Study of Starting Problem of Axisymmetric Divergent Dual Throat Nozzle

2017 ◽  
Vol 139 (6) ◽  
Author(s):  
Yangsheng Wang ◽  
Jinglei Xu ◽  
Shuai Huang
Keyword(s):  
Cavity Length ◽  
Expansion Ratio ◽  
Divergence Angle ◽  
Nozzle Throat ◽  
Convergence Angle ◽  
Cavity Bottom ◽  
Oscillation Phenomenon ◽  
Thrust Vector ◽  
Shock Oscillation ◽  
Simulation Results

Compared to the conventional axisymmetric dual throat nozzle, the axisymmetric divergent dual throat nozzle (ADDTN) can offer larger thrust vector angles. However, the starting problem maybe exists in the ADDTN and results in a huge thrust loss. In this paper, the ADDTN starting problem has been studied by steady and unsteady numerical simulations. The effects of nozzle geometric parameters on internal nozzle performance have been discussed in detail, including cavity divergence angle, cavity convergence angle, cavity length, expansion ratio, rounding radius at the nozzle throat, and rounding radius at the cavity bottom. And, the shock oscillation phenomenon is found inside the recessed cavity in some high-expansion ratio configurations. In addition, a bypass is proposed in this study to solve the ADDTN starting problem. The main numerical simulation results show that the expansion ratio is the most sensitive parameter affecting the starting characteristic of ADDTN, followed by the cavity divergence angle and the cavity length. And, among these parameters, the parameters of cavity convergence angle and rounding radius at the cavity bottom contribute the least to the starting problem. Besides, the ADDTN configurations of large rounding radius at the nozzle throat tend to start.

scholarly journals Computational fluid dynamics simulations of the flow field characteristics in a novel exhaust purification muffler of diesel engine

2018 ◽  
Vol 37 (4) ◽  
pp. 816-833 ◽  
Author(s):  
Fu Jun ◽  
Zhang ZengFeng ◽  
Chen Wei ◽  
Mao Hong ◽  
Li JianXing
Keyword(s):  
Flow Field ◽  
Pressure Loss ◽  
Cavity Length ◽  
Great Influence ◽  
Expansion Ratio ◽  
Ceramic Foam ◽  
Length Ratio ◽  
Maximum Pressure ◽  
Flow Field Characteristics ◽  
Exhaust Purification

The purpose of this paper is to improve the emission performance of diesel engines. A novel exhaust purification muffler was proposed and designed. The flow field characteristics of the exhaust purification muffler were studied based on the finite volume method, the pressure loss of the exhaust purification muffler was 3315 Pa, and the pressure loss of the exhaust purification muffler was just 2% higher than the original muffler. Then, a three-dimensional numerical simulation model was established and used to investigate the effect of different expansion ratio, cavity length ratio, and ratio of length to diameter on the flow field characteristics in an exhaust purification muffler of diesel engine. The study was shown that the porous media (ceramic foam) had a great influence on the flow field distribution, where the air flow velocity was stable and the pressure distribution was trapezoidal, having a good pressure reduction and deceleration effect. With the increase of the expansion ratio parameter, the airflow cross-section area changed when air entered into the inlet silencing cavity, which had great influence on the velocity field and the pressure loss. Because of the improvement of cavity length ratio parameter, the flowing distance in the inlet silencing increased, which caused more local turbulence and pressure fluctuation. Also with the increase of the ratio of length to diameter parameter, the volume of inlet silencing chamber and the air flow space increased. The change of the structural parameters of each scheme had a certain influence on the pressure loss. The maximum pressure loss changing value among the expansion ratio schemes was 878 Pa, then the maximum pressure loss changing value among the cavity length ratio schemes was 328 Pa, and it was 89 Pa among the cavity length ratio schemes. The pressure loss caused by the expansion ratio parameter changed greatly, and the pressure loss changing value caused by the change of the cavity length ratio parameter and the ratio of length to diameter parameter was relatively small. In this paper, a muffler which contained a ceramic foam and had the functions of exhaust soot purification and noise elimination was supplied. The effects of the structure factors on flow field characteristics were studied. The guidance for the design and improvement of muffler is able to be supplied in this paper.

scholarly journals Realization of Multimode OAM Beams with Almost the Same Divergence Angles

2021 ◽  
Vol 2021 ◽  
pp. 1-10
Author(s):  
Yunfan Zhang ◽  
Xianling Liang ◽  
Weihao Qi ◽  
Hongliang Wu ◽  
Qian Chen ◽  
...  
Keyword(s):  
Radiation Source ◽  
New Method ◽  
Divergence Angle ◽  
Maximum Difference ◽  
Theoretical Relationship ◽  
Parabolic Reflector ◽  
Simulation Results

This paper proposes a new method of realizing multimode OAM beams with almost the same divergence angles. The theoretical relationship between the divergence angle of the OAM beam and its radiation source is presented, and the radiation source distributions for various mode OAM beams with the same divergence angle range are discussed. In order to verify this method, an eight-mode OAM antenna constructed by a bifocal parabolic reflector and dual OAM feeds is designed and simulated. The simulation results show that the divergence angle ranges of 3 dB beamwidth for OAM modes l = ± 1 , ± 2 , ± 3 , ± 4 are 2 . 2 ° , 4 . 6 ° , 2.2 ° , 5.0 ° , 2.4 ° , 4.4 ° ,  and  2.6 ° , 4.8 ° , the divergence angles corresponding to the maximum beam directions are 3.5 ° , 3.6 ° , 3.5 ° ,  and  3.8 ° , respectively, and the maximum difference is within 0.3 ° .

Detailed Experimental Measurement and RANS Simulation of a Low Pressure Turbine With High Lift Blading

2019 ◽  
Author(s):  
Ethan Perez ◽  
John T. Schmitz ◽  
Nicholas A. Jaffa ◽  
Aleksandar Jemcov ◽  
Joshua D. Cameron ◽  
...  
Keyword(s):  
Total Pressure ◽  
Low Pressure ◽  
Aerodynamic Characteristics ◽  
Expansion Ratio ◽  
High Lift ◽  
Time Resolved ◽  
Low Pressure Turbine ◽  
Hot Wires ◽  
Simulation Results ◽  
Improved Performance

Abstract The aerodynamic characteristics of high–lift airfoil designs is of interest for improved performance and reduced blade count in Low–Pressure Turbine (LPT) design. The present paper presents both experimental measurements as well as numerical simulation results from a single-stage LPT. The airfoils were designed for an embedded stage with a total pressure expansion ratio of 1.75 and a rotor Zweifel coefficient of 1.35. The measurement program was highly unique in that detailed measurements were obtained using a variety of different probe types, including time–resolved total pressure and hot–wires. Agreement between various measurement types was generally good, but differences beyond typically stated uncertainty bounds were noted. The computations were done using RANS and a mixing model via commercially available software. The numerical results were evaluated to determine the efficacy of this type of model for prediction and design of high–lift airfoils. The computations agreed very well with the experimental results in the midspan region, but losses were over–predicted in the lower 40% span near the hub. A basic description and understanding of the flow physics in the LPT stage are presented based on the relative agreement between the experiments and computations.

The Numerical Simulation of Aerated Cavity Length and Negative Pressure on Stepped Spillway Combined with Y-Shape Asymmetrical Flaring Gate Pier

2013 ◽  
Vol 864-867 ◽  
pp. 2185-2192
Author(s):  
Xiao Xia Hou ◽  
Ju Rui Yang ◽  
Jian Shu Zhen
Keyword(s):  
Negative Pressure ◽  
Cavity Length ◽  
Lateral Side ◽  
Stepped Spillway ◽  
Body Type ◽  
Two Phase ◽  
Vof Model ◽  
Contraction Ratio ◽  
Simulation Results ◽  
Contraction Angle

In order to study the aerated cavity length and negative pressure on stepped spillway which combined with Y-shape asymmetric flaring gate pier body type, this paper applied RNG turbulence model,VOF model of water vapor two-phase, iterative solution of geometry reconstruction format of unsteady flow to generate free surface. Numerically simulated the length of aerated cavity and negative pressure of stepped spillway which combined with asymmetrical Y-shape flaring gate pier that with the contraction ratio respectively of 598, 0.497 and 0.445, the range from the upstream reservoir to downstream stilling basin. And compared the simulation results with experimental results, found that the aerated cavity length on steps basically consistent with the measured cavity length, the maximum error is 9.7%. The simulation results shows that the aeration cavity length on steps increases with asymmetric flaring gate pier contraction ratio decreases, and the aerated cavity length of lateral side with smaller contraction angle is larger 4 to 5 times than lateral side with larger contraction angle.

Investigation on Shock Oscillation Phenomenon in a Supersonic Air Inlet

2011 ◽  
Author(s):  
Tomohiro Nakayama ◽  
Tetsuya Sato ◽  
Masahiro Akatsuka ◽  
Atsushi Hashimoto ◽  
Takayuki Kojima ◽  
...  
Keyword(s):  
Air Inlet ◽  
Oscillation Phenomenon ◽  
Shock Oscillation

The Numerical Simulation for Effects of Y-Shape Flaring Gate Pier Body Type on Aerated Cavity Length and Negative Pressure of Steps

2014 ◽  
Vol 488-489 ◽  
pp. 847-853
Author(s):  
Xiao Xia Hou ◽  
Ju Rui Yang ◽  
Jian Shu Zheng
Keyword(s):  
Numerical Simulation ◽  
Unsteady Flow ◽  
Negative Pressure ◽  
Cavity Length ◽  
Stable Solution ◽  
Surface Velocity ◽  
Stepped Spillway ◽  
Body Type ◽  
Contraction Ratio ◽  
Simulation Results

Numerical simulation technology has been widely used to study the energy dissipation problem of hydroelectric engineering construction which combined flaring gate pier with stepped spillway. The main parameter of flaring gate pier is contraction ratio. This paper numerically simulated the length of aerated cavity and negative pressure of steps for stepped spillway combined with symmetrical Y-shape flaring gate pier which with the contraction ratio respectively of 0.4, 0.7 and 0.445. The RNG turbulence model ,VOF model of water vapor two-phase and iterative solution of geometry reconstruction format for unsteady flow has been applied to generate free surface. Velocity and pressure coupling method using PISO algorithm, with unsteady flow algorithm approaches stable solution of steady flow. And range from the upstream reservoir to downstream stilling basin. Comparatively analyze the experimental and simulation results of aeration cavity length, the two are basically in good agreement, and the maximum error is 10%. Therefore, the numerical simulation has a certain rationality and reliability. Simulation results show that aeration cavity length increased with the contraction ratio decreases, while the maximum negative pressure decreased, and more extensive distribution of negative pressure in stepped spillway.

The Achievement of Dynamic Load Simulator of Servo Mechanism of Multiple DOF Thrust Vector

2013 ◽  
Vol 457-458 ◽  
pp. 416-422
Author(s):  
Jia Song ◽  
Jin Ying Zhang ◽  
Meng Sun ◽  
Meng Sun
Keyword(s):  
Actual System ◽  
Thrust Vector Control ◽  
Servo Mechanism ◽  
Hydraulic Load ◽  
Thrust Vector ◽  
Output Load ◽  
Load Simulator ◽  
Simulation Results ◽  
Vector Control System ◽  
Resonant Characteristic

In order to better analyze the load resonant characteristic of thrust vector servo mechanism of spacecrafts, multiple DOF mathematical models were established. Combined with the need of simulated actual conditions for ground tests, a comprehensive load simulator containing mechanical and hydraulic load was presented. The simulation results show that, the dynamic characteristics of output load displacement of the simulator is in agreement with the characteristics of actual system. The simulation and experimental results verify the feasibility of this load simulator structure, which could provide design reference for developing equipment of thrust vector control system for ground tests.

Effect Factors of Flow Regenerated Noise from Muffler Unit with Simple Expansion

2013 ◽  
Vol 387 ◽  
pp. 323-327
Author(s):  
Hai Jun Zhao ◽  
Xing Guo Zhao ◽  
Guo Hua Wang
Keyword(s):  
Cavity Length ◽  
Velocity Structure ◽  
Design Method ◽  
Orthogonal Experiment ◽  
Expansion Ratio ◽  
Work Piece ◽  
Model Parameters ◽  
Structure Parameters ◽  
Effect Factors ◽  
Simple Expansion

Structure parameters of work piece on muffler unit with simple expansion are determined using orthogonal experiment design method, and relationship model of total sound power of flow regenerated noise and flow velocity structure parameters is built, and the model parameters are solved, and quantity study of effect factors for the noise is performed. Results show that inlet diameter and expansion cavity length have high effect on flow regeneration noise, the reducing of the inlet diameter and improving expansion cavity length is in favor of the reduction of flow regeneration noise from muffler unit with simple expansion, and expansion ratio has less influence on the noise, the reducing of the expansion ratio makes the regenerated noise become less down.

scholarly journals CFD Modeling and Simulation of Hydrodynamics in a Fluidized Bed Dryer with Experimental Validation

2011 ◽  
Vol 2011 ◽  
pp. 1-9 ◽  
Author(s):  
Mahdi Hamzehei
Keyword(s):  
Fluidized Bed ◽  
Fluid Dynamic ◽  
Expansion Ratio ◽  
Industrial Applications ◽  
Solid Particles ◽  
Cfd Modeling ◽  
Momentum Exchange ◽  
Fluidized Bed Dryer ◽  
Wide Range ◽  
Simulation Results

Gas-solid fluidized bed dryers are used in a wide range of industrial applications. With applying computational fluid dynamic (CFD) techniques, hydrodynamics of a two-dimensional nonreactive gas-solid fluidized bed dryer was investigated. A multifluid Eulerian model incorporating the kinetic theory for solid particles was applied to simulate the unsteady state behavior of this dryer and momentum exchange coefficients were calculated by using the Syamlal-O'Brien drag functions. A suitable numerical method that employed finite volume method was used to discretize the equations. Simulation results also indicated that small bubbles were produced at the bottom of the bed. These bubbles collided with each other as they moved upwards forming larger bubbles. Also, solid particles diameter and superficial gas velocity effect on hydrodynamics were studied. Simulation results were compared with the experimental data in order to validate the CFD model. Pressure drops and bed expansion ratio as well as the qualitative gas-solid flow patterns predicted by the simulations were in good agreement with experimental measurements at superficial gas velocities higher than the minimum fluidization velocity. Furthermore, this comparison showed that the model can predict hydrodynamic behavior of gas solid fluidized bed reasonably well.

scholarly journals Performance Improvement of a Low-Power Wind Turbine Using Conical Sections

Energies ◽  
2021 ◽  
Vol 14 (17) ◽  
pp. 5233
Author(s):  
Janesh N. Mohanan ◽  
Kumaravel Sundaramoorthy ◽  
Ashok Sankaran
Keyword(s):  
Wind Turbine ◽  
Maximum Velocity ◽  
Divergence Angle ◽  
Velocity Variation ◽  
Small Scale ◽  
Empirical Equations ◽  
Simulation Data ◽  
Ansys Fluent ◽  
Convergence Angle ◽  
Power Variation

This paper examines the performance of conical sections (concentrator and diffuser) to improve the energy-recovery prospects of small-scale wind turbines. Detailed simulation studies of the conical sections with convergence angle viz., concentrator, and divergence angle viz., diffuser were conducted using ANSYS Fluent® software. Using simulation data, a trend analysis was conducted, and the empirical equations were derived for calculating the velocity variation and power variation in terms of the convergence/divergence angles. Working prototype models with optimum angles were fabricated for both the diffuser and concentrator. These models were then augmented with a wind turbine coupled with a 100 W, 24 V DC generator and tested to validate the simulation results. Upon analyzing the simulation data, it was found that a maximum velocity variation of 23.3% was achieved at an angle of 4.5° for the diffuser, whereas a maximum power variation of 65.1% was achieved at an angle of 3.6° for the same diffuser. The aforementioned improvement was achieved by optimizing divergence angle alone. The proposed designs of the diffuser- and concentrator-augmented wind turbine, as well as the empirical equations for calculating the velocity variation and power variation in terms of the divergence and convergence angle, are the major contributions of this article.

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