Role of low-bandwidth open-loop control of combustion instability using a high-momentum air jet—mechanistic details

2006 ◽  
Vol 147 (1-2) ◽  
pp. 22-31 ◽  
Author(s):  
J UHM ◽  
S ACHARYA
Keyword(s):  
Combustion Instability ◽  
Open Loop ◽  
High Momentum ◽  
Open Loop Control ◽  
Loop Control ◽  
Air Jet

Open Loop Control of Combustion Instability With a High-Momentum Air-Jet

2004 ◽  
Author(s):  
Jong Ho Uhm ◽  
Sumanta Acharya
Keyword(s):  
Low Frequency ◽  
Sine Wave ◽  
Open Loop ◽  
Effective Control ◽  
High Momentum ◽  
Open Loop Control ◽  
Low Frequencies ◽  
Loop Control ◽  
Wave Modulation ◽  
Air Jet

A new strategy for open-loop control of combustion oscillations using a high-momentum air-jet modulated at low frequencies is presented in this paper. The oscillations in the swirl-stabilized spray combustor of interest are dominated by an acoustic mode (235 Hz) with a low frequency (13 Hz) bulkmode (of the upstream cavity) oscillation superimposed. The most effective strategy for control is shown to be achieved through the use of a new concept which utilizes a high-momentum air-jet injected directly into the region of flame dynamics. It is shown that with a low frequency modulation (15 Hz) of the high momentum air-jet, the pressure oscillations can be reduced significantly (by a factor of nearly 10). Square wave modulation is shown to be considerably more effective than sine-wave modulation. These results are extremely promising since high bandwidth actuation is not required for effective control.

Assessing the Role of Vergence Changes in the Perception of Random-Dot Stereograms by Using Open-Loop Control of Vergence

Perception ◽  
1996 ◽  
Vol 25 (1_suppl) ◽  
pp. 131-131 ◽  
Author(s):  
B J Rogers ◽  
M F Bradshaw
Keyword(s):  
Open Loop ◽  
Open Loop Control ◽  
Complex Surfaces ◽  
Loop Control ◽  
Random Dot Stereograms ◽  
Disparity Range ◽  
The Difference ◽  
Random Dot Stereogram ◽  
University Of Chicago Press

The fact that the 3-D shape of surfaces depicted by random dot stereograms can take several seconds or even tens of seconds to appear has been attributed to the failure to make appropriate vergence changes [B Julesz, 1971 Foundations of Cyclopean Perception (Chicago, IL: University of Chicago Press)]. Alternatively, the long latencies could be a consequence of the processing time needed to match the disparate images. To distinguish between these possibilities we measured perceptual latencies in a situation in which vergence changes had no effect on retinal disparities. To do this, horizontal eye movements were recorded with the aid of close-fitting scleral search coils in both eyes and the difference signal used to shift horizontally the two halves of a random-dot stereogram by equal and opposite amounts. When the amount of shift was equal to the magnitude of the vergence change, changes of vergence had no effect on the pattern of disparities—open-loop vergence. Three observers were presented with a sequence of stereograms depicting both ‘simple’ surfaces (a single square lying in front of the surround) and ‘complex’ surfaces, including spirals, ‘wedding cakes’, and saddle shapes under both normal and open-loop conditions. Under open-loop conditions, the complete 3-D shape was never perceived when the disparity range of the stereogram was large (>40 min arc), demonstrating the necessity of vergence changes, but the 3-D structure of ‘complex’ surfaces did build up over a period of several seconds indicating a separate disparity processing limitation.

Low-bandwidth open-loop control of combustion instability

2005 ◽  
Vol 142 (4) ◽  
pp. 348-363 ◽  
Author(s):  
Jong Ho Uhm ◽  
Sumanta Acharya
Keyword(s):  
Combustion Instability ◽  
Open Loop ◽  
Open Loop Control ◽  
Loop Control

Open-loop control of compensation for optical propagation through a turbulent shear flow

1998 ◽  
Author(s):  
C. Truman ◽  
Lenore McMackin ◽  
Robert Pierson ◽  
Kenneth Bishop ◽  
Ellen Chen
Keyword(s):  
Shear Flow ◽  
Open Loop ◽  
Turbulent Shear ◽  
Turbulent Shear Flow ◽  
Open Loop Control ◽  
Loop Control ◽  
Optical Propagation

Precise open-loop control of MEMS deformable mirror shape

2008 ◽  
Author(s):  
Thomas Bifano ◽  
Jason Stewart ◽  
Alioune Diouf
Keyword(s):  
Open Loop ◽  
Deformable Mirror ◽  
Open Loop Control ◽  
Loop Control

Active Control of Combustion Instability Using Symmetric and Asymmetric Premix Fuel Modulation

2007 ◽  
Author(s):  
Daniel Guyot ◽  
Christian Oliver Paschereit
Keyword(s):  
Heat Release ◽  
Closed Loop ◽  
Modulation Frequency ◽  
Combustion Instability ◽  
Open Loop ◽  
Closed Loop Control ◽  
Nox Emissions ◽  
Loop Control ◽  
Asymmetric Modulation ◽  
Control Schemes

Active instability control was applied to an atmospheric swirl-stabilized premixed combustor using open loop and closed loop control schemes. Actuation was realised by two on-off valves allowing for symmetric and asymmetric modulation of the premix fuel flow while maintaining constant time averaged overall fuel mass flow. Pressure and heat release fluctuations in the combustor as well as NOx, CO and CO2 emissions in the exhaust were recorded. In the open loop circuit the heat release response of the flame was first investigated during stable combustion. For symmetric fuel modulation the dominant frequency in the heat release response was the modulation frequency, while for asymmetric modulation it was its first harmonic. In stable open loop control a reduction of NOx emissions due to fuel modulation of up to 19% was recorded. In the closed loop mode phase-shift control was applied while triggering the valves at the dominant oscillation frequency as well as at its second subharmonic. Both, open and closed loop control schemes were able to successfully control a low-frequency combustion instability, while showing only a small increase in NOx emissions compared to, for example, secondary fuel modulation. Using premixed open loop fuel modulation, attenuation was best when modulating the fuel at frequencies different from the dominant instability frequency and its subharmonic. The performance of asymmetric fuel modulation was generally slightly better than for symmetric modulation in terms of suppression levels as well as emissions. Suppression of the instability’s pressure rms level of up to 15.7 dB was recorded.

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