Jonathan D. Blotter

Flow Rate Measurements Using Flow-Induced Pipe Vibration

This paper focuses on the possibility of a non-intrusive, low cost, flow rate measurement technique. The technique is based on signal noise from an accelerometer attached to the surface of the pipe. The signal noise is defined as the standard deviation of the frequency averaged time series signal. Experimental results are presented that indicate a nearly quadratic relationship between the signal noise and mass flow rate in the pipe. It is also shown that the signal noise - flow rate relationship is dependant on the pipe material and diameter.

Design of a Linear Ultrasonic Piezoelectric Motor

A new geometrically unique ultrasonic motor (USM) was designed, prototyped, and tested. USMs operate by vibrating a drive tip in an elliptical motion while in periodic contact with a driven surface. Piezoelectric elements are used to create the elliptical motions and are driven at near resonance frequencies to create the needed displacements for the motor to operate. The motor in this article consists of an arched frame, a center ground, and two piezoelectric elements connected to the center ground. Several finite element models were developed to design the motor and to predict performance. The models predicted a linear motor capable of pushing up to 5 N and a maximum speed of 0.4 m/s. A prototype frame was built out of tool steel and run against an oxide ceramic plate. The prototype motor achieved a maximum speed of 55.6 mm/s and a push force of 0.348 N at a preload of 6 N. The prototype frame’s steady-state displacements were approximately 20% of the expected output from the finite element models. Reasons for these discrepancies are discussed and investigated.

Experimental and numerical investigation of turbulent flow induced pipe vibration in fully developed flow

Flow-induced pipe vibration caused by fully developed pipe flow has been observed but not fully investigated when turbulent flow prevails. This article presents experimental results that indicate a strong correlation between the volume flow rate and a measure of the pipe vibration. In this work, the standard deviation of the frequency-averaged time-series signal, measured using an accelerometer attached to the pipe, is used as the measure of pipe vibration. A numerical, fluid-structure interaction (FSI) model used to investigate the relationship between pipe wall vibration and the physical characteristics of turbulent flow is also presented. This numerical FSI approach, unlike commercial FSI software packages, which are based on Reynolds averaged Navier-Stokes flow models, is based on large eddy simulation (LES) flow models that compute the instantaneous pressure fluctuations in turbulent flow. The results from the numerical LES models also indicate a strong correlation between pipe vibration and flow rat...

Eigenvalue equalization filtered-x algorithm for the multichannel active noise control of stationary and nonstationary signals

The FXLMS algorithm, which is extensively used in active noise control, exhibits frequency dependent convergence behavior. This leads to degraded performance for time-varying and multiple frequency signals. A new algorithm called the eigenvalue equalization filtered-x least mean squares (EE-FXLMS) has been developed to overcome this limitation without increasing the computational burden of the controller. The algorithm is easily implemented for either single or multichannel control. The magnitude coefficients of the secondary path transfer function estimate are altered while preserving the phase. For a reference signal that has the same magnitude at all frequencies, the secondary path estimate is given a flat response over frequency. For a reference signal that contains tonal components of unequal magnitudes, the magnitude coefficients of the secondary path are adjusted to be the inverse magnitude of the reference tones. Both modifications reduce the variation in the eigenvalues of the filtered-x autocorrelation matrix and lead to increased performance. Experimental results show that the EE-FXLMS algorithm provides 3.5-4.4 dB additional attenuation at the error sensor compared to normal FXLMS control. The EE-FXLMS algorithms convergence rate at individual frequencies is faster and more uniform than the normal FXLMS algorithm with several second improvement being seen in some cases.

Measurement of sound power and absorption in reverberation chambers using energy density

Reverberation chamber measurements typically rely upon spatially averaged squared pressure for the calculation of sound absorption, sound power, and other acoustic values. While a reverberation chamber can provide an approximately diffuse sound field, variations in sound pressure consistently produce uncertainty in measurement results. This paper explores the benefits of using total energy density or squared particle velocity magnitude (kinetic energy density) instead of squared pressure (potential energy density) for sound absorption and sound power measurements. The approaches are based on methods outlined in current ISO standards. The standards require a sufficient number of source-receiver locations to obtain suitable measurement results. The total and kinetic energy densities exhibit greater spatial uniformity at most frequencies than potential energy density, thus requiring fewer source-receiver positions to produce effective results. Because the total energy density is typically the most uniform of the three quantities at low frequencies, its use could also impact the usable low-frequency ranges of reverberation chambers. In order to employ total and kinetic energy densities for sound absorption measurements, relevant energy-based impulse responses were developed as part of the work for the assessment of sound field decays.

Cavitation Inception and Head Loss Due to Liquid Flow Through Perforated Plates of Varying Thickness

This paper reports results of an experimental investigation of the loss coefficient and onset of cavitation caused by water flow through perforated plates of varying thickness and flow area to pipe area ratio at high speeds. The overall plate loss coefficient, point of cavitation inception, and point where critical cavitation occurs are functions of perforation hole size, number of holes, and plate thickness. Sixteen total plates were considered in the study with the total perforation hole area to pipe area ratio ranging from 0.11 and 0.6, the plate thickness to perforation hole diameter ranging from 0.25 to 3.3, and the number of perforation holes ranging from 4 to 1800. The plates were mounted in the test section of a closed water flow loop. The results reveal a complex dependency between the plate loss coefficient with total free-area ratio and the plate thickness to perforation hole diameter ratio. In general, the loss coefficient decreases with increasing free-area ratio and increasing thickness-to-hole diameter ratio. A model based on the data is presented that predicts the loss coefficient for multiholed perforated plates with nonrounded holes. Furthermore, the data show that the cavitation number at the points of cavitation inception and critical cavitation increases with increasing free-area ratio. However, with regard to the thickness-to-hole diameter ratio, the cavitation number at inception exhibits a local maximum at a ratio between 0.5 and 1.0. Empirical models to allow prediction of the point of cavitation inception and the point where critical cavitation begins are presented and compared to single hole orifice plate behavior.

Cavitation at Sharp Edge Multi-Hole Baffle Plates

This paper reports results of an experimental investigation of cavitation caused by water flow through sharp edge multi-hole baffle plates at high speeds and large pressure drops. Such cavitation can be destructive to industrial systems due to the induced pipe wall vibrations that result. Incipient and critical cavitation numbers are design limits that are frequently needed in the design of systems implementing baffle plate type geometries to prevent adverse cavitation effects. The overall baffle plate loss coefficient, point of cavitation inception, and point where critical cavitation occurs are functions of baffle hole size, number of holes, and plate thickness. Sixteen total baffle plates were considered in the study with hole sizes ranging from 0.16 cm to 2.54 cm, total through area ranging between 11% and 60%, plate thickness ranging from 0.32–0.635 cm, and number of holes ranging from 4 to 1800. The plates were mounted in the test section of a 10.2 cm diameter schedule 40 pipe closed water flow loop. The focus of this paper is on how the influencing parameters affect the loss coefficient and the point of cavitation inception. The results show a complex dependency between the baffle plate loss coefficient with total through area ratio and the thickness to baffle hole diameter ratio. In general the loss coefficient decreases with increasing openness and increasing thickness to hole diameter ratio. A model based on the data is proposed to predict the loss coefficient for multi-holed baffle plates. Further, the data show that the cavitation number at the point of cavitation inception increases with increasing openness. However, with regard to the thickness to hole diameter ratio, the cavitation number at inception exhibits a local maximum at a ratio between 0.5 and 1.0. Models to allow prediction of the point of cavitation inception and the point where critical cavitation begins are presented in the paper.Copyright

Near-field vector intensity measurements of a small solid rocket motor

Near-field vector intensity measurements have been made of a 12.7-cm diameter nozzle solid rocket motor. The measurements utilized a test rig comprised of four probes each with four low-sensitivity 6.35-mm pressure microphones in a tetrahedral arrangement. Measurements were made with the rig at nine positions (36 probe locations) within six nozzle diameters of the plume shear layer. Overall levels at these locations range from 135 to 157 dB re 20 microPa. Vector intensity maps reveal that, as frequency increases, the dominant source region contracts and moves upstream with peak directivity at greater angles from the plume axis.

Energy-Based Acoustical Measurements of Rocket Noise

Energy-based acoustical measurements are investigated in the context of more fully characterizing rocket noise source regions. Near-field measurements made on statically fired GEM-60 motors are described and the performance of two types of four-microphone tetrahedral probes is discussed. Vector intensity plots reveal the magnitude and directionality of the near-field sound radiation as a function of frequency, position, and time in the plume. HE development of the next-generation space flight vehicles has prompted renewed interest regarding source characterization and near-field propagation models of rocket noise. This source characterization is required to determine the vibroacoustic impact on flight hardware and structures in the vicinity of the launch pad. Brigham Young University has been involved in an effort to develop and validate an energy-based acoustic probe suitable for use in rocket fields, in particular the RS-68B engine to be used on the Ares V vehicle. Energy-based acoustical measurements require estimation of both the collocated acoustic pressure and the threedimensional particle velocity. From the pressure, a scalar, and the particle velocity vector, a number of energybased quantities can be calculated, including vector acoustic intensity, specific acoustic impedance, potential, kinetic, and total energy densities, and the Lagrangian density. Knowledge of one or more of these quantities may

Obtaining the complex pressure field at the hologram surface for use in near-field acoustical holography when pressure and in-plane velocities are measured

Acoustical-based imaging techniques have found merit in determining the behavior of vibrating structures. These techniques are commonly used in numerous applications to obtain detailed noise source information and energy distributions on source surfaces. Source reconstructions using near-field acoustical holography (NAH) are reliant upon accurate measurement of the pressure field at the hologram surface. For complex acoustic fields this requires fine spatial resolution and therefore demands large microphone arrays. In this paper, an interpolation method is developed for obtaining the complex pressure field at the hologram surface from pressure and velocity measurements. Because particle velocity measurements provide directional information, a more accurate characterization of the pressure field with fewer measurement locations is obtained. The processing technique presented does not relate directly to the holographic reconstruction itself. However, the interpolation scheme presented serves as a preprocess...