Throat Section Research Articles

Reynolds Number Effect on Aerodynamic and Starting Characteristics of a Two-Dimensional Hypersonic Inlet

The Reynolds number effect induced by model scaling and inflow conditions will affect the aerodynamic and starting characteristics of a two-dimensional hypersonic inlet. This effect is investigated through a numerical simulation method. First, the numerical simulation method is validated through experimental data. The static pressure from the numerical simulation method agreed well with wind tunnel tests. Then, this simulation method is used to study the Reynolds number effect on a two-dimensional hypersonic inlet caused by the model scaling and inflow conditions. The numerical simulation results indicate that as the Reynolds number decreases from 4.86 × 106 to 9.71 × 104 with model scaling increases from 1 to 1/50, the relative boundary layer thickness at the entrance of the inlet increases from 10.4% to 21.2%; as the flight altitude increases from 25.5 km to 36.5 km, which causes the Reynolds number to decrease from 5.67 × 106 to 1.07 × 106, the relative boundary layer thickness at the entrance of the inlet increases from 9.8% to 13.2%. Finally, the Reynolds number effect on the aerodynamics and starting characteristics caused by these two different factors are compared. The results show that the effect of scaling the model is similar to the effect of changing the altitude. As the relative boundary layer thickness increased by 1.0%, the total pressure recovery at the throat section decreased by 0.8%, and the inlet starting Mach number increased by 0.1.

Numerical method for calculating the nozzle thrust of a wide-range rocket engine

A numerical method for calculating the thrust of a wide-range rocket engine nozzle has been developed. This type of engine is equipped with an annular nozzle with a flat central body and is designed to operate in the upper atmosphere and in vacuum. The nozzle forms a jet converging to the axis of symmetry due to which a more compact torch of the working fluid is formed. Nozzles of this type have important design advantages over conventional external expansion nozzles. They are more compact, simpler in terms of cooling, but they have increased losses in the bottom region due to the presence of a flat bottom near the central body. Therefore, the design of such engines needs parametric optimization. Currently, for engines equipped with an annular nozzle with a flat central body, there are no validated methods that would allow parametric optimization. The characteristics of the jet, the loss of specific impulse, and the magnitude of thrust for a given type of nozzle depend on three main parameters: the area of the bottom region of the central body, the area of the throat section, and the angle of rotation of the inner edge of the nozzle to the axis of symmetry. The gas flow in the bottom region is accompanied by complex shock-wave processes that require a lot of time for numerical calculations. To optimize the design of the nozzle, it is required a simple engineering method to calculate the thrust of the nozzle according to its main parameters. The calculation of the nozzle thrust is based on the integral distribution of pressure forces over its surface obtained by performing numerical calculations in a wide range of external pressure. The Reynolds-averaged Navier-Stokes equations closed by the SST-modification of the k-ω turbulence model are solved. Based on the results of numerical simulation, the calculated coefficients for one-dimensional engineering dependencies are determined; they make it possible to calculate the speed and pressure in a random section of the combustion chamber and engine nozzle. A simple engineering method for calculating the thrust of the chamber nozzle of a wide-range rocket engine has been developed. The technique is verified by comparison with the results of a numerical experiment. The problem of parametric optimization of the rocket engine combustion chamber, capable to operate in a wide range of altitudes, was solved, and it is of interest to the space industry. The developed method of calculation makes it possible to carry out a wide range analysis of the influence of the ratio of geometric dimensions, regime parameters on the thrust of the combustion chamber and nozzles of a wide-range rocket engine, and to estimate the thrust value at different engine operating heights.

Experimental investigation of internal and external flow fields of jetting nozzles with different structures

Jetting has been widely used in the petroleum fields, the nozzle has been investigated for a long time and the structure has been optimized for different applications as the key part of jetting. However, most of these researches are focused on the outer flow with simulations, the real flow characteristics are not been revealed clearly. A visual experimental platform was built with Particle Image Velocimetry (PIV) and a high-pressure pump. 40 nozzles of different profiles were machined and measured. The internal and outer flow fields were captured by PIV under low velocity, and the pressure drop and flow displacement were measured under high-pressure conditions in this paper. The jetting performance such as discharge coefficient, flow core length, jet angle, and velocity distributions were analyzed. The internal flow characteristics including the flow field near the nozzle wall were captured by PIV. The converging angle and the throat section length play an important role in the jetting performance and are suggested to be set to 15° and 3 times the nozzle diameter when designed. The throat length has little effect on the flow field of the streamlined nozzle compared to the cone-straight nozzle, especially the concave curve nozzle. The vortex generated at the corner and the entrance of the throat section can indicate the boundary layer separation and transition, which agrees with our previous simulation work. All work will provide theoretical support for the design of the nozzle on-site application.

How Nanoparticle Aerosols Transport through Multi-Stenosis Sections of Upper Airways: A CFD-DPM Modelling

Airway stenosis is a global respiratory health problem that is caused by airway injury, endotracheal intubation, malignant tumor, lung aging, or autoimmune diseases. A precise understanding of the airflow dynamics and pharmaceutical aerosol transport through the multi-stenosis airways is vital for targeted drug delivery, and is missing from the literature. The object of this study primarily relates to behaviors and nanoparticle transport through the multi-stenosis sections of the trachea and upper airways. The combination of a CT-based mouth–throat model and Weibel’s model was adopted in the ANSYS FLUENT solver for the numerical simulation of the Euler–Lagrange (E-L) method. Comprehensive grid refinement and validation were performed. The results from this study indicated that, for all flow rates, a higher velocity was usually found in the stenosis section. The maximum velocity was found in the stenosis section having a 75% reduction, followed by the stenosis section having a 50% reduction. Increasing flow rate resulted in higher wall shear stress, especially in stenosis sections. The highest pressure was found in the mouth–throat section for all flow rates. The lowest pressure was usually found in stenosis sections, especially in the third generation. Particle escape rate was dependent on flow rate and inversely dependent on particle size. The overall deposition efficiency was observed to be significantly higher in the mouth–throat and stenosis sections compared to other areas. However, this was proven to be only the case for a particle size of 1 nm. Moreover, smaller nanoparticles were usually trapped in the mouth–throat section, whereas larger nanoparticle sizes escaped through the lower airways from the left side of the lung; this accounted for approximately 50% of the total injected particles, and 36% escaped from the right side. The findings of this study can improve the comprehensive understanding of airflow patterns and nanoparticle deposition. This would be beneficial in work with polydisperse particle deposition for treatment of comprehensive stenosis with specific drugs under various disease conditions.

Impact of changing nozzle profiles on thermal and structural loads acting on nozzle wall

A nozzle of rockets is a window for the combustion chamber to the ambient air. It is subjected to several thermal and mechanical loads acting on the internal wall. So, the nozzle structural behavior has a significant impact on the mission achievement. The aim of this paper is studying a variety of nozzle profiles shape and its influences on structural behavior. Computational fluid dynamics software was applied to investigate the temperature and pressure on the internal wall of the nozzle while observing if there is any change at nozzle ballistic performance or not. Four different convergent profiles had been investigated to study its effect on structural stresses acting on nozzle wall. The results showed body temperature distribution, static pressure and thermal-structural stresses at nozzle wall. Changing the internal profile of the nozzle convergent caused significant change in pressure and temperature loads acting on nozzle wall structure. Conical shape convergent profile produced less stresses at throat section by 19.8% compared to original profile.

Comparative evaluation of DES and SAS turbulence models for incompressible flow in a Venturi tube

Computational fluid dynamics employs the Large Eddy Simulation (LES) and Reynolds-averaged Navier-Stokes (RANS) models and combines both models to perform a hybrid RANS/LES simulation of the transient state flow field, within which there are the Detached Eddy Simulation (DES) and Scale-Adaptive Simulation (SAS) models. In the present work, the objective is to evaluate the DES and SAS turbulence models for flow (water) in a Venturi tube, for 2D computational domains. The domain was discretized for grids with quadrilateral cells, and the flow field was studied for four flow rates. The results of the pressure flow field simulations for the DES and SAS models were compared with experimental data reported in the literature, which fit the experiments. However, the DES k-ε model presented a negative pressure drop for a region of the flow adjacent to the wall, at the entrance of the throat section, the other models DES S-A, DES SST k-ω and SAS presented positive pressures. The discharge coefficients yielded values in the range of 0.94-0.951, which were lower than the experiments, for errors in the range of 1.57-2.76%.

Computational investigation of a venturi-type mixer for gaseous fuel application in a dual-fuel engine

The combined application of biogas (BG) and producer gas (PG) in diesel engines is a challenge and has scarcely been addressed so far. The present contribution focused on designing a venturi-type mixer to regulate the flow of these gases in a diesel engine under the dual-fuel (DF) mode. The mixer is simulated using CFD software (ANSYS 15.0) with five combinations of BG-PG flow, viz. 80-20%, 60-40%, 50-50%, 40-60% and 20-80% to analyse the flow behaviour, distribution and mixing quality of these gases with the air. The results indicated significant pressure drops at the throat section, which increases the velocity and turbulence inside the mixer to achieve a homogeneous mixture of gases in the divergent section. Moreover, the study resulted in lean air–fuel mixture for all flow combinations in 1.23–1.51. The proposed mixer seem to be suitable for DF engine operation with the combined application of BG and PG.

A Venturi tube design for studying travelling bubble cavitation

Abstract Travelling bubble cavitation always appears in forms of nearly spherical travelling bubbles. These bubbles grow from the freestream/surface nuclei in the low-pressure region in the flow channel. As the inception of travelling bubble cavitation is very sensitive to the boundary layer flow, attached cavitation would be likely to appear simultaneously if the flow is not well-controlled. In this study, based on the interaction between cavitation inception and boundary layer, a Venturi tube for studying travelling bubble cavitation is designed with the aid of a computational fluid dynamics (CFD) approach. The flow channel of this Venturi tube is composed of an inlet straight pipe (10 mm × 10 mm square), a contraction section, a throat section (5 mm × 5 mm square) and two diffuser sections (diffuser 1 and diffuser 2). For visualization convenience, each cross section of the Venturi tube is square. From CFD results, no flow separation occurs near the throat section and the adverse pressure gradient is relatively small, which indicates attached cavitation may not occur. The manufactured Venturi tube is installed in a blow-down type tunnel and tested with Reynolds number at roughly 3 - 3.75 × 104 and the pressure recovery number at 2.95 - 4.41. The velocity of the Venturi inlet varies from about 6 m/s to 7.5 m/s. Experiment results shows travelling bubble cavitation can be generated successfully and pure travelling bubble cavitation inception is achieved in this Venturi tube. The formation of travelling bubbles is recorded by a Phantom VEO 710L high-speed camera with framing rate of 24000 fps.

Prediction of operating parameters and output power of ducted wind turbine using artificial neural networks

The performance of a ducted wind turbine was simulated in this study utilizing an artificial neural network under various duct operating conditions. Ducted wind turbines have been identified as one of the cleanest and most effective future renewable energy possibilities. Different methods have been used throughout time to exploit the flow stream power successfully. However, the Ducted Wind Turbine System is one method that is still in its early phases. The operation of the ducted wind turbine is analyzed in this research under different wind conditions. The ANN algorithm is recommended for generating turbine power at various wind speeds. The proposed neural network model is shown to perform better for estimating turbine power curves. The ANN models used the free-stream wind speed, wind speed in the throat section, turbulence intensity, and wind power in the intake part of the duct as input datasets and the output power of wind in the throat section as output datasets. At the same time, a three-layer backpropagation training method from the Multilayer Perceptron algorithm approach, a Levenberg–Marquardt, was selected as the best ANN. It was evaluated by comparing to a Radial-based functions approach with a single hidden layer. The optimum number of neurons in the MLP method’s first and second hidden layers, as well as the RBF method’s single hidden layer, has been determined to be 55 and 70, respectively. At 77 and 70 epochs, the best MSE evaluation efficiency of MLP and RBF networks was estimated to be 0. 000103 and 0. 000353, respectively.

Numerical Simulation of Cavitation of Water Jet Nozzle Based on Realizable k-ε Model

In order to study the cavitation characteristics of water jet nozzles, a realizable model was selected to simulate the flow field inside the nozzle at the inlet pressure of 15 MPa. The pressure at the starting point of the nozzle throat section dropped to the minimum, and the liquid velocity reached the maximum. From the vapor volume distribution map of the nozzle, it can be seen that the vapor fraction is the largest on the wall of the expansion section, and a local reflux is formed in the expansion section, which results in the gradual diffusion of the vapor fraction distribution along the wall of the expansion section. In addition, the influence of nozzle inlet pressure on the vapor fraction and vapor fraction distribution region in the expansion section is analyzed. The results show that the larger vapor fraction and vapor fraction distribution region can be produced under the 25 MPa inlet pressure. At the pressure inlet of 25 MPa, six groups of numerical simulations were carried out with different the length to diameter ratio of the nozzle throat section (L4/d0). The results show that when L4/d0 is 2, it is more conducive to the formation of cavitation and the quality of cavitation is better.

Efekat dužine grla na obrasce protoka u konusnim mlaznicama van dizajna

In the present work, a flow field study was performed for off-design conical nozzles with non-circular cylindrical throat sections such as those found in experimental sounding rocket motor applications. The flow field was simulated with the RANS model in ANSYS-Fluent R16.2 code for 2D domains. The governing equations used are conservation of mass, momentum, energy, and state. Sutherland's equation for viscosity as a function of temperature and the Spalart-Allmaras turbulence model was used to simulate overexpanded flow turbulence. The results showed pressure and Mach number fluctuations as the throat length increased. In the throat section, it is concluded that for the length range of 5 to 15% of the throat diameter, the flow accelerates without the presence of internal shock.

Performance optimization of a dual-rotor ducted wind turbine by using response surface method

• The effect of different dual-rotor wind turbine operating conditions on ducted wind turbines was studied. • ANOVA was used to model the effect of dual rotor design factors on extracted power. • Response Surface Method applied to experimental data in order to optimize the dual rotor wind turbine performance. • Key parameters were affecting the performance of the turbine investigated by RSM. • A suitable dual rotor wind turbine for ducted wind turbines was designed, and RSM was an excellent method to optimize DWTs. The presented study evaluates and optimizes the performance of dual-rotor wind turbines installed inside a developed duct. The effect of different operating conditions on the extracted power was compared between dual-rotor wind turbines (DRWT) and single rotor wind turbines (SRWT). These operating conditions include the type of dual-rotor wind turbines installed in the throat section of the duct, the distance between the two rotors of a turbine, and the flow velocity through the duct throat that were evaluated by the multivariate statistical method response surface methodology. The central composite design of the response surface method was utilized to fit the designed model based on the least-squares method. Also, the multiple regression method was applied for the empirical data to match variable operating conditions with the developed model by analysis of variance (ANOVA). Afterward, some experiments were carried on to validate this method. The results showed a maximum power ratio of about 55% at the optimized conditions for dual rotor wind turbines. Determined P-values for designed parameters of models were less than 0.05, which makes its effect on the model significant. Furthermore, the power ratio obtained from empirical data was compatible with the considered model.

Internal flow mechanism of cone-straight nozzle

Cone-straight nozzle has been widely used in well bore cleaning, assisting drilling in petroleum industries due to its good clustering properties. The structure including cone angle and throat length has also been studied by scholars and been optimized. However, the internal flow properties have not been investigated clearly especially the boundary layer flow. In this paper LES model is used to capture the small-scale flow state near the nozzle wall. The RNG k-epsilon model is used to validate the accuracy of the LES simulation, the simulation data shows a good agreement. Three different inlet velocities are considered in simulations. The velocity distribution, shear stress, boundary layer thickness, skin friction coefficient and Reynolds stress are analyzed, the boundary layer separation and transition are discussed. The state of flow inside nozzle is laminar with inlet velocity of 1 m/s and gradually transferred into turbulent with the increasing inlet velocity. The most severe turbulence is at the entrance of the throat section, the vortex structure appears at the entrance of converging section and dose not survive, the vortex structure appears in sequence along the throat section wall when the inlet velocity is set to 5 m/s and 10 m/s the flow properties along the conical nozzle are revealed clearly, the main flow resistance is mainly produced in throat section. All these works aim to provide theoretical support for the further processing optimization of the nozzle structure and reduce the flow resistance of nozzle.

Numerical studies for effect of geometrical parameters on water jet pump performance via entropy generation analysis

This paper presented an implementation of entropy generation analysis in the main flow field of a water jet pump via the CFD method. This study aimed to identify the inefficient location of energy conversion and to analyse entropy generation sources in each region of the water jet pump. The 2D-axisymmetric model and realisable k-ε (RKE) turbulence model at steady-state conditions were performed to validate jet pump performance and to assess the entropy generation. Likewise, the effects of the projection ratio and throat-aspect ratio as independent parameters were investigated. As a result, the throat is the most inefficient part due to the high total entropy generation rate, following by diffuser part. Also, the entropy generation rate was assessed dominant than viscous dissipation due to the turbulent dissipation, which was caused by a turbulent shear stress layer of mixing the streams. In conclusion, the projection ratio influenced the growth of the shear stress layer as well as the entropy generation. Further, the throat-aspect ratio affected the distribution of entropy generation in the throat section. An appropriate combination of both parameters has an impact on the jet pump performance improvements reducing the entropy generation rate in the future.

An experimental study of the effect of the projection ratio and throat-aspect ratio on the efficiency and loss coefficient of a water jet pump

This study focuses on the influence of dimensionless geometry parameters on the performance and loss coefficient of the throat and diffuser of the water jet pump apparatus. A water jet pump system was designed for a total of nine experimental cases with three different projection ratios and three throat-aspect ratios . The volumetric and pressure ratios - performance parameters are measured at a constant motive pressure and under varying backpressure. The efficiencies of the water jet pump in each configuration were assessed and compared. It was found that increasing 2 or 3 times of projection ratio degrades efficiency about 2% to 5.5%, respectively. Higher projection ratio ( > 1) expands the water jet diameter, which clogs the secondary flow. Hence, the changes in > 3 may have a significant impact on efficiency degradation. Shorter may cause the loss of kinetic energy in the diffuser, while longer reduces momentum transfer on the secondary flow. Moreover, the changes in and influence friction loss coefficient in the throat and diffuser section, and it reduces with increasing of volumetric ratio. It can be concluded that the appropriate value of projection ratio and throat-aspect ratio plays a role in the kinetic energy dissipation. It is also responsible for the location friction process, at a different volumetric ratio. However, the experimental results denoted the best efficiency and loss coefficient was achieved at a low projection ratio ( = 1) and small throat-aspect ratios ( = 5). The best efficiency of the study was about 23.37%.

Starting transients in second throat vacuum ejectors for high altitude testing facilities

The present study aims to investigate the process of vacuum generation in a second throat vacuum ejector system employed for the high altitude testing of rocket motors. The study shows that the vacuum generation progresses with four distinct stages during the initial start-up process. The initial stage consists of a gradual evacuation process (first stage) which is followed by a transition region (second stage) in which the pressure starts to drop fastly and eventually leading to a rapid evacuation stage (third stage). This is followed with the reappearance of a gradual evacuation stage (fourth stage) which terminates with the onset of the started mode operation. It is found that the various stages of evacuation are closely linked to the internal shock wave movement in the supersonic nozzle. The gradual evacuation is found to be caused by the relatively large nozzle exit pressure caused by the multiple shock cells in the nozzle. The rapid evacuation occurs due to the sudden movement of the first shock cell to the nozzle exit and the reappearance of the gradual evacuation happens during the transformation of the nozzle jet from an overexpanded to underexpanded state. The parametric studies show that with increase in diffuser convergent cone angle, the contribution of vacuum generation from the fourth stage reduces due to a reduction in the maximum possible jet expansion. A same trend in vacuum generation is observed when nozzle distance from the second throat section of the ejector diffuser reduces.

A CFD study on hydrocarbon mean residence time in a horizontal oil\u2013water separator

This study presents computational fluid dynamics analyses on oil–water flow characteristics in a horizontal separator. The performance of these vessels are inferred from mean residence time and cumulative residence time distribution of the hydrocarbon phase inside the separator. The authors model a separator used by previous researchers and evaluate mean residence time of the hydrocarbon phase in a two-phase mixture of oil and water. Three different water-cuts of 21%, 32%, and 57% are used. Additional analyses are done to assess how certain geometric features of the separator influence hydrocarbon mean residence time. The results show that the addition of a second perforated baffle plate does not improve the hydrocarbon mean residence time significantly. However, introducing a downward slanting throat section between the primary zone and the gravity separation zone improves the hydrocarbon mean residence time at 21% and 32% water-cuts. The results suggest oil–water separators with a throat section may be more efficient than regular horizontal separators without the throat section at low water-cuts.

A Wet Gas Metering System Based on the Extended-Throat Venturi Tube.

Although the use of a classical Venturi tube for wet gas metering has been extensively studied in the literature, the use of an extended-throat Venturi (ETV) tube has rarely been reported since its first proposal by J. R. Fincke in 1999. The structure of an ETV is very simple, but due to the complexity of multiphase flow, its theoretical model has not been fully established yet. Therefore, in this paper theoretical models have been developed for the convergent and throat sections of an ETV, and the gradients of front and rear differential pressures are derived analytically. Several flowrate algorithms have been proposed and compared with the existing ones. Among them, the iteration algorithm is found to be the best. A reasonable explanation is provided for its performance. The relationship between the differential pressure gradient and the flowrate relative error is also studied, such that the relative error distributions varying with ETV measured flowrates can be derived. The gas flowrate error of ETV increases with the liquid content whilst the liquid flowrate error of ETV decreases with the liquid content, and the relative errors of liquid flowrate are generally 2 to 3 times larger than that of the gas flowrate. Finally, the ETV tends to be more accurate than the classical Venturi tube. The ETV can be designed more compact under the same signal intensity due to its significantly higher velocity in the throat section.

Análisis numérico del comportamiento del flujo en la sección de la garganta de una tobera cónica experimental

El patrón de flujo en toberas supersónicas lo definen los perfiles aerodinámicos de la geometría de las paredes internas, entre otros parámetros, donde la garganta es una sección crítica. En el presente trabajo, el objetivo es analizar el comportamiento del flujo en la sección recta de la garganta de una tobera cónica experimental de un motor de cohete sonda de combustible sólido. El flujo sobreexpandido se simuló con el código ANSYS-Fluent en un dominio computacional 2D, empleando el modelo RANS y el modelo de turbulencia de Menter, y la ecuación de Sutherland para la viscosidad en función de la temperatura. Se llevaron a cabo cinco casos de estudio para la longitud de garganta en el rango de 1-10 mm. Se obtuvo fluctuaciones de número de Mach, presión y temperatura, ondas de choque oblicuas en la sección de la garganta para la longitud de 10 mm; para longitudes menores disminuyó la intensidad de la magnitud del choque. Se concluye que para la longitud de garganta de 1 mm el flujo es transónico sin la presencia de choques oblicuos. En la sección divergente, las ondas de choque varían en su intensidad y cambian de posición.

The effect of stenosis rate and Reynolds number on local flow characteristics and plaque formation around the atherosclerotic stenosis

Atherosclerosis causes plaque to build-up in arteries. Effect of the specific local hemodynamic environment around an atherosclerotic plaque on the thrombosis formation does not remain quite clear but is believed to be crucial. The aim of this study is to uncover the flow effects on plaques formation. To study the mechanically regulated plaque formation, the flow fields in artery blood vessels with different stenosis rates at various Reynolds numbers were simulated numerically with the two-dimensional axisymmetric models, and the hemodynamic characteristics around the plaque were scaled with stenosis rate and Reynolds number. The results showed that increases of both Reynolds number and stenosis rate facilitated the occurrence of flow separation phenomenon, extended recirculation zone, and upregulated the maximum normalized wall shear stress near the plaque throat section while downregulated the minimal normalized wall shear stress at the front shoulder of plaque, as it should be; in the atherosclerotic plaque leeside of the recirculation zone, an obvious catch bond region of wall shear stress might exist especially under low Reynolds number with stenosis rate smaller than 30%. This catch bond region in the plaque leeside might be responsible for the LBF (low blood flow)-enhanced formation of the atherosclerotic plaque. This work may provide a novel insight into understanding the biomechanical effects behind the formation and damage of atherosclerotic plaques and propose a new strategy for preventing atherosclerotic diseases.