Nozzle Cross Section Research Articles

Numerical simulation for axis switching of pulsating jet issued from rectangular nozzle at low Reynolds number

Axis switching of a jet ejected from a rectangular nozzle affects flow mixing characteristics. To elucidate such a mixing mechanism, the axis switching and vortex structure deformation should be investigated in detail. This study performed a numerical analysis of the axis switching of a pulsating jet ejected from a rectangular nozzle at a low Reynolds number. At all aspect ratios, a rectangular vortex ring similar to the shape of the nozzle cross-section is periodically shed downstream, and the side of the vortex ring deforms into a hairpin shape downstream. A vortex pair is generated inside the vortex ring downstream of the nozzle corner. When the aspect ratio is AR = 1.0, the vortex pair consists of symmetrical vortices, while as AR increases, the asymmetry of the vortex pair enlarges. At AR = 1.0, regeneration of a vortex ring occurs downstream. For AR = 2.0, alternately on the long and short sides of the nozzle, an upstream vortex ring overtakes a downstream vortex ring. Regardless of AR, downstream near the nozzle, as the vortex pair existing inside the vortex ring distorts the vortex ring, the positions of the side and corner of the vortex ring exchange, resulting in a 45° axis switching. For AR > 1.0, further downstream, the hairpin part of the vortex ring on the long side develops away from the jet center compared to the short side, causing a 90° axis switching. As a result, high turbulence occurs over a wide area, strengthening the mixing action. As AR increases, intensive interference between the vortex rings on the upstream and downstream sides diffuses the vortices downstream. Then, as turbulence by the diffused vortices widely occurs, the mixing effect is further strengthened.

The results of studies of agrotechnical indicators of the uniformity of rain distribution by a jet fan rain-forming nozzle when watering mushrooms

The materials of the article consider the studies carried out to determine the agrotechnical indicators of the uniformity of rain distribution when using the proposed design of a jet fan rain-forming nozzle installed on an automated plant for watering champignons. The flow-pressure characteristics of rain created by jet fan-shaped rain-forming nozzles with various nozzle cross-section shapes are presented.

Efficiency of cavity dissolution in rock salt by water submerged jets

To create cavities when dissolving rock salt, it is most expedient to supply the solvent through the nozzles of a perforated pipe in the form of submerged jets. This article examines the physical dissolution of a cavity with water from a stationary nozzle with a diameter of 0.004 m at two constant velocities at the nozzle cross-section. The efficiency of cavity dissolution, which has an almost cylindrical shape with a semi-cylindrical bottom, was analyzed at a nozzle cross-section speed of 8.85 m/s. The obtained results are explained on the basis of the fact that the formed cavity is a short dead-end channel where longitudinal compression acts. The flow in such a channel is caused by the back pressure exerted by its end. And the back pressure, in turn, hinders the development of the jet that flows out of the stationary nozzle, limiting its range. The cessation of significant expansion of the jet is indirectly confirmed by the use of an empirical formula for the distribution of the maximum water velocity along the axis of the jet. Its value at the end of the section of the most intense dissolution of the cavity becomes 8.85 times smaller compared to the speed at the nozzle cross-section. The boundaries of the area of the most intense dissolution of the cavity are determined by the relationship between the depth of the cavity, the diameter of the nozzle, the velocity at its cross-section, and the time of dissolution, which can be used to model the dissolution of cavities at different values of the velocity at the cross-section of the nozzle at its constant diameter. It was found that the relationship between the radius and depth of the cavity is linear. The angle between the boundary of the cavity size change and the axis of the nozzle is 20°23'. These results show that the dissolution of cavities is effective in a limited range of their dissolution time, the limits of which depend on the velocity of the solvent at the nozzle section. To confirm the obtained results, it is necessary to investigate the geometric characteristics of the cavities for other values of the nozzle diameters.

Research on jet noise characteristics of aeroengine double S-bend nozzles with different cross sections

PurposeThis study aims to improve the survivability and maneuverability of the fighter,and study the stealth performance of fighter in the jet noise of aeroengine, it is of great significance to study the jet noise characteristics of double S-bend nozzles.Design/methodology/approachThe multiparameter coupling and super-ellipse design methods are used to design the cross section of double S-bend nozzle. Taking unsteady flow information as the equivalent sound source, the noise signal at the far-field monitoring points were calculated with Ffowcs Williams–Hawkings (FW–H) method, and then, the sound source characteristics of the double S-bend nozzle are analyzed.FindingsThe results show that the internal flow of the S-bend nozzle with rectangular section is smoothed and the aerodynamic performance is better than super-ellipse section, the shear layer length of rectangular section is longer, the thickness is smaller and the mixing ability is stronger. The sound pressure level of the two S-bend nozzles decreases with the increase of the monitoring angle, and the sound pressure on the horizontal plane is greater than the vertical plane. In the direction of 40°–120°, the jet noise of rectangular nozzle is smaller, and the multiparameter coupled rectangular cross section structure is more applicable.Practical implicationsIt is beneficial to reduce the jet noise of the engine tail nozzle and improve the stealth performance of the aircraft.Originality/valueThere is very little research on the jet noise characteristics of the double S-bend nozzle. The multiparameter coupling and the super-ellipse method are used to design the nozzle flow section to study the aerodynamic performance and jet noise characteristics of the double S-bend nozzle and to improve the acoustic stealth characteristics of the aircraft.

Numerical characterization of hydrogen under-expanded jets: influence of the nozzle cross-section shape

This historical moment is characterized by a great awareness regarding the need to reduce the Greenhouse Gas emissions (GHG), which are responsible for the climate change and its detrimental consequences. Green hydrogen produced by means of Power-to-Gas technologies from renewables is gaining momentum as a possible clean fuel for the future mobility. In such a context, traditional injectors for hydrocarbon fuels are currently being tailored to be used with hydrogen. The short time available for the injection process leads to the employment of a high inlet pressure, resulting in the formation of an under-expanded jet. In this work, the main characteristics of these jets are analyzed by means of Computational Fluid Dynamics (CFD) for a Nozzle Pressure Ratio (NPR) equal to 10. Then, to provide insights regarding the dependence of the air-hydrogen mixing on section shape of the nozzle, comparisons have been performed by changing the nozzle cross-section (circular, rectangular, and elliptical), keeping constant the mass flow rate to highlight the different levels of axial penetration and radial spread observed when varying the aspect ratio (1.5, 5.0, 8.0).

Insights into ZrO2- and Al2O3-based submerged entry nozzle clogging for the continuous casting of RE-treating sulfur resistant casing steel

The ZrO2- and Al2O3-based submerged entry nozzle (SEN) clogging during continuous casting of a RE-treating sulfur resistant casing steel is studied experimentally based on morphological analysis and the related thermodynamic calculations. The results show that the ceramic cloggings exists both in the inner-wall and outlet regions of SEN, while the latter is the main reason for terminating the casting with its clogging reaching 77% in the nozzle cross section area. The clogging is caused by RE-containing inclusions from molten steel and reoxidation products by the reaction between RE in molten steel and the initial formed cloggings on nozzle refractory. The possible existence state of RE in molten steel with its content has been discussed, and the clogging mechanism studied in detail. To prevent nozzle clogging, suggestions are given for continuous casting of the RE-treating steel with a modified RE treatment strategy for less solid inclusions and solute [RE] presented in liquid steel during refining process. Additionally, the optimization of nozzle geometry and its refractory materials may help as well.

Numerical analysis of non-excited and excited jets issuing from non-circular nozzles

This paper concentrates on the application of passive and active flow control methods to jet flows. The passive control is obtained by shaping a nozzle cross-section (hexagonal, hexagram, square, triangular) and the active one by an external excitation. The research is performed by applying the large eddy simulation method (LES). The obtained results are thoroughly validated by comparisons with theoretical, experimental and numerical data for non-excited jets. The presented results comply well with the reference data, both in terms of the mean velocity profiles, velocity fluctuations profiles and the Strouhal number of the preferred oscillation frequency (Stp). Based on its value, the excitation frequencies (Stf) are chosen such to cover the range of Stp and its subharmonics. The applied excitation is defined as a sinusoidal function, which enforces the axial velocity oscillations at the level of 10% of the bulk velocity. It is shown that the dynamics of the excited non-circular jets is significantly different from the dynamics of their non-excited counterparts. It is demonstrated that by changing Stf one may modify both the instantaneous as well as their time-averaged behaviour, i.e., the centreline velocity decay, turbulence intensity, directional spreading rate and the entrainment rate. It is found that not all jets are prone to excitations to the same extent. In the far-field, the dependence of the velocity decay rate on Stf is the most pronounced in the jets issuing from circular and hexagonal nozzles. In the near-field, regardless of Stf the excitation causes a faster velocity drop, shortening of the potential core and increase of the centreline fluctuations in all jets. However, in the hexagram jet, the fluctuations turn out to be the least sensitive to change of Stf. Apparently, in this case, the complex nozzle shape determines the velocity oscillations so strongly that a relatively low amplitude excitation has only a small influence. In this respect, the jets issuing from square and triangular nozzles show the opposite, as for them the impact of the excitation is the strongest. Depending on Stf three qualitatively different scenarios of the fluctuations growth are identified by either manifesting their smooth increase or the occurrence of local maxima and minima. The entrainment in the square and triangular jets also turned out to be more dependent on the excitation rather than by the nozzle geometry. In the near-field, the excitation with Stp/2<Stf<Stp leads to almost doubling the entrainment maximum found for the non-excited jets.

Irreversibility analysis of induced swirl flow inside the pipes of flat-plate solar collector using dual tangential nozzles

Abstract In the present research, dual-nozzle swirl generator was installed at the blocked end of the straight tube to inject flow tangential to the wall of the pipe with various injection inclinations compared to the longitudinal axis. This causes a swirl flow inside the pipe. Altering some decisive variables, including injection angle, side of nozzle cross-section, pipe diameter, and flow rate, caused to attain various cases with unique hydraulic-geometrical characteristics. Classes ‘A…-D50-N…-M…’ and ‘A…-D20-N…-M…’ bear the main characteristics of the cases embodied in their sub-classes. Entropy generation (St), Nu*, NE, Heat Transfer Improvement (HTI) index and ${\eta}_{w-s}$ were used as effective tools for the basement of the system based on the irreversibility concept. The results showed that all of the cases of class ‘A…-D50-N…-M…’ cause lower frictional-contributed and higher thermal-contributed entropy generation compared to the class ‘A…-D20-N…-M…’. The highest values of the HTI index are 1.5 and 1.763 obtained by ‘A30-D20-N5-M0.4’ and ‘A90-D20-N6.25-M0.1’, respectively.

Развитие средств термодинамического расчета характеристик ракетного двигателя с использованием языка программирования Julia

The experience in developing an algorithm and a program for the thermal-chemical calculation of the characteristics of a rocket engine is presented. The program is written in Julia. To calculate the equilibrium composition of combustion products the freely distributed library Ipopt is used. The program is interfaced to the database on thermodynamic properties of individual substances IVTANTERMO. For the convenience of processing, the information on thermodynamic properties is stored in two text files of a special form. The program has been developed using the simplest working process model according to which the flow is one-dimensional, the product flow is adiabatic, there are no friction losses, the product flow is equilibrium, and the speed of condensed particles is equal to the gas flow speed. Ratios for calculating the derivatives of composition, as well as equilibrium values of heat capacity and sound velocity are given. The text of the program can be used in the study process and can easily be adapted to more complex models of the rocket engine workflow. The calculation results obtained using the developed program are in good agreement with the results of TERRA calculations. The execution time of one calculation for a four-element fuel, which includes the determination of the combustion products characteristics in the chamber, the critical cross section and at the nozzle cross section, varies in the range of 3--5 s

Effect of nozzle geometry on the dynamics and mixing of self-similar turbulent jets.

The effect of nozzle geometry on the dynamics and mixing of turbulent jets is experimentally investigated. The jets with a Reynolds number of 13,000 were issued from four different pipes with circular, elliptical, square and triangular cross sections. The velocity field was measured in the self-similar region of the jets using an acoustic Doppler velocimeter. Statistical parameters, such as the mean velocities, velocity variances, spreading rates, mass flow rates, and entrainment rates are presented. The results show that despite having approximately similar decay rates for the mean centerline velocities, the radial profiles of the axial mean velocity varied in jets with different nozzle cross sections and were widest for elliptical jets and narrowest for the triangular ones. On the other hand, velocity variances were greatest for the triangular jet when compared to the jets released from cross sections of other geometries. Furthermore, the spreading rate, mass flow rate, and entrainment rate were highest for the elliptical jet, and lowest for the triangular jet. From this it can be inferred that the elliptical jet has the highest mixing and dilution. The results of this study could help to improve the initial mixing of pollutants by optimizing the initial conditions.

Methods for determining the technological parameters of an advanced jet well installation

The article considers the use of a jet pump design with separate workflows for the production of high-viscosity oil. The authors have developed an improved design of a jet well unit with separate workflows, in which the working fluid, moving through the inner annulus, reaching the pump housing, is divided into two streams. A portion of the working mixture - 40% (depending on the cross section of the nozzle of the twisting chamber) enters the twisting chamber of the hydrodynamic cavitator, via which the working fluid passes, creating gas bubbles. These bubbles flake under the action of external pressure at the outlet of the chamber when the liquid passes through a stepped diffuser. The second portion of the working mixture - 60% (depending on the cross section of the jet nozzle) enters the pump nozzle, where flowing at high speed, forms a zone of reduced pressure, resulting in the mixture and oil from the subpacker enter the mixing chamber of the device. We have considered the conditions that can provide the effect of gushing, taking into account the fact that with the use of jet devices can achieve this effect. There may be two cases: 1) the extraction of fluid from wells is limited; 2) the extraction of fluid from wells is unlimited. The initial data, technological parameters and the sequence of their determination are given for the variant when light oil is used as a working liquid, and the working pressure of the surface power plant is not set. Determining the technological parameters of the well unit is a solution to the direct problem, and then - the reverse one. The improved method for calculating the technological parameters of a jet well unit with separate workflows, the design of which has no analogues in Ukraine, is proposed. This technique has been tested during industrial tests of a prototype of an equipment set for the extraction of high-viscosity oils. The method of operation of the pumping-ejector downhole jet unit with a hydrodynamic pulsator for the extraction of high-viscosity oils is protected by a patent of Ukraine.

Inducing swirl flow inside the pipes of flat-plate solar collector by using multiple nozzles for enhancing thermal performance

In this numerical study, an attempt has been made to improve the thermal performance of the flat-plate solar collector (FPSC) by inducing the swirl flow inside the tube by the considered nozzles. To this end, the effect of the number of circumferential nozzles and their inclination angles was taken into the account. The considered number of nozzles was "single", ''dual'', ''triple'', and ''quad''. For each of the said cases, the inclination angle of nozzles was taken 30°, 45°, 60°, and 90° (A30, A45, A60, A90). Moreover, the mass flow rate of single-nozzle pipe was considered 0.2 kg/s, 1 kg/s, and 2 kg/s. To analyze all of the cases under identical conditions, the said mass flow rates were distributed equally among all of the nozzles (for ''dual'', ''triple'', and ''quad''). All of the characteristics were defined in a form of "A…-D…-N…-M…'' where ''A…'', "D…", "N…", and "M…" stand for angle of injection, diameter of pipe, nozzle cross-section edge, and mass flow rate, respectively. Numerical simulation (3-dimensional) of the system was performed by Finite Volume Method (FVM). The turbulence nature of flow was simulated by the k-omega SST (shear stress transport) turbulent model. Results showed that the "single-nozzle'' swirl generator had the highest thermal performance factor (TPF) so that for all cases its values were greater than unit. Mass flow rate growth increases Nu, heat extraction rate, and kinetic energy rate (KER) while drops friction factor and outlet temperature. Increment of injection angle increases outlet temperature and friction factor and reduces KER. The maximum and minimum values of TPF are 4.19 and 0.44 which belong to "single; A30-D50-N12.5-M0.2" and "quad; A90-D50-N12.5-M0.5", respectively.

Stereoscopic particle image velocimetry study of the single side entrainment behaviour of multiple air jets with different nozzle cross-sections

Achieving energy savings in the building sector while maintaining high air quality of indoor environments requires efficient ventilation systems. Active chilled beams (ACBs) are a promising solution for the ventilation in non-residential buildings. Their functionality is often based on the single side entrainment of multiple air jets. In order to enhance this entrainment and thus increase the efficiency of ACBs, this study investigates the specific flow situation of a single side entrainment experimentally. Additionally to the reference circular type, three different cross-sections (elliptic, cross-like, lobed) of an orifice nozzle are investigated with different experimental methods. The unique flow situation in ACBs with multiple interacting jets entraining air from one side is extracted to a test bench. First, the general nozzle efficiency and total entrainment is investigated. Then, the detailed understanding of the entrainment process is achieved with stereoscopic particle image velocimetry (stereo-PIV). The results show that a minimum distance between the jets is necessary for the development of individual flow behaviour affecting the entrainment. For a larger nozzle distance we measured an increased overall entrainment for the non-circular nozzle geometries, with the lobed geometry showing the greatest improvement. The PIV results show how the jets from the different nozzle geometries pass through different stages of entrainment behaviour and profile transformation.

Attempt of Thin-Wall Molding of Copper by Cold Spray Using Rectangular Cross-section Nozzle

Attempt of Thin-Wall Molding of Copper by Cold Spray Using Rectangular Cross-section Nozzle

Influence of Engine Parameters on the Power-Unit Performance in Supersonic Aircraft

Research permits refinement of the outline of a low-noise high-efficiency power unit for use in supersonic commercial airplanes of the 2030s. Engines with features that will be feasible by then are considered. The influence of the design parameters of a motor with modified critical nozzle cross section on the outline and effective characteristics of the power unit is studied.

Stability of One-Dimensional Steady Flows with Detonation Wave in a Channel of Variable Cross-Sectional Area

The stability of one-dimensional steady flows of an ideal (inviscid and non-heat-conducting) gas in channels of variable cross section with combustion in a structurally stable detonation wave is studied. The detonation wave represents a discontinuity surface propagating normally to the axis of the channel. It was previously established that, in this formulation, steady flows with combustion in a Chapman–Jouguet detonation wave are always unstable, in contrast to combustion flows in an overcompressed detonation wave. The stability analysis of such flows is reduced to the numerical solution of an initial-boundary value problem describing the evolution of finite flow perturbations between the moving detonation wave and the minimal nozzle cross section (in the case of a sudden contraction) or the exit nozzle cross section. The problem is solved by applying a modified Godunov scheme of higher order accuracy. More specifically, a Riemann solver with switching (between the overcompressed and Chapman–Jouguet detonation waves) with an explicitly represented detonation wave is created. Examples of stable flows and flows collapsing due to large initial perturbations are given, and their dynamics with transitions to a Chapman–Jouguet detonation wave and back are computed.

Experimental study of swirling flow characteristics in a semi cylinder vortex cooling configuration

This study utilised planar Particle Image Velocimetry (PIV) to investigate the flow characteristics in a semi cylindrical confinement with 2 jet inlets. The water based experimental study aims to understand the basic flow behaviour in a gas turbine leading edge vortex cooling configuration. The time averaged and fluctuating flow fields were collected at 3 cross sections and 1 longitudinal section at 3 different inlet Reynolds numbers. The snapshot based Proper Orthogonal Decomposition (POD) was applied to extract the coherent flow characteristics. Results showed that the vortex flow consists a large-scale vortex in the chamber with a small recirculating corner vortex. The core vortex is similar to the Rankine vortex with a near solid body rotating vortex, surrounded by a jetting vortex layer and a boundary layer along the chamber wall. The jetting vortex layer featuring a proportional decline of circumferential velocity is different to the potential layer in a typical Rankine vortex. The jetting vortex at a high velocity level is mainly responsible for the high heat transfer rate for vortex cooling. A turning region at θ≈170° separating the circumferential velocity behaviour was noticed, which provides a flow dynamic explanation to the heat transfer intensity along the surface wall for vortex cooling. The region at the interface between the solid body rotating vortex and the jetting vortex features with relatively low velocity magnitude but strong shear and large fluctuating velocity intensity. The longitudinal section has a low average velocity (approximately 10% of that in the cross sections in magnitude), indicating the vortex flow is strongly rotational but weakly helical. However, the fluctuating velocity intensity has a comparative level to cross sections. POD analysis reveals that the first 4 modes contain about 23.2% of the fluctuating velocity energy. In nozzle cross sections, the coherent vortex near the surface wall dominates the fluctuation energy and is responsible for the heat transfer enhancement. In the cross section between nozzles, the coherent flow structure displays a vortex pair in the core and a minor corner vortex.

Experimental and CFD analysis of swirl, nozzle arrangement, cross-section and jets diameter on heat transfer in multi-jet air impingement cooling

Experimental investigation and CFD analysis were performed to study the effects of swirl, nozzle arrangement, cross section of nozzle, number of jets and jet diameter on heat transfer coefficient in multi-jet air impingement cooling for a target surface of 100 ?150 mm size supplied with a constant heat flux of 7666 W/m2. The normalized heat transfer coefficient based on unit volume of air is evaluated through measurement of temperature for flow Reynolds numbersin the range of 8000-22000 with H/D ratiosof 1, 2, 4, and 6. Investigations with and without swirl reveal that among the tested conditions, for 8 mm jets, introducing swirl reduces the heat transfer where as for 10 mm and 12 mm jets, swirl improves the average heat transfer rate. For sets of 12 nozzles configurations, the staggered arrangement for 6 mm and 8 mm nozzles results in higher heat transfer rate than in-line arrangement unlike in 4 mm nozzles where in-line arrangement is better. Heat transfer coefficients for circular, square and triangular cross-sections of same flow area have been compared. Circular cross-section offers better heat transfer coefficient for all the tested conditions. For a given number of nozzles, there is an optimum diameter corresponding to maximum value of normalized heat transfer coefficient. The results are corroborated with CFD analysis for a few representative conditions tested.

Model of solid fuel rocket engine: thermal emission characteristics from a plume calculated with account for temperature and speed non-equilibrium between gas and particle flows

The paper presents a method for study of thermal emission characteristics from heterogeneous combustion products in a plume of a model solid-fuel rocket engine. Simulation experiments found the influence of speed and temperature types of non-equilibrium on spectral and integral densities of radiation energy flux and emissivity factors. The values of non-equilibrium were determined at different critical nozzle cross sections and at different average sizes of particle. It was found that the speed non-equilibrium has a minor influence within the gas emission bands; meanwhile it is stronger for transparency bands of gas phase. The non-equilibrium in temperature is the main factor in calculating the emission characteristics of the flow, while the speed delay of particles relative the gas flow is manifested stronger at this background.

A Soft Aquatic Actuator for Unsteady Peak Power Amplification

A soft hydraulic actuator is presented which uses elastic energy storage for the purpose of pulsed-jet propulsion of soft unmanned underwater vehicles. The actuator consists of a flexible membrane that can be inflated using a micropump and whose elastic potential energy may be released on demand using a controllable valve, in a manner inspired by the swimming of squids and octopuses. It is shown that for equivalent initial elastic energy, the drop in peak thrust is linearly proportional to the decrease in nozzle cross section. Peak hydraulic power amplification of the soft actuator of approximately 75% is achieved with respect to that of the driving pump, confirming that passive elasticity can be exploited in aquatic propulsion to replicate the explosive motion skills of agile sea-dwelling creatures.