Exit Shape Research Articles

Influence of the Trailing Edge Shape of Impeller Blades on Centrifugal Pumps with Unsteady Characteristics

The flow field structure and pressure pulsation characteristics in two series of trailing edges of a centrifugal pump are investigated using the SST k-w turbulence model. Series 1 involves varying the impeller exit angle, and Series 2 involves varying the impeller exit shape. The entropy generation rate analysis method is used to evaluate the numerical simulation results. Vortex cores within the flow field are identified by applying the Ω criterion. The influence of different trailing edge configurations on the energy loss characteristics of the pumps is explored. The dynamic mode decomposition (DMD) method is used to analyze pressure pulsations at the volute considering unsteady flows in centrifugal pumps with different trailing edge shapes. The findings suggest that different trailing edge shapes can be used to adjust the energy loss proportions in various components of the pump. In Series 1, the efficiency remains nearly constant with changes in the outlet angle on both sides of the trailing edge. In Series 2, the efficiency is enhanced by 1.18% with the elliptical edge shape on both sides (EBS) compared to the original trailing edge (OTE) shape. In Series 1 and Series 2, greater entropy generation rates are accompanied by greater pressure pulsations at the pump outlet. The DMD results demonstrate a noticeable impact of the different trailing edges on the pressure distribution of various modes within the volute. Moreover, the impeller outlet pressure inhomogeneity coefficient changes under different modes. This study holds great significance for selecting the appropriate trailing edges for centrifugal pumps.

A comparative study of purge slot exit shape on the film cooling effectiveness of a gas turbine shroud

To achieve higher efficiency and performance, a modern gas turbine withstands the extremely high thermal environment. In the turbine endwall passage, a high and non-uniform heat transfer appears due to various secondary flow. The purge flow injected through the upstream slot between the stationary and rotating pars can thermally protect the endwall surface by forming air film layer on it. However, since an excessive amount of purge flow reduce the system efficiency, it is needed to effectively inject the purge flow with a limited amount. Accordingly, in the present study, the effect of purge slot exit shape on the film cooling effectiveness (hereby FCE) of a shroud surface was discussed. As nondimensional design parameters of the purge slot, L/Ws, RW/Ws, and RL/Ws were defined, representing the geometric features: the slot width (Ws), the fillet radius at the windward side (RW) and fillet radius at the leeward side (RL) of slot exit, respectively. The measurement of the FCE was performed in a five-blade linear cascade rig using the PSP (Pressure sensitive paint) technique. The results showed that the FCE increased for wider slot width at a given blowing ratio condition. In addition, the fillet radius at the windward side (RW) has a negative effect on the FCE regardless of blowing ratio condition since the purge flow was easily disturbed by the accelerated mainstream injection. On the other hand, the Case 7 with the RW/Ws = 0.9 showed 5.1 % of the improvement of FCE at a higher blowing ratio M = 0.25 compared with the Case 2 with RW/Ws = 0, which represents the sharp edge at the windward side of the slot exit.

Numerical study on the influence mechanism of different types of burst disc on high pressure hydrogen spontaneous combustion in tube

High-pressure transportation and storage are the current main methods for storing hydrogen. Burst discs, which are common in high-pressure storage devices, can cause hydrogen leaks to ignite and create serious accidents when certain conditions are met. To investigate this, this paper studies the effect of different blasting slot shapes on the spontaneous combustion of leaked high-pressure hydrogen. Numerical simulations, using LES, EDC model, Ten-Step Burst Disc Opening Method and 19-Step Detailed Hydrogen Combustion Mechanism, were conducted to analyze the spontaneous combustion of hydrogen with annular grooves, star grooves, cross grooves and grooveless burst discs. The results of the study show that the shape of the groove in the bursting disc will significantly affect the shock wave structure and spontaneous combustion time of leaked high pressure hydrogen in the tube. Among the four types of bursting discs, the order of spontaneous combustion in the tube is annular groove (approximately 90 μs), star groove (approximately 110 μs), cross groove (approximately 120 μs), and grooveless bursting disc (approximately 130 μs). Secondly, the double spherical shock waves produced by annular groove bursting disc collide with each other, resulting in a higher rising speed of pressure and temperature in the tube than with other bursting discs. Finally, the spontaneous combustion time of the leaked hydrogen is proportional to the open area of the bursting disc. When the opening area is the same, the smaller the exit shape coefficient is, the shorter the spontaneous combustion time is. The research results can provide some reference for the design and application of bursting disc in high pressure hydrogen storage equipment.

Higher Expectations, Greater Disappointment: Ambivalent Sexism and Backlash After the Impeachment of the First Woman President of South Korea

ABSTRACT When the first female president of a country is impeached, how does the disgraceful exit shape people’s memory of her? Does sexism play a role in such retrospective evaluations? Do the voters who supported her remain loyal, or do they withdraw their support due to disappointment? This article utilizes the impeachment of Park Geun-hye of South Korea as a case to answer these questions. Using a public opinion survey conducted three years after the 2016 impeachment, I demonstrate that hostile sexism played a role in the negative retrospective evaluations of Park, while benevolent sexism did not. Moreover, those who voted for Park in the 2012 presidential election expressed more negative retrospective evaluations of Park than those who did not vote for her, suggesting a backlash effect. Voters who had high expectations of the first female president could experience deep disappointment when the historic first failed to meet their expectations.

Effect of exit geometry of blowing air on friction drag of an underwater plate

Air layer drag reduction (ALDR) is one of the important techniques for reducing the frictional resistance of ships and underwater vehicles. The air injection configuration directly influences air layer coverage on the surface and hence drag reduction. Several shapes of air exit have been investigated in the past, including narrow slots, regular-shaped holes, porous media, and arrays/combinations of them. A new exit shape, i.e. modified Nekomimi, is proposed and investigated numerically for ALDR of an underwater flat plate. The work is inspired by air film cooling technology where it is desirable to have an air layer segregating wall from main gas flow. The Reynolds number examined is 6970–22890, based on local turbulent boundary layer thickness, for the incoming water flow or 700–5550, based on the equivalent exit diameter of blowing air. Results show that the Nekomimi exit produces a larger and more even air layer coverage, as indicated by the air volume fraction on the plate, accounting for a more pronounced drag reduction and net energy saving than a circular exit with the same area or spanwise dimension. Multi-Nekomimi-exit arrangement is also investigated to obtain a larger air-layer coverage on the plate, showing good promise in engineering applications.

Surrogate-based optimization and experiment validation of a fan-shaped film cooling hole with a large lateral space

The exit shape of a fan-shaped hole plays an important role to improve the film cooling effectiveness. In this study, a fan-shaped cooling hole on a flat plate was optimized through Reynolds Averaged Navier-Stokes (RANS) analysis for a specific cooling application of unusually large lateral span. A novel hole was configured with four linear dimensions including the leading and trailing edge lateral widths, the exit longitude, and the round metering length. Two rounds of Latin Hypercube Samples were used to narrow the design space for an accurate surrogate model. The first samples were used to evaluate individual variable sensitivity. The second samplings of predominant variables were then combined with the first sampling to build a Kriging surrogate model to predict the film cooling effectiveness of new candidates. A multi-island algorithm was adopted to obtain the optimization solution. The enhanced cooling effectiveness of the final optimal design got verified in an experiment. Results show the improved prediction accuracy of Kriging model and the fast convergence rate of the optimization solution. For a cooling case with a relatively large lateral span, an optimal fan-shaped hole intends to increase the lateral expansion width and to reduce longitude opening width. The spatial averaged cooling effectiveness of the optimized hole achieved a 70% increment over the baseline one.

Modeling and Experimental Characterization of the Influence of the Discrete Axial Nozzle Exit Shape on the Powder Stream in the Direct Laser Deposition Process

Modeling and Experimental Characterization of the Influence of the Discrete Axial Nozzle Exit Shape on the Powder Stream in the Direct Laser Deposition Process

Metastability and exit problems for systems of stochastic reaction–diffusion equations

In this paper we develop a metastability theory for a class of stochastic reaction–diffusion equations exposed to small multiplicative noise. We consider the case where the unperturbed reaction–diffusion equation features multiple asymptotically stable equilibria. When the system is exposed to small stochastic perturbations, it is likely to stay near one equilibrium for a long period of time but will eventually transition to the neighborhood of another equilibrium. We are interested in studying the exit time from the full domain of attraction (in a function space) surrounding an equilibrium and, therefore, do not assume that the domain of attraction features uniform attraction to the equilibrium. This means that the boundary of the domain of attraction is allowed to contain saddles and limit cycles. Our method of proof is purely infinite dimensional, that is, we do not go through finite dimensional approximations. In addition, we address the multiplicative noise case, and we do not impose gradient type of assumptions on the nonlinearity. We prove large deviations logarithmic asymptotics for the exit time and for the exit shape, also characterizing the most probable set of shapes of solutions at the time of exit from the domain of attraction.

Systems of small-noise stochastic reaction–diffusion equations satisfy a large deviations principle that is uniform over all initial data

Large deviations principles characterize the exponential decay rates of the probabilities of rare events. Cerrai and Röckner (2004) proved that systems of stochastic reaction–diffusion equations satisfy a large deviations principle that is uniform over bounded sets of initial data.This paper proves uniform large deviations results for a system of stochastic reaction–diffusion equations in a more general setting than Cerrai and Röckner. Furthermore, this paper identifies two common situations where the large deviations principle is uniform over unbounded sets of initial data, enabling the characterization of Freidlin–Wentzell exit time and exit shape asymptotics from unbounded sets.

Optimization of the hole exit shape of the vortex generator jets in a compressor cascade

Vortex generator jets usually use a circular hole. The hole exit shape is also an important parameter, so the change of the shape will have a significant influence on the control effect of the compressor. In this article, the optimization design of the hole exit shape is studied in order to find the optimal geometry. The 2D hole exit shape is represented with a binary coded and initialized with the B-spline. The surrogate-based optimizer consists of a parametric design code, a computational fluid dynamics solver, a Kriging model, an infill sample criterion, and a genetic algorithm. First, the design of the symmetric hole is studied in a low ratio of the jet to inlet mass flow. The circumferential length of the designed hole is fixed. Second, both the symmetric hole and the asymmetric hole are studied. And the area of the hole exit shape is fixed. The results show that the optimal hole shape can enhance the strength of the jet vortex and reduce the total pressure loss of the compressor cascade. A better control effect can also be obtained in a high jet mass flow.

Design and Decomposition Analysis of Mixing Zone Structures on Flame Dynamics for a Swirl Burner

The recirculation zone and the swirl flame behavior can be influenced by the burner exit shape, and few studies have been made into this structure. Large eddy simulation was carried out on 16 cases to distinguish critical geometry factors. The time series of the heat release rate were decomposed using seasonal-trend decomposition procedure to exclude the effect of short physical time. Dynamic mode decomposition (DMD) was performed to separate flame structures. The frequency characteristics extracted from the DMD modes were compared with those from the flame transfer functions. Results show that the flame cases can be categorized into three types, all of which are controlled by a specific geometric parameter. Except one type of flame, they show nonstationary behavior by the Kwiatkowski–Phillips–Schmidt–Shin test. The frequency bands corresponding to the coherent structures are identified. The flame transfer function indicates that the flame can respond to external excitation in the frequency range 100–300 Hz. The DMD modes capture the detailed flame structures. The higher frequency bands can be interpolated as the streamwise vortices and shedding vortices. The DMD modes, which correspond to the bands of flame transfer functions, can be estimated as streamwise vortices at the edges.

Effect of Exit Shape of Submerged Entry Nozzle on Flow Field and Slag Entrainment in Continuous Casting Mold

In steel continuous casting with submerged entry nozzles at a domestic steel plant, nozzle clogging was largely alleviated and defect rates of hot-rolled and cold-rolled sheets relating to slag entrainment were reduced for a nozzle with an approximately oval exit relative to a nozzle with a rectangular exit. Numerical and physical models were built to investigate the above phenomena. A turbulent model was applied in large eddy simulation to obtain the evolution of turbulent features within the nozzle and mold, while particle image velocimetry was adopted to monitor fluid flow beneath the slag–steel interface. Main results were that the flow speed of the main stream from the approximately oval exit was higher than that from the rectangular exit, while the zone of a velocity magnitude below 0.2 m/s within the approximately oval exit was smaller than that within the rectangular exit, indicating that inclusions tended to reside for longer in the latter. At the same casting speed, that slag entrainment occurred more frequently for the nozzle with a rectangular exit was found to have no direct relationship with the velocity magnitude and vorticity at 1/4 mold width on the top surface. Meanwhile, slag entrainment always occurred at the moment that vorticity changed most rapidly. The current study thus provided new insight into the structural parameter optimization of the submerged entry nozzle.

Experimental study of a lenticular jet.

Non-circular jets, particularly elongated jets and jets with sharp corners, are of interest due to their enhanced large- and small-scale mixing and combustion stability. Non-circular jet geometries such as elliptic, triangular, rectangular, and square have been extensively studied. The non-uniform curvature and elongated design of elliptic and rectangular jets has been shown to facilitate axis switching. Additionally, jets with sharp corners have been shown to facilitate small-scale mixing and further vortex ring deformation, as has been observed in triangular, square, and rectangular jets. There are, however, currently no data on the flow characteristics of a jet that combines these two features, i.e., it enhances both large- and small-scale mixing. The jet is issuing from a nozzle shape defined by two arcs of a circle connecting at sharp corners in the shape of an eye (hereafter termed 'lenticular'). The current study uses experimental techniques to characterize the lenticular jet and compare its behavior to previously studied circular and non-circular jets. Additionally, snapshot POD analysis was used to identify coherent structures and their dynamic features. The lenticular jet was found to have higher entrainment and stronger mixing than a traditional round jet, and comparable mixing and entrainment characteristics as previously studied non-circular jet geometries. It is particularly interesting to compare the jet behavior of the lenticular jet to an elliptic jet. The geometry of these two jets is extremely similar, the difference being sharp corners along the major axis of the lenticular jet. By comparing the lenticular jet and the elliptic jet, the effect of sharp corners, which have been shown to increase small-scale mixing and vortex ring deformation, can be observed. It was found that along the minor axis, where geometry was similar, shear layer turbulence intensity and spreading rate of the jets were also similar. Along the major axis, however, introducing corner features in the lenticular jet lowered the spread rate, resulted in a faster breakdown of turbulence in the shear layer, increased exit turbulence, and resulted in anisotropic centerline turbulence.

The Acoustic Performance of 3D Printed Multiple Jet Nozzles with Different Configurations

This work investigated multiple jet nozzles with various geometrical shape, number of exits, and material on reducing noise radiated from jet flows. Nozzles are categorized in two groups with few and many exit numbers, each with various exit shapes, slot and circular, and geometry. Firstly, nozzles are designed and then fabricated by a 3D printer, Form Labs, Form2USA, with polymeric resin. Also, the nozzle with the most noise reduction made of stainless steel. Noise and air thrust were measured at three air pressure gauges, 3, 5, 7 BAR and directions from nozzle apex, 30°, 90°, 135°. Nozzles with slot exit shape made of both plastic and stainless steel revealed the most noise reduction among all nozzles with few exit numbers, nearly 11–14 dB(A) and 11.5–15 dB(A), respectively. On average, slotted nozzle noise reduction was nearly 5–6 dB(A) more than finned nozzle. However, nozzles with more exit numbers, finned and finned-central exit, illustrated much more noise reduction than nozzles with few exit numbers, by almost 16–18 dB(A), they represented similar sound. All tested nozzles and open pipe demonstrated equal air thrust at each pressure gauges. The nozzles with slotted exit shape, either plastic or stainless steel, can provide reasonable noise reduction in comparison to other configuration with few exit numbers. In contrast, nozzles with more exit numbers demonstrated the most noise reduction.

Experimental and Numerical Investigation on Nozzle Exit Shape and Plume for Aft-Boom Mitigation of Supersonic Transport

This paper describes effects of nozzle geometry and a jet plume on the near-field signature and the thrust performance to explore concepts of aft-boom mitigation for future supersonic transport. Numerical analyses of four kinds of convergent-divergent nozzles were conducted to investigate the sensitivity of the near-field signature and the thrust. The results showed that reducing expansion region at the boat-tail is important to reduce both the peak pressure of near-field signature and the nacelle drag. A nozzle shape, which has an inclined exit shape without a boat-tail portion at lower side, demonstrated a good potential to reduce aft-boom. Supersonic wind tunnel tests using a jet with high-pressure air were also performed to validate the numerical analyses and the results showed good agreement with numerical analyses.

Effect of nozzle exit shape on the geometrical features of horizontal turbulent jet flame

The accidental releases of high pressure gas fuel could lead to the jet fires, resulting in a serious of disastrous events. This paper presents a systematical investigation upon the effect of nozzle exit shape on the horizontal jet flame geometry by experiments. The nozzles of circular, rectangular, equilateral triangle and elliptic exits were used for experimental tests. New correlations for the horizontally projected flame length, vertically projected flame height and lift-off distance are established for horizontal jet fires ejected from the exits of different shapes. The exit shape coefficient (the ratio of hydraulic to equivalent diameters) is found to dominate the phenomenological constant in the classic correlation of flame length, and the dependency of phenomenological constant on exit shape coefficient is quantified. It is also clarified that Richardson number (the ratio of flame buoyancy to exit momentum) dominates the ratio of vertically projected flame height to horizontally projected flame length. The hydraulic diameter is proposed to revise the dimensionless flow number, for physically addressing the effect of exit shape on the lift-off distance of horizontal jet flame.

Mechanism modeling and validation in ultrasonic vibration assisted drilling with variable cross section drilling tool of brittle materials

Ultrasonic vibration assisted drilling (UAD) is used for brittle materials machining for many years, but the processing mechanism in UAD is still not clear, especially in edge chipping damage aspect. A new cutting force model is presented for UAD in this paper, and the cutting force forming and changing can be clearly described in drilling process. Depending on the mathematic model, the entering hole cutting force and exiting hole cutting force can be predicted, the exit edge chipping damage phenomena can be theoretically relieved due to the cutting force control. The variable cross section drilling tool is used for verify the theoretical deduction, and significant improvement in hole exit shape accuracy is presented by the experiment results. In order to reveal the working function of ultrasonic energy, the dynamic relationship between ultrasonic parameters and drilling parameters is carried out. The influence of processing parameters on drilling quality is analyzed in theory and validated by experiment. Smaller edge chipping size and good surface integrity can be obtained by process technology optimizing.

Experimental investigation on effect of exit shape of nozzle on the flow Mach number and noise

ABSTRACT Experimental investigation conducted to identify the noise reduction characteristics through various shape of nozzle exit. Circular, triangular and oval are three shapes for this study. Compressor, microcontroller, microphone, sound producer, system with MATLAB software and different shapes of nozzle exit these all are major elements. These three different shapes of nozzle exit processed with three different pressure levels such as 60, 80 and 100 bar. MAT LAB used to produce direct response for the corresponding condition.

Experimental investigation on convective heat transfer induced by piston-driven synthetic jet with a transmission pipe

An experimental research is performed to illustrate the effects of the transmission pipe and nozzle exit shape on the synthetic jet impingement heat transfer, by using a piston-driven actuator. Three transmission pipes (namely short pipe, moderate pipe and long pipe) and two nozzle exit shapes (round and chevron) are taken into considerations. The experimental tests are conducted at five operational frequencies (f = 5 Hz, 10 Hz, 15 Hz, 20 Hz and 25 Hz) and four dimensionless jet-to-surface distances (H/d = 2, 4, 6 and 8). The results show that the heat transfer around the jet stagnation is generally decreased by the long-pipe nozzle in comparison with the orifice-nozzle case, especially at higher operational frequencies. However, at a high operational frequency and a small jet-to-surface distance, of particular interest is that the short-pipe nozzle could improve the synthetic jet impingement heat transfer when compared to the orifice-nozzle case. The chevron nozzle is confirmed to be benefit for the synthetic jet heat transfer enhancement. Its role behaves distinctly at different jet-to-surface distances and operational frequencies. At low operational frequencies, the favorable jet-to-surface distance for the synthetic jet impingement heat transfer is altered due to the presence of the chevron exit when compared to the round-exit nozzle. While at larger operational frequencies, the relationships of the circumferentially-averaged Nusselt number varying with the jet-to-surface distance in the round synthetic jet impingement remain in the chevron synthetic jet impingement.

Magnetic-enhanced keyhole TIG welding process

Improving of K-TIG welding process with a cusp magnetic field was experimentally tested. A cusp magnetic field setup was designed with water-cooled permanent magnetic poles. Stationary welding experiments were carried out to test the influence of magnetic field to the arc shape. Bead-on-plate welding processes were carried out to test the influence of magnetic field to the arc voltage and weld shape. Keyhole exit image sequence was captured with a vision system. It was found that, in the magnetic-enhanced K-TIG welding process, (1) the arc was constrained and changed into oval shape; (2) arc voltage was increased, front weld was narrowed and backside weld was widened; (3) keyhole exit shape also changed; (4) threshold current for fully penetrated keyhole was decreased and (5) the stainless steel weld microstructure experienced invisible change. The results show that the cusp magnetic field is feasible to improve the K-TIG arc behaviour and reduce the heat input.