EXPERIMENTAL STUDY OF INFLUENCE OF ACTIVE METHODS OF FLOW CONTROL ON THE FLOW FIELD PAST A CYLINDER

2009 ◽  
Vol 16 (4) ◽  
pp. 353-366 ◽  
Author(s):  
Milan Matejka ◽  
Petr Pick ◽  
Jiri Nozicka ◽  
Pavel Prochazka
Keyword(s):  
Experimental Study ◽  
Flow Field ◽  
Flow Control

Experimental Study of Turbulent Macroinstabilities in an Agitated System with Axial High-Speed Impeller and with Radial Baffles

1996 ◽  
Vol 61 (6) ◽  
pp. 856-867 ◽  
Author(s):  
Oldřich Brůha ◽  
Ivan Fořt ◽  
Pavel Smolka ◽  
Milan Jahoda
Keyword(s):  
Experimental Study ◽  
Flow Field ◽  
High Speed ◽  
Experimental Results ◽  
Turbulent Regime ◽  
Frequency Of Occurrence ◽  
Visualization Method ◽  
Entire Flow

The frequency of turbulent macroinstability occurrence was measured in liquids agitated in a cylindrical baffled vessel. As it has been proved by preceding experimental results of the authors, the stochastic quantity with frequency of occurrence of 10-1 to 100 s-1 is concerned. By suitable choosing the viscosity of liquids and frequency of impeller revolutins, the region of Reynolds mixing numbers was covered from the pure laminar up to fully developed turbulent regime. In addition to the equipment making it possible to record automatically the macroinstability occurrence, also the visualization method and videorecording were employed. It enabled us to describe in more detail the form of entire flow field in the agitated system and its behaviour in connection with the macroinstability occurrence. It follows from the experiments made that under turbulent regime of flow of agitated liquids the frequency of turbulent macroinstability occurrence is the same as the frequency of the primary circulation of agitated liquid.

Flow Control for an Airfoil with Leading-Edge Rotation: An Experimental Study

2000 ◽  
Vol 37 (4) ◽  
pp. 617-622 ◽  
Author(s):  
Ahmed Z. Al-Garni ◽  
Abdullah M. Al-Garni ◽  
Saad A. Ahmed ◽  
Ahmet Z. Sahin
Keyword(s):  
Experimental Study ◽  
Flow Control ◽  
Leading Edge

scholarly journals Model-Based Analysis of Flow Separation Control in a Curved Diffuser by a Vibration Wall

Energies ◽  
2021 ◽  
Vol 14 (6) ◽  
pp. 1781
Author(s):  
Weiyu Lu ◽  
Xin Fu ◽  
Jinchun Wang ◽  
Yuanchi Zou
Keyword(s):  
Flow Field ◽  
Flow Control ◽  
Flow Separation ◽  
Vibration Frequency ◽  
Flow Instability ◽  
Control Technique ◽  
Simplified Model ◽  
Main Stream ◽  
Control Performance ◽  
Flow Separation Control

Vibration wall control is an important active flow control technique studied by many researchers. Although current researches have shown that the control performance is greatly affected by the frequency and amplitude of the vibration wall, the mechanism hiding behind the phenomena is still not clear, due to the complex interaction between the vibration wall and flow separation. To reveal the control mechanism of vibration walls, we propose a simplified model to help us understand the interaction between the forced excitation (from the vibration wall) and self-excitation (from flow instability). The simplified model can explain vibration wall flow control behaviors obtained by numerical simulation, which show that the control performance will be optimized at a certain reduced vibration frequency or amplitude. Also, it is shown by the analysis of maximal Lyapunov exponents that the vibration wall is able to change the flow field from a disordered one into an ordered one. Consistent with these phenomena and bringing more physical insight, the simplified model implies that the tuned vibration frequency and amplitude will lock in the unsteady flow separation, promote momentum transfer from the main stream to the separation zone, and make the flow field more orderly and less chaotic, resulting in a reduction of flow loss.

Experimental Investigations on the Efficiency of Active Flow Control in a Compressor Cascade With Periodic Non-Steady Outflow Conditions

2017 ◽  
Author(s):  
Marcel Staats ◽  
Wolfgang Nitsche
Keyword(s):  
Flow Field ◽  
Flow Control ◽  
Flow Separation ◽  
Active Flow Control ◽  
Experimental Investigations ◽  
Compressor Cascade ◽  
Steady Regime ◽  
Stator Blade ◽  
Active Flow ◽  
The Impact

We present results of experiments on a periodically unsteady compressor stator flow of the type which would be expected in consequence of pulsed combustion. A Reynolds number of Re = 600000 was used for the investigations. The experiments were conducted on the two-dimensional low-speed compressor testing facility in Berlin. A choking device downstream the trailing edges induced a periodic non-steady outflow condition to each stator vane which simulated the impact of a pressure gaining combuster downstream from the last stator. The Strouhal number of the periodic disturbance was Sr = 0.03 w.r.t. the stator chord length. Due to the periodic non-steady outflow condition, the flow-field suffers from periodic flow separation phenomena, which were managed by means of active flow control. In our case, active control of the corner separation was applied using fluidic actuators based on the principle of fluidic amplification. The flow separation on the centre region of the stator blade was suppressed by means of a fluidic blade actuator leading to an overall time-averaged loss reduction of 11.5%, increasing the static pressure recovery by 6.8% while operating in the non-steady regime. Pressure measurements on the stator blade and the wake as well as PIV data proved the beneficial effect of the active flow control application to the flow field and the improvement of the compressor characteristics. The actuation efficiency was evaluated by two figures of merit introduced in this contribution.

scholarly journals Improvement of Pump Performance at Off-Design Conditions

1985 ◽  
Author(s):  
J. Paulon ◽  
C. Fradin ◽  
J. Poulain
Keyword(s):  
Experimental Study ◽  
Flow Field ◽  
Mass Flow ◽  
Flow Characteristic ◽  
Three Dimensional ◽  
Operating Conditions ◽  
Pump Performance ◽  
Wide Range ◽  
Mass Flows ◽  
Design Value

Industrial pumps are generally used in a wide range of operating conditions from almost zero mass flow to mass flows larger than the design value. It has been often noted that the head-mass flow characteristic, at constant speed, presents a negative bump as the mass flow is somewhat smaller than the design mass flows. Flow and mechanical instabilities appear, which are unsafe for the facility. An experimental study has been undertaken in order to analyze and if possible to palliate these difficulties. A detailed flow analyzis has shown strong three dimensional effects and flow separations. From this better knowledge of the flow field, a particular device was designed and a strong attenuation of the negative bump was obtained.

scholarly journals 1110 Experimental study of the flow field generated by periodic agitator wings

2001 ◽  
Vol 2001 (0) ◽  
pp. 154
Author(s):  
Norio Tori ◽  
Hideharu MAKITA ◽  
Nobumasa SEKISHITA
Keyword(s):  
Experimental Study ◽  
Flow Field
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