Nozzle Edge Research Articles

Expansion of a Helium Jet under the Influence of High-Intensity Sound

The results of a comparative investigation of the influence of high-intensity sound (sound pressure level at the nozzle edge L=165 dB) on the expansion of turbulent helium and air jets are given. The jets and sound waves were visualized by means of the direct schlieren method using a spark light source with an exposure of 2·10-7 s. It is shown that the helium jet expands much faster than an air jet with the same dynamic pressure.

Effect of the Nozzle Edge Shape on the Acoustic Sensitivity of a Jet

The effect of the nozzle edge shape on the acoustic sensitivity of jets, that is, on the dependence of the jet parameters on the amplitude and frequency of the acoustic oscillations produced by an external source, is experimentally studied. The investigation was performed for nozzle edge configurations, the variation of which did not result in a change in the jet characteristics without external acoustic excitation. This means that the change in the edge shape alone had no influence on the flow pattern at the nozzle exit or the boundary layer flow regime on the nozzle walls. Measurements of the dependence of the mean velocity and the velocity fluctuation intensity on the jet axis on the distance from the nozzle exit showed that a change in the nozzle edge shape can lead to a change in the acoustic sensitivity of the jet when the jet is exposed to external acoustic action.

Effects of nozzle trailing edges on acoustic field of supersonic rectangular jet

Effects of nozzle trailing edges on acoustic field of supersonic rectangular jet

Dynamics of Sulfate Aerosol Formation in Engine Jets

The effect of SO2, SO3, HSO3, and H2SO4 formation in the jet duct on the dynamics of sulfate H2O/H2SO4 aerosol formation in the wake of a subsonic aircraft is analyzed numerically. It is shown that the presence, in addition to SO2, of SO3, HSO3, and H2SO4 at the nozzle edge leads to an increase in the nucleation rate and intensification of the coagulation process. A significant quantity of large particles (of radius greater than 9 nm) is formed in the jet. This quantity depends on the sulfur content of the fuel.

The emission of a gas jet from a conical nozzle

The axially symmetric, subsonic emission of a jet of compressible fluid from a conical nozzle is considered. Subject to the assumptions that a solution of the corresponding boundary-value problem exists and that a certain asymptotic expansion holds in the case of this solution, it is proved that, in an axially symmetric jet of a compressible fluid at a critical pressure on the free surface, the gas velocity reaches the sound velocity in a certain plane which is perpendicular to the axis and located at a finite distance from the nozzle edge. Results are presented for a jet of a perfect gas with an adiabatic exponent γ = 1.4. Approximate formulae are given which enable one to determine the form of a jet with a sonic velocity on the free surface.

Structure and parameters of the shock layer formed when a supersonic underexpanded jet interacts with a counterpropagating hypersonic flow in the transition regime

The method of molecular dynamics (the Bird system) has been used to mathematically model a planar, strongly underexpanded supersonic jet that encounters a hypersonic flow of rarefied gas. Particular attention is paid to the structure and parameters of the shock layer close to the plane of symmetry. The results of calculations are presented for currents of a monatomic gas, simulating argon, with a Mach number of the external flow of M∞=5.48, a Mach number at the nozzle edge of Ma=1, a ratio of the density at the nozzle edge to the density of the unperturbed flow equal to 130, and various stagnation temperatures of the external flow and of the jet. The evolution of the structure and the parameters of the shock layer as the Knudsen number Kn∞ varies from 0.02 to 0.35 is considered. The results are compared with the data calculated for the shock layer when argon flows around thermally insulated cylinders. The main features and regularities of the relaxation of the translational degrees of freedom of the gas for external and jet flows are considered. Data are presented on the form of the distribution function over velocities and its evolution as gas moves through the shock layers.

Characteristics of the structure of the phase inhomogeneity and of nonequilibrium of the active medium beyond a three-dimensional expansion nozzle array of a gasdynamic laser

A numerical simulation was made of the three-dimensional structure of the flow and of nonequilibrium of the active medium beyond a three-dimensional expansion nozzle array of a gasdynamic laser. The dependences of the optical homogeneity of the active medium, of the average integral radiation intensity in an aperture, and of the overall laser efficiency on the gas pressure at the nozzle edges and on the angle of encounter of supersonic jets were derived for two nozzle array configurations: with preliminary mixing of the active components and with supersonic mixing beyond the nozzle array edge.

Excitation Force and Blade Inlet Flow Characteristics of Radial Turbines Subject to Nozzle Wake Effect.

The authors developed a method to estimate nozzle-wake exciting forces (NEF) using Fourier series development of angular momentum flux (AMF) at the blade inlet of radial turbines. The NEF is strongly affected by the nozzle profiles. Application of this method to the evaluation of the NEF and AMF resulted in fundamental standards for selection of the number of nozzle blades and the profiles. The values of each order of NEF are obtained from Fourier series development of AMF. There is an increasing region of NEF to the distance from a nozzle trailing edge. The maximum estimation error of the blade vibration stress, which is calculated using the values of the first order of NEF and the coefficients of effective exciting force, is 10%. The coefficient of effective exciting force is 1/3 in the first and second modes, and 1/2 in third mode. Those coefficients are evaluated as the ratio of NEF and equivalent exiting forces calculated using the measured data of vibration stresses at two different points on the blade.

Self-Excited Oscillation in an Axisymmetric Jet with a Coaxial Ring.

Self-excited oscillation of an axisymmetric jet impinging upon a ring is investigated experimentally. The discreat vortices impinge upon the downstream sharp edge of the ring, in turn producing an upstream influence, thereby closing the loop for sustaining oscillations, as confirmed by the form of phase analysis of velocity and pressure signals. The fundamental frequency component exhibits an overall phase difference of (2nπ) +1/2 (n=0, 1, 2) between the nozzle lip and edge. Furthermore, the fundamental component propagates with phase speed, which is about 0.52∼0.59Uo. Spectral analysis of velocity fluctuation reveals multiple frequency components having substantial amplitudes relative to that of the fundamental frequency component ; using coherence analysis it is shown that the lowest frequency component can interact with the fundamental component either to reinforce itself or to produce an additional frequency component.

Cone in a supersonic flow near a surface with a turbulent boundary layer

The published information about the interaction of incident shocks and a turbulent boundary layer relate to cases of a thin boundary layer (δ ∼ 1–3 mm) on a flat surface. The present study relates to supersonic flow with Mach number M = 3 and stagnation pressure p0=1.2 MPa past cones near a surface with a thick boundary layer formed on a plate abutting the lower edge of a plane nozzle.

Some Results on the Analytical Solution of Cylindrical Shells With Large Openings

An analytical solution for cylindrical shells with large openings has been developed by the asymptotic method. In comparison with previous analytical solutions obtained by Eringen, Van Dyke and Lekkerkerker, the following three areas have been improved by the present method: 1) The modified Morley’s equation, which is applicable to ro/RT≫1, is used instead of Donnell’s shallow shell equation. 2) The accurate expression of boundary curve of hole is expanded in terms of powers of ρo = ro/R, while the previous approximate geometric description corresponds to the first term of the expansion. 3) The accurate boundary conditions for generalized forces are expanded in terms of powers of ρo and truncated after the terms of ρo3; the previous approximate boundary conditions correspond to the terms of order up to ρo, in the asymptotic expansions. The present solutions are in good agreement with Van Dyke’s solutions for small openings. The analytical results show that the error caused by the previous approximate boundary conditions is significant and has the order O(ρo); the error caused by the previous approximate geometric description of hole boundary has the order O(ρo2); and finally, the error caused by using Donnell’s shallow shell equation is very small for ρo ≤ 0.7. For openings with ρo > 0.25, say, noticeable differences exist between the present and the previous results. The stress analysis of cylindrical shells connected with nozzles has been developed by using the present solution. For increasing the accuracy of stress analysis in the nozzle, the exact description of the edge of nozzle is given and the near-edge boundary layer stress state in the nozzle is considered. The results obtained are in good agreement with those by Eringen for small openings and with those by F.E.M. and experiments for large openings.

Visual Observation and Numerical Simulation of an Underexpanded Annular Impinging Jet.

An underexpanded annular impinging jet is visualized using a Mach-Zehnder interferometer and is also simulated solving compressible Navier-Stokes equations. A turbulence model developed by Coakley is used in the present simulation. It is shown that the calculated density distribution in the jet agrees fairly well with the measured distribution. Both the visual observation and the simulation show that the characteristics of the underexpanded annular impinging jet depend significantly on the distance H between the nozzle exit plane and the impinged flat plate. The annular impinging jet diverges in the downstream direction provided H is smaller than the critical value Hc. However, for H>Hc, the stream lines issuing from the inner edge of the annular nozzle join at a point near the nozzle exit.

水滴の急加速分裂に関する研究

水滴の分裂は気流の速度分布によって強く影響を受ける。本研究はモデル化したノズル板の端から高速気流によって水滴が離脱, 急加速および分裂する状態を高速度カメラによて調べたものであり, 次の内容について考察している。a) 発生水滴径および分裂までの距離の気流速度による影響, b) 水滴の加速の状態, およびc) 分裂開始時のウェーバ数。ここで, 水滴の変形から分裂までの過程には2つの形態がみられ, 分裂開始時のウェーバ数は一様な平行気流中のものよりも広範囲に分布し, また比較的大きな値を示している。

On-line surveillance instrumentation for full scale thermal shock trials under real pressurized water conditions (German HDR-program)

Within the framework of the HDR reactor safety research program, thermal shock tests on a saturated steam outlet nozzle edge have been conducted under simulated realistic operation conditions ( T = 300° C , p = 11 MPa ) for the past three years. On the one hand, the tests are to improve our understanding of crack formation and crack growth under thermal shock conditions and, on the other hand, to evaluate and improve the suitability of non-destructive test methods for the on-line surveillance, the detection and quantitative description of natural cracks and crack fields. For on-line monitoring of the thermal shock tests conducted on the A2 nozzle, thermocouples and strain gauges (both on the inside and the outside), clip gauges (CMOD measurement), stationary US-probes, the potential drop technique (potential measurement on the inside), and acoustic emission tests have been used. In the final two test phases (approx. 800 load cycles) by a new six-channel R&D acoustic emission analysis system (signal parameter processor) developed and built at IzfP has been applied.

Flow in the peripheral zone of a freely expanding axisymmetric ideal-gas jet

When an ideal gas flows from a nozzle into a vacuum a substantial part of the jet is occupied by the peripheral zone in which the angle of inclination of the velocity vector W to the axis of symmetry is close to or exceeds π/2. The known solutions [1–4] for the far field are unsuitable for describing the jet, since they are valid only at relatively small values of θ. In this study the author obtains an analytic solution describing in explicit form the shape of the streamlines and the distribution of the parameters in the peripheral zone of a jet flowing into a vacuum from a nozzle with an arbitrary parameter distribution in the exit section. At the nozzle edge the solution describes Prandtl-Mayer flow. As the radial coordinate tends to infinity, the streamlines tend to asymptotes whose angle of inclination depends on the distribution of the parameters in the nozzle exit section, and the local Mach numbers increase without bound.

Enhancement of the efficiency of a mixing gasdynamic laser by two-stage gas mixing

A study is made of the possibility of increasing the efficiency of a mixing gasdynamic laser by cooling hot N2 with a cold gas and creation of a thermal nonequilibrium state in the subsonic part of the nozzle. The necessary amount of CO2 and H2O are added beyond the nozzle edge. Calculations are reported for a mixing gasdynamic laser and it is shown that promising results can be expected if two-stage mixing of gases is used.

Cracking in feedwater pipework of light water reactors: Causes and remedies

The present paper deals with cracking in ferritic pipework of light water reactor (BWR) feedwater systems whose causes are unsuitable design and manufacture and, at least occasionally, unsuitable water quality. Thus in two BWR plants in the German Federal Republic large circumferential cracks have been found in the circumferential welds in the main feedwater pipelines immediately adjacent to the reactor pressure vessel, and in a further BWR large longitudinal cracks have been found in pipe bends of the reactor water purification pipework connected to the main feedwater pipelines. The piping regions near the reactor pressure vessel feedwater nozzles represent a boundary region of varying thermodynamic states of the pressurised water. The reactor pressure vessel is heated to saturation temperature by the radioactive decay heat, and then cooler water, and sometimes (during start-up) cold water is injected into the reactor pressure vessel in order to maintain a constant water level about 2 m above the upper edge of the feedwater nozzles. In order to improve the state of knowledge regarding the stressing conditions under prevailing operating conditions, extensive strain and temperature measurements have been carried out. The results of these measurements carried out in several BWRs confirm the occurrence of rapid temperature changes in the feedwater pipework in the regions where it connects to the reactor pressure vessel, leading to varying stresses which at times reach the plastic region. These processes are triggered by special operating states such as start-up and shut-down or hot standby operation with feedwater flows smaller than 6% relative to normal operation under full load.

Stability of a hydrogen diffusion flame in an accompanying air flow

As a result of this experimental and theoretical study we obtained relations showing how the velocity head ratio affects the mixture ratio, the extent of fuel combustion and the gas temperature in the recirculation zone on the interval qa=0.01-100. These relations are needed to establish the laws of diffusion-flame stability and to evaluate the thermal state of the nozzle edges in the high-temperature recirculation zone.

Grating interferometer with an unusual fringe direction

A grating interferometer is described which has an astigmatic component in the collimator. In such an interferometer the fringes may be directed parallel to the shear direction. The adjustment procedure is given, and interferograms of shock wave diffraction at a nozzle edge are presented.

Sound absorption caused by vorticity shedding, demonstrated with a jet flow

From previous measurements it has become evident that a low frequency sound wave can be absorbed significantly when transmitted through a nozzle and a jet flow. The basic underlying physical phenomenon is that acoustic energy is converted into energy of fluctuating vorticity, which is shed from the nozzle edge. In the meantime, different theories have become available which already yield an excellent quantitative description of this effect. These theories are discussed, and a derivation of the simplest of them, a multipolea analysis, is presented. It is demonstrated that this absorption effect is not restricted just to jet flows but occurs also in flows through apertures or through blade rows. A variety of applications is shown including a jet noise muffler and a new non-reflective termination.