Dynamic Pressure Signal Research Articles

Experimental investigations on pressure oscillation induced by steam-air mixture gas sonic jets in subcooled water

Present paper aims to experimentally investigate pressure oscillation induced by steam-air mixture gas sonic jets in subcooled water. Dynamic pressure signals and jet images are recorded and analyzed. Experimental results show that: the pressure oscillation dominant frequency decreases with the rise of water temperature, inlet pressure and air mass fraction. Air mass fraction has a complex effect on pressure oscillation intensity. When water temperature is less than 55 °C, as the air mass fraction increases, the pressure oscillation intensity increases first, and then decreases slightly, and then increases quickly. When water temperature is more than 55 °C, as the air mass fraction increases, the pressure oscillation intensity decreases first, and then increases quickly. The interfacial fluctuation height and pressure oscillation intensity dependency to the air mass fraction is the same near the nozzle exit. In addition, the validity of previous analysis model for steam sonic jet pressure oscillation dominant frequency is evaluated. A modified function considering the effect of air mass fraction is developed. The predicted results of steam-air mixture gas sonic jet pressure oscillation dominant frequency agree well with the experimental results. More than 98% of the data points are inside the error band of ±20%.

발전용 모델 가스터빈 연소기의 입구에서 음향반사계수 결정

A phenomenon that potentially influences the reliability of power generation systems is the presence of thermo-acoustic oscillations in the combustion chamber of a land- based gas turbine. To develop specific measures that prevent the instability, it is essential to predict and/or evaluate the underlying physics of the thermo-acoustics, which requires the acoustic boundary condition at the exit of the burner, that is, at the inlet of the combustor. Here we report a procedure for calculating acoustic reflection coefficients at the burner exit by utilizing two microphone method (TMM) for dynamic pressure signals. The procedure has been verified by comparing its results with reported ones and further successfully employed to determine the acoustic boundary condition of the burner of a partially-premixed model gas turbine combustor.

Thermoacoustic Damping Rate Determination From Combustion Noise Using Bayesian Statistics

In this paper, we present a method to determine the quantitative stability level of a lean-premixed combustor from dynamic pressure data. Specifically, we make use of the autocorrelation function of the dynamic pressure signal acquired in a combustor where a turbulent flame acts as a thermoacoustic driver. In the proposed approach, the unfiltered pressure signal including several modes is analyzed by an algorithm based on Bayesian statistics. For this purpose, a Gibbs sampler is used to calculate parameters like damping rates and eigenfrequencies in the form of probability density functions (PDF) by a Markov-chain Monte Carlo (MCMC) method. The method provides a robust solution algorithm for fitting problems without requiring initial values. A further advantage lies in the nature of the statistical approach since the results can be assessed regarding its quality by means of the PDF and its standard deviation for each of the obtained parameters. First, a simulation of a stochastically forced van-der-Pol oscillator with preset input values is carried out to demonstrate accuracy and robustness of the method. In this context, it is shown that, despite a large amount of uncorrelated background noise, the identified damping rates are in a good agreement with the simulated parameters. Second, this technique is applied to measured pressure data. By doing so, the combustor is initially operated under stable conditions before the thermal power is gradually increased by adjusting the fuel mass flow rate until a limit-cycle oscillation is established. It is found that the obtained damping rates are qualitatively in line with the amplitude levels observed during operation of the combustor.

Effects of Stall Precursor-Suppressed Casing Treatment on a Low-Speed Compressor With Swirl Distortion

Swirl inlet distortion is usually encountered in modern flight vehicles since their inlet ducts usually consist of one or two bends, such as S-inlet duct. An experimental device is first designed to simulate the swirl inlet distortion and then used to test the effectiveness of a novel casing treatment (CT) on a low-speed compressor under the swirl distortions of various intensities. The influences of co- and counter-rotating swirl inlet distortion on the test compressor and the stabilization ability of this novel CT are well demonstrated by the illustrations of static pressure rise curves and efficiency curves. The dynamic prestall pressure signals are also captured to reflect the perturbation energy in the flow field through which the mechanism of the novel CT will be indicated. The relevant results show that counter-rotating swirl distortion in small intensity could increase the compressive ability of compressor with small efficiency loss, and the co-rotating swirl distortion always brings about detrimental effects on compressor performance. At the same time, the distortion of twin swirls can cause nonuniform total pressure profile which can seriously damage the compressor performance. Besides, the stall precursor-suppressed (SPS) CT shows a good capability of stall margin (SM) enhancement no matter what swirl inlet distortions are encountered in the test compressor.

An Apparatus for the Performance Estimation of Pressure Fluctuation Energy Harvesters

Hydraulic pressure fluctuation energy harvesters are promising alternatives to power up wireless sensor nodes in hydraulic systems. The characterization of these harvesters under dynamic and band-limited pressure signals is imperative for the research and development of novel concepts. To generate and control these signals in a hydraulic medium, a versatile apparatus capable of reproducing pressure signals is proposed. In this paper, a comprehensive discussion of the design considerations for this apparatus and its performance is given. The suggested setup enables the investigation of devices tailored for the harvesting of energy in conventional hydraulic systems. To mimic these systems, static pressures can be tuned up to 300 bar, and the pressure amplitudes with a maximum of 28 Bar at 40 Hz and 0.5 bar at 1000 Hz can be generated. In addition, pressure signals found in commercial hydraulic systems can be reproduced with good accuracy. This apparatus proves to be an accessible, robust, and versatile experimental setup to create environments for the complete performance estimation of pressure fluctuation energy harvesters.

Asymmetric Fuzzy Control of a Positive and Negative Pneumatic Pressure Servo System

The pneumatic pressure control systems have been used in some fields. However, the researches on pneumatic pressure control mainly focus on constant pressure regulation. Poor dynamic characteristics and strong nonlinearity of such systems limit its application in the field of pressure tracking control. In order to meet the demand of generating dynamic pressure signal in the application of the hardware-in-the-loop simulation of aerospace engineering, a positive and negative pneumatic pressure servo system is provided to implement dynamic adjustment of sealed chamber pressure. A mathematical model is established with simulation and experiment being implemented afterwards to discuss the characteristics of the system, which shows serious asymmetry in the process of charging and discharging. Based on the analysis of the system dynamics, a fuzzy proportional integral derivative (PID) controller with asymmetric fuzzy compensator is proposed. Different from conventional adjusting mechanisms employing the error and change in error of the controlled variable as input parameters, the current chamber pressure and charging or discharging state are chosen as inputs of the compensator, which improves adaptability. To verify the effectiveness and performance of the proposed controller, the comparison experiments tracking sinusoidal and square wave commands are conducted. Experimental results show that the proposed controller can obtain better dynamic performance and relatively consistent control performance across the scope of work (2–140 kPa). The research proposes a fuzzy control method to overcome asymmetry and enhance adaptability for the positive and negative pneumatic pressure servo system.

Determination of an acoustic reflection coefficient at the inlet of a model gas turbine combustor for power generation

A phenomenon that potentially influences the reliability of power generation systems is the presence of thermo-acoustic oscillations in the combustion chamber of a land- based gas turbine. To develop specific measures that prevent the instability, it is essential to predict and/or evaluate the underlying physics of the thermo-acoustics, which requires the acoustic boundary condition at the exit of the burner, that is, at the inlet of the combustor. Here we report a procedure for calculating acoustic reflection coefficients at the burner exit by utilizing two microphone method (TMM) for dynamic pressure signals. The procedure has been verified by comparing its results with reported ones and further successfully employed to determine the acoustic boundary condition of the burner of a partially-premixed model gas turbine combustor.

A method to identify thermoacoustic growth rates in combustion chambers from dynamic pressure time series

The stochastic nature of combustion instabilities in practical land-based gas turbines and aeroengines combustors has seldom been investigated. It is shown here that a wealth of information about the constructive acoustic-flame interactions can be gained by scrutinising the effects of the inherent turbulence-induced noise, which forces the nonlinear thermoacoustic dynamics. In particular, one presents a method, based on the Fokker–Planck formalism, to identify from dynamic pressure signals the linear growth rates, the type of flame response nonlinearity and the potential defining the system acoustic energy. It is applied to and validated against experimental data measured in a lab-scale combustion chamber.

Temporal kurtosis of dynamic pressure signal as a quantitative measure of combustion instability

In this study, the kurtosis of dynamic pressure (DP) signal is implemented to quantify the thermoacoustic stability of a combustion process. The variation of the temporal characteristics of DP signal experiencing the three phases of thermoacoustic stability (i.e., stable, transitional, and unstable with limit cycle oscillation) was explained in terms of the temporal kurtosis (TK), the instantaneous kurtosis evaluated with a subset of DP signal. The explanation suggested that TK would be a promising parameter as a quantitative measure of combustion instability (CI). The feasibility of TK as an indicator of CI was investigated using DP data obtained from combustion tests with a rocket engine, with a lab-scale gas turbine combustor, and with a lab-scale aero engine combustor. In these feasibility studies, the time history of TKs reflected the temporal changes in combustion stability during the combustion processes successfully. It turns out that TK can serve as a real-time indicator of the change in stability condition and also as a precursor of upcoming severe instability. It is expected that the implementation of TK in quantifying the progress of thermoacoustic instability would significantly enhance the performance of commercialized monitoring systems of CI.

Study of gas–liquid two-phase flow patterns of self-excited dust scrubbers

Self-excited dust scrubbers are widely used in the purification of a high dust concentration. However, the existing research has been primarily focused on the macroscopic performance of the dust scrubbers and has neglected the gas–liquid two-phase flow patterns that are closely related to its dust collection principle. This paper employed high-speed photography technology to acquire video images of liquid-phase patterns and employed high-frequency acquisition technology to acquire the corresponding dynamic pressure signals of the gas-phase of the self-excited dust scrubber. Using the probability density distribution (PDD), wavelet analysis, and power spectral density (PSD) estimation, in combination with the dynamic image analysis of the gas–liquid two-phase flow, a quantitative study of the gas–liquid two-phase flow patterns of self-excited dust scrubbers was conducted. This study provides strong supporting data to overcome the bottleneck that limits theoretical studies on self-excited dust scrubbers.

Pressure oscillation induced by steam jet condensation in subcooled water flow in a channel

An experimental study was carried out on the pressure oscillation caused by direct contact condensation (DCC) of steam jet in water. The published researches on pressure oscillation caused by DCC were generally performed in large space pools. However, the condensation oscillation characteristics of steam jet in water flow in a confined space have not been fully understood yet. During this experiment, the steam and water were introduced into a confined channel at the same side. The dynamic pressure signals were measured without interfering the flow field. The behavior of the interface was captured by a high speed camera. The main inlet parameters, i.e. steam mass flux, water Reynolds number and water temperature were tested in the range of 150–600kg/(m2s), 78,000–172,000 and 25–60°C, respectively. The results indicated that flow patterns were determined by these three inlet parameters. According to the structure and behavior of the interface, the flow patterns under various test conditions could be divided to unstable and stable types. As flow patterns transformed from stable to unstable, the pressure oscillation intensity increased sharply. The dominant frequency for subsonic steam jet condensation oscillation in water flow was in the range of 168–1177Hz. The frequency increased with the increase of water Reynolds number, but decreased with the increase of steam mass flux and water temperature. Moreover, a correlation for the dominant frequency was given as a function of the condensation driving potential, steam mass flux, Weber number and water Reynolds number. The predicted values agreed well with the present experimental values at the maximum deviation of ±20%.

Identification of neural firing patterns, frequency and temporal coding mechanisms in individual aortic baroreceptors.

In rabbit depressor nerve fibers, an on-off firing pattern, period-1 firing, and integer multiple firing with quiescent state were observed as the static pressure level was increased. A bursting pattern with bursts at the systolic phase of blood pressure, continuous firing, and bursting with burst at diastolic phase and quiescent state at systolic phase were observed as the mean level of the dynamic blood pressure was increased. For both static and dynamic pressures, the firing frequency of the first two firing patterns increased and of the last firing pattern decreased due to the quiescent state. If the quiescent state is disregarded, the spike frequency becomes an increasing trend. The instantaneous spike frequency of the systolic phase bursting, continuous firing, and diastolic phase bursting can reflect the temporal process of the systolic phase, whole procedure, and diastolic phase of the dynamic blood pressure signal, respectively. With increasing the static current corresponding to pressure level, the deterministic Hodgkin-Huxley (HH) model manifests a process from a resting state first to period-1 firing via a subcritical Hopf bifurcation and then to a resting state via a supercritical Hopf bifurcation, and the firing frequency increases. The on-off firing and integer multiple firing were here identified as noise-induced firing patterns near the subcritical and supercritical Hopf bifurcation points, respectively, using the stochastic HH model. The systolic phase bursting and diastolic phase bursting were identified as pressure-induced firings near the subcritical and supercritical Hopf bifurcation points, respectively, using an HH model with a dynamic signal. The firing, spike frequency, and instantaneous spike frequency observed in the experiment were simulated and explained using HH models. The results illustrate the dynamics of different firing patterns and the frequency and temporal coding mechanisms of aortic baroreceptor.

Experimental analysis on the impact force of viscous debris flow

AbstractA miniaturized flume experiment was carried out to measure impact forces of viscous debris flow. The flow depth (7.2–11.2 cm), velocity (2.4–5.2 m/s) and impact force were recorded during the experiment. The impact process of debris flow can be divided into three phases by analyzing the variation of impact signals and flow regime. The three phases are the sudden strong impact of the debris flow head, continuous dynamic pressure of the body and slight static pressure of the tail. The variation of impact process is consistent with the change in the flow regime. The head has strong–rapid impact pressure, which is shown as a turbulent‐type flow; the body approximates to steady laminar flow. Accordingly, the process of debris flows hitting structures was simplified to a triangle shape, ignoring the pressure of the tail. In order to study the distribution of the debris flow impact force at different depths and variation of the impact process over time, the impact signals of slurry and coarse particles were separated from the original signals using wavelet analysis. The slurry's dynamic pressure signal appears to be a smooth curve, and the peak pressure is 12–34 kPa when the debris flow head hits the sensors, which is about 1.54 ± 0.36 times the continuous dynamic pressure of the debris flow body. The limit of application of the empirical parameter α in the hydraulic formula was also noted. We introduced the power function relationship of α and the Froude number of debris flows, and proposed a universal model for calculating dynamic pressure. The impact pressure of large particles has the characteristic of randomness. The mean frequency of large particles impacting the sensor is 210 ± 50–287 ± 29 times per second, and it is 336 ± 114–490 ± 69 times per second for the debris flow head, which is greater than that in the debris flow body. Peak impact pressure of particles at different flow depths is 40–160 kPa, which is 3.2 ± 1.5 times the impact pressure of the slurry at the bottom of the flow, 3.1 ± 0.9 times the flow in the middle, and 3.3 ± 0.9 times the flow at the surface. The differences in impact frequency indicate that most of the large particles concentrate in the debris flow head, and the number of particles in the debris flow head increases with height. This research supports the study of solid–liquid two phase flow mechanisms, and helps engineering design and risk assessment in debris flow prone areas. Copyright © 2015 John Wiley & Sons, Ltd.

The pressure field of imploding lightbulbs

The implosion of A19 incandescent lightbulbs in a high-pressure water environment is studied in a 1.77-m-diameter steel tank. Underwater blast sensors are used to measure the dynamic pressure field near the lightbulbs and the implosions are photographed with a high-speed movie camera at a frame rate of 24,000 pps. The movie camera and the pressure signal recording system are synchronized to enable correlation of features in the movie frames with those in the pressure records. It is found that the gross dimensions and weight of the bulbs are very similar from one bulb to another, but the ambient water pressure at which a given bulb implodes (\(P_a\), called the implosion pressure) varies from 6.29 to 11.98 atmospheres, probably due to inconsistencies in the glass wall thickness and perhaps other detailed characteristics of the bulbs. The dynamic pressures (the local pressure minus \(P_a\), as measured by the sensors) first drop during the implosion and then reach a strong positive peak at about the time that the bulb reaches minimum volume. The peak dynamic pressure varies from 3.61 to 28.66 atmospheres. In order to explore the physics of the implosion process, the dynamic pressure signals are compared to calculations of the pressure field generated by the collapse of a spherical bubble in a weakly compressible liquid. The wide range of implosion pressures is used in combination with the calculations to explore the effect of the relative liquid compressibility and the bulb itself on the dynamic pressure field.

Simulation Study of AC Contactor Dynamic Contacts Contact Pressure Based on ADAMS

A multi-body dynamics simulation model of CJ20-25 AC contactor was established with Pro/E �ƒ Pro/Engineer)in this paper. A coupling simulation with machine, electric, magnetic on the contactor has been achieved in this model. Dynamic parameters which were called use the secondary development technology of ADAMS. The dynamic contact pressure signal of an AC contactor was obtained with ADAMS's own simultane- ous solution such as electromagnetic suction, kinematics and dynamics equations. The simulation results and actual measurement of contactor contact pressure signals are very similar. However, the complexity of the meas- ured contacts vibration is greater than the simulation results because the actual working condition is more com- plex. This result provides a theoretical foundation to the dynamic contacts contact pressure test.

An improved wavelet adaptive logarithmic threshold denoising method for analysing pressure signals in a transonic compressor

This paper proposes an improved wavelet threshold denoising algorithm based on orthogonal wavelet transform. The algorithm, called adaptive logarithmic threshold denoising algorithm based on wavelet (ALTDAW), processes the dynamic pressure signals generated by a transonic axial compressor. Combined with an adaptive logarithmic threshold function, it sets the optimal threshold for each decomposition level. In this way, noise is effectively identified and eliminated. Since ALTDAW is adaptable, it reduces the maximum decomposition level, thereby decreasing the processing time and improving the computational efficiency. In numerical experiments, the performance of ALTDAW was compared with that of the classical soft and hard threshold algorithms. Relative to the classical algorithms, ALTDAW increased the signal-to-noise ratio (SNR) by 27.9% and 44.2%, and reduced the processing time by 38.5% and 37.6%, respectively. The practicality of the algorithm was validated on the complex dynamic pressure signals of a transonic axial compressor. When processing these signals, the algorithm depicted that disturbance passes through the tips and the spike three revolutions before the compressor stalls, consistent with the physical properties of transonic axial compressors.

Leak detection monitoring system of long distance oil pipeline based on dynamic pressure transmitter

A dynamic pressure transmitter (DPT) is designed in this paper for long distance oil and gas pipeline, of which the design principle and main performance indices are introduced. A novel leak detection monitoring system (LDMS) of long distance oil pipeline based on DPT is designed, and the detection principle and system composition are specified. Dynamic pressure signals along the pipeline can be obtained by the DPT, and then the pipeline leak can be detected by extracting the wavelet packet entropy (WPE) of the signals. The WPE signal feature extraction method for judgment of pipeline leak is explored and developed. In addition, the influence of the wavelet basis and calculating window width on the identification performance of the WPE are further discussed. The application examples show that the DPT has higher detection sensitivity and leak resolution than the traditional pressure transmitter. The system can identify the pipeline leak correctly and reduce false alarm rate effectively. It can also improve detection sensitivity and localization accuracy. The system can correctly detect leaks with a rate of 96.7% and the greatest localization error is 101m.

Research of Characteristics Extraction Based on Dynamic Pressure Signal

The accuracy of pattern recognition was determined by the feature selection, and two methods of the characteristic description were discussed. The results show that the statistical characteristics could be used as a dynamic pressure signal descriptor, and the oscillation characteristic of curve is not suitable for describing dynamic pressure signal by itself. The selection of descriptors of dynamic pressure signal is the precondition to identify the leak signal and the non-leak signal effectively.

Wavelet analysis of the shaft order perturbation and stall inception in an axial compressor

An experiment was carried out in a low-speed large-scale axial-compressor. Dynamic pressure signals were measured and analyzed with a wavelet transform. At all stable operating condition, a shaft order perturbation was observed from the dynamic pressure signals and wavelet power spectrums. By measuring the tip clearance, blade pitches and blade thickness distributions, a rotor asymmetry was identified in this compressor, which is strongly linked to the shaft order perturbation. Modal wave appears at the near-stall operating point. The propagation speed of the modal wave is about 20% rotating speed. At the peak of the modal wave, the intensity of the shaft-order-perturbation increases obviously, while it decays very fast at the trough of modal wave. By throttling the compressor, modal stall occurs in several seconds and only one stall-cell was detected. The stall cell grows smoothly out of the modal wave and its propagation speed is increased to 30% rotor speed. In several revolutions before stall, the intensity of the modal wave is increasing and a shaft order perturbation produced by modal-wave grows into stall inception which indicate stall onset but not trigger stall.

Effects of CO2 dilution on combustion instabilities in dual premixed flames

There has been a rapid increase in the demand for biogas applications in recent years, and dry low NOx and dry low emission gas turbine combustors are promising platforms for such applications. Combustion instability is the most important drawback in dry low NOx gas turbine combustors and has, therefore, attracted considerable research interest lately. As a fundamental study towards the use of biogas in dry low NOx and dry low emission gas turbine combustors, this article investigates the influence of CO2 in surrogate biogas on combustion instability. Tests were conducted using a dry low NOx type, a dual lean premixed gas turbine combustor. For a dual flame with dual swirl, the pilot fuel mass fraction affects the flame structure, and the flame structure, in turn, determines the temperature distribution in the combustion chamber and the combustion instability. The effects of the pilot fuel mass fraction, which is an important parameter of the combustor, and the CO2 dilution rate, which is a major contributor of biogas combustion, on the combustion characteristics and instability are investigated through dynamic pressure signal and phase-resolved OH* images. Combustion instability decreases for higher CO2 dilution rates, whose effects depend on the pilot fuel mass fraction. The instability reaches its maximum at a pilot fuel mass fraction of 0.3. Tests confirm that combustion instability diminishes with CO2 dilution, as it reduces the perturbation in the heat emission, and the flame speed decreases resulting in a greater flame surface or volume. Further, investigation of the Rayleigh Index, which represents the coupling strength of the heat release fluctuation and the natural frequency, shows that CO2 dilution weakens the coupling strength, resulting in less combustion instability.