Papers by Keyword: Turbulence

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Authors: Y.L. Liu, B. Lv, P. Zhang, W.L. Wei
Abstract: In this paper, we use 3D time-averaged equations and the 3D k-ε turbulence model to numerically simulate the flow in a horizontal sedimentation tank. The PISO algorithm is used to couple velocity and pressure. The results show that the model can provide a reference in designing sedimentation tanks.
Authors: Wen Li Wei, Pei Zhang, Yu Ling Liu
Abstract: In this paper, we use two-phase mixture model and the 3D Realizable k-ε turbulence model to numerically simulate the advection secondary turbulence flow in a circular secondary clarifier. The PISO algorithm is used to decouple velocity and pressure. The results show that the model can provide a reference in designing sedimentation tanks.
Authors: Karinate Valentine Okiy
Abstract: The turbulent airflow in a circular duct with sudden expansion was investigated utilizing three turbulence models. The turbulence models chosen are: the k-epsilon model, the shear stress transport model and the Reynolds-stress model. The performance of the models was investigated with respect to the flow parameter-recirculation length. The turbulent kinetic energy and velocity predictions were compared between the turbulence models and with experimental data, then interpreted on the basis of the recirculation length. From the results, the shear stress transport model predictions of recirculation length had the closest agreement with the experimental result compared to the other model. Likewise, the convergence rate for the shear stress transport model was reasonable compared to that of the Reynolds model which has the slowest convergence rate. In light of these findings, the shear stress transport model was discovered to be the most appropriate for the investigation of turbulent air flow in a circular duct with sudden expansion. Keywords: Turbulence, recirculation length, sudden expansion, Turbulence models.
Authors: Feng Ji, Xiao Jian Feng, Dong Liang Wang
Abstract: Traditional wind turbines are difficulty to work well in built-up areas due to wind conditions of low speed, turbulence and frequent changing direction. A long-term wind observation work has been done to understand the characteristics of urban wind by installing a small weather station on the balcony at top floor of a residential building. Based on the observation results, a new structure for low speed wind turbine in built-up areas was designed. This structure can be used for either horizontal axis wind turbine or vertical axis wind turbine. Some mesh models were established to simulate the effect through CFD software. In this structure, growth rate of wind velocity is about 1.25 times; wind turbulence converts to laminar; and yawing angel of turbine motor shafts neednt change any more. Prototype testing draws better conclusions: growth rate of wind velocity is more than 1.4 times. Therefore, traditional wind turbines can work well in built-up areas through this new structure.
Authors: Yan Hua Yang, Xiao Qiang Liu, Ming Jin Zhang
Abstract: In this paper, we adopt theoretical method to study the evolution characteristic of the two dimensional turbulent vortex structures in a meander channel. The disturbance growth rates under different bank curvatures are simulated. The result showed that the change of growth rate of smaller vortices is more intensive than bigger vortices. Future more, we consider the coherent vortex structure as a kind of disturbance to study the evolution characteristics of multi-scale turbulent structures in a meander channel, make basis for finding “meander channel-forming vortices” which is controlling the river shape and adapt to the meander river in theoretic.
Authors: Da Lei Song, Zhao Long Su, Yong Fang Wang, Li Ping Chen
Abstract: Considering the problem that vibration signals which are generated by three-axis accelerations will impact turbulence signal, an improved motion compensation algorithm based on discriminant analysis is proposed. The characteristics of three axis acceleration signals are got by using cross validation discriminant analysis method to test the performance of de-noising among different filtering orders which are got by three-axis accelerations vibration signals. Finally the discriminant function is found to get the optimal filter order. The results of simulation and real sea experiment data statistical analysis shows that the algorithm improves the de-noising performance and can be better applied to ocean turbulence signal de-noising processing.
Authors: Stanislav Pospíšil, Jiří Náprstek
Abstract: We study the response of a dynamic system to additive random noise and external determin- istic periodic force to investigate vibration of a slender prismatic beam in a cross flow with a turbulence component. The aim of the study is to find such parameter combinations, which should be avoided in practice to eliminate response amplitude increase due to the effect of the stochastic resonance. We assume the non-linear oscillator (beam) with one generalized degree of freedom in the divergence-like regime. It is described by the version of the Duffing equation. We conduct the theoretical investigation with the use of relevant Fokker-Planck equation together with verification by numerical simulation of corresponding stochastic differential system. Real characteristics of a sectional model, fixed in the special stand allowing the snap-through effect, in the wind tunnel are employed.
Authors: Thamy C. Hayashi, Isabel Malico, J.F.C. Pereira
Abstract: The influence of inserting ceramic foam in a pipe with a 1:4 sudden expansion was numerical investigated. The foam, with a thickness to diameter ratio of 0.60, was positioned at different distances from the sudden pipe expansion wall. Three different porosities were analyzed (10, 20 and 60 pores per inch) for pore Reynolds numbers in the range of 20-400, corresponding to pipe Reynolds numbers of 2400 to 22000 in the pipe section upstream the sudden expansion. Predictions of the sudden pipe expansion cavity assuming laminar flow within the foam yield the penetration of the separated flow region into the foam. Considering turbulent flow in the porous foam and the model of Pedras and Lemos [14] prevents this penetration. The numerical and physical models used could not reproduce completely the foam influence on the separated turbulent flow region between the sudden pipe expansion and the foam inlet.
Authors: Boualem Laribi, Abdellah Abdellah Hadj
Abstract: This article discusses the development and the establishment of turbulent flow downstream of disturbers like a valve 50% open, valve 70% open, Tee and 90° double bend in perpendicular planes. Associated with these disturbers, a perforated plate flow conditioner is installed to examine his performances to produce the fully developed pipe flow as suggested by standards ISO5167 and AGA3. The study focused mainly on the numerical analysis of the velocity contours at several axial stations downstream the disturbers. For the simulation, code CFD Fluent was used. The study of the disturbed flow is examined with three Reynolds numbers. The results show a very good prediction of the CFD code Fluent for the flow development downstream the disturbers and conditioner which makes the code very efficient for conception of a new flow conditioner not described by the standards. It was also found that the valve 50% open could be considered a reference disturber for analyzing the development of turbulent flows. As interesting results, is the effectiveness of the perforated plate to produce the flow developed pipe flow at about z/D=10 downstream the disturber. This result is very important for flow measurement accuracy as suggested by the standards. An experimental study is needed to validate these results.
Authors: Yong Li, Yan Ping Li, Ping Kong, Shu Yin Wei, Qian Zhang, Jian Jun Fang
Abstract: The new duster is used to remove the coal dust from the coal conveying system of thermal power plant. Many of plastic globules are filled into the duster. The water is sprayed from the upper of duster. The airflow of containing coal dust flows through the filler from bottom to top, and change to clean air. The application of the turbulent duster in the coal conveying system of the thermal power plant shows: the efficiency of dust collection is 99%. In particular, it can remove 67% of coal dust smaller than 5 microns. The duster adopts fully automatic control technology. The amount of water consumed is very low. It can be effectively used for coal conveying system of thermal power plant. After air purification with coal dust, the air quality meets the requirements of the health standard.
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