Dynamic Pressure Generator Research Articles

Optimization of an impulse pressure generator based on the drop-weight method.

An optimized impulse dynamic pressure generator based on a drop-weight method was developed as a secondary standard. The impulse pressure generator was characterized in detail using various parameters in order to obtain a proper reference dynamic pressure, to calibrate a dynamic pressure sensor. Both a hardware filter and a software filter were successfully employed to eliminate unavoidable noise when the impulse pressure was generated. Five variables were considered to optimize the system. A larger effective area piston-cylinder assembly should be used to obtain a faster impulse pressure. To control the peak pressure using a variable drop height is easier rather than drop weight because the change is linearly proportional to the impact speed associated with the drop height. An increase in drop weight causes an increase in duration as well as an increase in peak pressure. In addition, the pressure transmission medium is very important for generating the optimized impulse pressure, so an appropriate fluid choice is required. The viscosity and bulk modulus among the fluid properties are considered as design variables. High viscosity fluids with high bulk modulus can achieve high peak pressures without jittering. The drop weight based impulse pressure generator design and implementation method is proposed based on the detailed characterizations in this study.

The effect of heat conduction on the piston-in-cylinder dynamic pressure generator

This paper deals with the effect of heat conduction on the piston-in-cylinder dynamic pressure generator in order to indicate the transition from isothermal to adiabatic behaviour when increasing the pulsation frequencies. A mathematical model for the perfect gas in the cylindrical chamber is used to study the physical background of the effect of heat conduction on frequency characteristics of the pressure generator. Frequency characteristics of the pressure generator were theoretically obtained for different gases and average pressures.

Development of a dynamic pressure generator based on a loudspeaker with improved frequency characteristics

This paper presents the development and analysis of a measurement system with a dynamic pressure generator that is designed for the purpose of investigating the frequency characteristics of pressure connecting tubes. The developed dynamic pressure generator (DPG) consists of an electrodynamic loudspeaker that generates stable and adjustable sinusoidal pressure pulsations inside the air chamber within the generator housing. As the frequency characteristics of the DPG are defined by the properties of the loudspeaker diaphragm, the air chamber and the connections of the reference pressure sensor to the DPG, the DPG dimensions were optimized with the help of physical–mathematical modeling. Experimental analysis of the developed DPG, which enables flush mounting of the reference pressure sensors, showed improved amplitude and phase-frequency characteristics in comparison with the previous configuration of the DPG based on two loudspeakers.

An investigation on characterization of dynamic pressure transducers using material impact test machine

The need for reliable dynamic measurements and characterization of pressure transducers are important, especially in the fields of aerospace, defense and machinery manufacturing. Such measurements are performed on systems in which input pressure varies over time and must accurately capture the dynamic variations in pressure over short time intervals. This study presents a research work and measurements on the dynamic calibration of pressure transducers using a drop mass system and a high-speed impact tester. The impact test machine also uses the drop mass principle similar to some secondary level dynamic measurement instruments. The pulses which are produced by the impact test machine can be used as a dynamic pressure generator for the test and characterization of pressure transducers. For this purpose, a new experimental calibration setup was constructed on the impact test machine. The dynamic behaviors of pressure transducers were investigated using pulses obtained from varying dropping speeds and energies of the drop mass in this new setup. Experimental results were compared with the results obtained from a manual drop mass pulse generator. Results show that while there is some variance about 15% at 200 MPa as the variance becomes less than 5% at 300, 400, and 500 MPa. As a result, it is concluded that an impact test machine can be used as a reliable dynamic pulse generator.

Dynamic pressure generator for dynamic calibrations at different average pressures based on a double-acting pneumatic actuator

The ability to conduct dynamic calibrations of pressure sensors at different average pressures is very important because the dynamic properties of pressure sensors also depend on the value of the average pressure during the pressure pulsations. The main limitation of periodic dynamic pressure generators is the difficulty in achieving sinusoidal pulsations at higher amplitudes and frequencies in a gaseous medium due to the nonlinearities that result from the physical gas dynamics. This paper presents a newly developed dynamic pressure generator based on a double-acting pneumatic actuator in which the piston is driven by an electrodynamic shaker. In order to minimize the static preload of the shaker, which is due to the pressure acting on the piston, and therefore to enable the generation of larger pressure pulsations at different average pressures with the same excitation force, the cylinder chambers above and below the piston are pressurized with the same initial static gas pressure. As the dynamic characteristics of the dynamic pressure generator are also defined by the properties of the piston and both the cylinder chambers, the actuator dimensions were optimized with the help of mathematical modeling. In order to demonstrate the capabilities and limitations of the developed dynamic pressure generator, both mathematical and experimental analyses were performed.

Miniature low-pass mechanical filter for improved frequency response with MEMS microphones & low-pressure transducers

We present an acoustic low-pass mechanical filter for high intensity, high temperature silicon piezoresistive microelectromechanical system (MEMS) microphones and low-pressure (<170kPa) differential transducers that has been tuned such that only static pressure and low frequency (DC to 1–10Hz) dynamic pressures are passed to the backside of the pressure sensitive diaphragm. We present an analytical modelof the frequency response of the low-pass mechanical filter that is based on 1D wave propagation with viscous dissipation. We compare the model to experimental results obtained using a spinning valve dynamic pressure generator to demonstrate improved performance of the transducer in the frequency range of 1–2800Hz. Experimental test results yield a −3dB point at 5±4Hz for the low-pass mechanical filter. The addition of this filter enables the use of a MEMS microphone without a controlled static pressure supplied to the transducer's differential tube or the addition of several meters of tubing to prevent the transmission of low frequency content to the backside of the pressure sensitive diaphragm. The spinning valve dynamic pressure tests demonstrate a flat frequency response (±2dB, 25% deviation from the accepted input signal) from 20Hz to 2.8kHz (test limitation) for a close-coupled measurement at the front of the microphone, which is expected to remain constant over the operating temperature range of the transducer and at various static ambient pressures both above and below atmospheric pressure.

An Experimental and Theoretical Investigation of Wave Propagation in Teflon and Nylon Tubing With Methods to Prevent Aliasing in Pressure Scanners

Accurate static and dynamic pressure measurements provide the feedback needed to advance gas turbine efficiency and reliability as well as improve aircraft design and flight control. During turbine testing and aircraft flight testing, flush mounting pressure transducers at the desired pressure measurement location is not always feasible and recess mounting with connective tubing is often used as an alternative. Resonances in the connective tubing can result in aliasing within pressure scanners even within a narrow bandwidth and especially when higher frequency content dc to ∼125 Hz is desired. We present experimental results that investigate tube resonances and attenuation in 1.35 mm inner diameter (I.D.) (used on 0.063 in. tubulations) and 2.69 mm I.D. (used on 0.125 in. tubulations) Teflon and Nylon tubing at various lengths. We utilize a novel dynamic pressure generator, capable of creating large changes in air pressure (&lt;1 psi to 10 psi, &lt;6.8 kPa to 68.9 kPa), to determine the frequency response of such tubing from ∼1 Hz to 2800 Hz. We further compare these experimental results to established analytical models for propagation of pressure disturbances in narrow tubes. While significant theoretical and experimental work relating to the frequency response of connective tubing or transmission lines has been published, there is limited literature presenting experimental frequency response data with air as the media in elastic tubing. In addition, little progress has been made in addressing the issue of tubing-related aliasing within pressure scanners, as the low sampling rate in scanners often makes postprocessing antialiasing filters ineffective.

Diagnosis of oscillating pressure-driven flow in a microdiffuser using micro-PIV

In this study, the characteristics of oscillating pressure-driven flow in a microdiffuser are examined by μPIV (micro Particle Image Velocimetry) diagnostics. Utilizing a cam-follower system, a dynamic pressure generator is built in-house to provide a time-varying sinusoidal pressure source. Three parameters are examined experimentally: the excitation frequency, the cam size, and the half-angle of the microdiffuser. Driven by oscillating pressure, we find that there exists an optimal half-angle such that maximum net flow is attained in the expansion direction. Contrarily to the prediction of hydraulics theory which only considers steady flow, flow in the microdiffuser of the optimal half-angle does not necessarily remain attached. Rather, maximum net flow can also occur in microdiffusers where vortices retain a slender shape. When vortex bubbles are slender, the μPIV results reveal that the core flow accelerates to a higher forward velocity during the first half of the cycle and flow rectification is actually enhanced. Due to the three-dimensional flow structure, fluid is drawn out of the vortices near the reattachment point to join the core flow and consequently magnifies the forward flow. As the half-angle increases, vortices become rounder and the core flow is drastically narrowed to reduce flow rectification.

Characteristics of a dynamic pressure generator based on loudspeakers

The dynamic pressure generator under discussion consists of two, face-to-face-orientated electrodynamic loudspeakers and the air chamber between. The aim of this paper is to investigate the static and dynamic characteristics of this pressure generator. Physical modelling and an experimental analysis were employed to demonstrate its capabilities and limitations. The generator's static sensitivity, which was defined by the ratio between the generated pressure and the excitation electric current, mainly depends on the ratio between the force factor and the effective area of the loudspeakers. The presented system has relatively good precision and stability, and a small sensitivity to changes in the internal volume. Its dynamic characteristics are defined by the properties of the loudspeaker diaphragm, the air chamber between the loudspeakers and the connection of the device under test to the pressure generator.

Active mixing in diverging microchannels

In this study, active mixing in diverging microchannels is investigated experimentally. Using a custom-built dynamic pressure generator as the actuation source, the influences of the half-angle of the diverging section and the phase difference of the two actuating pressures in mixing performance are explored. Two flow characteristics, hydrodynamic instability and fluid lamellae, are identified as the main mechanisms leading to mixing enhancement. Even at very low Reynolds numbers, flow instability occurs in large half-angle diverging micromixers. The resulting tendril structures provide extra stretching and folding of the interface, and the degree of mixing increases accordingly. Nevertheless, flow instability alone is insufficient. To achieve excellent mixing in the diverging microchannels, the presence of both mechanisms is necessary. While pulsatile pressures vary in-phase, incoming streams flow collaterally and there is no fluid lamella effect. The concentration field is highly inhomogeneous even though tendril structures appear near the throat. In contrast, flow remains quite stable under anti-phase actuation. Fluid flows reciprocally between the two upstream branches during more than three quarters of a cycle, and patterns a series of fluorescence bands. Mixing is limited to molecular diffusion and performs poorly. When the phase difference shifts away from 0 and π, mixing performance improves significantly. To obtain the best results, a phase difference between 0.25π and 0.5π (or 1.5π and 1.75π) and a diverging micromixer with a large half-angle are preferred.

In‐vitro comparison of sensors and amplifiers to measure left ventricular pressure in mice

Several companies market catheters to measure left ventricular (LV) pressure in mice, and it is often assumed that all sensors are similar, but there may be important differences in fidelity, stability, and immunity to noise and artifacts. We used an electronic signal generator, a dynamic pressure generator, and a laboratory scale to measure the frequency and step responses, immersion response, stability, accuracy, linearity, and sensitivity to side forces of amplifiers and 4 solid‐state sensors each from Millar, Scisense, and RADI. All sensors were stable after immersion with drifts of &lt;1 mmHg/hr over 5 hrs, had flat frequency responses to &gt;1 kHz, and were accurate and linear to within ±2 mmHg from 0‐300 mmHg. The amplifiers from Millar, Scisense, and RADI had time delays of 0.2, 3.2 and 10.6 ms; rise times of 300, 50, and 250 mmHg/ms; and 6 dB‐down frequency responses of 1200, 300, and 600 Hz respectively. The Scisense (but none of the other) catheters showed a 5.3 mmHg/g response to lateral forces applied to the sensor tip. Given that all of these semi‐rigid catheters straighten the normally curved vascular path upon insertion, the dynamic cardiac forces could generate significant "pressure" signals. We conclude that there are significant differences in solid‐state mouse pressure sensors and amplifiers which could generate unrecognized offsets, time delays, and distortions of raw signals and derivatives in‐vivo.

The Measurement and Analysis of Pressure Square Wave Generator

Investigating the dynamic characteristics is a significant study for actual hydraulic pressure system because the dynamic environment is used more often than static one. A dynamic pressure generator is called pressure square wave generator (PSWG) that developed in our team and generate square-like waveform and change testing pressure and frequency form 0.1 to 5 MPa and 12 to 2 KHz, respectively. In this study, dynamic performance of PSWG was investigated under different testing tangent velocity of rotor of PSWG including detailed transient response of a pressure square-like wave, rise time and deviation of magnitude. Results show that the tangent velocity of the rotor of PSWG affects the transient response of pressure square-like wave form. The desired transient response can be obtained when the tangent velocity is larger than 0.5 m/s. Furthermore, the larger the tangent velocity used, the smaller the rise time will be.

Method of evaluating frequency characteristics of pressure transducers using newly developed dynamic pressure generator

A dynamic pressure generator using a rotating valve has been developed to evaluate the dynamic characteristics and performance of pressure transducers. The waveform of the generated dynamic pressure is square, and the amplitude and fundamental frequency can be varied. In this paper, the generator using a novel rotating valve and the method of evaluating the frequency characteristics of pressure transducers using the generator are described. With the amplitude of the dynamic pressure of 10 kPa and varying the fundamental frequency in 1-Hz increments between 10 and 50 Hz, we measured the generated dynamic pressure using two different pressure transducers, and to obtain the amplitude spectrum of the measured waveform using frequency analysis. Then, the magnitude of the harmonic components in the spectrum are shown as a function of frequency. From the simultaneous outputs of two transducers, the frequency characteristics of one transducer was compared with that of the other.