jet

It is generally accepted that one of the main sources of acoustic radiation from a turbulent jet is due to spatial instability wave packets propagating downstream within the jet. This approach has enabled to explain and predict the principal features of sound radiated by a supersonic jet. Therefore the problem of noise control for the jet could be considered as a problem of instability wave control. Instability wave developed in the tone‐excited jet issued from axisymmetric, semi‐infinite duct is considered. The flow field in the vicinity of the nozzle edge is investigated for the purpose of identifying instability wave parameters. Instability wave turned out to be damped completely on the condition that the amplitude and the phase of the external forcing are chosen in accordance with those of the instability wave. The robust strategy of instability wave experimental suppression based on the near field measurements is formulated. Similar problem in two‐dimensional case was recently analyzed in Kopiev & Fa...

Contouring spike nozzles and determining the optimal direction of their primary flows

Problems related with the optimal contouring of two-dimensional and axisymmetric spike nozzles providing maximum thrust for given dimensions and external pressure are studied. The nozzles under consideration are self-adjustable which is ensured by the non-zero inclination of their primary supersonic flow to the plane (axis) of symmetry. Along with the optimal contouring of the spike, the optimal orientation of the “primary” nozzle producing the primary flow is obtained. In the exact formulation, its optimal inclination is determined by an exhaustive search for the configurations providing maximum thrust for a given spike length and various fixed inclinations of the primary nozzle. The spike and primary nozzle contours of these configurations are generally joined through a bend with the formation of an expansion fan in the flow around the bend. The efficiency of a simpler approximate method for contouring the spike and determining a near-optimal inclination of the primary nozzle is demonstrated. The method is based on passage to a modified formulation of the problem differing from the original one in that it is only the part of the spike extending beyond the primary nozzle edge that is preassigned rather than its entire length. In the modified formulation, there is no a bend in the flow around which an expansion fan could be formed, while the inclination of the primary nozzle is determined in the process of designing the unique optimal configuration.

Near-Field Flow Measurements of a Cavitating Jet Emanating From a Crown-Shaped Nozzle

The effect of a crown-shaped nozzle on cavitation is studied experimentally in the near-field of a 25 mm diameter (D) water jet at ReD=2×105 using particle image velocimetry (PIV) and high speed shadowgraphy recorded with a 5000 fps digital camera. The objectives are to passively control the jet flow structure and to examine its consequences on the physical appearance of cavitating bubbles. The experiments are performed in a closed-loop facility that enables complete optical access to the near-nozzle region. The cavitating and noncavitating mean velocity fields are obtained up to three nozzle diameters downstream and compared to those of a companion round nozzle. PIV measurements are taken in two distinct azimuthal planes passing through the tip and bottom points of the crown nozzle edge. The data include shear layer momentum thickness and vorticity thickness, spanwise vorticity distribution and streamwise normal Reynolds stress. Significant deviation from an axisymmetric shear layer is observed in the noncavitating flow consistently up to one diameter downstream, after which identical asymptotic conditions are achieved in both round and crown-shaped nozzles. Maximum magnitudes of spanwise vorticity and streamwise normal Reynolds stress are the highest downstream of the nozzle tip edges under noncavitating conditions. Significant modifications in trends and magnitudes are observed for the shear layer momentum thickness under cavitating conditions up to one diameter downstream. Qualitative flow visualization reveals that bubble growth occurs at different conditions depending on azimuthal location. Bubbles, in the form of elongated filaments, are the dominant structures produced downstream of the valley edges of the nozzle with an inclination of 45 deg with respect to the direction of the flow, and are observed to persist with significant strength up to two diameters downstream. These filaments are stretched between periodic larger-scale, spanwise bubbly clusters distorted in the shape of the nozzle outlet. The tip edges produce cavitating bubbles under conditions similar to that of a classical round nozzle. In summary, it was demonstrated that passive control of turbulent structures in the jet does impact the cavitation process.

Structure of Underexpanded Jets from Square Nozzles

The structure of underexpanded jets issuing from nozzles with square outlets is investigated numerically and experimentally. This type of nozzle is of interest for its use in the clustered combustors of linear aerospike engines. The numerical results indicate that the first shock cell is composed of two types of shock waves; intercepting shock waves corresponding to the oblique shock wave observed in underexpanded jets from two-dimensional planar nozzles, and recompression shock waves that appear downstream of the overexpanded regions. The overexpanded regions are formed by the interaction of expansion fans generated at neighboring nozzle edges. It is shown that the jet expands almost two-dimensionally on the symmetry planes, whereas shock waves suppress expansion on the diagonal planes, resulting in a cross shaped jet cross section.

Coolant film flow over the edge of a nozzle in a rarefied gas

The flow of a thin liquid film over the nozzle wall under the action of tangential friction and pressure gradient is considered. For the slow flow of the film with constant thermal physical properties, analytical dependences of the film thickness and temperature at the interface on the coordinate along the nozzle edge are derived. The flow of the film over the variable-curvature nozzle edge when the gas expands into vacuum is considered. At the initial section of the curvilinear edge, the film thickness increases in inverse proportion to the root of the friction stress at the interface. Near the end point of the nozzle, the film thickens drastically because of a decrease in the friction and, consequently, the curvature of the interface diminishes. As a result, the deceleration of the liquid by the Laplace pressure gradient drops, which causes an additional sharp growth of the thickness of the film with the possibility of its dynamic and thermal disintegration and, eventually, contamination of the spacecraft surface.

Transonic instability in entrance part of mixing chamber of high-speed ejector

The paper deals with experimental and numerical study of flow structure in two-dimensional model of supersonic ejector. Schlieren pictures of flow structure were taken, static pressure distributions on side wall were measured and Fluent software to calculate the flow structure in supersonic ejector was used. For certain region of back pressure ratio pb/p02 and stagnation pressure ratio of both streams p01/p02 the terminal shock wave is close to the trailing edge of the primary flow nozzle and a transonic instability occurs. The instability causes the movement of position of boundary layer separation, the structure of shock waves changes and all flow structure oscillates. The movie of these regimes during schlieren experiments was taken and relevant numerical modelling was performed.

High speed lithium flow experiments for IFMIF target

Lithium flow was tested in a free surface test channel under pressurized or evacuated condition for the IFMIF target. The test channel, with a two-staged contraction nozzle designed after water test, was newly added to the Li loop facility in Osaka. Stable flow was obtained at the velocity of up to 13.8 m/s in 0.15 MPa, and up to 8.5 m/s at medium vacuum condition. In the course of circulation, wakes on free surface were begun to be observed due to small adhesives on the channel wall. These from the nozzle edge are considered to be prevented by keeping the edge clean. Those from the corners of the nozzle and sidewall were also observed. The shape was found to agree well with the theoretical prediction, Wake shape was estimated for IFMIF geometry, and it was indicated that the wakes emerge from the corners will not disturb the presently designed beam region.

Effect of Delta Tabs on Axis Switching of a Coaxial Square Jet

The effects of delta tabs in the near field of a coaxial square jet have been studied experimentally using a laser Doppler anemometer. The tabs are added to the centers of the four sidewalls of the inner nozzle trailing edge, with the tip of each tab tilted into the inner jet, that is, θ = 45 deg, or into the outer jet, that is, θ = -45 deg. For each tab orientation, three velocity ratios have been considered: γ u = 0, 0.5, and 1.0 for θ = 45 deg and γ u = 1.0, 2.0, and oo for θ = -45 deg. The results illustrate that tabs increase the mixing between the inner jet and outer jet and may promote or suppress the phenomenon of axis switching, depending on the orientation of the tabs. Axis switching is defined as follows: As a noncircular (here square) jet spreads, its cross-section may evolve from the initial shape similar to that the jet exit, to have its axis rotated some angle at some downstream location. In the case of θ =45 deg, the cross-sectional shape of the inner mixing layers is bifurcated into a four-finger structure, which tends to suppress the onset of axis switching. When θ = -45 deg, it exhibits an eightfold mode, and a rapid axis-switching occurs in the near-field. The effect of tabs is briefly discussed using inviscid vortex dynamics.

Control of the Parameters of an Exhaust Jet by Increasing the Eddy Viscosity at the Nozzle Edge

We studied the possibility of changing the parameters of the exhaust wake in the far field of the jet behind a large passenger aircraft (aerobus) by increasing the coefficient of eddy viscosity at the edge of the nozzle of a double‐flow engine with a high double‐flow ratio (>10) without mixing with the aid of artificial turbulizers created in the outer and inner ducts. Within the model of turbulence with one differential equation for the coefficient of viscosity, we obtained numerical solutions for velocity, temperature, concentrations of vapor and condensate, and the coefficient of viscosity for different variants which disclose the essence of a physico‐mathematical model of the phenomenon and predict possible changes of the parameters of the exhaust jet with artificial increase of viscosity in the initial section and the jet volume.

Circular vortex formation in a pulsed jet penetrating through a filter layer

A method for the formation of a laminar circular vortex is proposed that excludes the interaction of a pulsed jet with the nozzle edge. Another method is suggested for visualization of the gas flow and measurement of the gas velocity distribution in a jet penetrating through a filter layer. Critical conditions for the formation of a circular vortex are established, determining the jet power as a function of the thickness of a flat filter layer formed by granulated silica gel. It is shown that a mechanism of the laminar circular vortex formation is controlled only by the gas flow acceleration in the jet.

旋回流動研磨法による高硬度ステンレス鋼微細穴の仕上げ加工と端面の面取り

It is necessary that the inner wall of the tiny nozzle used in a water jet cleaner is very smooth and also its nozzle edge is chamfered. Finishing of the inner wall of the tiny nozzle is very difficult by ordinary finishing methods. Gyration flow finishing method recently has been newly developed in which polishing is conducted using polishing fluid suspended peach seeds and grains into olive oil. Present study focuses on the effect of the polishing fluid supplied from the back side of workpiece. It is found that the suck out of polishing fluid from the back side of workpiece is very effective for chamfering of the nozzle edge. Experiments show that the size of the peach seed has an influence on chamfering quantity of the nozzle. It is shown that the jet force of the water jet cleaner of which nozzle is polished by the polishing method is made to increase by 30%.

Design of two-dimensional plane rapid expansion nozzles

A simple approximative method for design of the transonic region of rapid expansion nozzles is described for two-dimensional plane case using elements of the exact solution of the transonic potential equation for nozzles with continuous contours of slender body type. The results are in satisfactory correspondence with known experiments and values gained by the hodograph method. The features of the flow near the nozzle edge such as the bellied downstream form of the sonic line and the succession of other dominating lines are discussed as well as the special conditions for establishing a method of characteristics for the calculation of the supersonic nozzle region.

Wavelet Multiresolution Analysis of Stereoscopic Particle-Image-Velocimetry Measurements in Lobed Jet

A wavelet-based vector multiresolution technique was developed and applied to a high-resolution stereoscopic particle image velocimetry system for studying the three-dimensional multiscale structurefeatures of the lobed jet mixing e ow. The instantaneous three-dimensional velocity vectors were successfully decomposed into large- and small-scale velocity e elds, and existence of very strong multiscale turbulent structures were cone rmed in the near e eld of the lobed jet. Within the central scale range of 16 mm, the instantaneous pairs of large-scale streamwise and horseshoe vortices can be clearly observed around the lobe peak regions and lobe troughs, respectively, and begin to breakdown and spread outward at downstream. The stronger small-scale streamwise vortices were found in the lobe regions, which e rst spread outward along the lobes and then develop to the whole measured e owe eld. These small-scale streamwise vortices also play an important role in the enhance mixing process. The stronger alternate positive and negative peaks of small-scale axial velocity component, which appear at the trailing edge of the lobed nozzle in the near e eld, indicate the existence of the Kelvin ‐Helmholtz or normal vortices.