Comparisons of DES and LES Turbulent Model for Simulation of Surface Ship Airwake

2016 ◽  
Author(s):  
Congmin Li ◽  
Weijian Jiang ◽  
Jie Cheng ◽  
Zongxin Yu ◽  
Zhiguo Zhang
Keyword(s):  
Experimental Measurement ◽  
Measurement Data ◽  
Separated Flow ◽  
Flow Region ◽  
Turbulent Model ◽  
Ship Model ◽  
Surface Ship ◽  
Simulation Results ◽  
Turbulent Models ◽  
Computational Resources

Due to the combination of the forward speed and the prevailing wind for surface ship traveling in the ocean, the airflow passing over the ship’s superstructure causes the formation of a disturbed flow region and the large speed gradients of the mean wind over the flight deck, known as the ship airwake. This airwake would cause significant influence on the performance of the helicopter rotor during its taking off or landing, increase the operation workload of the pilot and even cause safe-landing issues, especially when the wind sweeps over the deck. This paper presents a numerical simulation of flow across the ship superstructure using DES and LES turbulent model. The ship model used for simulation is the standard SF2 surface ship model with experimental measurement data which could be used for the CFD code validation. The simulation results are compared with the experimental measurement data, and the comparison with experimental results shows good match for both DES and LES turbulent models. Simulation results show that a series of vortex had been generated after the flow separation with asymmetric characteristics. From upstream to downstream, the vortex intensity decreases, but suddenly increases after encountering the chimney. The comparison between DES and LES turbulent models shows the similar flow field and vortex structure around the ship superstructure with same grid sets. Both DES and LES are superior to RANS in solving ship airwake. The comparisons of DES and LES turbulent models show that DES can reflect the separated flow with limited computational resource and LES simulation could get higher resolution of the fluid flow structure with enough computational resources.

Numerical Study of the Gas Flow in the Swirl Tube

2012 ◽  
Vol 550-553 ◽  
pp. 3194-3200
Author(s):  
Guang Cai Gao ◽  
Jian Jun Wang ◽  
You Hai Jin
Keyword(s):  
Numerical Simulation ◽  
Flow Field ◽  
Reynolds Stress ◽  
Experimental Measurement ◽  
Gas Flow ◽  
Numerical Study ◽  
Separation Performance ◽  
Turbulent Model ◽  
Simulation Results ◽  
Good Agreement

The gas flow field in the swirl tube was studied by experimental measurement and numerical simulation. The results show that the simulation results based on the Reynolds stress turbulent model is in good agreement with the measured results probed by the five orifice Pitot-tube. Meantime, it is analyzed that there is short cut stream at the end of the exit tube, and at the dust discharge jaws, the particles are prone to be re-entrained from the hopper. All results above provide a base for further research on the optimization of the structure and the improvement of the separation performance of the swirl tube.

scholarly journals Modeling of German Low Voltage Cables with Ground Return Path

Energies ◽  
2021 ◽  
Vol 14 (5) ◽  
pp. 1265 ◽  
Author(s):  
Johanna Geis-Schroer ◽  
Sebastian Hubschneider ◽  
Lukas Held ◽  
Frederik Gielnik ◽  
Michael Armbruster ◽  
...  
Keyword(s):  
Low Voltage ◽  
Measurement Data ◽  
Analytical Calculation ◽  
Laboratory Measurement ◽  
Model Parameters ◽  
Calculation Methods ◽  
Modeling Approach ◽  
Measurement Results ◽  
Simulation Results ◽  
Return Path

In this contribution, measurement data of phase, neutral, and ground currents from real low voltage (LV) feeders in Germany is presented and analyzed. The data obtained is used to review and evaluate common modeling approaches for LV systems. An alternative modeling approach for detailed cable and ground modeling, which allows for the consideration of typical German LV earthing conditions and asymmetrical cable design, is proposed. Further, analytical calculation methods for model parameters are described and compared to laboratory measurement results of real LV cables. The models are then evaluated in terms of parameter sensitivity and parameter relevance, focusing on the influence of conventionally performed simplifications, such as neglecting house junction cables, shunt admittances, or temperature dependencies. By comparing measurement data from a real LV feeder to simulation results, the proposed modeling approach is validated.

scholarly journals Modification of Airflow Structure Due to Wave Breaking on a Submerged Topography

2021 ◽  
Author(s):  
Petter Vollestad ◽  
Atle Jensen
Keyword(s):  
Wind Wave ◽  
Separated Flow ◽  
Flow Region ◽  
Breaking Waves ◽  
Leeward Side ◽  
Geometrical Properties ◽  
Image Velocimetry ◽  
Wind Profiles ◽  
The Waves ◽  
Sheltered Area

AbstractExperimental results from a combined wind–wave tank are presented. Wind profiles and resulting wind–wave spectra are described, and an investigation of the airflow above breaking waves is presented. Monochromatic waves created by the wave maker are directed towards a submerged topography. This causes the waves to break at a predictable location, facilitating particle-image-velocimetry measurements of the airflow above steep breaking and non-breaking waves. We analyze how the breaking state modifies the airflow structure, and in particular the extent of the sheltered area on the leeward side of the waves. Results illustrate that while the geometrical properties of the waves greatly influence the airflow structure on the leeward side of the waves, the state of breaking (i.e., whether the waves are currently in a state of active breaking) is not observed to have a clear effect on the extent of the separated flow region, or on the velocity distribution within the sheltered region.

scholarly journals Modified Vector Field Path-Following Control System for an Underactuated Autonomous Surface Ship Modelin the Presence of Static Obstacles

2021 ◽  
Vol 9 (6) ◽  
pp. 652
Author(s):  
Haitong Xu ◽  
Miguel A. Hinostroza ◽  
C. Guedes Guedes Soares
Keyword(s):  
Control System ◽  
Vector Field ◽  
Path Following ◽  
Field Method ◽  
Integrated System ◽  
Ship Model ◽  
Surface Ship ◽  
Path Following Control ◽  
Exponentially Stable ◽  
Vector Field Method

A modified path-following control system using the vector field method for an underactuated autonomous surface ship model is proposed in the presence of static obstacles. With this integrated system, autonomous ships are capable of following the predefined path, while avoiding the obstacles automatically. It is different from the methods in most published papers, which usually study path-following and obstacle collision avoidance, separately. This paper considers the coupled path following and collision avoidance task as a whole. Meanwhile, the paper also shows the heading control design method in the presence of static obstacles. To obtain a strong stability property, a nonlinear autopilot is designed based on the manoeuvring tests of the free-running ship model. The equilibrium point of the controller is globally exponentially stable. For the guidance system, a novel vector field method was proposed, and the proof shows the coupled guidance and control system is uniform semi-global exponentially stable (USGES). To prevent the obstacles near the predefined path, the proposed guidance law is augmented by integrating the repelling field of obstacles so that it can control the ship travel toward the predefined path through the obstacles safely. The repelling field function is given considering the obstacle shape and collision risk using the velocity obstacle (VO) algorithm. The simulations and ship model test were performed to validate the integrated system of autonomous ships.

The Effect of Different Turbulence Models on the Emitter Discharge by Using Computational Fluid Dynamics

2013 ◽  
Vol 662 ◽  
pp. 586-590
Author(s):  
Gang Lu ◽  
Qing Song Yan ◽  
Bai Ping Lu ◽  
Shuai Xu ◽  
Kang Li
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Flow Field ◽  
Turbulence Models ◽  
Experimental Results ◽  
Turbulent Model ◽  
Simulation Results ◽  
Rsm Model ◽  
Dynamics Method ◽  
Emitter Discharge

Four types of Super Typhoon drip emitter with trapezoidal channel were selected out for the investigation of the flow field of the channel, and the CFD (Computational Fluid Dynamics) method was applied to simulate the micro-field inside the channel. The simulation results showed that the emitter discharge of different turbulent model is 4%-14% bigger than that of the experimental results, the average discharge deviation of κ-ω and RSM model is 5, 4.5 respectively, but the solving efficiency of the κ-ω model is obviously higher than that of the RSM model.

A Numerical and Experimental Investigation of Turbulent Heat Transport Downstream From an Abrupt Pipe Expansion

1983 ◽  
Vol 105 (4) ◽  
pp. 862-869 ◽  
Author(s):  
R. S. Amano ◽  
M. K. Jensen ◽  
P. Goel
Keyword(s):  
Heat Transfer ◽  
Numerical Solutions ◽  
Numerical Study ◽  
Separated Flow ◽  
Flow Region ◽  
Reynolds Numbers ◽  
Turbulent Heat ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Pipe Expansion

An experimental and numerical study is reported on heat transfer in the separated flow region created by an abrupt circular pipe expansion. Heat transfer coefficients were measured along the pipe wall downstream from an expansion for three different expansion ratios of d/D = 0.195, 0.391, and 0.586 for Reynolds numbers ranging from 104 to 1.5 × 105. The results are compared with the numerical solutions obtained with the k ∼ ε turbulence model. In this computation a new finite difference scheme is developed which shows several advantages over the ordinary hybrid scheme. The study also covers the derivation of a new wall function model. Generally good agreement between the measured and the computed results is shown.

scholarly journals Mechatronic Device for Locomotor Training

2016 ◽  
Vol 10 (4) ◽  
pp. 310-315 ◽  
Author(s):  
Sławomir Duda ◽  
Damian Gąsiorek ◽  
Grzegorz Gembalczyk ◽  
Sławomir Kciuk ◽  
Arkadiusz Mężyk
Keyword(s):  
Experimental Data ◽  
Numerical Simulation ◽  
Measurement Data ◽  
Healthy Person ◽  
Control Algorithms ◽  
Design Team ◽  
Locomotor Training ◽  
Interdisciplinary Design ◽  
Machine Control ◽  
Simulation Results

Abstract This paper presents a novel mechatronic device to support a gait reeducation process. The conceptual works were done by the interdisciplinary design team. This collaboration allowed to perform a device that would connect the current findings in the fields of biomechanics and mechatronics. In the first part of the article shown a construction of the device which is based on the structure of an overhead travelling crane. The rest of the article contains the issues related to machine control system. In the prototype, the control of drive system is conducted by means of two RT-DAC4/PCI real time cards connected with a signal conditioning interface. Authors present the developed control algorithms and optimization process of the controller settings values. The summary contains a comparison of some numerical simulation results and experimental data from the sensors mounted on the device. The measurement data were obtained during the gait of a healthy person.

scholarly journals Slit Wall Effect on the Stability of Wavy Vortex Flow

2014 ◽  
Vol 6 ◽  
pp. 853069 ◽  
Author(s):  
Dong Liu ◽  
Ying-ze Wang ◽  
Hyoung-Bum Kim ◽  
Fang-neng Zhu ◽  
Chun-lin Wang
Keyword(s):  
Numerical Simulation ◽  
Flow Field ◽  
Radial Velocity ◽  
Flow Regime ◽  
Experimental Measurement ◽  
Vortex Flow ◽  
Wall Effect ◽  
Taylor Vortices ◽  
Simulation Results ◽  
The Stability

The wavy vortex flow in the plain model was studied by experimental measurement; the preliminary feature of wavy vortex flow was obtained. This flow field in the plain model was also studied by numerical simulation. The reliability of numerical simulation was verified by comparing with the experimental and numerical simulation results. To study the slit wall effect on the wavy vortex flow regime, another two models with different slit number were considered; the slit number was 6 and 12. By comparing the wavy vortex flow field in different models, the axial fluctuation of Taylor vortices was found to be different, which was increased with the increasing of slit number. The maximum radial velocity from the inner cylinder to the outer one in the 6-slit number was increased by 12.7% compared to that of plain model. From the results of different circumferential position in the same slit model, it can be found that the maximum radial velocity in slit plane is significantly greater than that in other planes. The size of Taylor vortices in different models was also calculated, which was found to be increased in the 6-slit model but was not changed as the slit number increased further.

Time-Dependent Laminar Backward-Facing Step Flow in a Two-Dimensional Duct

1988 ◽  
Vol 110 (3) ◽  
pp. 289-296 ◽  
Author(s):  
F. Durst ◽  
J. C. F. Pereira
Keyword(s):  
Reynolds Number ◽  
Steady State ◽  
Separated Flow ◽  
Flow Region ◽  
Reynolds Numbers ◽  
Steady State Flow ◽  
Backward Facing Step ◽  
Step Flow ◽  
Recirculating Flow ◽  
State Flow

This paper presents results of numerical studies of the impulsively starting backward-facing step flow with the step being mounted in a plane, two-dimensional duct. Results are presented for Reynolds numbers of Re = 10; 368 and 648 and for the last two Reynolds numbers comparisons are given between experimental and numerical results obtained for the final steady state flow conditions. In the computational scheme, the convective terms in the momentum equations are approximated by a 13-point quadratic upstream weighted finite-difference scheme and a fully implicit first order forward differencing scheme is used to discretize the temporal derivatives. The computations show that for the higher Reynolds numbers, the flow starts to separate on the lower and upper corners of the step yielding two disconnected recirculating flow regions for some time after the flow has been impulsively started. As time progresses, these two separated flow regions connect up and a single recirculating flow region emerges. This separated flow region stays attached to the step, grows in size and approaches, for the time t → ∞, the dimensions measured and predicted for the separation region for steady laminar backward-facing flow. For the Reynolds number Re = 10 the separation starts at the bottom of the backward-facing step and the separation region enlarges with time until the steady state flow pattern is reached. At the channel wall opposite to the step and for Reynolds number Re = 368, a separated flow region is observed and it is shown to occur for some finite time period of the developing, impulsively started backward-facing step flow. Its dimensions change with time and reduce to zero before the steady state flow pattern is reached. For the higher Reynolds number Re = 648, the secondary separated flow region opposite to the wall is also present and it is shown to remain present for t → ∞. Two kinds of the inlet conditions were considered; the inlet mean flow was assumed to be constant in a first study and was assumed to increase with time in a second one. The predicted flow field for t → ∞ turned out to be identical for both cases. They were also identical to the flow field predicted for steady, backward-facing step flow using the same numerical grid as for the time-dependent predictions.

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