Exit Radius Research Articles

Designing jet deflector configuration for a semi-cryogenic rocket engine

This study deals with the design of a suitable configuration of jet deflector for supersonic exhaust gases from a semi-cryogenic launch vehicle engine using computational fluid dynamics. Computational model of combustion in semi-cryogenic engine, with kerosene as fuel and liquid oxygen as oxidizer, was developed in which exhaust gases from engine were impinged on the deflector surface. Different design configurations of deflector structure, obtained by the combination of various impingement angles of 15°, 20°, 25°, 30°, and 45°, and different exit radii of 5000, 10 000, and 20 000 mm, were used in the developed computational models to analyze impingement, deflection, and associated flow properties of exhaust gases, such as acoustics, force on deflector imparted by jet, temperature, and Mach number of flow field. A new ablation model was developed based on Vieille's law to determine the amount of refractory material ablated from deflector structure for different configurations. The developed models of ablation, combustion, and flow impingement were also validated with existing literature. It was found that the configuration with 20° impingement angle and 10 000 mm exit radius had ablation, acoustics, force, and flow properties in desired limit. Furthermore, to find the optimum uplift angle for designing jet deflector, configurations with uplift angles of 0°, 5°, 15°, and 25° were studied using the computational models developed in the study. It was observed that the configuration with 20° impingement angle, 10 000 mm exit radius, and 15° uplift angle was best suited for impingement and deflection of exhaust jet from the specified semi-cryogenic engine.

Development of correlation model for cavitating spray using Eulerian simulations

Modern high-pressure injection systems for heavy-duty applications are prone to cavitation, which may have a detrimental effect on the system integrity. The present study aims to develop reliable correlations for Lagrangian engineering simulations to predict the onset of cavitation. Using the extensive data generated from the high-fidelity Eulerian volume-of-fluid (VOF) simulations of a single-hole injector for a wide range of operating conditions, a proper set of discharge ( Cd) and contraction ( Ca) coefficients are determined. In particular, four significant factors characterizing nozzle geometry are considered: the K factor, inlet curvature radius, nozzle exit radius, and channel length, as well as ambient and injection pressures. The results showed that a larger K factor and inlet curvature radius yielded higher Cd and Ca values, while the exit radius and channel length had a less significant impact on the cavitation dynamics. The smaller pressure difference between the nozzle inlet and exit mitigated the cavitation formation. These trends were well described using the mathematical regression model. Furthermore, two other correlation models based on the regression learner and artificial neural network methods were also developed. Of these three models, the mathematical regression model yielded the best agreement with an external validation dataset.

Design of Turbo-Roundabouts Based on the Rules of Vehicle Movement Geometry on Curvilinear Approaches

The construction of turbo-roundabouts is an increasingly frequent choice when it comes to improving flow capacity and traffic safety at road intersections. The existing design guidelines, as a rule, give parameters for turbo-roundabouts with approaches set at right angles to each other. The article presents turbo-roundabout design methods, taking into account swept path analyses of the chosen design vehicles when the approach legs are curvilinear and oriented to each other at a non-right angle. Based on the analysis of three different design vehicles, it was proven that their swept paths have a major influence on the geometrical parameters of the roundabout and, consequently, on the land take area, i.e., they can significantly impact the project’s construction costs. In the case of curvilinear approaches, which are oriented to each other at a non-right angle, it is impossible to impose on the designer specific values of the circulatory lane widths and the entry and exit curve radii as they depend primarily on the chosen design vehicle. The aim of the article was to demonstrate that in the case of the curvilinear approach on the Basic type turbo-roundabout, the design process should include the swept path analysis for the chosen design vehicle for each of the approaches. This should lead to the design of wider swept paths and higher curve lane divider entry and exit radii.

Fuel ejector design and optimization for solid oxide fuel cells using response surface methodology and multi-objective genetic algorithm

Ejectors are the main devices used to circulate high-temperature anode exhaust gases for solid oxide fuel cells (SOFCs) for recovering and utilizing water vapor and heat. To optimize the performance of a high-temperature fuel ejector for SOFCs, we established a numerical model of the ejector and then validated it using the experimentally obtained primary flow and secondary flow mass flow rates. The influence of the primary nozzle exit position (NXP), length (Lm) and radius (Rm) of the mixing chamber, and other key structures, on ejector performance was examined via Response Surface Methodology (RSM). The performance of the ejector gradually decreased with increasing NXP and Lm and first increased and then decreased with increases in Rm. The sensitivity of the ejector performance to Rm, Lm, and NXP decreased sequentially, and its structure was optimized using a multi-objective genetic algorithm. The entrainment ratio of the optimized ejector reached 6.66, representing an increase of 23.37 % compared with the original ejector. This work proposes a design and optimization method for optimizing the ejector to meet the high entrainment ratio required by SOFCs. The response surface methodology was used to realize the research on the influence of multi-structural parameter coupling on the performance of the ejector, which significantly improved the optimization efficiency and accuracy. This study also introduced multi-objective genetic algorithm on the basis of response surface methodology to optimize the performance of the ejector. Through continuous gene mutation and iteration, the ejector has the best performance. This provides a new direction for future SOFC fuel ejector performance optimization, that is, introducing various optimization algorithms on the basis of multi-parameter coupling effects, and finally solving an optimal performance through continuous permutation, combination and iterative calculation.

The investigation of mechanisms on pipe diffuser leading edge vortex generation and development in centrifugal compressor

Pipe diffuser can adapt the high Mach number distorted flow in high pressure ratio centrifugal compressors because of its special scallop leading edge. However, the special leading edge could generate pair vortices and it is not clear if the pair vortices have positive or negative effect on pipe diffuser performance. Besides, the generation and development of pair vortices are also need to be investigated. This work is aimed at uncovering the influence of vortices on aerodynamic loss in pipe diffuser. Pipe diffusers with several different geometries are designed for a high pressure ratio centrifugal compressor used in a small gas turbine. The generation and evolution of pair vortices in pipe diffuser passages are studied by validated state-of-the-art CFD method. Detailed understandings of the influence of different geometries on pair vortices and pipe diffuser performance are provided. Through these works, it is found that the pair vortices could enhance the flow mixing of high and low energy flow in pipe diffuser passage near throat, thus the boundary layer becomes thin, and the flow separation is suppressed near pipe diffuser throat under large negative incidence. However, pair vortices also move low momentum flow to the pressure side and induced separation in pipe diffuser cone after throat, eventually. The diffuser inlet-to-impeller exit radius ratio and diffuser cross section shape could affect the compressor performance by changing the intensity of pair vortices. The diffuser with inlet-to-impeller exit radius ratio 1.02 and the pipe diffuser with the cross section with big fillets such as 3.37 mm are recommended for their good performance. The diffuser throat area and passage count can also have impact on pair vortices, but the compressor performance is not only influenced by pair vortices when these two parameters are changed.

Structural and molecular dynamics of ammonia transport in Staphylococcus aureus NH3-dependent NAD synthetase

Ammonia dependent NAD+ synthetase from multi drug resistance Staphylococcus aureus catalyzes ATP dependent formation of NAD+ from deamido-NAD+ and ammonia at the synthetase active site. Binding of ATP accompanies a large movement of flexible loop region (205-225) acting as a lid to the catalytic core. A 17 Å long ammonia tunnel with an entry and exit radius of 3.5 Å and 3.2 Å respectively allows transfer of ammonia from surface to the active site of the enzyme in each monomer to attack the C7N=O7N linkage of transient intermediate NAD-adenylate thus releasing NAD+. In this study, we report structural details of ammonia transport tunnel in Staphylococcus aureus NH3-dependent NAD synthetase and compared their architecture and dynamics with other bacterial and eukaryotic enzymes. Tunnel shows conformational variations in apo and substrate complexes and is less intricate compared to glutamine dependent counterparts. We have also performed steered molecular dynamic simulations of ammonia transport across the tunnel in enzyme-intermediate complex which reveals critical bottleneck residues and structural determinants during ammonium migration. Ordered water molecules and conserved charged residues form a network of hydrogen bonds and electrostatic interaction which facilitate the ammonium movement towards the active center. Analysis of the sMD simulated structural snapshots delineates the conformational reshaping of ammonia tunnel at the different step of the enzymatic reaction. Tunnel architecture and environment could offer the new target site to design novel small molecule inhibitors for the development of more efficient therapeutics against multi drug resistant S. aureus strains.

Numerical Investigation of an Integrated Ejector Nozzle with the Nozzle Pressure Ratio of 2.97

The design of the integrated ejector nozzle system directly affects the secondary mass flow rate and the trust characteristics of the aero-engine. The numerical simulation was used to study the effects of longitudinal distance between engine nozzle exit and aircraft surface and radius of ejector nozzle exit on the performance of the integrated ejector nozzle system. Results indicates:(1) As NPRs increases, secondary mass flow rate and thrust coefficient of ejector nozzle system generally increase;(2) the effect of D2/D0 is not obvious but D3/D0 has great effect, and the value of D3/D0 designed between 1.1 and 1.25, which is beneficial to the secondary mass flow rate and thrust coefficient of ejector nozzle system;(3) the combination design of D2/D0 and D3/D0 can restrain the flow separation between the primary flow and have inhibitory effect on the over-expansion of low nozzle pressure rate.

Aerodynamic Optimization Design of a Supersonic Compressor Rotor with High Pressure Ratio

Supersonic compressors have a high wheel speed and operational capability, which facilitate a high stage pressure ratio. However, the strong shock waves in the passage of a supersonic rotor and the interference between shock waves and boundary layers can lead to large flow loss and low efficiency. Moreover, the existing design of a high-load supersonic compressor has the problem of small stall margin. In this study, an automatic optimization method including 2D profile optimization and 3D blade optimization is proposed to achieve a high efficiency at the design point of a supersonic compressor rotor under the premise of reaching the desired mass flow rate and total pressure ratio. According to the analysis of flow near the stall point of the supersonic compressor rotor, the mechanism responsible for rotor tip stall is established, that is, the aerodynamic throat appeared inside the flow passage, reducing the ability of the blade tip to withstand back pressure, and the low-speed areas caused by the tip-leakage-vortex breakage and boundary layer separation reduced the flow capacity of the blade tip. Based on the reasons for rotor stall, three methods are proposed to improve the stall margin, which include increasing the exit radius of the upper meridian, forward sweep of the blade tip, and increasing the chord length of the blade tip. The above method is used to design a supersonic rotor with a total pressure ratio of 2.8, which exhibits an efficiency of 0.902 at the design point and a stall margin of 18.11%.

Theory and CFD-Verification of Stokesian Free Jet with Nonuniform Exit Pressure and Velocity

Jet with Re ≪ 1 is observed downstream of valves in lymphatic vessels of mice and it is an impending research target in developing treatment of noninvasive cancer, especially breast cancer. The jet has the characteristic that the pressure and velocity greatly vary at the exit because of flows with angle change of ninety degree at the exit periphery. A new theory of Stokesian free jet is presented as a model of the jet from a lymphatic valve to predict the pressure in the jet region. Navier-Stokes equations and continuity equation, expressed by the spherical coordinates, are solved under the Stokes approximation by taking radial pressure and velocity variations at the exit into account. Flow field is divided into two regions by the hemisphere with its origin at the exit center and the exit radius, inner region and outer one. The former is inside the hemisphere and the latter is outside it. The pressures in both regions are given by Legendre polynomials, multiplied by powers of the radial distance, and the velocity components are expanded by two series of unknown functions of the angle, multiplied by the powers of the distance. The pressure gradient and the stream lines in the outer-region solutions are patched with those in the inner-region one over the hemisphere, resulting in reasonable solutions in forms of infinite series for the pressures and the velocities. Numerical examples show nonuniformities of the exit pressure and velocities.

Multi-point design optimization of a high-performance intake for scramjet-powered ascent flight

Scramjet engines are one of the most promising hypersonic airbreathing propulsion techniques for efficient and economic access to space. Besides capturing and compressing the air to desirable flow conditions, the intake plays a vital role in determining the intake drag, flow compression efficiency, started flow condition that governs the overall scramjet engine performance. For access to space, the flight trajectory practically comprises varying freestream conditions and altitude to enable ascent flight, constituting an optimization problem with off-design conditions as well as design and physical constraints to be considered. This paper presents the results and insights obtained from a first ever multi-point multi-objective optimization study of an axisymmetric scramjet intake conducted by means of surrogate-assisted evolutionary algorithms coupled with high-fidelity computational fluid dynamics. It aims to minimize the intake drag and maximize the compression efficiency at two differing conditions, i.e., Mach 7.7 at an altitude of 30 km and Mach 10 at 33.5 km. Key design factors for high-performance intakes that can achieve desirable flow compression for the combustor are identified by global sensitivity analysis and examining the trade-off characteristics. Underlying flow physics is elucidated by probing into the representative flowfields at two design conditions with adaptive mesh refinement so as to gain insights into phenomena and characteristics to realize scramjet-powered ascent flight. It has been found that the non-dominated solutions constitute clusters with respect to length and exit radius, with each cluster characterized by distinct tendencies in terms of compression efficiency loss, total drag, static pressure ratio and mean exit temperature. Shorter scramjet intakes have been found to be prone to flow separation due to impingement of a reflected shock off the centerline on the third ramp that causes an adverse pressure gradient.

Effects of the actuation waveform on the drop size reduction in drop-on-demand inkjet printing

In this study the effects of the actuation waveforms on the droplet generation in a drop-on-demand inkjet printing are studied systematically by numerical simulations. Two different types of waveforms, namely the unipolar and bipolar actuations, are investigated for three fluids with different physical properties. We focus on two key parameters, which are the dwell time and the velocity amplitude. For the unipolar driving, the ejection velocity and the ejected liquid volume are both increased as the velocity amplitude becomes larger. The dwell time only has minor effects on both the ejection velocity and the ejected liquid volume. The ejection velocity decreases significantly for large liquid viscosity, while the influences of viscosity on the ejected liquid volume are much weaker. Four different droplet morphologies and the corresponding parameter ranges are identified. The droplet radius can be successfully reduced to about 40% of the nozzle exit radius. For the bipolar waveforms, same droplet morphologies are observed but with shifted boundaries in the phase space. The minimal radius of stable droplet produced by the bipolar waveforms is even smaller compared to the unipolar ones.

원뿔 컵 형상의 점진적 판재 성형 공정에서 형상에 따른 단면 형상의 변형 특성 분석

Incremental sheet metal forming can be used to manufacture various products without the punch and die set. However, it is difficult to manufacture the desired shape due to section deflection and springback of the sheet. Section deflection is caused by the force of the blank holder for fixing the sheet and the tool for forming the sheet. In this study, we analyzed the characteristics of the section deflection according to the geometries of the circular cup shapes in the sheet incremental forming process. The section deflection increased with an increase in the entering radius and forming angle in the section deflection region. However, section deflection was constant according to the exit radius. In addition, the secondary forming process for reducing the shape error was introduced. The secondary incremental forming process was conducted in the opposite direction. Characteristics of the shape error according to the entering depth of the tool among the forming parameters for reducing the shape error of the cup shape were analyzed. The springback in the cup-shape was reduced by the additional forming process with an optimum entering depth of the tool.

Study of expansion ratio on dual bell nozzle of LOX-RP1 engine for replacing the existing bell nozzle to dual bell nozzle

Numerical study was conducted on the LOX-RP1 engine bell nozzle to replace the dual bell nozzle for determining the optimum expansion ratio and greater thrust at sea level. Here base nozzle is a conventional Rao’s TIC nozzle, where throat radius, exit radius, inflection angle and exit angles are 138mm, 826mm, 33° and 8° respectively. The total length of dual bell nozzle and existing bell nozzle are kept same. Numerical analyses were carried out in ANSYS FLUENT software on different dual bell nozzle geometry to evaluate the thrust and expansion ratio. Numerical analysis is performed by two dimensional, axi-symmetric, steady state, pressure based solver with SST k-ω turbulence model at different ambient pressures to recreate the patterns of flow in the nozzle at different nozzle pressure ratio (NPR) and expansion ratio. The profile has made by commercial software SOLID WORKSTM. Numerical simulations and flow separation locations are validated with the experimental data published earlier. It is observed that with area ratio 150 and inflection angle 15° the thrust has increased by 5.46% at sea level and around 10.5% in vacuum, where the increase in exit radius and mass is only 96 mm and 6 kg respectively.

Developing crash modification factors for roundabouts using a cross-sectional method

Abstract The objective of the current study was to evaluate traffic and geometric features and their influences on the safety performance of roundabouts by developing suitable crash modification factors (CMFs). The cross-sectional method can be applied as an alternative method to estimate the CMFs when before-and-after studies are impractical to apply, e.g., lack of data from the period after implementing treatments. To accomplish the study objective, CMFs were derived from generalised linear models (GLMs), i.e., negative binomial (NB) regression, using data collected on regional roundabouts in Toowoomba City, Australia. Six years of crash data from 49 roundabouts included all recorded crashes as well as traffic and geometric features for the entire roundabouts. Several candidate models were developed using the GLMs. Five models were selected based on statistical significance, goodness-of-fit (GOF) measures, and cumulative residual (CURE) analysis. The results show that increasing the number of entry lanes, entry width, entry radius, traffic volume, circulatory roadway width, weaving width, and speed limit have positive effects on roundabout safety. On the other hand, increasing the number of legs, number of exit lanes, exit width, exit radius, weaving length, central island diameters, and presence of fixed object on a central island have negative effects on roundabout safety. The study shows that quantifying the risk factors can support road safety stakeholders to identify safety improvements at roundabouts more effectively and efficiently.

Spray characteristics of gel propellants in an open-end swirl injector

Gel propellants have both liquid and solid characteristics, giving them a broad array of application possibilities; because they are a type of power law fluid, high viscosity and difficulty in atomization have restricted their application in the aerospace field. Open-end swirl injectors can be combined with other nozzles to form gas-liquid coaxial nozzles, but at present, there are few studies on the application of gel propellants to open-end swirl injectors. A set of gel simulant spray systems was established to investigate the spray characteristics of gel propellants in an open-end swirl injector. Three types of gel simulants with different rheological parameters were used; and three open-end swirl injectors with different tangential channel diameters were designed to change the geometrical characteristic constant A of the swirl injectors associated with the injector exit radius, number of tangential inlets, radius of tangential inlets, etc. The thickness of the liquid film, and their spray characteristics in the open-end swirl injectors, were experimentally studied. The liquid film thickness of the gel propellant was measured using the conductance method. Details of the liquid film break-up and spray development were recorded with a high-speed camera. The effects of the above rheological and geometrical parameters on liquid film thickness, discharge coefficient, spray cone angle and liquid film breakup length, etc. were obtained, and the empirical equations were summarized.

Design optimization and experimental study of coaxial powder-feeding nozzle in the laser cladding process

To improve the powder convergence and cladding layer quality, the three-dimensional axisymmetrical powder flow through a coaxial feeding nozzle was simulated by the Eulerian-Eulerian two-fluid model. With the composite design via the response surface method, the significance between the main geometric dimensions of nozzle and fluidization characteristics of powder flow was analyzed and regression-fitted. Moreover, a mathematical model was constructed to optimize the nozzle structure, and the optimal nozzle was used in laser cladding experiments. The results show that appropriate powder flow can be obtained in the condition of the carrier gas more than 9 l/min, and the powder sending rate less than 7.5 g/min. The structural parameters of the optimized nozzle are as follows: nozzle angle of 62.94°, outlet width of 1.0mm, exit radius of 5.83mm, and flow separation angle of 3.00°. With the optimized nozzle, the waist diameter and focus depth of the original powder flow decreased by 39.4 and 46.4%, respectively, and the discrepancy between the experimental and simulation results was less than 9%. With the appropriate technological parameters, a layer with good geometry morphology and appropriate dilution rate can be prepared in the laser cladding process with a coaxial feeding nozzle.

Modeling of Unsymmetrical Single-lane Roundabouts based on Stopping Sight Distance

Evaluation of the adequacy of sight distance at roundabout is usually performed graphically as no quantitative guidelines are available for the lateral clearance needs. This paper presents analytical lateral clearance models to satisfy Stopping Sight Distance (SSD) at unsymmetrical single-lane roundabouts (with different entry and exit radii). The models are developed for three critical locations: approach sight distance, sight distance to exist crosswalk, and circulatory roadway sight distance. Two cases of approach sight distance are presented: sight distance to the crosswalk and sight distance to the yield line. The required lateral clearance at any specified point along the curve can also be determined. Design aids for the required maximum lateral clearance are established for the three locations of sight distance based on accurate SSD formula that accounts for effect of the radial deceleration component of the vehicle. For the circulatory roadway sight distance, infeasible combinations of the circulatory roadway radius and speed are identified based on acceptable driver’s field of peripheral vision. The models and results of this paper, which are applicable to both symmetrical and unsymmetrical roundabouts, should be of interest to highway engineers and designers.

Turbulence, entrainment and low-order description of a transitional variable-density jet

Geophysical flows occur over a large range of scales, with Reynolds numbers and Richardson numbers varying over several orders of magnitude. For this study, jets of different densities were ejected vertically into a large ambient region, considering conditions relevant to some geophysical phenomena. Using particle image velocimetry, the velocity fields were measured for three different gases exhausting into air – specifically helium, air and argon. Measurements focused on both the jet core and the entrained ambient. Experiments considered relatively low Reynolds numbers from approximately 1500 to 10 000 with Richardson numbers near 0.001 in magnitude. These included a variety of flow responses, notably a nearly laminar jet, turbulent jets and a transitioning jet in between. Several features were studied, including the jet development, the local entrainment ratio, the turbulent Reynolds stresses and the eddy strength. Compared to a fully turbulent jet, the transitioning jet showed up to 50 % higher local entrainment and more significant turbulent fluctuations. For this condition, the eddies were non-axisymmetric and larger than the exit radius. For turbulent jets, the eddies were initially smaller and axisymmetric while growing with the shear layer. At lower turbulent Reynolds number, the turbulent stresses were more than 50 % higher than at higher turbulent Reynolds number. In either case, the low-density jet developed faster than a comparable non-buoyant jet. Quadrant analysis and proper orthogonal decomposition were also utilized for insight into the entrainment of the jet, as well as to assess the energy distribution with respect to the number of eigenmodes. Reynolds shear stresses were dominant in Q1 and Q3 and exhibited negligible contributions from the remaining two quadrants. Both analysis techniques showed that the development of stresses downstream was dependent on the Reynolds number while the spanwise location of the stresses depended on the Richardson number.

Effects of conical nozzle and its geometry on properties of an inductively coupled plasma jet used for optical fabrication

The properties of a traditional inductively coupled plasma (ICP) jet, such as temperature and velocity, cannot satisfy the engineering application requirements in optical fabrication. Therefore, a conical nozzle was proposed to obtain a low-temperature jet with high stiffness and meet the requirements. Furthermore, the effects of the nozzle geometry on the plasma jet properties were analyzed. First, a numerical model was developed for ICP discharged from the nozzle into the ambient air. Second, the model was validated by comparing the computed temperature with three sets of experiments. A good agreement was obtained between the computed results and the experimental values, and the accuracy of the model was demonstrated. Subsequently, the properties of an argon plasma jet discharging from the nozzle into the air were examined by using the developed model. The effects of entrainment of cold air on the jet properties were also analyzed. The results indicated that the jet properties are considerably affected by entrainment of the air. Finally, the effects of nozzle geometry, such as length of the convergent section and the nozzle exit radius, on the jet properties were analyzed using single-factor simulations. An orthogonal study was then conducted for further optimization of the nozzle structure.

Extrusion of unleavened bread dough: Experiments and simulations

An experimental and numerical study on ram extrusion of bread dough was conducted in order to develop predictive models for the pressures involved, as well as the deformation of the extruded dough. Such studies are needed as high pressures can potentially lead to significant degassing, tearing, and shearing of the dough and hence poor bread quality; the latter limits the use of extrusion processes which would otherwise be a cost-effective forming process. A laboratory extrusion rig was designed, with dies of varying angles and exit radii. Rate dependent behavior was observed from tests conducted at different extrusion speeds, and higher extrusion pressure was reported for dies with smaller exit radius or larger die angle. A simulation of extrusion was performed to predict the extrusion pressure as well as the extrudate swell, as a function of die geometry and extrusion rate. A continuum approach was taken in the constitutive model of dough which is a starch filled system in a protein matrix. A nonlinear viscoelastic model combined for the first time with the Mullins model for filled rubbers is found to capture the continuum behavior well. A Coulomb friction law combined with a maximum shear stress limit was used to describe the contact definition between the extrusion barrel and the dough. Higher die angles and higher extrusion speeds require higher shear stress limit values for the model and the experiments to agree. A possible reason for this is that the shear stress limit depends on maximum strain as well as strain rate imposed during the extrusion process. Static zones were observed both experimentally and numerically. The onset of the static zones was predicted well but quantifying the geometry of the latter needs further studies.