Buzz Onset Research Articles

On the mechanism of transonic buzz passive suppression with global stability analysis

The control surface buzz may occur when the aircraft cruise at transonic Mach numbers, which would may lead to flight accidents. Transonic buzz could be a problem in aircraft design. The triggering of transonic buzz has been investigated in the previous publications. It is essentially a single degree of freedom flutter caused by the coupling of one structural mode and one pre-instability flow mode, thus, type A/B buzz usually occurs close to the buffet onset. With this mechanism, the buzz can be suppressed by improving the flow stability and buffet onset. Three buffet passive control techniques are applied to test the suppression effect on transonic buzz. The relationship between the flow stability and buzz onset is studied to verify the mechanism of buzz. CFD simulation and global stability analysis are applied to compute the flow stability with and without control techniques. Results show that, three control techniques can improve the flow stability and postpone the buffet onset. Meanwhile the buzz can be effectively suppressed. With the aeroelastic ROM and the root loci method, the coupling process between the structural mode and the controlled flow modes are revealed, indicating the buzz suppression effects are positively correlated with its improvement of the flow stability with control. This study can help to understand the mechanism of buzz deeply and propose the new thought of buzz suppression.

Source of buzz instability in a supersonic air inlet

An axisymmetric supersonic inlet is computationally studied at a freestream Mach number of 2.0. The Reynolds-Averaged Navier-Stokes (RANS) equations are solved in an unsteady state and the SST k-ω turbulence model is used in this study. Several throttling ratios have been set to study the inlet flow field from supercritical to subcritical conditions, including little buzz and big buzz. Recently, studies have been about the new reasons for the buzz initiation beyond the accepted buzz criteria. The primary purpose of the current research is to discover the source of the buzz phenomenon in a supersonic inlet by examining the Ferri and Dailey criteria, which are the main criteria for predicting the buzz onset. The results showed that the low-speed flow above the vortex sheet, generated due to the intersection of the conical shock with normal shock, and the flow separation near the cowl lip are the main reasons for the buzz onset in the current inlet. To further study the source of buzz instability, the boundary layer suction was used on the cowl surface to investigate its effects on the buzz onset. According to the results, the bleed can remarkably postpone the buzz phenomenon and increase the last stable throttling ratio of the inlet from 65.0% to 77.5%. Furthermore, the big buzz at the throttling ratio of 80.0% is converted to the little buzz and the inlet performance is significantly improved after applying the bleed.

Impact of Aerodynamic and Structural Parameters on Control Surface Buzz

A frequency-domain linearized Euler solver is employed to perform aeroelastic analysis for predicting the control surface buzz onset condition. The predictive capability of the linearized Euler solver for control surface buzz is verified by comparing the predicted onset buzz Mach numbers with wind tunnel data of the National Aerospace Plane flutter model. Using a generic fighter wing as the test bed, a parametric study is performed to investigate the impact of aerodynamic and structural parameters on control surface buzz. These parameters include angle of attack, hinge line sweep angle, airfoil camber, hinge stiffness, and control surface mass. The results of this parametric study suggest that the empirical buzz avoidance criterion used by aerospace industry to avert the buzz problem is oversimplified and should be revised.

Effects of boundary-layer bleed parameters on supersonic intake buzz

Extensive wind tunnel tests were conducted to study effects of the location, entrance slant angle, entrance width, and type (slot or porous) of boundary layer bleed on the buzz phenomenon in a supersonic air intake. The intake was a mixed-compression axisymmetric intake for the design Mach number of 2.0 that was studied at zero degrees angle of attack at three free stream Mach numbers of 1.8, 2.0, and 2.2 through shadowgraph visualization system and pressure recordings. For every free stream Mach number and bleed geometry, eight different back pressures were examined. Results showed that the bleed can significantly postpone the buzz onset and increase the stability range of the intake. The bleed location was the most effective parameter among the examined parameters of the bleed system. According to the results, the bleed restricts the domain of shock oscillations to downstream of the bleed entrance and consequently, it increases the frequency of buzz as compared with the no-bleed case. In addition, the slot bleed is more effective in stabilizing the intake flow field than the porous bleed.

Effects of bleed type on the performance of a supersonic intake

An extensive experimental investigation was conducted to reveal the effects of the porous and slot bleeds on the performance and flow control in a supersonic intake. The experiments were conducted on a supersonic intake at the design freestream Mach number of 2.0 and extended to the off-design Mach numbers of 1.8 and 2.2, all at the angle of attack of zero degrees. For every freestream Mach number, eight back pressures were examined, where a total of twenty-four cases were studied. It was found that the slot bleed may degrade the total pressure recovery of the intake, while employing the porous bleed leads to the enhancement of the total pressure recovery. Moreover, the bleed mass flow rate is smaller for the porous bleed and it leads to the lower flow distortion as compared with the slot bleed. However, the slot bleed is more powerful in postponing the buzz onset.

Prediction of the onset of supersonic inlet buzz

A computational fluid dynamics (CFD) simulation was conducted about the onset of supersonic inlet buzz. Then, a novel mathematical model for the onset was proposed with the aid of the CFD results. The simulation was conducted using a common approach in industrial applications, in which unsteady Reynolds-averaged Navier-Stokes equations with millions of computational grids were used. The numerical results were validated with the experimental data obtained from a wind tunnel test, in which the flow around an external-compression inlet model at a Mach number of 2.0 was tested. The inlet model consists of a wedge for the generation of an oblique shock wave, a subsonic diffuser with a rectangular cross-section for deceleration of the captured flow, and a flow plug for constriction of the exit of the diffuser. Both the numerical and experimental results show that the onset of buzz correlated well with the position of the shock wave triple point (STP), which means that the onset is closely related to the mass flux through the diffuser. The critical position of the STP for the occurrence of buzz was well predicted by this simulation. Therefore, the balance of the mass in the rear part of the diffuser was modeled. The modeling indicates that this system can be represented using a delay differential equation containing a delayed negative feedback due to the pressure waves propagating in the diffuser. The presence of this feedback mechanism is the origin of the self-sustained oscillation of the buzz. The analysis shows that the onset and frequency of the inlet buzz are well predicted using the derived equation. In general, the onset of buzz is characterized using three parameters: the sensitivities of mass flow rates into/out of the part to its mass and the time lag of changes between the inflow rate and the mass.

Supersonic inlet buzz detection using pressure measurement on wind tunnel wall

Feasibility of an innovative buzz detection technique through measuring the static pressure outside a mixed-compression supersonic inlet is studied. The buzz is an instability phenomenon that occurs almost in all supersonic inlets. During the buzz, shock oscillation along with pressure and mass flow fluctuations affects the performance characteristics of the inlet. The main objective of this paper is to introduce a simple and easy-to-implement method for investigation of the buzz phenomenon in a supersonic inlet. The experimental data for far field-based are compared with those of the model-based one at free stream Mach numbers of 1.8, 2.0, and 2.2 and at zero degrees angle of attack for a mixed-compression inlet. The results show that this technique can measure exact value of buzz frequency as well as its onset. The present method uses pressure data obtained from the wind-tunnel wall instead of measuring the pressure inside or on the model surfaces which in most cases is very hard. However, to sense flow oscillations, caused by the buzz onset the sensors on the wind-tunnel wall must be located downstream of the point where the oblique shock from the spike impinges on the tunnel wall. The location of the measurement point as well as the distance between the sensor and the origin of the shock wave system are very important.

Throttling Process and Buzz Mechanism of a Supersonic Inlet at Overspeed Mode

A rectangular external-compression supersonic inlet with a shock-on-lip Mach number of 2.0 is carefully studied at a freestream Mach number of 2.5. In the throttling process before the onset of buzz, the interaction between the ramp shock and the cowl-induced bow shock appears as regular reflection, Mach reflection, and λ-shaped pattern successively. It is interestingly found that the currently observed Mach reflection, which should have been broken down shortly after the emergence as reported previously, keeps fairly stable until the throttling ratio changes. In the remaining buzz stage, three types of instabilities of similar frequencies but of different oscillating behaviors and amplitudes are observed. The term medium buzz is adopted to describe the special buzz phenomenon with moderate oscillations. It is shown that both the little buzz and big buzz are characterized by the separation oscillation, whereas the medium buzz features the oscillation of the cowl-induced bow shock. Further analysis indicates that all three buzz phenomena probably share a common origin (i.e., the ramp-side flow separation). Also, it is demonstrated that the transition of buzz flows in the throttling process is attributed to the changes of disturbance strength and dominant role between two feedback loops.

Image analyses of supersonic air-intake buzz and control by natural ventilation

Intake buzz was initiated on a typical two-dimensional supersonic air-intake model at various supersonic Mach numbers up to 3 by gradually changing the back pressure from supercritical to subcritical operating condition in a wind tunnel. Schlieren pictures from a still camera and a high-speed camera were recorded. Analyses of individual high-speed images of the unvented intake were carried out to locate the time-dependent positions and velocities of the ramp shock around the cowl lip. The displacements of the shock indicate sinusoidal oscillations with dominant frequency of 102.4 Hz, close to that obtained from unsteady pressure measurements. Phase trajectories of shock position based on image analyses indicate that the shock oscillations have limit cycle type oscillation, typical of nonlinear dynamic systems. Natural ventilation of the intake was found to be extremely effective in increasing the total pressure recovery, suppress buzz oscillations and in delaying the onset of buzz by preventing the upstream propagation of disturbances through passive bleeding of the internal boundary layer.

Effects of Bleed Position on the Stability of a Supersonic Inlet

Effects of various boundary-layer bleed locations on the stability of an axisymmetric supersonic inlet has been investigated experimentally. The bleeds were located on the inlet compression cone and were designed to improve the stability margin of the inlet. The main objective of the study was to identify the boundary-layer bleed location and its effects on the improvement of the stability margin of the inlet. In addition, a buzz precursor detection methodology based on the rms level has been introduced. Experiments have been carried out on a mixed-compression inlet with a design Mach number of 2.0 and three different bleed locations at three freestream Mach numbers of 1.8, 2.0, and 2.2. All tests were conducted at an angle of attack of 0 deg. The results show that, based on the individual design of an inlet, a location can be found that the spilled normal shock stands at this location and consequently separation starts at the buzz onset. If the bleed slot is located in this place, the subcritical performance and stability margin of the inlet can be enhanced.

Buzz Cycle Description in an Axisymmetric Mixed-Compression Air Intake

Buzz phenomenon is shock oscillation ahead of the supersonic air intake when its mass flow rate is decreasing at off-design condition. The buzz onset and the buzz cycle of an axisymmetric mixed-compression supersonic intake have been experimentally investigated through pressure recording and shadowgraph flow visualization. The intake was designed for a freestream Mach number of 2.0; however, tests were conducted for , 2.0, and 2.2. All tests were performed at 0 deg angle of attack. Results show that there is a strong relation between the acoustic characteristics of the intake and the buzz fluctuations. This relation causes a new pattern for the buzz oscillations, large-amplitude oscillations with large frequency, that has features of both little buzz (Ferri-type instability) and big buzz (Dailey-type instability). Flow separation caused by the shock-wave/boundary-layer interaction and acoustic compression waves are the most important driving mechanisms in the buzz cycle. Both amplitude and frequency of the buzz oscillations vary as the backpressure is varied. As the freestream Mach number is increased, the dominant frequency of the buzz oscillations is decreased.

Flow in a Y-Intake at Supersonic Speeds

Numerical simulation of the flow in a twin intake via solution to unsteady viscous compressible equations using a stabilized finite-element method has been carried out for various sideslip angles and backpressure ratios. Various flow regimes that are possible in the entire parameter space are identified. They are classified on the basis of shock structure and their locations and the unsteadiness in the flow. Buzz instability is observed in the intake at low system mass rates for nonzero sideslip angles. The onset of buzz is identified by zero mass flow rate in the leeward duct. It is associated with asymmetric movement of the bow shocks upstream of the duct entry. The onset of buzz is accompanied with a loss in static and total pressure recovery and increase in flow distortion. The effect of initial condition is studied. The flow in a certain regime is sensitive to the time history of the backpressure. Hysteresis in the flow as well as in the onset of buzz are observed. The effect of bleed is studied. The amount of bleed and the regions on which it is applied are varied to understand their effect on the performance of the intake. The onset of buzz is delayed with application of bleed.

Effects of Boundary-Layer Bleed Parameters on Supersonic Intake Performance

The performance and the buzz onset of a supersonic mixed-compression axisymmetric intake are experimentally investigated. Effects of the slot bleed position, angle, and width on the intake performance and on the buzz initiation at three different Mach numbers of 1.8, 2.0, and 2.2 and at a zero degree angle of attack are studied. The intake performance is assessed using the total pressure recovery, mass flow ratio, flow distortion, and bleed mass flow ratio. The results show that applying the bleed at a position near the intake entrance and reducing the bleed entrance slant angle and width all improve the intake performance considerably. Moreover, these parameters postpone the buzz onset. In addition, it is found that the vertical position of the intersection point of the barrier and normal shocks plays an important role in the intake pressure recovery.

Immediate and punitive impact of mechanosensory disturbance on olfactory behaviour of larval Drosophila.

ABSTRACTThe ability to respond to and to learn about mechanosensory disturbance is widespread among animals. Using Drosophila larvae, we describe how the frequency of mechanosensory disturbance (‘buzz’) affects three aspects of behaviour: free locomotion, innate olfactory preference, and potency as a punishment. We report that (i) during 2–3 seconds after buzz onset the larvae slowed down and then turned, arguably to escape this situation; this was seen for buzz frequencies of 10, 100, and 1000 Hz, (ii) innate olfactory preference was reduced when tested in the presence of the buzz; this effect was strongest for the 100 Hz frequency, (iii) after odour-buzz associative training, we observed escape from the buzz-associated odour; this effect was apparent for 10 and 100, but not for 1000 Hz. We discuss the multiple behavioural effects of mechanosensation and stress that the immediate effects on locomotion and the impact as punishment differ in their frequency-dependence. Similar dissociations between immediate, reflexive behavioural effects and reinforcement potency were previously reported for sweet, salty and bitter tastants. It should be interesting to see how these features map onto the organization of sensory, ascending pathways.

Time-Frequency Analysis and Detection of Supersonic Inlet Buzz

Supersonic inlet buzz and, in particular, its onset were studied through the analysis of pressure records. These records are issued from an experimental study that was presented in a previous paper. The onset of buzz is a nonstationary phenomenon, and so the pressure signals could not be analyzed using classical signal-processing tools such as the Fourier transform, which does not take into account the possible evolutions in time. That is why time-frequency methods (spectrogram, wavelet transform, and Wigner-Ville distribution) were used. The evolution in time of the energy levels corresponding to buzz frequencies were studied. This analysis shows the existence of precursor phenomena that can appear several tenths of seconds before the onset of buzz. The detection of these precursors could, with the appropriate activation of a control device, allow the avoidance of buzz. Two change-detection algorithms (cumulative sum and generalized likelihood ratio) were tested on experimental pressure signals and proved their ability to successfully detect these precursors.

마하 2.5 초음속 공기흡입구의 버즈 특성에 관한 연구

초음속 흡입구는 설계점에서 안정된 작동을 보이지만 탈설계점에서는 흔히 버즈라고 불리는 공력 불안정성에 직면하게 되고, 결과적으로 현저한 엔진 성능의 저하를 초래하게 된다. 버즈의 일반적인 특성을 파악하기 위해 1단 꺽임각을 갖는 외부 압축식 축대칭 흡입구를 이용하여 실험적, 수치적 연구를 수행하였다. 본 연구를 통해, 흡입구 목에서 박리에 의한 흡입구 질식이 버즈의 주요 원인임을 밝힘으로써 버즈 현상의 메커니즘을 파악하였다. 여러 면적비율에 따라 간헐적 버즈와 연속적 버즈가 관찰되었고 그 천이과정이 파악되었다. 면적비율이 감소할수록 버즈 주파수가 증가하였으나, 각 면적비율에서 흡입구 내 모든 위치의 압력 진동 주파수는 동일한 특성을 갖는다. off-design conditions, supersonic air inlets often encounter the problem of aerodynamic instability, called inlet buzz, which causes the significant degradation of the engine performance. An experimental and numerical study was conducted to investigate the phenomenon of supersonic inlet buzz on a generic, axisymmetric, external-compression inlet with a single-surface center-body. It is understood the mechanism of buzz onset as proving that the origin of buzz is the flow choking induced by separation at the intake throat. Also it is observed the intermittent and continuous buzz mode as area ratio varies and understood the transition process through this study. The buzz frequency become to be higher as decreasing the area ratio, but for each area ratio, the frequency of pressure oscillation is the same at all points of intake.

Perceptual cues to the onset of voiced excitation in aspirated initial stops.

Previous experiments on the perception of initial stops differing in voice-onset time have used sounds where the boundary between aspiration and voicing is clearly marked by a variety of acoustic events. In natural speech these events do not always occur at the same moment and there is disagreement among phoneticians as to which mark the onset of voicing. The three experiments described here examine how the phoneme boundary between syllable-initial, prestress /b/ and /p/ is influenced by the way in which voicing starts. In the first experiment the first 30 ms of buzz excitation is played at four different levels relative to the steady state of the vowel and with two different frequency distributions: In the F1-only conditions buzz is confined to the first formant, whereas in the F123 conditions all three formants are excited by buzz. The results reject the hypothesis that voicing is perceived to start when periodic excitation is present in the first formant. The results of the third experiment show also that buzz excitation confined to the fundamental frequency for 30 ms before the onset of full voicing (formant excitation) has little effect on the voicing boundary. The second experiment varies aspiration noise intensity and buzz onset intensity independently. Together with the first experiment it shows that: (1) at all buzz onset levels a change in aspiration intensity moves the boundary by about the 0.43 ms/dB found by Repp [Lang. Speech 27, 173-189 (1979)]; (2) when buzz onsets at levels greater than - 15 dB relative to the final vowel level, changes in buzz onset level again move the /b/-/p/ boundary by the same amount; (3) when buzz onsets at levels less than - 15 dB relative to the vowel, decreasing the buzz onset level gives more /p/- percepts than Repp's ratio predicts. This last result, taken with the results of the first experiment, may reflect a decision based on overall intensity about when voicing has started.

Nonmonotonic discrimination functions for temporal gaps in noise‐buzz sequences. II: Filtering affects the discrimination peaks

It has been reported [P. L. Divenyi and W. F. Danner, J. Acoust. Soc. Am. Suppl. 1 55, S31 (1975) and J. D. Miller et al., J. Acoust. Soc. Am. 60, 410–417 (1976)] that discrimination of the gap bounded by a brief, filtered noise burst and a longer,/a/‐like buzz is a nonmonotonic function of the gap duration, in a way similar to the well‐known nonmonotonicity of the VOT discrimination functions [A. S. Abramson and L. Lisker, Proc. 6th Int. Congr. Phonet. Sci., 569–573 (1970)]. Earlier, we reported that discriminability of the gap in such sequences is affected by passing the stimulus through 1/3‐octave filters and that the discrimination thresholds are correlated with the difference between noise and buzz intensity within the particular bands—i.e., With one of the main attributes of temporal masking. The present experiments extend the previous ones, in that the continuum of “buzz‐onset‐times” was explored in finer steps (10, 15, 20, 25, 30, 35, 40, 55, and 70 ms from noise onset to buzz onset). In addition to determining gap discrimination thresholds for the original, unfiltered stimulus, thresholds were also obtained at three filter settings (780, 1230, and 2550 Hz center frequencies). Three trained listeners participated. While the smallest thresholds at the 780 and 1230‐Hz filter settings occurred at the same gap duration as for the unfiltered stimulus (15 ms), the threshold minimum at the 2550‐Hz filter setting occurred at longer gap durations (20 and 25 ms). Implications of these results for variations in voicing category boundaries as well as for the possible role of listening bands in the perception of speech will be discussed. [Work supported by NIH Grant NS 16019 and by the Veterans Administration.]