Commercial vortex shedding flow meters use the relation between the mean flow velocity and the vortex frequency generated by bluff bodies. Usually, the vortices are detected by pressure sensors in the pipe wall or inside the bluff body. Using ultrasound for vortex detection is a powerful, advantageous alternative combination. The ultrasonic beam is modulated by the velocity components of the vortices and varying fluid density. The modulation depends on the structures of the vortices, which are influenced by the bluff body geometry. Measurements and simulations show that conventional triangular bluff bodies with the large size used for pressure measurements are unsuitable for ultrasonic measurements because of the lack of knowledge about secondary vortices. They can be avoided by turning the bluff body facing the tip to the inflow. As ultrasound is very sensitive to the smallest influences, the bluff body size can be reduced considerably. Even the shape can be adapted. The best results are obtained with a 3 mm threaded rod as the bluff body in a pipe of 100 mm diameter. Pressure losses behind such small bluff bodies can be neglected.

The coincidence of turbulent structures in a gaseous flow raises a lot of questions concerning physics and signal processing. The determination of correlation functions with complex modulated signals can be simplified by undersampling the signal as only the sidebands include the information needed. Demodulation can be performed by Quadratur-Amplitude-Demodulation (QAD) techniques. The cross correlation function of the recovered amplitudes and phases result in a distinct maximum at the turbulence travelling time of the flow.The same signal processing can be applied to ultrasonic measurements in vortex shedding flow meters. On account of the high sensitivity of ultrasound to turbulences the size of bluff bodies can be drastically reduced in comparison to conventional vortex flow meters. Various shapes have been examined with surprising results.

Measurement of gas flow velocity with ultrasound by cross correlation functions were causing intensive investigations of complex modulated signals. The ultrasound signal is modulated in amplitude and in phase as well by various physical effects explained. The demodulation of the signal by undersampling and the separation of amplitude and phase modulated parts by Hilbert-transform are described. Cross correlation functions applied to these separated signals result in well defined measurements of flow velocity.

Carrier-based measurements usually obtain signals which are as well modulated in amplitude as in phase. Such complex modulated information needs to be separated with special methods extensively described in the literature. One problem is common for all methods: the costly processing of signals makes the use of microprocessors necessary. But this again raises the price of a measurement device so that a cheaper, completely hardware-based demodulation principle is desired. A basic method with hard restrictions concerning the modulation depth was introduced at the XVth IMEKO World Congress in Osaka and additional improvements for a more reliable device are shown in this paper.

Natural variations of pressure, density and velocity occuring in streaming fluid modulated ultrasonic signals. The characteristics of modulated ultrasonic signal in gas flow are strongly dependent on velocity. This paper describes a way to find a velocity dependent characteristic quality detected in the modulated signal and to determine the flow rate on the basis of signal analysis of only one ultrasonic barrier.

This paper continues the research presented at the IMEKO XV World Congress in Osaka/JP. It gives deeper insights into the topic of measuring the average volume flow with ultrasound based flow meters in a pulsating fluid. Pulsations are very common in industrial applications so that flow meters have to cope with this kind of disturbances. Especially ultrasonic flow meters are expected to react very sensitively to this effect because they measure any kind of pressure changes. By generating pulsations with a rotating paddle the following article will give impressions about possible influences and the maximum operating range of a cross-correlation and a vortex frequency meter. In addition to the IMEKO basic interpretations are proved by new theoretical considerations.

Designing bluff-bodies for the ultrasonic vortex frequency measurement almost leads to very different geometries as they are used for the vortex detection method by pressure sensors. In some cases they have the same form but they are facing their backside to the inflow. The developing process is not only restricted by the demand for a constant Strouhal number and a strong linear dependency of the vortex frequency to the mean flow velocity but also by the vortex detection method.

Abstract: The high sensitivity of ultrasound on small turbulences leads to new considerations on the dimensioning of bluff-bodies and the positioning of the ultrasound beam. Smaller dimensions cause smaller pressure loss, higher vortex frequencies and higher signal resolution. The high sensitivity of ultrasound on modulating influences admits the measurement not only behind but also in front of the bluff-body with the advantage of better signal-to-noise ratio.

The ultrasonic cross-correlation flowmeter is not only a reliable measurement device due to recent improvements in signal processing; it can even be used for gaining further knowledge about the properties of turbulent flow. This paper shows as well considerations about fluctuations, measuring time and ergodicity as arrangements and necessities for multi path measurements. Results are used for averaging and first tomographic approaches for the visualization of turbulent flow.

The classical analysis by correlation functions has been applied in some branches of engineering far a long time. They were mainly used in communication and control technique. In other fields, especially in the measurement of nonelectrical quantities correlation functions were introduced in the last seventies and at the beginning of the eighties. Measurements could only be performed analogously. They were expensive and were applied only in laboratories. Digital signal processing nowadays allow cost-saving solutions. Correlation methods gain more and more acceptance in industrial applications.

Most commercial vortex-shedding flowmeters rely on a known relationship between the vortex-shedding frequency and the mass flow, needing a regular and well-defined vortex structure as well as a shedding mechanism. However, in most known current designs, the pressure sensors are included into the bluff body, imposing severe restrictions on the shape of the body. This results in rather irregular pressure signature of the vortex system, leading to problems in the signal processing. In the present work, the flow about the bluff body in a vortex-shedding flowmeter is numerically investigated using a Navier–Stokes solver, capable of handling unsteady, compressible and viscous flows in two-dimensional and three-dimensional geometries. The computations are compared with experimental results obtained by ultrasonic measurements downstream of the bluff body. Several different body shapes are studied, trying to optimize the resulting pressure signature downstream of the body. Recommendations regarding an aerodynamically optimal shape of the bluff body are made.

The determination of correlation functions with modulated signals can be simplified by undersampling the signals as only the sidebands include the information needed. The demodulation is performed by Quadrature-Amplitude-Demodulation (QAD) techniques. The cross correlation function of the recovered amplitudes and phases result in a district maximum at the turbulence travelling time of a gaseous flow. Measurements confirm the procedures presented with high stability and low uncertainty.

In high precision multisensoric measurement arrangements there are n different sets of calibration parameters for n sensors. III the measurement software an assignment between channel and sensor parameters is done. Mistakes in assignment may cause errors. The compensation of users mistakes was matched by an automatic assignment with evolutionary strategies.

Despite of intensive research in cross-correlation ultrasonic flow measurement in the 80s, the measurement principle did not succeed in industry because of the complex signal processing necessary. The rapid increase of the performance of digital processors which took place in recent years requires a new view on this complexity. Especially the possibility of performing exact measurements in distorted flow profiles by using several ultrasound paths offers new perspectives. The work described herein concentrates on the processing of the ultrasound signals and on the measurement results obtained with the processing algorithm that was used. Furthermore, a model to explain the physical background of the measurement principle is presented.

The present paper investigates vortex shedding flowmeters coupled with a detection of the vortex frequency by an ultrasound barrier behind the bluff body. After a short explanation of the measurement principle a novel digital algorithm for determining the vortex frequency is presented. Another issue deals with the influence of the bluff body geometry on the measurement process. Comparisons between numerical simulations and experiments were performed in order to analyse the relationship between the shape of the vortex body and the vortices developing behind it.

Stover, J; Lenzlinger, P; Hans, V; Stocker, R; Imhof, H†; Trentz, O; Morganti-Kossmann, C; Kossmann, T Author Information

A profound inflammatory response is initiated immediately following traumatic brain injury (TBI) and is characterized by the release of several cytokines with pro- and anti-inflammatory functions. In order to elucidate which cytokines are released in the human brain in response to injury as well as in the peripheral compartment, IL-1, IL-6, IL-8, IL-10, TNF-α and TGF-β were monitored in CSF and serum of severely brain-injured patients. Furthermore, we investigated the possible modulation of systemic reactions by IL-6 and the ability of IL-6 and IL-8 to promote the synthesis of nerve growth factor.

Lenzlinger, P M; Stover, J F; Hans, V; Morganti-Kossmann, M C; Trentz, O; Kossmann, T Author Information

Lenzlinger, P. M.; Hans, V.; Morganti-Kossmann, M. C.; Joller, H.; Trentz, O.; Kossmann, T. Author Information