Convergent Nozzle Research Articles

Influence of slot profiles on the characteristics of jets

PurposeThe purpose of this research is to study and investigate the flow control of 0.8 Mach jet using three tab configurations. The tabs with the slots will eventually lead to generation of vortices and thus enhances the mixing characteristics.Design/methodology/approachThe jet flow control is achieved by the usage of three tabs, namely, Tab A, Tab B and Tab C that are placed at the exit plane of the convergent nozzle at 180 degrees apart. Three tabs with different slot profile are designed with the same constant blockage ratio of 7.3%. The tabs produce vortices of varying sizes that directly influence and modify the jet structure, thereby enhancing the efficiency in mass entrainment and mixing. The tabs are studied numerically first and then are compared with the results of the experiments.FindingsThe results are compared with that of the results of the uncontrolled jet. For Mach 0.8 jet, Tab C is found to reduce the core length and gives reduction of 90.23%, in comparison to Tab A and Tab B, which provides 84.1% and 87.79%, respectively. The results of numerical are then compared with the centerline results obtained via experiments. With the engagement of Tabs A, B and C, the jet structure is seen to have been modified at Mach 0.8 with Tab C performing better.Practical implicationsThe tabs are a passive control device that can be practically enabled in the aircraft nozzles to control the flow and even suppress the noise emanated by the jet. Tabs can be effectively used for better thrust vector control and assist in jet noise suppression. Thus, this study on tabs and its uses are important and essential in aerospace technology.Originality/valueThis particular study on mechanical slotted tabs is innovatively carried out by designing the tabs in such a way that one such has not been designed before. The slots run through the adjacent sides of the tabs which is a novelty in itself, whereas perforations made only through the opposite sides of the tabs are studied by various researchers till now. The slots in the adjacent faces modify the flow physics in such a way that it enhances mixing by the creation of turbulence because of the interaction between the main stream and the secondary jet exactly at the core. So far, such slots and profiles are not investigated. By the usage of such tabs, the flow to mix faster is much closer to the core of the jet by creating mixed size vortices and thus has higher efficiency.

Visualization of supersonic free jet flow structures subjected to various temperature and pressure ratio conditions

The standard Z-type schlieren visualization technique was used to experimentally investigate the effects of inlet boundary conditions (temperature and pressure) and nozzle geometry (convergent and convergent-divergent nozzles (C-D)) on a supersonic flow structure. The focus was on the Mach disk's length (Lm) and width (Wm). The inlet temperature (Tin) was 123 to 288 K, and the nozzle pressure ratio (NPR=Pin/Patm) was 3 to 20. When varying the NPR, over and under-expanded flow conditions were observed in the studied nozzle configurations. The results illustrate that when increasing NPR at Tin = 288 K, Lm increases for both over and under-expanded flow conditions. However, when increasing NPR in over-expanded conditions, Wm increases to reach the saturation point and then decreases for a C-D nozzle with a larger exit diameter, while it becomes constant for a small exit diameter. In contrast, Wm increased when increasing NPR for all nozzles in the under-expanded regime. At 123 K < Tin < 173 K, the shock cells were shrunken for C-D nozzles at NPR=5, and subsequently, Lm decreased. Nevertheless, Wm increased until Tin = 153 K and then decreased until Tin = 123 K, which disturbed the Mach disks and shock cells that governed the decrease in Wm.

Process and nozzle design for high-resolution dry aerosol direct writing (dADW) of sub-100 nm nanoparticles

One of the essential requirements to create nanoparticle (NP)-based applications and functions is the ability to control their deposition in specific locations. Many methods have been proposed, with wet direct writing (DW) techniques such as inkjet printing being the most employed. These methods generally depend on off-line and solvent-based NP synthesis leading to contamination and impurity in the final NP film as well as inhomogeneity in the deposition caused by solution-substrate interactions. This paper introduces a dry aerosol direct writing (dADW) method, which combines spark ablation-based and solvent-free NP synthesis with spatially selective deposition using aerodynamic focusing in a vacuum chamber. The challenge is to print high-resolution lines and spots of nanoparticles with a diameter < 100 nm. We study two aerodynamic nozzle concepts, a converging nozzle (CN) and a sheath gas nozzle (SGN), and investigate numerically how their design, as well as operating parameters, relate to the deposition process performance. This is quantified by three criteria: contraction factor, focusing ratio, and collection efficiency. We also compared our numerical results to experimental assays by manufacturing two SGNs and three CNs and evaluating the performance of each nozzle in terms of resolution, sharpness and thickness of the line. Using one of the SGN designs with an outlet diameter of 248 µm and an aerosol to total flow rate ratio of 0.17, we achieved a high-resolution line with a width of 67 µm, i.e., equal to 27% of the nozzle diameter, when printing < 100 nm Au NPs. The presented additive manufacturing method enables, therefore, the creation of high-resolution and sharp patterns of metallic nanoparticles, which can be employed in a wide range of applications, ranging from interconnects to optical and gas sensors.

CFD Analysis of Nozzle Flow with Sudden Expansion In Aerospace Engineering

As the need for missiles and rockets has increased exponentially, the challenges associated with the gas dynamics of these vehicles continues to be a concern. The pressure in the downstream is sub atmospheric whenever there is a sudden expansion. This low pressure in the recirculation zone causes significant drag, accounting for almost two-thirds of the net drag of the aerospace vehicles. Hence, the purpose of this paper is to deliver a Computational Fluid Dynamic (CFD) analysis of the impact geometry and flow parameters have on the thrust force generated by the flow from convergent divergent nozzles to a suddenly expanded circular duct with a wider cross-sectional area. By observing all of the results, it is possible to conclude that the flow field in an enlarged duct is greatly influenced by the area ratio.

Numerical Investigation on the Height of Detonation Wave in Rotating Detonation Engine

Three-dimensional numerical simulations were conducted on a non-premixed rotating detonation engine (RDE) with different exhaust nozzles (i.e. without a nozzle, with a divergent nozzle, with a convergent nozzle, and with a Laval nozzle). Aside from describing the flow-field structure inside the chamber, the detonation wave height of the detonation wave, and the outlet Mach number were also investigated. It is found that the convergent and Laval nozzles make the flow-fields more complex in chamber by the reflected shock waves. The height rises with the increase of air mass flow rate when detonation chamber exit is in choke state, but it decrease when detonation chamber exit is not in choke state.

Experimental Study of Three Stream Coaxial Jets

A core Mach 2 jet from the convergent-divergent nozzle in the presence of two coaxial sonic streams from convergent nozzles was investigated experimentally at different nozzle pressure ratios using visualization technique. The jet field was visualized using shadowgraph for nozzle pressure ratio (NPR) 3 to 6. From the visualization results, it was observed that the core length of Mach 2 jet for NPRs 3 to 6 increased with increasing coflow NPRs, indicating reduced mixing of coflow three stream jets as compared to Mach 2 jet (without coflows). From the present study, it was clear that the use of two sonic coflows on Mach 2 jet would result in core elongation for all the NPRs thus acting as a mixing inhibitor. But the sonic coflows were found to weaken the waves in Mach 2 jet, which is advantageous from the aeroacoustic point of view.

Performance of a turbojet engine with fluidic thrust vectoring

AbstractThe objective of the present work is to estimate the performance of a turbojet engine during Fluidic Thrust Vectoring (FTV) employed by injecting the secondary-jet at the throat of a convergent nozzle. The nozzle performance maps and effective nozzle throat area obtained from experiments are coupled with the performance of a conventional engine (without FTV) using an iterative algorithm developed as a part of this work. The performance is estimated for different flow rates of secondary-jet sourced either from a separate compressor or the engine’s compressor. During FTV, the operating point shifted towards the surge line with increased turbine entry temperature. The desired and obtained vector angles and thrust magnitudes are different. At high secondary-jet flow rates, the turbine operation moved out of its performance map. These aspects should be incorporated while integrating the FTV at the system level, thus, asserting the importance of FTV studies coupled with engine performance.

A Wavelet-Based Time-Frequency Analysis on the Supersonic Jet Noise Features with Chevrons

A detailed investigation of the statistical properties of the near-field pressure fluctuations induced by an under-expanded jet, by varying the nozzle exit shapes has been presented. Experiments using different convergent Chevron nozzles were carried out in the anechoic chamber at the University of Bristol to assess the importance of the Chevron shape on the near pressure field emitted by a single stream under-expanded jet. Measurements were carried out through an axial microphone array traversed radially to various positions for jet in an under-expanded condition at Mach number M = 1.3. The intermittent behavior is investigated considering the standard statistical indicators and a wavelet-based conditional approach, including the phase angle. The intermittent degree of various features related to different scales, such as Screech tones and broadband shock associate noise were estimated. A series of recently developed wavelet-based tools were assessed as a viable approach to investigate the noise emitted by under-expanded jets.

Aerodynamic and Infrared Radiation Characteristics of the Spherical Convergent Flap Nozzle under Vector Actuations

In present work, the aerodynamic characteristics and the infrared radiation (IR) features of the spherical convergent flap nozzle (SCFN) under vector actuating operations have been studied numerically. The infrared radiation (IR) features of the nozzle under different vector actuation angle have been studied using the reverse Monte-Carlo method (RMCM). Several parameters, such as IR intensity, radiation brightness, and the spectral radiant intensity of the nozzle, are analyzed in detail. The results show that SCFN radiation intensity distribution gradually transitions from two-peak distribution to single-peak distribution. When the pitching motion is activated, the “second peak” located downstream of the deflection vector angle is gradually weakened and disappears. The peak gradually approaches the peak of the mixer, and the contribution of the mixer gradually dominates. With the increase of geometric vector angle in the pitching direction, the detection angle of the nozzle’s infrared radiation intensity peak is less than the geometric vector angle, meanwhile the decrease of the peak value of the infrared radiation intensity of the nozzle is parabolic with the geometric vector angle. Along the direction of the pitching operation, the average value of the infrared radiation at a detection angle of −35° to 35° decreases linearly. When the yaw motion is activated, the infrared radiation intensity distribution in the backward direction of the nozzle exhibits a single-peak feature, and the detection angle at which the peak is located is also smaller than its geometric vector angle. Using the detection angle of the peak as the axis of symmetry, the curve of the infrared radiation intensity distribution behind the nozzle is symmetrical. As the geometric vector angle in the yaw direction increases, along the direction of the pitching operation, both the average value of infrared radiation at a detection angle of -35° to 35° and the peak value of the backward infrared integrated radiation intensity of the nozzle decrease linearly. Besides, the maximum drop is much smaller than the maximum drop during pitching operation.

The concave-wall jet characteristics in vertical cylinder separator with inlet baffle component

The concave-wall jet was formed in the vertical cylinder separator with inlet baffle component. The effect of curvature of radial baffle on the jet flow in the separator was investigated by the experiment of concentration and the numerical simulation of species transport. The results show that the concave-wall jet was confined within the narrow region near the concave-wall and the flow disturbance in the center of separator was weakened. The distribution of concentration and the flow region of wall jet depended on the curvature of radial baffle ( K ). Compared with the turbulent intensity of the plate baffle ( K = 0), that of concave baffle ( K = 2) reduced by 6.1% and the turbulent intensity of convex baffle ( K = −2) increased by 13.5%. The best flow stability was obtained by the concave baffle because the baffle outlet was similar to convergent nozzle. The outlet convergent angle was between 0° and 19.5° when 0 ≤ K ≤ 2. The secondary vortices were caused by the tangential velocity irregularity on the cross-section of two axial baffles in the separator with convex baffle. The baffle with K ≥ 0 was more suitable in separator inlet than that with K < 0.

The design and flow simulation in a convergent and divergent nozzle using taguchi

The nozzle is a complex structural design to direct a controlled rate of flow of the gases to increase the velocity based upon the required parameters. A nozzle comes with different shapes depending upon the mission and their work. The design of the nozzle is significant for understanding the performance and the characters of the Rocket. The engine's performance is dependent upon the geometrical design of the nozzle. The main factors that affect the outlet velocity of the nozzle are area ratio, pintle design, length of the pintle, position of the pintle, mass flow rate. In this paper, the observation over the flow simulation over the converging- Diverging nozzle by varying the area ratio, placing the pintle position and the pintle design, and the position of the pintle by changing the inlet mass flow rate from 350kg/sec, 450kg/sec and the 550kg/sec and observed flow variations to determine the optimal result using the Taguchi optimization method. The flow simulation for the designed nozzle is performed using Solid Works. The Taguchi had obtained a reference that the area ratio will have the maximum amount of influence on the Nozzle performance, followed by the pintle's position, angle of the pintle, mass flow rate, and the length of the pintle. The optimal condition that is obtained in the Taguchi is that the nozzle with an area ratio of 120 and the placement of the nozzle length of 0.1215m which has an angle of the 35˚ and placing the pintle at a distance of 0.4745m for the inlet, can produce a maximum amount of outlet velocity.

Experimental circuit for the generation of cavitation in oil flow

The paper deals with the flow of oil through an experimental hydraulic circuit with a convergent divergent nozzle with a circular cross-section. Under different physical conditions, i.e. changes in pressure, flow and temperature, the formation and development of cavitation is monitored. As it is a highly dynamic flow in a transparent nozzle, cavitation is monitored using a high-speed camera and the frequency of formation and dissolution of the cavitation bubble and the movement of the cavitation cloud is then determined. The authors deal with the issue of the amount of dissolved or undissolved air in the hydraulic oil. Both variants of air influence the formation, development and size of the cavitation area. This cavitation is in this case called air cavitation. In technical practice, the issue of air cavitation is relevant, especially in the pump suction, where vacuum, leaks and hence air intake may occur.

Investigation of Some Significant Flow Characteristics in Convergent Diesel Nozzles with Rough Walls

Investigation of Some Significant Flow Characteristics in Convergent Diesel Nozzles with Rough Walls

Behavior of Vortices Moving in the Vicinity of Supersonic Jet

An underexpanded jet is one of supersonic jets. The jet becomes underexpanded when the pressure ratio exceeds the critical value across the convergent nozzle discharging it. The jet is not uniform because of the presence of the expansion wave, the compression wave and the shock wave formed in it. In the jet boundary, many vortices are generated by the shearing stress between the supersonic flow of jet and still atmosphere. The interaction of vortices and jet is closely related to the high frequency sound radiating from such flow field. The high frequency sound is called Screech Tone. This Screech Tone has been studied extensively and its relationship to the vortex has been discussed. However, measurement methods are still not established for vortex moving in the vicinity of the jet boundary. In this study, the vortex moving in the vicinity of the jet was experimentally examined. The device consisting of a laser and an optical sensor was applied to measure the vortex. The vortex was measured at several points around the jet and frequency and time differences between points were investigated. The flow field was visualized using optical methods. And the high frequency sound emitted from the flow field is measured using a microphone.

Relation between Sound Radiated from Underexpanded Impinging Jet and Disturbance Convection Velocity

An underexpanded jet perpendicularly impinging on a flat plate was experimentally studied in this study. The flow field radiates noise including screech, and its frequency and sound pressure are varied against the nozzle pressure ratio and the nozzle-plate spacing. A feedback loop in the flow field is known to describe the screech phenomena well, and disturbances moving along the jet boundary play an important role in the feedback loop. This study focused on contribution of the disturbance velocity to the sound pressure variation of the screech. The jet issued from a circular convergent nozzle with a diameter D. Sound pressure measurement and visualization were carried out at different nozzle-plate spacings l/D. The sound pressure measurement showed the screech due to the jet impingement was very weak in a certain range of l/D. The Schlieren photographs described the disturbance did not develop in such range. The disturbance velocity is one of the parameters for the screech phenomena. The disturbance velocity was estimated from frequency characteristics of the sound pressure. Characteristics of the disturbance velocity changed in the weak screech range of l/D, where there are disturbances with different velocities. This denotes the change of the disturbance velocity characteristics attenuated the sound pressure of the screech.

Consideration of the effects of increasing spray cone angle and turbulence intensity on heavy-duty diesel engine pollution and specific outputs using CFD

In this article, the effects of increasing spray cone angle and turbulence intensity on the performance and emission of heavy-duty diesel engine has been examined in two separate stages using AVL-Fire CFD code. First, the injector and its spray have been simulated with various geometries. In this step, the Eulerian-Eulerian model has been applied for injector simulation and the Eulerian -Lagrangian model has been applied for spray simulation. The numerical results of this step indicate that creating swirly flow inside the nozzle decreasing penetration length while, fuel spray cone angle increasing during the injection process. In the subsequent step, the heavy-duty diesel engine has been simulated with its conventional and different nozzle hole geometries. In this step, the Eulerian-Lagrangian model has been applied to simulate the engine cycle. The numerical results of this step show that the nozzle with spiral rifling like guides has better performance and lower emission compared to other nozzle geometries. In this case, the fuel consumption is decreasing 32% than cylindrical nozzle hole, while the engine power and its torque increasing 63%. In addition, the amount of nitrogen oxide (NOx) and carbon monoxide (CO) for the spiral convergent conical nozzle geometry reducing 15% and 30% respectively than cylindrical nozzle hole while engine has no soot emission problem. Diesel injector and engine CFD results and experimental data have been validated from previous researches.

Temperature distributions of internal flow and external jet fields of double serpentine convergent nozzle for turbofan

In order to clarify the temperature distribution of a double-serpentine convergent nozzle wall and the exhaust plume characteristics downstream the nozzle exit based on the real exhaust mixer configuration of a turbofan engine, the temperature distribution of the internal and external jet flow fields of the double-serpentine convergent nozzle are simulated numerically. The simulation results show that the coupling effect between S-shaped circular-to-rectangular profile and the exhaust mixer has a joint influence on the "hot streak" distribution of the double-serpentine convergent nozzle wall and the exhaust plume characteristics downstream the nozzle exit. The "Hot streak" is distributed in the shape similar to several ribbons in the central areas of the upper and lower wall of the second serpentine passage and in the exit area. The maximum value of temperature on the lower wall is 867 K and increases 25.1% compared with that on the upper wall. However, the average value of temperature of the lower wall is merely 7.1% higher than that of the upper wall. The "whale tail" high-temperature core area is formed on the exit plane of the double-serpentine convergent nozzle. It leads to two wide high-temperature jet flow areas in the high-temperature core area downstream the nozzle exit. The low-temperature flow occurs along the two sides of the exhaust plume core area due to the lateral-direction motion towards vortices.

Mode switch in tonal under-expanded impinging jets

The dominant resonance mode switch pattern concerning nozzle pressure ratio and impinging distance for under-expanded jets issuing from a convergent nozzle and impacting a flat surface is demonstrated for the first time. Schlieren visualization and acoustic measurements have been carried out to simultaneously capture the dynamic and acoustic properties of impinging jets with a nozzle pressure ratio ranging from 2.00 to 4.30 (from moderately under-expanded to highly under-expanded) and an impingement distance extent 3.0D to 11.0D, where D is the nozzle exit diameter. Five bands within which symmetric mode predominates have been discovered. Jets within these bands also exhibit high amplitudes in overall sound pressure level. Besides, dominant frequencies within any band remain relatively stable when impinging distance is fixed, while a negative correlation between dominant frequencies and impingement distance has been found. Dynamic mode decomposition has been applied to schlieren snapshot sequences to achieve dimension reduction, by which the sound source location of tones can be determined. It is found that symmetric mode finds its genesis near the impingement surface, whereas the source related to asymmetric mode lies in the shear layer near the third shock cell or the standoff shock, depending on the number of shock cells between the nozzle exit and the impinging surface. This difference in acoustic feedback paths serves as the cause of the mode switch. Further, the symmetric mode's source location's stability results in the stability of dominant frequencies within a band when impinging distance is fixed.

Numerical analysis of indirect noise generated by compositional inhomogeneities using large eddy simulation

In the present work, indirect noises generated by compositional disturbances in a non-isotropic convergent nozzle are studied using Large Eddy Simulations (LESs). An in-house compressible LES code, Boundary Fitted Flow Integrator-LESc, is utilized to simulate the noise generation in the system. A non-reflective outlet boundary condition is used to eliminate numerical reflections and to ensure the reproduction of the operating conditions in the experiments. The experiments are designed to feature two configurations with different injection positions, which enable the separation of direct and indirect noises. Different operating conditions are investigated, including different injection gases and air mass flow rates. This present paper compares computational results with the experimental measurements. The results revealed that the processes of direct and indirect noise generation are successfully reproduced in the LES, with the noise magnitudes in good agreement with those in the measurements. Injection of gases with smaller (He) and larger (CO2) molar masses compared to air is found to generate negative and positive indirect noises, respectively, in the LES, which is consistent with the experimental findings. The effect of different air mass flow rates is also investigated and discussed, and the direct noise and indirect noise amplitudes are both found to be closely related to the air mass flow rate.

Parametric research on drag reduction and thermal protection of blunt-body with opposing jets of forward convergent nozzle in supersonic flows

Extreme drag and aerodynamic heat are the main penalties for blunt forebody of supersonic vehicles. This results in shorter flight range and higher fuel consumption, and aerodynamic heat seriously affects the performance of internal electronics. In the current study, the flow field mechanism of a blunt body model with a supersonic opposing jet in a supersonic flow field is numerically study. The physical model is a two-dimensional axisymmetric blunt forebody model with a convergent nozzle structure, and the numerical calculation model is a coupling of the two-dimensional axisymmetric Reynolds average method and the shear stress transport(SST) turbulence model. The calculation results in this paper are compared with the experimental data in the literature, which verifies the accuracy, and the calculation verifies the grid independence. An active flow control method that controls a single pressure parameter is proposed, and the formation process of the opposing jet in the convergent nozzle is considered, and the flow field structure of the opposing jet formed by the convergent nozzle with different nozzle sizes is studied. The results show that a single pressure parameter can control the formation of a supersonic opposing jet to form a long penetration mode and a short penetration mode. The ratio of the ambient pressure to the jet pressure at the stagnation point of the blunt body can directly affect the flow field structure of the opposing jet, and reasonable control of opposing jet parameters is an effective way for thermal protection and drag reduction of blunt body structures.