Dynamic Pressure Measurements Research Articles

Extracting flame describing functions in the presence of self-excited thermoacoustic oscillations

One of the key elements in the prediction of thermoacoustic oscillations is the determination of the acoustic response of flames as an element in an acoustic network, in the form of a flame describing function (FDF). In order to obtain a response, flames often have to be confined into a system with its own acoustic response. Separating the pure flame response and that of the system can be complicated by the non-linear effects that the flame can have on the overall system response. In this paper, we investigate whether it is possible to obtain a flame response via the usual methods of dynamic chemiluminescence and pressure measurements, starting from an unforced system with incipient self-excitations at a given frequency fs, in the form of a stabilized flame at atmospheric pressure with a 700 mm tube as a combustor. The flame is forced at discrete frequencies from 20 to 400 Hz, away from the self-excitation, and the response of the flame is measured using OH* chemiluminescence. This response was compared to a flame response measured in a short tube with no other excitations.The results show that both the gain and phase can be entirely dominated by the behavior of the self-excitation, so that in general it is not possible to extract reliable gain and phase information as if the forced and self-excited modes acted independently and linearly. Although the gain in this particular case was not significantly affected, the phase information of the original flame became dominated by the triggered self-excitation. Boundary conditions and systems used for flame acoustic forcing therefore need to be carefully controlled whenever there is a possibility of self-excitation.

A Study of Bulk Modulus, Entrained Air, and Dynamic Pressure Measurements in Liquids

Accurate static and dynamic pressure measurements in liquids, such as fuel, oil, and hydraulic fluid, are critical to the control and health monitoring of turbomachinery and aerospace systems. This work presents a theoretical and experimental study of the frequency response of pressure transducers and pressure measurement systems in liquid media. First, we theoretically predict the frequency response of pressure transducers based upon a lumped-parameter model. We then present a liquid-based dynamic pressure calibration test apparatus that validates this model by performing several critical measurements. This system first uses a vibrating liquid column to dynamically calibrate and experimentally determine the frequency response of a test pressure transducer, measurement system or geometry. Second, this calibration system experimentally extracts the bulk modulus of the fluid and the percent of entrained and/or dissolved air by volume. Bulk modulus is determined by measuring the speed of sound within the liquid and through static pressure loading while measuring the deflection of the liquid column. Bulk modulus and the entrained/dissolved gas content within the liquid greatly impact the observed frequency response of a pressure transducer or geometry. Gases, such as air, mixed or dissolved into a fluid can add substantial damping to the dynamic response of the fluid measurement system, which makes measurement of the bulk modulus and entrained and/or dissolved air critical for accurate measurement of the frequency response of a system when operating with a liquid media. All experimental results are compared to theoretical predictions.

Effects of kerosene heating on dynamic characteristics of GOx/kerosene combustor

The objective of this study was to observe low-frequency instabilities caused by heating of kerosene under supercritical operating conditions. Gaseous oxygen and liquid kerosene were injected using a shear-coaxial injector. Under specific heating conditions, the fuel heating system induced an extremely low frequency pressure fluctuation ranging from 9.9 to 11.4Hz. When pressure oscillation occurred in the heating system, low-frequency combustion instability was subsequently induced in the range of 30–200Hz. To understand the effects of the fuel heating temperature on the combustion instability, the dynamic pressure and OH* chemiluminescence intensity were measured in a combustion chamber at high speed. Further, the reacting spray of the combustion was visualized by a shadowgraph technique. In this experiment, an approximate fuel pressure of 3.0MPa was employed in order to attain a supercritical condition of kerosene. The measured dynamic pressure and chemiluminescence intensity in the time domain were converted to frequency-domain spectra by fast Fourier transform. Analysis of the dynamic pressure and chemiluminescence intensity measurements confirmed that the low-frequency pressure oscillation in the heating system had an influence on the combustion instability. From the visualization data, it was also revealed that there existed varying amplitude levels of flow rate fluctuation. This fluctuation in turn caused a periodic injection of kerosene at a frequency similar to both the combustion instability frequency and the OH* chemiluminescence intensity frequency.

Vibration Modeling and Experimental Results of Two-Phase Twin-Screw Pump

In turbomachines, the transfer of energy between the rotor and the fluid does not—in theory—result in lateral forces on the rotor. In positive displacement machines, on the other hand, the transfer of energy between the moving components and the working fluid usually results in unbalanced pressure fields and forces. Muhammed and Childs (2013, “Rotordynamics of a Two-Phase Flow Twin Screw Pump,” ASME J. Eng. Gas Turbines Power, 135(6), p. 062502) developed a model to predict the dynamic forces in twin-screw pumps, showing that the helical screw shape generates hydraulic forces that oscillate at multiples of running speed. The work presented here attempts to validate the model of Muhammed and Childs (2013, “Rotordynamics of a Two-Phase Flow Twin Screw Pump,” ASME J. Eng. Gas Turbines Power, 135(6), p. 062502) using a clear-casing twin-screw pump. The pump runs in both single and multiphase conditions with exit pressure up to 300 kPa and a flow rate 0.6 l/s. The pump was instrumented with dynamic pressure probes across the axial length of the screw in two perpendicular directions to validate the dynamic model. Two proximity probes measured the dynamic rotor displacement at the outlet to validate the rotordynamics model and the hydrodynamic cyclic forces predicted by Muhammed and Childs (2013, “Rotordynamics of a Two-Phase Flow Twin Screw Pump,” ASME J. Eng. Gas Turbines Power, 135(6), p. 062502). The predictions were found to be in good agreement with the measurements. The amplitude of the dynamic pressure measurements in two perpendicular plans supported the main assumptions of the model (constant pressure inside the chambers and linear pressure drop across the screw lands). The predicted rotor orbits at the pump outlet in the middle of the rotor matched the experimental orbits closely. The spectrum of the response showed harmonics of the running speed as predicted by the model. The pump rotor's calculated critical speed was at 24.8 krpm, roughly 14 times the rotor's running speed of 1750 rpm. The measured and observed excitation frequencies extended out to nine times running speed, still well below the first critical speed. However, for longer twin-screw pumps running at higher speed, the coincidence of a higher-harmonic excitation frequency with the lightly damped first critical speed should be considered.

Dynamic Pressure Measurement and Uncertainty Analysis Using a Piezoelectric Transducer for a Combustion Engine

This paper analyses the uncertainty of pressure measurements in-cylinder and in injection pipe conducted during the studies of a compression ignition engine. Type A and type B evaluations were used to determine the uncertainties of the results. The results are presented for the engine running on diesel or bio-fuel and operating under full load conditions. The results of normality tests provide grounds to reject H0 in some cases. Slightly lower standard uncertainty of the maximum pressure measurement calculated using type A evaluation were acquired for the engine running on bio-fuel.

Botulinum Toxin Type A Injection for Spastic Equinovarus Foot in Children with Spastic Cerebral Palsy: Effects on Gait and Foot Pressure Distribution.

PurposeTo investigate the effect of intramuscular Botulinum toxin type A (BoNT-A) injection on gait and dynamic foot pressure distribution in children with spastic cerebral palsy (CP) with dynamic equinovarus foot.Materials and MethodsTwenty-five legs of 25 children with CP were investigated in this study. BoNT-A was injected into the gastrocnemius (GCM) and tibialis posterior (TP) muscles under the guidance of ultrasonography. The effects of the toxin were clinically assessed using the modified Ashworth scale (MAS) and modified Tardieu scale (MTS), and a computerized gait analysis and dynamic foot pressure measurements using the F-scan system were also performed before injection and at 1 and 4 months after injection.ResultsSpasticity of the ankle plantar-flexor in both the MAS and MTS was significantly reduced at both 1 and 4 months after injection. On dynamic foot pressure measurements, the center of pressure index and coronal index, which represent the asymmetrical weight-bearing of the medial and lateral columns of the foot, significantly improved at both 1 and 4 months after injection. The dynamic foot pressure index, total contact area, contact length and hind foot contact width all increased at 1 month after injection, suggesting better heel contact. Ankle kinematic data were significantly improved at both 1 and 4 months after injection, and ankle power generation was significantly increased at 4 months after injection compared to baseline data.ConclusionUsing a computerized gait analysis and foot scan, this study revealed significant benefits of BoNT-A injection into the GCM and TP muscles for dynamic equinovarus foot in children with spastic CP.

A Novel Miniaturised Sensor for Combined Static and Dynamic Pressure Measurements in Harsh Environments

In this study a sensor for harsh environments is presented, that combines the advantages of two principles for pressure monitoring in one package. Highly dynamic and very precise measurements are performed with piezoelectric single crystals. In addition, the static pressure is monitored with platinum thin film strain gauges, designed for high temperature environments. A novel membrane transmits the environmental pressure to both sets of measuring elements that are placed in a closed housing. Experiments show that the setup is stable at least up to 500̊C. Sensor calibration is performed at room temperature with oil at pressure levels ranging up to 50bar. The linearity of the piezoelectric system is within ±1.2% FSO, the linearity of the strain gauges within 3.5% FSO. For demonstration purposes, an oscillating pressure output gained from both piezoelectric and strain gauge sensor elements is presented at 12Hz, showing a good agreement between both transducer principles.

Foot Pain and Pronated Foot Type Are Associated with Self-Reported Mobility Limitations in Older Adults: The Framingham Foot Study

Background: The foot plays an important role in supporting the body when undertaking weight-bearing activities. Aging is associated with an increased prevalence of foot pain and a lowering of the arch of the foot, both of which may impair mobility. Objective: To examine the associations of foot pain, foot posture and dynamic foot function with self-reported mobility limitations in community-dwelling older adults. Methods: Foot examinations were conducted on 1,860 members of the Framingham Study in 2002-2005. Foot posture was categorized as normal, planus or cavus using static pressure measurements, and foot function was categorized as normal, pronated or supinated using dynamic pressure measurements. Participants were asked whether they had foot pain and any difficulty performing a list of eight weight-bearing tasks. Multivariate logistic regression and linear regression models were used to examine the associations of foot pain, posture, function and ability to perform these activities. Results: After adjusting for age, sex, height and weight, foot pain was significantly associated with difficulty performing all eight weight-bearing activities. Compared to those with normal foot posture and function, participants with planus foot posture were more likely to report difficulty remaining balanced [odds ratio (OR) = 1.40, 95% confidence interval (CI) 1.06-1.85; p = 0.018] and individuals with pronated foot function were more likely to report difficulty walking across a small room (OR = 2.07, 95% CI 1.02-4.22; p = 0.045). Foot pain and planus foot posture were associated with an overall mobility limitation score combining performances on each measure. Conclusion: Foot pain, planus foot posture and pronated foot function are associated with self-reported difficulty undertaking common weight-bearing tasks. Interventions to reduce foot pain and improve foot posture and function may therefore have a role in improving mobility in older adults.

Dynamic and viscoelastic interfacial behavior of β-lactoglobulin microgels of varying sizes at fluid interfaces

HypothesisMicrogel particles formed from the whey protein β-lactoglobulin are able to stabilize emulsion and foam interfaces, yet their interfacial properties have not been fully characterized. Smaller microgels are expected to adsorb to and deform at the interface more rapidly, facilitating the development of highly elastic interfaces. MethodsMicrogels were produced by thermal treatment under controlled pH conditions. Dynamic surface pressure and dilatational interfacial rheometry measurements were performed on heptane–water droplets to examine microgel interfacial adsorption and behavior. Langmuir compression and atomic force microscopy were used to examine the changes in microgel and monolayer characteristics during adsorption and equilibration. FindingsMicrogel interfacial adsorption was influenced by bulk concentration and particle size, with smaller particles adsorbing faster. Microgel-stabilized interfaces were dominantly elastic, and elasticity increased more rapidly when smaller microgels were employed as stabilizers. Interfacial compression increased surface pressure but not elasticity, possibly due to mechanical disruption of inter-particle interactions. Monolayer images showed the presence of small aggregates, suggesting that microgel structure can be disrupted at low interfacial loadings. The ability of β-lactoglobulin microgels to form highly elastic interfacial layers may enable improvements in the colloidal stability of food, pharmaceutical and cosmetic products in addition to applications in controlled release and flavor delivery systems.

Intraoperative dynamic pressure measurements in carpal tunnel syndrome: Correlations with clinical signs

ObjectiveThis study was designed to evaluate the correlations between dynamic carpal tunnel pressure and clinical signs. MethodsFrom December 2008 to May 2010, open carpal tunnel release (OCTR) was performed on a total of 90 hands (83 patients). All patients completed neurological and provocation tests (two-point discrimination, Tinel test, Phalen test, reverse-Phalen test and assessment of thenar muscle atrophy). Carpal tunnel pressure (CTP) was measured in two parts of carpal tunnel (proximal and distal carpal tunnel) and in three different postures (neutral, wrist flexion and wrist extension). ResultsThere were 74 females and nine males aged 36 to 86 years (mean age 54). CTP values were more elevated in the wrist extension than wrist flexion in the proximal carpal tunnel but not at the distal carpal tunnel. There was no statistically significant correlation among CTP, provocation testing, and clinical signs. However, two-point discrimination (2-PD) showed a statistically significant correlation with CTP, especially in the proximal area in the wrist extension posture (P<0.01). Duration of symptoms (SD) statistically correlated with CTP in the distal carpal tunnel in the neutral posture (P<0.01). Conclusions2-PD and duration of symptoms are correlated with the CTP value in specific areas and with hand postures. This emphasizes the importance of releasing the entire carpal tunnel lesion since CTP values appear to vary within the carpal tunnel space and according to hand posture.

Isolated Chronic Exertional Compartment Syndrome of the Lateral Lower Leg

Background:Exercise-induced lower leg pain may be caused by chronic exertional compartment syndrome (CECS). The anterior (ant-CECS) or deep posterior compartment (dp-CECS) is usually affected. Knowledge regarding CECS of the lateral compartment (lat-CECS) is limited.Purpose:To describe demographic characteristics and symptoms in a consecutive series of patients with isolated CECS of the lateral compartment of the leg.Study Design:Case series; Level of evidence, 4.Methods:Since 2001, patients undergoing dynamic intracompartmental pressure (ICP) measurements for suspected CECS in a single institution were prospectively monitored. Individuals with a history possibly associated with lat-CECS and elevated ICP measurements (Pedowitz criteria) were identified. Exclusion criteria were concomitant ipsilateral ant-CECS/dp-CECS, acute compartment syndrome, recent significant trauma, peroneal nerve entrapment, or vascular claudication.Results:During an 11-year time period, a total of 26 patients with isolated lat-CECS fulfilled study criteria (15 females; median age, 21 years; range, 14-48 years). Frequently identified provocative sports were running (n = 4), walking (n = 4), field hockey (n = 3), soccer (n = 3), and volleyball (n = 2). Exercise-induced lateral lower leg pain (92%) and tightness (42%) were often reported. The syndrome was bilateral in almost two-thirds (62%, n = 16). Delay in diagnosis averaged 24 months (range, 2 months to 10 years).Conclusion:Young patients with exercise-induced pain in the lateral portions of the lower leg may suffer from isolated CECS of the lateral compartment. ICP measurements in the lateral compartment in these patients are recommended.

Parameters optimization of magnetic fluid micro-pressure sensor

Micro pressure sensors are widely used in several applications. In this paper parameters optimization of the magnetic fluid micro-pressure sensor is presented, including some theoretical aspects on the prototype. The proposed magnetic fluid micro-pressure sensor could be used in either static micro-pressure measurement or dynamic micro-pressure measurement. Under the premise of appropriate anti-pressure, the structure parameters of the magnetic fluid micro-pressure sensor should be small and the cost should be low when the sensor is used in static micro pressure measurement. However, when the sensor is used in dynamic micro pressure measurement, the overshoot should be small, and the regulation time should be short. In view of the two cases, different optimization methods are used to research. Nonlinear programming and simulation analysis are used to optimize the static micro pressure measurement, and theoretical derivation and experiment research are used to optimize the dynamic micro pressure measurement. In particular, the conclusions of preliminary design are given along with the suggestions of parameter setting in the future.

Evaluating the central pressure point to determine the optimal saddle setback

Background : Over half of all cyclists describe discomfort at the saddle as limiting condition. (Detori & Norvell, 2006) The saddle setback is an important parameter to consider when aiming to improve the comfort for sportive road bike riders in a professional analysis of the position on the bike. Traditional method Knee Over Pedal Spindle (KOPS) determines the saddle setback using the distance that the patella come over the centre of the pedal spindle This method, however, lacks empirical background and following expert advices gives a range of 80 mm for optimal setback position. (Burke and Pruit, 2003; Gressmann 2006). This paper empirically analyses the effect a change of the saddle position in the sagittal plane (setback) by ±10mm has on the position of the knee joint as well as the pressure parameters central pressure point (COP), maximal pressure and loaded surface on the saddle. Methods : In a lab-setting 18 sportive male cyclists were tested using a standardized watt-based protocol (7 minutes warm-up/ 100W, 5 * 4 minutes measurement/ 200W). The sitting position was standardized knee angle (mean 139.3°), hip angle at 78°-85° (mean 82°), shoulder angle at 90° (mean 90°) on a stationary fit bike (Size Cycle, USA). KOPS was measured with a high speed camera (60 HZ sampling rate) and the 2d motion analysis software GP BikeView (GebioM). Saddle pressure was measured with the saddle pressure system GB Bike (GebioM), which measures the saddle pressure with 64 sensors at a sampling rate of 200 HZ. Besides actual pressure, the additional GB Bike software also provide information centre of pressure, maximal pressure and the loaded surface The basis setup of the saddle in the sagittal plane was performed dynamically using the KOPS- method. The measurement sequence of setback +10 +5 -5 -10 was randomized, while sitting height and length remained constant. Results : Regarding saddle setback and KOPS it appeared that 12 of the subjects (67%) react to changes in setback by adjusting their position on the saddle, i.e., these riders sit different on their saddle, resulting in the same knee over pedal spindle. The other subjects (33%) did not change their position on the saddle, consequently a change in KOPS was measured by these riders. Setback positions +10mm and -10mm results in a highly significant change in the position of the riders’ COP on the saddle (p=0.01). Setback positions +5mm and -5mm results in a significant change of position (p = 0.04). There is a moderate relation between adjusting the COP towards the back of the saddle and reducing the maximal pressure in the pubic area as well as increasing the loaded area under the ischial tuberositis (r2 = 0.6/0.78). Conclusion: According to the currently available evidence, the KOPS-method provides for a position of the knee joint above the pedal spindle a range of approximately 80mm when following the different expert advices. Including the analysis and interpretation of the COP’s position during a dynamic saddle pressure measurement adds valuable information to finely adjust the saddle position in the sagittal plane within this range. Furthermore, analysing the position of the COP provides a means to quantify the comfort in the sitting area.

Combustion Instability Mode Transition in a Pilot Bluff-Body Stabilized Combustor

The pilot flame’s effects on dynamic stability have been investigated in a pilot bluff-body stabilized combustor at atmospheric pressure. During the experiment, the pilot fuel proportion increased from 6 to 20% with an interval of 2%, while the total equivalence ratio remained unchanged. Simultaneous dynamic pressure and unsteady heat release rate measurement and analysis were used to identify and characterize combustion instability modes. Combustion dynamics were captured by a high-speed camera. High-speed images were further analyzed by using proper orthogonal decomposition. With the increase of pilot fuel proportion, the transition between combustion instability modes of 33 and 130 Hz was observed. Based on acoustic mode analysis, the 33 and 130 Hz modes corresponded to the first and second longitudinal acoustic mode, respectively. The results show that the pilot fuel proportion affects the local equivalence ratio distribution in the shear layer and the recirculation zone. As a result, it has significant effects on the dynamics of pilot and main flame interactions, which lead to different unsteady heat release characteristics. Finally, the phenomenon of mode transition occurs when different acoustic modes have been excited.

Particle-based optical pressure sensors for 3D pressure mapping.

This paper presents particle-based optical pressure sensors for in-flow pressure sensing, especially for microfluidic environments. Three generations of pressure sensitive particles have been developed- flat planar particles, particles with integrated retroreflectors and spherical microballoon particles. The first two versions suffer from pressure measurement dependence on particles orientation in 3D space and angle of interrogation. The third generation of microspherical particles with spherical symmetry solves these problems making particle-based manometry in microfluidic environment a viable and efficient methodology. Static and dynamic pressure measurements have been performed in liquid medium for long periods of time in a pressure range of atmospheric to 40 psi. Spherical particles with radius of 12 μm and balloon-wall thickness of 0.5 μm are effective for more than 5 h in this pressure range with an error of less than 5%.

Design and Experimentation of Simulated Combustor Model for Aircraft Afterburner Applications

AbstractAn experimental study of the recirculation zone and mixing lengths for bluff-body stabilized flames is conducted at non-reactive conditions. This paper reports the prediction of recirculation zone length from dynamic pressure measurements. The auxiliary turbulence created from the wall of the combustor is also studied and maintained to levels as low as 5%. The experiments are conducted by varying the velocity from 5 m/s to 8 m/s for V-Gutters bluff-body with induced angles of 60, 90 and 120

The correlation between blood pressure and kidney function decline in older people: a registry-based cohort study

ObjectivesTo examine the relation between static and dynamic blood pressure (BP) measurements and the evolution of kidney function in older people, adjusted for the presence of multimorbidity.DesignRetrospective cohort study during...

Visual Criteria for Measuring Two-phase Flow Rate in Venturi with Flow Homogenizer

A simple use of Venturi might be used to measure two-phase flow rate within relatively low GVF(gas volume fraction). Upstream flow entering Venturi can be improved with installed flow homogenizer which is easily fabricated by 3-dimensional printer with multiple holes. Simultaneous measurement between high-speed flow visualization and dynamic differential pressure measurement was made to find visual criteria for two-phase flow rate measurement with different GVF ranged from 0% to 30%. It was observed that the two-phase flow rate can be reliably measured up to 15% of GVF using flow homogenizer. FFT(Fast-Fourier Transform) results proved that the long flow homogenizers (type 2 and 4) showed a lower amplitude of differential pressure (Δp) than the short flow homogenizers (type 1 and 3) respectively. So the optimized flow homogenizer can be useful to measure two-phase flow rate at low GVF.

Experimental Characterization of a Pump–Turbine in Pump Mode at Hump Instability Region

The unsteady phenomena of a low specific speed pump–turbine operating in pump mode were characterized by dynamic pressure measurements and high-speed flow visualization of injected air bubbles. Analyses were carried out on the pressure signals both in frequency and time–frequency domains and by bispectral protocol. The results obtained by high-speed camera were used to reveal the flow pattern in the diffuser and return vanes channels The unsteady structure identified in the return vane channel appeared both at full and part load condition. Furthermore, a rotating stall structure was found and characterized in the diffuser when the pump operated at part load. The characteristics of these two unsteady structures are described in the paper.

Validation of Transverse Instability Damping Computations for Rocket Engines

The reliable numerical evaluation of thermoacoustic stability is one of the most important unresolved problems in the development of liquid rocket engines. To provide data for code validation, a transonic cold-flow test facility was built, which comprises a rocket engine model for acoustic measurements. It consists of a cylindrical chamber with inflow through a perforated plate representing the faceplate and a choked nozzle at the exit. The flow is excited with a siren and complex eigenfrequencies, and the nozzle admittances for the most critical first-transverse mode are extracted from dynamic pressure measurements. These data are used to benchmark three stability assessment tools of widely varying numerical complexity. Results obtained with one- and three-dimensional methods based on the solution of the linearized Euler equations and results from nonlinear Navier–Stokes computations (unsteady Reynolds-averaged Navier–Stokes) are compared with the experimental data. All three codes reproduce the measured first-transverse-mode frequency, but only the two linearized Euler equation methods provide satisfactory values for first-transverse-mode damping and nozzle admittance. The nozzle admittances calculated from the unsteady Reynolds-averaged Navier–Stokes results exhibit large scatter, but the average of the data from 11 monitor points is close to the measured values and mode decomposition during data analysis is expected to reduce scatter further. However, the employed unsteady Reynolds-averaged Navier–Stokes method overpredicts nozzle damping.