Buzz Phenomenon Research Articles

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.

Menelisik Fenomena Online Buzz pada IPO Saham Teknologi

In recent years, the initial public offerings of technology companies on the Indonesia Stock Exchange have drawn great interest of investors. However, difficulties arise in assessing the valuation of a relatively new company, hence retail investors may turn to other fundamental factors such as sales growth and issuing size with online media become a source of information and forum for discussions. These online activities are increasing ahead of the IPO, causing a high online buzz phenomenon. This study aims to examine the effect of sales growth, issuing size and online buzz on technology stock underpricing. Using path analysis techniques on a sample of 23 technology stocks that conducted IPOs between 2000 – 2022, this research found that higher issuing size will generate higher online buzz. However, this study unable to find evidence of significant relationship between sales growth on online buzz, online buzz on underpricing and issuing size on underpricing. The limited sample in this study can be used as a consideration for further research opportunities on IPO in other sectors with larger population. It is also interesting to conduct both quantitative and qualitative study on online buzz in various market conditions to enrich the literature on company IPOs.

Nonlinear damping model for supersonic air-intake buzz

Air-intake buzz was initiated at Mach number of 3.0 on a two-dimensional isolated air-intake model in a wind tunnel by throttling the exit area. Schlieren images of shock oscillation around the intake entry during buzz were recorded using a high-speed camera. The recordings show a strong coupling between the bow-shock at the cowl lip and the oblique shock from the ramp. Image analyses were carried out, considering each image as a matrix of pixels and the change of intensity of light analyzed. A dominant frequency of 103.8 Hz (Strouhal no = 0.008 based on throat height) associated with the shock oscillations and harmonics of the shock oscillations are indicated. Phase-plots of the intensity and the rate of change of intensity show nearly perfect ellipse after filtering at the dominant frequency. Thus, the buzz phenomenon is associated with a limit-cycle oscillation as in a nonlinear Van-Der Pol oscillator. The computed damping factor synchronizes with the amplitude at all times, establishing that buzz is a stable and self-sustained oscillation with equilibrium between inertial and damping forces. It is proposed that a control scheme based on feed-forward control system using a suitable forcing function could be mathematically developed to suppress supersonic air-intake buzz.

Review of Supersonic Intake buzz, problems associated and possible solutions

Supersonic intake buzz is a type of shock oscillation that could occur at any supersonic inlet of an aircraft and which can alter the mass flow and pressure at inlet. It may lead to combustion instability also. A lot of experiments have been performed to understand the buzz characteristics while visualizing the flow characteristics through flow visualization techniques. Also, there have been a great effort and research to understand the supersonic buzz phenomenon through numerical simulation with the help of computational software packages. There could be different parameters affecting the buzz. Some of them was discovered by the researchers all over the world. Intake buzz distortion get substantially affected by change in angle of attack. Decrease in throttle area was also found to produce prominent effect on buzz by increasing its dominant frequency. The suppression of buzz has become a topic of active research. The suppression of buzz can help in increasing the efficiency of supersonic inlet and efficient compression, so can result in benefit of increasing the economic output and reducing the fuel consumption. Intake performance was found to be increased with small cowl deflection and by the use of buzz predictor and margin controller. Buzz could be controlled by deflecting the air in an advantageous way and generating a weaker gradient at inlet lip.

Inlet buzz phenomenon driven by flow choking in high-enthalpy Mach 4.5 flows using circular scramjet models

Inlet buzz driven by flow choking in circular dual-mode scramjets is experimentally investigated in high-enthalpy Mach 4.5 flows. Circular scramjet models with two different diverging combustors are used to investigate the correlation between the buzz frequency and flow choking driven by thermal and non-thermal loading. Flow and combustion dynamics are characterized by wall pressure histories, high-speed flame chemiluminescence, and flow luminosity to quantify and visualize the unsteady shockwave and flame propagations driven by fluid-combustion interactions. The circular geometry shows distinct physics from fluid/combustion dynamics due to the absence of corner boundary-layer effects that can distort flame propagation in rectangular geometries. It is observed that the 2° combustor can be thermally choked inside the diverging section while the 5° combustor can only be choked by additional non-thermal loading from its excessive area expansion. Correspondingly, different cyclic oscillations develop from the interactions between fluid and combustion during an unstart event due to the different characteristics of the choking. The 2° combustor is temporarily unchoked during a buzz cycle and the scramjet has a lower fundamental buzz frequency from the extended time to establish flow choking in the diverging section. In contrast, the 5° combustor is always choked during the buzz and the scramjet model has higher buzz frequencies that can be predicted by resonance modes of an acoustic duct with an open- and a closed-end.

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.

Buzz Tweet Classification Based on Text and Image Features of Tweets Using Multi-Task Learning

This study investigates social media trends and proposes a buzz tweet classification method to explore the factors causing the buzz phenomenon on Twitter. It is difficult to identify the causes of the buzz phenomenon based solely on texts posted on Twitter. It is expected that by limiting the tweets to those with attached images and using the characteristics of the images and the relationships between the text and images, a more detailed analysis than that of with text-only tweets can be conducted. Therefore, an analysis method was devised based on a multi-task neural network that uses both the features extracted from the image and text as input and the buzz class (buzz/non-buzz) and the number of “likes (favorites)” and “retweets (RTs)” as output. The predictions made using a single feature of the text and image were compared with the predictions using a combination of multiple features. The differences between buzz and non-buzz features were analyzed based on the cosine similarity between the text and the image. The buzz class was correctly identified with a correctness rate of approximately 80% for all combinations of image and text features, with the combination of BERT and VGG16 providing the highest correctness rate.

Study of buzz phenomenon in suddenly expanded flow structure using experiments and visualization

Experimental investigations have been carried out on a suddenly expanded duct in a view to determine buzz phenomenon for different Mach numbers (M), nozzle pressure ratios (NPR), and mass flow rates (MFR). The experimental facility was designed with sensitive and high-frequency pressure controls. The experiments were conducted for Mach numbers ranging from 2.0 to 3.0, with multiple NPRs of 3, 5, 7, and 9. In combination with the high-speed camera, shadowgraph mapping techniques were employed to provide optical depiction of the shock system in front of the inlet and to study the buzz features. Displacement of the shock and buzz frequency were calculated by shadowgraphs. The information gathered from the shadowgraphs was assessed against the pressure measurements and the values were in good agreement with each other. The results observed that for nominal values of MFR, the buzz frequency decreased with increasing Mach number. Furthermore, for an increasing NPR, the shock displacement further increases. The results also showed that there were significant pressure fluctuations in the expanded duct for lower Mach numbers.

Experimental Study of the Buzz Phenomenon Occurring on the Supersonic Intake for High Mach Integrated Control Experiment (HIMICO)

Experimental Study of the Buzz Phenomenon Occurring on the Supersonic Intake for High Mach Integrated Control Experiment (HIMICO)

Neuro-Fuzzy Network-Based Reduced-Order Modeling of Transonic Aileron Buzz

In the present work, a reduced-order modeling (ROM) framework based on a recurrent neuro-fuzzy model (NFM) that is serial connected with a multilayer perceptron (MLP) neural network is applied for the computation of transonic aileron buzz. The training data set for the specified ROM is obtained by performing forced-motion unsteady Reynolds-averaged Navier Stokes (URANS) simulations. Further, a Monte Carlo-based training procedure is applied in order to estimate statistical errors. In order to demonstrate the method’s fidelity, a two-dimensional aeroelastic model based on the NACA651213 airfoil is investigated at different flow conditions, while the aileron deflection and the hinge moment are considered in particular. The aileron is integrated in the wing section without a gap and is modeled as rigid. The dynamic equations of the rigid aileron rotation are coupled with the URANS-based flow model. For ROM training purposes, the aileron is excited via a forced motion and the respective aerodynamic and aeroelastic response is computed using a computational fluid dynamics (CFD) solver. A comparison with the high-fidelity reference CFD solutions shows that the essential characteristics of the nonlinear buzz phenomenon are captured by the selected ROM method.

Experimental investigation into the effects of Mach number and boundary-layer bleed on flow stability of a supersonic air intake

A series of experiments were conducted to study impacts of the free stream Mach number, back pressure and bleed on the stability of a supersonic intake. The flow stability is related to the buzz phenomenon; oscillation of all shock waves of the intake and it may further occur during the time when the intake mass flow rate is decreasing. The present intake is an axisymmetric intake for Mach number of 2.0. The results showed that the stability margin of the intake decreases when the freestream Mach number increases for both bleed off and bleed on cases. For the configuration without bleed, the frequency of buzz oscillation is increased when the freestream Mach number is decreased or when the back pressure is increased. By applying the bleed and consequently preventing the flow separation, the intake is more stable and the shocks oscillate with a smaller amplitude during the buzz phenomenon. When the bleed is applied, the buzz triggering mechanism varied from the Dailey criterion to that of the Ferri one, a phenomenon that changes the stability characteristics of the intake considerably.

Effect on the drag coefficient of various spiked cylinders during buzz phenomenon subjected to hypersonic flows

Pulsation mode of transient flow behavior may occur in a violent manner in case of spiked cylinders depending on the geometry, type of spikes, and free stream conditions. Drastic pressure fluctuations near the face of the afterbody have been observed in most cases of pulsating flow mode and thus resulting in drastic variations in the coefficient of drag of the spiked body. The transient analysis of variations in Cd with spike length for various spiked cylinders have been carried out in the current work. The variations in Cd during one complete cycle as well as variations in time-averaged value of Cd with increase in L/D ratios have been analyzed. These variations have been explained with respect to the localized pressure fluctuations, shift in foreshock–aftershock interaction region, effect of effective shielding, and increasing spike lengths. It was found that aerodisk spiked cylinder had the least time-averaged Cd. The Cd for various other spiked bodies has also been summarized over a range of feasible spike lengths and an optimum design of the spiked body in terms of the spike shape and L/D has also been suggested.

Acoustic Modeling and Vibration Characteristics of Supersonic Inlet Buzz

The buzz phenomenon of a typical supersonic inlet is analyzed on the basis of numerical simulations and duct acoustic theory. Considering that the choked inlet could be treated as a duct with one end closed, a one-dimensional (1D) mathematical model based on the duct acoustic theory is proposed to describe the periodic pressure oscillation of the little buzz and the big buzz. The results of the acoustic model agree well with that of the numerical simulations and the experimental data. It could verify that the dominated oscillation patterns of the little buzz and the big buzz are closely related to the first and second resonant mode of the standing wave, respectively. The discrepancies between the numerical simulation and the ideal acoustic model might be attributed to the viscous damping in the fluid oscillation system. In order to explore the damping, a small perturbation jet is introduced to trigger the resonance of the buzz system and the nonlinear amplification effect of resonance might be helpful to estimate the damping. Through the comparison between the linear acoustic model and the nonlinear simulation, the calculated pressure oscillation damping of the little buzz and the big buzz are 0.33 and 0.16, which could be regarded as an estimation of real damping.

Spatiotemporal Characterization and Suppression Mechanism of Supersonic Inlet Buzz with Proper Orthogonal Decomposition Method

The buzz phenomenon of a typical supersonic inlet is analyzed using the unsteady Reynolds Average Navier-Stokes (RANS) simulation and proper orthogonal decomposition (POD) method. The dominant flow patterns and characteristics of the buzzed flow are obtained by decoupling the computed pressure field into spatial and temporal sub-parts based on the POD method. The supersonic inlet buzz phenomenon could be approximated as a product of decoupled temporal and spatial terms, and the one-dimensional (1D) mathematical model is therefore proposed. The standard deviations of the unsteady pressure fields from both the numerical simulation and the model prediction are compared. The limited discrepancy can be observed, and the good agreement validates the credibility of the proposed 1D model. The numerical simulation and the 1D model prediction are presented to explore the unsteady-jet control with a small perturbation. The results of the 1D model and the numerical simulation achieve good agreements with each other in terms of the overall trend. Finally, POD modal energy is employed to analyze the buzz suppression mechanism. When the jet frequency is identical to the dominant frequency of the buzz and the jet phase is opposite to the oscillation phase of the captured mass flow, the buzz suppression could be more efficient. The buzz suppression mechanism could be explained in two aspects. For one thing, the complex flow structure is suppressed and the first average modal energy in the inlet is increased. For another, the energy redistribution among each POD mode is achieved and the flow stability is gradually enhanced.

Numerical study on the start and unstart phenomena in a scramjet inlet-isolator model.

Inlet unstart and buzz in scramjet engines must be prevented for the stable operation of the engines. In the present study, the characteristics of the inlet start, unstart and buzz phenomena in a scramjet engine inlet model are investigated using numerical analysis with the RANS-based OpenFOAM solver. The results for the inlet start case with a small computational domain that includes only the inlet-isolator part are in good agreement with existing numerical and experimental results. However, for the inlet unstart case, the computational domain must be wide enough to consider the interactions between the upstream of the inlet and the internal flow of the inlet to predict the inlet unstart and buzz phenomena in the inlet test model. The present results show fairly good agreement with existing experimental results with the buzz phenomenon. The effects of boundary layer profiles on the buzz oscillation frequency and amplitude are also addressed.

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.

Study of buzz phenomenon using visualization of external shock structure

An experimental study was carried out on an axisymmetric supersonic inlet with external compression in order to investigate the buzz phenomenon at different angles of attack and mass flow rates. The model was equipped with accurate and high-frequency pressure sensors, and the tests were conducted at Mach numbers varying from 1.8 to 2.5, for various angles of attack. Shadowgraph visualization technique, together with a high-speed camera, was used to provide the visual description of the shock structure in front of the inlet and to study the characteristics of buzz. Furthermore, pressure distribution over the spike surface was measured using several pressure sensors. Frequency of the buzz and shock displacement were measured by inspection of visualization pictures in each test. The obtained data from shadowgraphs were compared with those obtained from pressure measurements, and good agreement was found between them. The results revealed that for a moderate value of mass flow rate, the frequency of shock oscillation decreases as Mach number increases. Further, by increasing angle of attack, the shock displacement of oscillation will increase. At non-zero angles of attack, the displacement and frequency of shock motion show different behaviors on the leeward and windward sides of the body.

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.

Buzz Flows in an External-Compression Inlet with Partially Isentropic Compression

A rectangular external-compression supersonic inlet with partially isentropic compression is experimentally studied at a freestream Mach number of 2.0. During the test, the inlet operates at the little buzz state after going through the supercritical state and the steady subcritical state. A striking feature of the little buzz state is that both the most upstream and downstream positions of the unsteady separation point of the forebody boundary layer take on a linear variation trend with the increase of throttling ratio, yielding an intensifying flow oscillation. Then, the mixed buzz phenomenon that the little and big buzz coexist appears. As the throttling ratio further rises, the occurrence probability of little buzz is reduced, and finally the big buzz state takes place. In this state, two unique transient flow patterns with the inflow and supersonic backflow coexisting at the duct entrance can be observed. Different from the prevailing viewpoint, the present little buzz belongs to the Dailey instability and shares a common origin with the big buzz in essence. Furthermore, a theoretical analysis based on Fisher’s criterion indicates that a single shear layer from a -shaped terminal shock with an upstream Mach number below 1.60 is unable to trigger the Ferri instability of a supersonic inlet.

Multiple input describing function analysis of non-classical aileron buzz

This paper focuses on the computational study of nonlinear effects of unsteady aerodynamics for non-classical aileron buzz. It aims at a comprehensive investigation of the aileron buzz phenomenon under varying flow parameters using the describing function technique with multiple inputs. The limit cycle oscillatory behavior of an asymmetrical airfoil is studied initially using a CFD-based numerical model and direct time marching. Sharp increases in limit cycle amplitude for varying Mach numbers and angles of attack are investigated. An aerodynamic describing function is developed in order to estimate the variation of limit cycle amplitude and frequency with Mach number and angle of attack directly, without time marching. The describing function results are compared to the amplitudes and frequencies predicted by the CFD calculations for validation purposes. Furthermore, a limited sensitivity analysis is presented to demonstrate the potential of the approach for aeroelastic design.