Numerical Investigation of Turning Diffuser Performance by Varying Geometric and Operating Parameters

2012 ◽  
Vol 229-231 ◽  
pp. 2086-2093 ◽  
Author(s):  
Normayati Nordin ◽  
Vijay R. Raghavan ◽  
Safiah Othman ◽  
Zainal Ambri Abdul Karim
Keyword(s):  
Numerical Investigation ◽  
Turbulence Model ◽  
Transport Model ◽  
Turbulence Models ◽  
Reynolds Stress Model ◽  
Pressure Recovery ◽  
Maximum Pressure ◽  
Operating Parameters ◽  
Flow Uniformity ◽  
Outlet Pressure

This paper presents a numerical investigation of pressure recovery and flow uniformity in turning diffusers with 90o angle of turn by varying geometric and operating parameters. The geometric and operating parameters considered in this study are area ratio (AR= 1.6, 2.0 and 3.0) and inflow Reynolds number (Rein=23, 2.653E+04, 7.959E+04, 1.592E+05 and 2.123E+05). Three turbulence models, i.e. the standard k-e turbulence model (std k-e), the shear stress transport model (SST-k-W) and the Reynolds stress model (RSM) were assessed in terms of their applicability to simulate the actual cases. The standard k-e turbulence model appeared as the best validated model, with the percentage of deviation to the experimental being the least recorded. Results show that the outlet pressure recovery of a turning diffuser at specified Rein improves approximately 32% by varying the AR from 1.6 to 3.0. Whereas, by varying the Rein from 2.653E+04 to 2.123E+05, the outlet pressure recovery at specified AR turning diffuser improves of approximately 24%. The flow uniformity is considerably distorted with the increase of AR and Rein. Therefore, there should be a compromise between achieving the maximum pressure recovery and the maximum possible flow uniformity. The present work proposes the turning diffuser with AR=1.6 operated at Rein=2.653E+04 as the optimum set of parameters, producing pressure recovery of Cp=0.320 and flow uniformity of su=1.62, with minimal flow separation occurring in the system.

scholarly journals Numerical Investigation on Influence of Gas and Turbulence Model for Type III Hydrogen Tank under Discharge Condition

Energies ◽  
2020 ◽  
Vol 13 (23) ◽  
pp. 6432
Author(s):  
Moo-Sun Kim ◽  
Joon-Hyoung Ryu ◽  
Seung-Jun Oh ◽  
Jeong-Hyeon Yang ◽  
Sung-Woong Choi
Keyword(s):  
Turbulence Model ◽  
Turbulence Intensity ◽  
Gas Flow ◽  
Transport Model ◽  
Numerical Models ◽  
Turbulence Models ◽  
Reynolds Stress Model ◽  
Hydrogen Gas ◽  
Discharge Temperature ◽  
Compressed Gas

The high-pressure gaseous hydrogen (HPGH2) storage method is widely used owing to the low density of hydrogen gas at ambient temperature and atmospheric pressure. Therefore, rigorous safety analysis of the filling and discharging of compressed gas in a hydrogen tank is required to achieve reliable operational solutions for the safe storage of hydrogen. In this study, the behavior of compressed hydrogen gas in a hydrogen tank was investigated for its discharge. Numerical models for the adaptation of gas and turbulence models were examined. Gas model effects were examined to account for hydrogen gas behavior at the discharge temperature and pressure conditions. Turbulence model effects were analyzed to consider the accuracy of each model: the assessment of the turbulence models was compared in terms of the turbulence intensity. From the study of gas model effect, the Redlich–Kwong equation was found to be one of the realistic gas models of the discharging gas flow. Among the turbulence models, the shear stress transport model and Reynolds stress model predicted the compressed gas behavior more accurately, showing a lower turbulence intensity than those of the realizable and renormalization group models.

Sensitization of the SST Turbulence Model to Rotation and Curvature by Applying the Spalart–Shur Correction Term

2009 ◽  
Vol 131 (4) ◽  
Author(s):  
Pavel E. Smirnov ◽  
Florian R. Menter
Keyword(s):  
Turbulent Flows ◽  
Turbulence Model ◽  
Transport Model ◽  
Correction Term ◽  
Computational Cost ◽  
Turbulence Models ◽  
Reynolds Stress Transport Model ◽  
Wide Range ◽  
Sst Model ◽  
The One

A rotation-curvature correction suggested earlier by Spalart and Shur (1997, “On the Sensitization of Turbulence Models to Rotation and Curvature,” Aerosp. Sci. Technol., 1(5), pp. 297–302) for the one-equation Spalart–Allmaras turbulence model is adapted to the shear stress transport model. This new version of the model (SST-CC) has been extensively tested on a wide range of both wall-bounded and free shear turbulent flows with system rotation and/or streamline curvature. Predictions of the SST-CC model are compared with available experimental and direct numerical simulations (DNS) data, on the one hand, and with the corresponding results of the original SST model and advanced Reynolds stress transport model (RSM), on the other hand. It is found that in terms of accuracy the proposed model significantly improves the original SST model and is quite competitive with the RSM, whereas its computational cost is significantly less than that of the RSM.

Investigation of Annular Jet Flows in a Subsonic Air-Air Ejector With Multi-Ring Entraining Diffuser

2015 ◽  
Author(s):  
A. Namet-Allah ◽  
A. M. Birk
Keyword(s):  
Boundary Conditions ◽  
Turbulence Model ◽  
Nozzle Exit ◽  
Turbulence Models ◽  
Domain Size ◽  
Pressure Recovery ◽  
Cfd Simulations ◽  
The Core ◽  
Measured Flow ◽  
Air Ejector

The current paper presents a cold flow simulation study of a low Mach number air-air ejector with a four ring entraining diffuser that is used in a variety of applications including infrared (IR) suppression of exhaust from helicopters and fixed wing aircraft. The main objectives of this investigation were to identify key issues that must be addressed in successful CFD modelling of such devices, and recognize opportunities to improve the performance of these devices. Two-dimensional CFD simulations were carried out using commercial software, Ansys14. Studies of mesh and domain size sensitivity were made to ensure the CFD results were independent of both factors. A turbulence model independence study using k-ε, k-ω and RSM turbulence models was performed to figure out the appropriate turbulence model that produced the best agreement with the experimental data for several of ejector performance criteria. The measured flow properties in the annulus were used as input boundary conditions for the CFD simulations. However, in the comprehensive turbulence model study, the measured flow parameters at the nozzle exit were also applied as inlet boundary conditions for the CFD simulations. The measured flow velocity at the nozzle exit, at one centerline section inside the mixing tube and at the diffuser exit and the system pressure recovery were compared with the CFD predictions. The ejector pumping ratios, back pressure coefficient and diffuser gap velocities were also compared. It was found that the RANS-based CFD predictions were sensitive to the changes in the ejector domain size, mesh refinement and inlet boundary condition locations. With the annulus inlet boundary conditions, the tested turbulence models under predicted the size of the core separation downstream of the system, back pressure, pumping ratio and pressure recovery in the mixing tube and diffuser. However, the ability of the RNG turbulence model to predict the ejector performance parameters was better than that of the other turbulence models at all inlet flow conditions. Nevertheless, applying the inlet boundary conditions at the nozzle exit enhanced the capability of the RANS-based turbulence model particularly in predicting the ejector pumping ratios, pressure recovery and the size of the core separation. Finally, the acceptable agreement between the experimental data and the CFD predictions provides a valid tool to continue improving these devices using CFD techniques.

scholarly journals Numerical Investigation of the Trailing Edge Shape on the Added Damping of a Kaplan Turbine Runner

2021 ◽  
Vol 2021 ◽  
pp. 1-11
Author(s):  
Zhang Ming ◽  
P. A. Mbango-Ngoma ◽  
Du Xiao-zhen ◽  
Chen Qing-Guang
Keyword(s):  
Numerical Investigation ◽  
Turbulence Model ◽  
Turbulence Models ◽  
Hydraulic Turbine ◽  
Vibration Level ◽  
High Excitation ◽  
Trailing Edge ◽  
Kaplan Turbine ◽  
Turbine Runner ◽  
The One

Hydraulic turbine runners experience high excitation forces in their daily operations, and these excitations may cause resonances to runners, which may induce high vibrations and shorten the runner's lifetimes. Increasing the added damping of runners in water can be helpful to reduce the vibration level during resonances. Some studies have shown that the modification of the trailing edge shape can be helpful to increase added damping of hydrofoils in water. However, the influence of blade trailing edge shape on the added damping of hydraulic turbine runners has been studied in a limited way before. Due to the difficulties to study this problem experimentally, the influence of blade trailing edge shape on a Kaplan turbine runner has been studied numerically in this paper and the one-way FSI method was implemented. The performances of three different turbulence models, including the k − ϵ , k − ω   SST , and transition SST models, in the added damping simulation of the NACA 0009 hydrofoil were evaluated by comparing with the available results of the two-way FSI simulation in the references. Results show that, unlike the significantly different performances in the two-way FSI method, the performances of all the turbulence models are very close in the one-way FSI method. Then, the k − ϵ turbulence model was applied to the added damping simulation of a Kaplan turbine runner, and results show that the modification of the blade trailing edge shape can be helpful to increase the added damping to some extent.

scholarly journals Improving the methodology for calculation of energy losses in axial turbine cascades

2021 ◽  
pp. 104-109
Author(s):  
М.Ю. Левенталь ◽  
Ю.М. Погодин ◽  
Ю.Р. Миронов
Keyword(s):  
Standard Deviation ◽  
Turbulence Model ◽  
Empirical Model ◽  
Turbulence Models ◽  
Operating Parameters ◽  
Cfd Analysis ◽  
Sample Standard Deviation ◽  
Rans Model ◽  
Wide Range ◽  
Turbine Cascades

Представлена оценка неопределенности прогнозирования потерь энергии в решетках профилей осевых турбин. В сравнении с экспериментальными данными рассмотрены эмпирическая модель ЦИАМ и метод CFD анализа в рамках RANS модели. Геометрические и режимные параметры решеток профилей варьируются в широком диапазоне. Результаты CFD расчета отличаются существенно в зависимости от модели турбулентности. Наименьшая неопределенность получена для модели рейнольдсовых напряжений RSM. Определено выборочное стандартное относительное отклонение для анализируемой базы данных. Применительно к CFD расчету данное отклонение составило 18,6%, применительно к эмпирической модели ЦИАМ 46,4%. Разработана эмпирическая модель коррекции потерь полученных по результатам CFD анализа с моделью турбулентности RSM. Корректирующая функция включает в себя геометрические и режимные параметры решеток и особенности течения в межлопаточном канале (всего 14 параметров). Использование разработанного подхода позволило снизить неопределённость прогнозирования потерь в 2 раза. В результате работы выборочное стандартное относительное отклонение предсказания потерь для рассматриваемой базы решеток профилей составило 9,3%. Estimation of the uncertainty in predicting profile losses using various models was performed. In comparison with the experimental data, empirical model of CIAM and method of CFD analysis are considered. RANS models are used. The geometric and operating parameters of the analyzed turbine cascades vary over a wide range. Turbulence models strongly influence loss prediction uncertainty. The smallest uncertainty was obtained using the RSM turbulence model. The sample standard deviation for the considered turbine cascades base was determined. The deviation for CFD analysis is 18.6%. For the empirical model of CIAM the deviation is 46.4%. The new empirical model has been created to correct the results of calculating losses according to the RANS model using the RSM turbulence model. The corrective function takes into account the influence of the geometric and operating parameters of the turbine cascades and the features of the airfoil flow (14 parameters in total). The developed approach allows reducing the uncertainty in the estimation of losses according to the RANS model by 2 times. As a result, the sample standard deviation in the prediction of losses is 9.3% for the considered turbine cascades base.

Design and Analysis of Airfoil-Shaped Impeller Blades of Centrifugal Pump

2016 ◽  
Vol 852 ◽  
pp. 539-544
Author(s):  
Parth Shah ◽  
M. Ashwin Ganesh ◽  
Thundil Kuruppa Raj
Keyword(s):  
Centrifugal Pump ◽  
Transport Model ◽  
Turbulence Models ◽  
Suction Side ◽  
3D Analysis ◽  
Centrifugal Pumps ◽  
Pump Impeller ◽  
Outlet Pressure ◽  
Shear Stress Transport Model ◽  
Centrifugal Pump Impeller

This paper deals with a comparative study of the outlet pressure-energy between a conventional and normal blade impeller and an airfoil-shaped blade impeller of a centrifugal pump. Although the volute casing is an important component along with an impeller [1], the present comparative analysis makes the volute casing redundant to the study, hence neglected. All centrifugal pumps are usually designed and manufactured using backward swept blades with equal camber on the top and bottom sides. An increased camber on the top side is an ideal trait for a lift generating airfoil. The purpose is to implement the principle of lift generation of airfoil for centrifugal pumps. As a result, a local suction side and pressure side can be visualized using CFX-post processor. The 3D analysis of such a centrifugal pump impeller is designed in SOLIDWORKS® and analyzed using ANSYS® CFX. The SST (Menter’s Shear Stress Transport) model is used as it combines both the k-ω and k-ε turbulence models.

Numerical Investigation on a Stator Vane Bypass Transition Over a Separation Bubble Using v′2-f and LCL-Models

2006 ◽  
Author(s):  
Axel Heidecke ◽  
Bernd Stoffel
Keyword(s):  
Numerical Investigation ◽  
Turbulence Model ◽  
Separation Bubble ◽  
Turbulence Models ◽  
Suction Side ◽  
Navier Stokes ◽  
Stream Line ◽  
Bypass Transition ◽  
Mean Flow ◽  
Stator Vane

With this paper, results of a numerical investigation of the influence of the inlet condition variation on a stator vane suction side boundary layer and its separation tendencies are presented. The profile used for the examination is a so called high-lift-profile and designed for a laminar-turbulent transition over a steady separation bubble in a 1.5-stage low pressure turbine. Hence, the turbulence model must be capable for these effects. Especially, the stream line curvature has to be kept properly which leads to higher level turbulence models. The calculations were conducted with a two-dimensional Navier-Stokes solver using a finite volume discretisation scheme. The turbulence models used are the v′2-f and the LCL turbulence model which are both of higher order. In the first part of the paper, wake free averaged inflow conditions were used. Through this, the influence of the mean flow on the bubble could be examined.

Analysis of Unsteady Turbulent Merging Jet Flows With Temperature Difference

2002 ◽  
Author(s):  
Geun Jong Yoo ◽  
Won Dae Jeon
Keyword(s):  
Temperature Variation ◽  
Turbulent Flows ◽  
Turbulence Model ◽  
Flow Characteristics ◽  
Turbulence Models ◽  
Jet Flow ◽  
Reynolds Stress Model ◽  
Jet Flows ◽  
Test Cases ◽  
Temperature Variance

Suitable turbulence model is required in the course of establishing a proper analysis methodology for thermal stripping phenomena. For this purpose, three different turbulence models of k-ε model, modified k-ε model, and full Reynolds stress model and VLES are applied to analyze unsteady turbulent flows with temperature variation. Four test cases are selected for verification. These are vertical jet flows with water and sodium, parallel jet flow with sodium, and merging pipe flow through T-junction with sodium. The geometries of test cases well represent common places where thermal stripping might be occurred. The turbulence model computation shows overall jet flow characteristics well and good comparison of mean temperature distribution. Temperature variance (θ′2) is rather over-predicted, but location of high temperature variance is matched well with that of the large amplitude of temperature variation of experimental results. Meanwhile, mixing of hot and cold jet flow is found to be not that active.

Evaluation of RANS Approach in Predicting the Physics of Incompressible Turbulent Jets-Into-Crossflows

2007 ◽  
Author(s):  
Khodyar Javadi ◽  
Mohammad Taeibi-Rahni ◽  
Masoud Darbandi
Keyword(s):  
Large Scale ◽  
Transport Model ◽  
Three Dimensional ◽  
Turbulence Models ◽  
Simple Algorithm ◽  
Numerical Data ◽  
Turbulent Jets ◽  
Reynolds Stress Model ◽  
Shear Stress Transport Model ◽  
Near Wall

This work is conducted with evaluation of different turbulence models capabilities in predicting three dimensional jet-into-crossflow (JICF) interactions. For this purpose, first of all, comprehensive discussions on the near wall flow complexities due to discharge of a jet into a crossflow are presented. In this regards, large scale coherent structures such as: counter rotating vortex pairs (CRVP’s), near wall secondary motions, horseshoe vortices, and wall jets like are discussed. Secondly, the abilities of different turbulence models in predicting such flows (JICF) are evaluated. Our evaluation is based on three points of view including: 1) JICF characteristics, 2) computed location, and 3) sensitivity to different flow variables. In this regard, the turbulence models such as k-ε, k-ω, shear stress transport model (SST), and Reynolds stress model (RSM) are employed. Their related results are compared to credential available experimental/numerical data as well themselves. Since the same basic code with the same grid density as well as numerical discretization scheme is used, it is save to conclude that, any differences in the results are due to the abilities of turbulence models. The flow field computation was governed by Reynolds Averaged Navier-Stokes (RANS) equations performing finite volume method with SIMPLE algorithm over a non-uniform structured grid.

Two-dimensional numerical investigation of film cooling by a cool jet injected at various angles for different blowing ratios

2008 ◽  
Vol 222 (7) ◽  
pp. 1215-1224 ◽  
Author(s):  
S Bayraktar ◽  
T Yilmaz
Keyword(s):  
Experimental Data ◽  
Renormalization Group ◽  
Numerical Investigation ◽  
Turbulence Model ◽  
Film Cooling ◽  
Flow Characteristics ◽  
Turbulence Models ◽  
Cooling Efficiency ◽  
Two Dimensional ◽  
Transverse Jet

This paper presents the thermal and flow characteristics of a cold transverse jet, injected at five different angles (α = 30°, 45°, 60°, 75°, and 90°) into a hot crossflow with four different blowing ratios ( M = 0.1, 0.3, 0.5, and 0.8). Three turbulence models, namely, standard k−∊, renormalization group (RNG) k−∊, and realizable k−∊ are tested for obtaining the accurate turbulence model to predict the effectiveness of film cooling. The tested turbulence models were compared with available experimental data in the literature. The results evinced that the RNG k−∊ turbulence model is the most appropriate among the three. It is also observed that maximum cooling efficiency is obtained at α = 30° and M = 0.8.

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