Partial Cavitation as Drag Reduction Technique and Problem of Active Flow Control

2003 ◽  
Vol 40 (03) ◽  
pp. 181-188
Author(s):  
Eduard Amromin ◽  
Igor Mizine
Keyword(s):  
Drag Reduction ◽  
Flow Control ◽  
Active Flow Control ◽  
Total Drag ◽  
Reduction Techniques ◽  
Partial Cavitation ◽  
Wide Range ◽  
Hull Design ◽  
Successful Employment ◽  
Active Flow

Partial cavitation can substantially reduce the ship total drag in a wide range of her speed. Vented partial cavitation manifested certain advantages in comparison with other drag reduction techniques. Its successful employment, however, requires both a special hull design and development of an active flow control system. Such a system will stabilize the cavity under perturbations of incoming flow in seas. The paper includes an analysis of achievements in drag reduction, description of design fundamentals of ships with cavitating hulls/elements, and suggestions on application of ship drag reduction by cavitation.

scholarly journals Reinforcement learning for bluff body active flow control in experiments and simulations

2020 ◽  
Vol 117 (42) ◽  
pp. 26091-26098
Author(s):  
Dixia Fan ◽  
Liu Yang ◽  
Zhicheng Wang ◽  
Michael S. Triantafyllou ◽  
George Em Karniadakis
Keyword(s):  
Reinforcement Learning ◽  
Fluid Mechanics ◽  
Drag Reduction ◽  
Flow Control ◽  
Bluff Body ◽  
Control Strategies ◽  
Active Flow Control ◽  
Reduction Process ◽  
Automatic Sequence ◽  
Active Flow

We have demonstrated the effectiveness of reinforcement learning (RL) in bluff body flow control problems both in experiments and simulations by automatically discovering active control strategies for drag reduction in turbulent flow. Specifically, we aimed to maximize the power gain efficiency by properly selecting the rotational speed of two small cylinders, located parallel to and downstream of the main cylinder. By properly defining rewards and designing noise reduction techniques, and after an automatic sequence of tens of towing experiments, the RL agent was shown to discover a control strategy that is comparable to the optimal strategy found through lengthy systematically planned control experiments. Subsequently, these results were verified by simulations that enabled us to gain insight into the physical mechanisms of the drag reduction process. While RL has been used effectively previously in idealized computer flow simulation studies, this study demonstrates its effectiveness in experimental fluid mechanics and verifies it by simulations, potentially paving the way for efficient exploration of additional active flow control strategies in other complex fluid mechanics applications.

scholarly journals Experimental and numerical results of active flow control on a highly loaded stator cascade

2011 ◽  
Vol 225 (7) ◽  
pp. 907-918 ◽  
Author(s):  
M Hecklau ◽  
C Gmelin ◽  
W Nitsche ◽  
F Thiele ◽  
A Huppertz ◽  
...  
Keyword(s):  
Flow Control ◽  
Active Flow Control ◽  
Numerical Results ◽  
Pressure Probe ◽  
Compressor Cascade ◽  
Time Resolved ◽  
Inlet Velocity ◽  
Wide Range ◽  
Active Flow ◽  
Highly Loaded

This article presents experimental and numerical results for a compressor cascade with active flow control. Steady and pulsed blowing has been used to control the secondary flow and separation characteristics of a highly loaded controlled diffusion airfoil. Investigations were performed at the design incidence for blowing ratios from approximately 0.7 to 3.0 (jet-to-inlet velocity) and a Reynolds number of 840 000 (based on axial chord and inlet velocity). Detailed flow field data were collected using a five-hole pressure probe, pressure taps on the blade surfaces, and time-resolved Particle Image Velocimetry. Unsteady Reynolds-averaged Navier–Stokes simulations were performed for a wide range of flow control parameters. The experimental and numerical results are used to understand the interaction between the jet and the passage flow. The benefit of the flow control on the cascade performance is weighted against the costs of the actuation by introducing an efficiency which takes the presence of the jets into account.

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