Investigation of High-Frequency Separation Control Mechanisms for Delay of Unsteady Separation

2016 ◽  
Author(s):  
Stuart I. Benton ◽  
Miguel Visbal
Keyword(s):  
High Frequency ◽  
Frequency Separation ◽  
Separation Control ◽  
Control Mechanisms ◽  
Unsteady Separation

scholarly journals Kepler eclipsing binaries with δ Scuti components and tidally induced heartbeat stars

2015 ◽  
Vol 11 (A29B) ◽  
pp. 648-652
Author(s):  
Zhao Guo ◽  
Douglas R. Gies ◽  
Rachel A. Matson
Keyword(s):  
Binary Stars ◽  
High Frequency ◽  
Eclipsing Binaries ◽  
Frequency Separation ◽  
High Frequency Oscillations ◽  
Orbital Frequency ◽  
Scuti Stars ◽  
Large Frequency ◽  
Δ Scuti Stars ◽  
Stellar Density

Abstractδ Scuti stars are generally fast rotators and their pulsations are not in the asymptotic regime, so the interpretation of their pulsation spectra is a very difficult task. Binary stars, especially eclipsing systems, offer us the opportunity to constrain the space of fundamental stellar parameters. Firstly, we show the results of KIC9851944 and KIC4851217 as two case studies. We found the signature of the large frequency separation in the pulsational spectrum of both stars. The observed mean stellar density and the large frequency separation obey the linear relation in the log-log space as found by Suarez et al. (2014) and García Hernández et al. (2015). Second, we apply the simple ‘one-layer model’ of Moreno & Koenigsberger (1999) to the prototype heartbeat star KOI-54. The model naturally reproduces the tidally induced high frequency oscillations and their frequencies are very close to the observed frequency at 90 and 91 times the orbital frequency.

scholarly journals Interpretation of Four Unique Phenomena and the Mechanism in Unsteady Flow Separation Controls

Energies ◽  
2019 ◽  
Vol 12 (4) ◽  
pp. 587 ◽  
Author(s):  
Weiyu Lu ◽  
Guoping Huang ◽  
Jinchun Wang ◽  
Yuxuan Yang
Keyword(s):  
Numerical Simulation ◽  
Unsteady Flow ◽  
Flow Control ◽  
Flow Separation ◽  
Flow Instability ◽  
Control Flow ◽  
Separation Control ◽  
Pulsed Jet ◽  
Unsteady Separation ◽  
Flow Theories

Unsteady flow separation controls are effective in suppressing flow separations. However, the unique phenomena in unsteady separation control, including frequency-dependent, threshold, location-dependent, and lock-on effects, are not fully understood. Furthermore, the mechanism of the effectiveness that lies in unsteady flow controls remains unclear. Thus, this study aims to interpret further the unique phenomena and mechanism in unsteady flow separation controls. First, numerical simulation and some experimental results of a separated curved diffuser using pulsed jet flow control are discussed to show the four unique phenomena. Second, the bases of unsteady flow control, flow instability, and free shear flow theories are introduced to elucidate the unique phenomena and mechanism in unsteady flow separation controls. Subsequently, with the support of these theories, the unique phenomena of unsteady flow control are interpreted, and the mechanisms hidden in the phenomena are revealed.

Numerical simulation of active separation control by a synthetic jet

2007 ◽  
Vol 574 ◽  
pp. 25-58 ◽  
Author(s):  
JULIEN DANDOIS ◽  
ERIC GARNIER ◽  
PIERRE SAGAUT
Keyword(s):  
Numerical Simulation ◽  
High Frequency ◽  
Velocity Ratio ◽  
Low Frequency ◽  
Separated Flow ◽  
Synthetic Jet ◽  
Frequency Separation ◽  
Frequency Effect ◽  
Stream Velocity ◽  
Mean Velocity

Direct numerical simulation (DNS) and large-eddy simulation (LES) are carried out to investigate the frequency effect of zero-net-mass-flux forcing (synthetic jet) on a generic separated flow. The selected test case is a rounded ramp at a Reynolds number based on the step height of 28 275. The incoming boundary layer is fully turbulent withRθ=1410. The whole flow in the synthetic jet cavity is computed to ensure an accurate description of the actuator effect on the flow field. In a first step, DNS is used to validate LES of this particular flow. In a second step, the effect of a synthetic jet at two reduced frequencies of 0.5 and 4 (based on the separation length of the uncontrolled case and the free-stream velocity) is investigated using LES. It is demonstrated that, with a proper choice of the oscillating frequency, separation can be drastically reduced for a velocity ratio between the jet and the flow lower than one. The low frequency is close to the natural vortex shedding frequency. Two different modes of the synthetic jet have been identified. Avorticity-dominated modeis observed in the low-frequency forcing case for which the separation length is reduced by 54%, while anacoustic-dominated modeis identified in the high-frequency forcing case for which the separation length is increased by 43%. The decrease of the separation length in the low-frequency forcing case is correlated with an increase of the turbulent kinetic energy level and consequently with an increase of the entrainment in the separated zone. A linear inviscid stability analysis shows that the increase of the separation length in the high-frequency forcing case is due to a modification of the mean velocity profile suggested by Stanek and coworkers. The result is a lower amplification of the perturbations and consequently, a lower entrainment into the mixing layer. To our knowledge, it is the first time that Stanek's hypothesis has been assessed, thanks to numerical simulations of fully turbulent flow.

NARX modelling of unsteady separation control

2013 ◽  
Vol 54 (2) ◽  
Author(s):  
J. Dandois ◽  
E. Garnier ◽  
P.-Y. Pamart
Keyword(s):  
Separation Control ◽  
Unsteady Separation

scholarly journals The persistence of balance in geophysical flows

2007 ◽  
Vol 570 ◽  
pp. 365-383 ◽  
Author(s):  
DAVID G. DRITSCHEL ◽  
ÁLVARO VIÚDEZ
Keyword(s):  
Gravity Waves ◽  
Acoustic Waves ◽  
High Frequency ◽  
Vertical Motion ◽  
Geophysical Flows ◽  
Frequency Separation ◽  
Planetary Rotation ◽  
Highly Nonlinear ◽  
Flow Evolution ◽  
Nonlinear Flows

Rotating stably stratified geophysical flows can exhibit a near ‘balanced’ evolution controlled by the conservative advection of a single scalar quantity, the potential vorticity (PV). This occurs frequently in the Earth's atmosphere and oceans where motions tend to be weak compared with the background planetary rotation and where stratification greatly inhibits vertical motion. Under these circumstances, both high-frequency acoustic waves and lower-frequency inertia–gravity waves (IGWs) contribute little to the flow evolution compared with the even-lower-frequency advection of PV. Moreover, this ‘slow’ PV-controlled balanced evolution appears unable to excite these higher-frequency waves in any significant way – i.e. balance persists.The present work pushes the limits of balance by systematically exploring the evolution of a range of highly nonlinear flows in which motions are comparable with the background rotation. These flows do not possess a frequency separation between PV advection and IGWs. Nonetheless, the flows exhibit a remarkable persistence of balance. Even when flows are not initialized to minimize the amount of IGWs initially present, and indeed even when flows are deliberately seeded with significant IGW amplitudes, the flow evolution – over many inertial periods (days) – remains strongly controlled by PV advection.

Functional restitution of cardiac control in heart transplant patients

2002 ◽  
Vol 282 (3) ◽  
pp. R900-R908 ◽  
Author(s):  
Eran Toledo ◽  
Itzhak Pinhas ◽  
Dan Aravot ◽  
Yael Almog ◽  
Solange Akselrod
Keyword(s):  
High Frequency ◽  
Sinoatrial Node ◽  
Control Group ◽  
Control Mechanisms ◽  
Very High Frequency ◽  
Transplant Patients ◽  
Cardiac Control ◽  
Principal Finding ◽  
Noninvasive Characterization ◽  
The Time Domain

Cardiovascular control is fundamentally altered after heart transplantation (HT) because of surgical denervation of the heart. The main goal of this work was the noninvasive characterization of cardiac rate control mechanisms after HT and the understanding of their nature. We obtained 25 recordings from 13 male HT patients [age = 28–68 yr, time after transplant (TAT) = 0.5–62.5 mo]. The control group included 14 healthy men (age = 28–59 yr). Electrocardiogram, continuous blood pressure (BP), and respiration were recorded for 45 min in the supine position and then during active change of posture (CP) to standing. The signals were analyzed in the time domain [mean and variance of heart rate (HR) and rise time of HR in response to CP] and the frequency domain [low and high frequency (LF and HF)]. Our principal finding was the consistent pattern of evolution of the HR response to standing: from no response, via a slow response (>40 s, TAT > 6 wk), to a fast increase (<20 s, TAT > 24 mo). HR response correlated with TAT ( P < 0.001). LF correlated with HR response to CP ( P < 0.0001); HF and HR did not. An important finding was the presence of very-high-frequency peaks in the power spectrum of HR and BP fluctuations. Extensive arrhythmias tended to appear at the TAT that corresponds to the transition from slow to fast HR response to CP. Our results indicate a biphasic evolution in cardiac control mechanisms from lack of control to a first-order control loop followed by partial sympathetic reinnervation and, finally, the direct effect of the old sinoatrial node on the pacemaker cell of the new sinoatrial node. There was no indication of vagal reinnervation.

Physiology and topography of neurons with multipeaked tuning curves in cat primary auditory cortex

1991 ◽  
Vol 65 (5) ◽  
pp. 1207-1226 ◽  
Author(s):  
M. L. Sutter ◽  
C. E. Schreiner
Keyword(s):  
High Resolution ◽  
Auditory Cortex ◽  
High Frequency ◽  
Primary Auditory Cortex ◽  
Frequency Separation ◽  
Similar Response ◽  
Dorsal Part ◽  
Response Latencies ◽  
Tuning Curves ◽  
Frequency Peak

1. The physiology and topography of single neuron responses along the isofrequency domain of the middle- and high-frequency portions [characteristic frequencies (CFs) greater than 4 kHz] of the primary auditory cortex (AI) were investigated in the barbiturate-anesthetized cat. Single neurons were recorded at several locations along the extent of isofrequency contours, defined from initial multiple-unit mapping. For each neuron a high-resolution excitatory tuning curve was determined, and for some neurons high-resolution two-tone tuning curves were recorded to measure inhibitory/suppressive areas. 2. A physiologically distinct population of neurons was found in the dorsal part of cat AI. These neurons exhibited two or three distinct excitatory frequency ranges, whereas most neurons in AI responded with excitation to a single narrow frequency range. These were called multipeaked neurons because of the shape of their tuning curves. At frequencies between the excitatory regions, the multipeaked neurons were inhibited or unresponsive. 3. Multipeaked neurons exhibited several distinct threshold minima in their frequency tuning curves. Most of the multipeaked neurons (88%) displayed two frequency minima, whereas the rest exhibited three minima. 4. The frequency separation between threshold minima was less than 1 octave in 71% of the double-peaked neurons recorded. Occasionally, the frequency peaks of these neurons closely corresponded to a response to second and third harmonics without a response to the fundamental frequency. 5. Multipeaked neurons exhibited a wide range of total bandwidths (highest excitatory frequency minus lowest excitatory frequency expressed in octaves). Bandwidths of the isolated peaks within the same neuron were also quite variable. 6. Response latencies to tones with frequencies within each peak of a multipeaked neuron could vary considerably. In 71% (17) of the neurons, tones corresponding to the high-frequency peak (CFh) elicited a longer response latency (greater than 4 ms) than those corresponding to the low-frequency peak (CF1). 7. Inhibitory/suppressive bands, as demonstrated with a two-tone paradigm, were often present between the peaks. Typically, neurons with excitatory peaks of similar response latencies showed an inhibitory band located between the peaks. 8. Ninety percent of the topographically localized multipeaked neurons were in the dorsal part of AI (greater than 1 mm dorsal to the maximum in the sharpness-of-tuning map). Although these neurons were restricted to dorsal AI, only 35% of neurons in this region were multipeaked. 9. Multipeaked neurons could show decreased response latencies and thresholds to two-tone combinations.(ABSTRACT TRUNCATED AT 400 WORDS)

Unsteady Separation Control on Wind Turbine Blades using Fluidic Oscillators

AIAA Journal ◽  
2010 ◽  
Vol 48 (7) ◽  
pp. 1302-1311 ◽  
Author(s):  
Ciro Cerretelli ◽  
Werner Wuerz ◽  
Emad Gharaibah
Keyword(s):  
Wind Turbine ◽  
Turbine Blades ◽  
Separation Control ◽  
Wind Turbine Blades ◽  
Unsteady Separation

Synchronous Rhythmical Vasomotion in the Human Cutaneous Microvasculature during Nonpulsatile Cardiopulmonary Bypass

2002 ◽  
Vol 97 (5) ◽  
pp. 1110-1117 ◽  
Author(s):  
Mihai V. Podgoreanu ◽  
Robert G. Stout ◽  
Habib E. El-Moalem ◽  
David G. Silverman
Keyword(s):  
Cardiopulmonary Bypass ◽  
High Frequency ◽  
Spectral Power ◽  
Low Frequency ◽  
Approximate Entropy ◽  
Laser Doppler ◽  
Control Mechanisms ◽  
Laser Doppler Flow ◽  
Doppler Flow ◽  
Normalized Units

Background The origin, control mechanisms, and functional significance of oscillations in microvascular flow are incompletely understood. Although the traditional belief has been that only low-frequency oscillations (0.04-0.10 Hz) can originate at the microvascular level, recent evidence in healthy volunteers has suggested that high-frequency oscillations (&gt; 0.10 Hz) also may have a microvascular origin (as opposed to being mechanically transmitted respiratory-induced variations in stroke volume). The current study determined if such oscillations would emerge in the absence of cardiac and respiratory activity during nonpulsatile cardiopulmonary bypass (NP-CPB). Methods Forehead and finger laser Doppler flow, arterial pressure, and core temperature were simultaneously recorded in eight patients during NP-CPB. Analyses included time- domain indices, frequency-domain indices (auto power spectral density), and a measure of regularity (approximate entropy) for standardized time segments. Results Nonpulsatile cardiopulmonary bypass was associated with the emergence of rhythmical oscillations in laser Doppler flow, with characteristic frequencies for the forehead (0.13 +/- 0.03 Hz) and finger (0.07 +/- 0.02 Hz). Forehead vasomotion became progressively synchronized, with a gain in high-frequency spectral power from 17.5 (minute 1) to 89.1 (minute 40) normalized units, and a decrease in approximate entropy from 1.2 (before NP-CPB) to less than 0.5 (minute 40). Conclusions The emergence of forehead microvascular oscillations at greater than 0.10 Hz (characteristic of parasympathetic frequency response), in the absence of cardiac and respiratory variability, demonstrates their peripheral origin and provides insights into parasympathetic vasoregulatory mechanisms. The progressive synchronization of forehead vasomotion during NP-CPB, suggestive of increased coupling among microvascular biologic oscillators, may represent a microcirculatory homeostatic response to systemic depulsation, with potential implications for end-organ perfusion.

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