On the Determination of the Transfer Function of Infinite Line Pressure Probes for Turbomachinery Applications

2012 ◽  
Author(s):  
Nicolas Van de Wyer ◽  
Jean-François Brouckaert ◽  
Rinaldo L. Miorini
Keyword(s):  
Transfer Function ◽  
Frequency Response ◽  
Pressure Fluctuations ◽  
Axial Compressor ◽  
Fast Response ◽  
Experimental Results ◽  
Geometrical Parameters ◽  
Electrical Transmission ◽  
Infinite Line ◽  
Line Pressure

This paper deals with the use of the infinite line pressure probes (ILP) to measure fluctuating pressures in hot environments in turbomachinery applications. These probes, sometimes called waveguide measuring systems, and composed of a series of lines and cavities are using a remote pressure sensor. Ideally they should form a non-resonant system. This is however not always the case and the frequency response of these systems is of course limited by the tubing (diameter and length) but is also highly dependent on other geometrical parameters like sudden expansions or discontinuities in the tubing, or parasite cavities. The development of a new model for ILP simulation, based on the analogy between the propagation of the pressure waves in a line-cavity system and the electrical transmission line, is presented. Unlike the models based on the Bergh and Tijdeman equations, this approach allows the simulation of systems presenting parallel branches. This makes the model appropriate for the prediction of the frequency response of ILP. The model is validated by a comparison of the results with the theory of Bergh and Tijdeman, and with experimental results from the literature and from shock tube tests. Finally, the model is applied for the optimization of ILPs, representative of the systems used in the aeronautics industry, and compared to the experimental results performed on an axial compressor. In those tests, a typical ILP geometry is installed on the compressor casing to measure static pressure fluctuations in the rotor tip gap. Simultaneous measurements with a fast response flush-mounted sensor provided data for comparison and validation of the predicted transfer function.

Surge and Rotating Stall in Axial Flow Compressors—Part II: Experimental Results and Comparison With Theory

1976 ◽  
Vol 98 (2) ◽  
pp. 199-211 ◽  
Author(s):  
E. M. Greitzer
Keyword(s):  
Quantitative Description ◽  
Axial Compressor ◽  
Axial Flow ◽  
Rotating Stall ◽  
Experimental Results ◽  
System Response ◽  
Physical Parameters ◽  
Geometrical Parameters ◽  
Compression System ◽  
Transient System

This paper reports an experimental study of axial compressor surge and rotating stall. The experiments were carried out using a three stage axial flow compressor. With the experimental facility the physical parameters of the compression system could be independently varied so that their influence on the transient system behavior can be clearly seen. In addition, a new data analysis procedure has been developed, using a plenum mass balance, which enables the instantaneous compressor mass flow to be accurately calculated. This information is coupled to the unsteady pressure measurements to provide the first detailed quantitative picture of instantaneous compressor operation during both surge and rotating stall transients. The experimental results are compared to a theoretical model of the transient system response. The theoretical criterion for predicting which mode of compression system instability, rotating stall or surge, will occur is in good accord with the data. The basic scaling concepts that have been developed for relating transient data at different corrected speeds and geometrical parameters are also verified. Finally, the model is shown to provide an adequate quantitative description of the motion of the compression system operating point during the transients that occur subsequent to the onset of axial compressor stall.

Vibration Characteristics of Rotating Thin Disks—Part I: Experimental Results

2012 ◽  
Vol 79 (4) ◽  
Author(s):  
Ramin M. H. Khorasany ◽  
Stanley G. Hutton
Keyword(s):  
Frequency Response ◽  
Natural Frequency ◽  
Linear Theory ◽  
Lateral Force ◽  
Vibration Characteristics ◽  
Experimental Results ◽  
Rotating Disks ◽  
Critical Speeds ◽  
Applied Forces ◽  
Thin Disks

Analysis of the linear vibration characteristics of unconstrained rotating isotropic thin disks leads to the important concept of “critical speeds.” These critical rotational speeds are of interest because they correspond to the situation where a natural frequency of the rotating disk, as measured by a stationary observer, is zero. Such speeds correspond physically to the speeds at which a traveling circumferential wave, of shape corresponding to the mode shape of the natural frequency being considered, travel around the disk in the absence of applied forces. At such speeds, according to linear theory, the blade may respond as a space fixed stationary wave and an applied space fixed dc force may induce a resonant condition in the disk response. Thus, in general, linear theory predicts that for rotating disks, with low levels of damping, large responses may be encountered in the region of the critical speeds due to the application of constant space fixed forces. However, large response invalidates the predictions of linear theory which has neglected the nonlinear stiffness produced by the effect of in-plane forces induced by large displacements. In the present paper, experimental studies were conducted in order to measure the frequency response characteristics of rotating disks both in an idling mode as well as when subjected to a space fixed lateral force. The applied lateral force (produced by an air jet) was such as to produce displacements large enough that non linear geometric effects were important in determining the disk frequencies. Experiments were conducted on thin annular disks of different thickness with the inner radius clamped to the driving arbor and the outer radius free. The results of these experiments are presented with an emphasis on recording the effects of geometric nonlinearities on lateral frequency response. In a companion paper (Khorasany and Hutton, 2010, “Vibration Characteristics of Rotating Thin Disks—Part II: Analytical Predictions,” ASME J. Mech., 79(4), p. 041007), analytical predictions of such disk behavior are presented and compared with the experimental results obtained in this study. The experimental results show that in the case where significant disk displacements are induced by a lateral force, the frequency characteristics are significantly influenced by the magnitude of forced displacements.

The Effect of the Operating Point on the Pressure Fluctuations at the Blade Passage Frequency in the Volute of a Centrifugal Pump

2002 ◽  
Vol 124 (3) ◽  
pp. 784-790 ◽  
Author(s):  
Jorge L. Parrondo-Gayo ◽  
Jose´ Gonza´lez-Pe´rez ◽  
Joaquı´n Ferna´ndez-Francos
Keyword(s):  
Centrifugal Pump ◽  
Pressure Fluctuations ◽  
Fast Response ◽  
Strong Increase ◽  
Flow Rates ◽  
Blade Passage ◽  
Pressure Transducers ◽  
Leading Role ◽  
Dynamic Forces ◽  
Response Pressure

An experimental investigation is presented which analyzes the unsteady pressure distribution existing in the volute of a conventional centrifugal pump with a nondimensional specific speed of 0.48, for flow-rates from 0% to 160% of the best-efficiency point. For that purpose, pressure signals were obtained at 36 different locations along the volute casing by means of fast-response pressure transducers. Particular attention was paid to the pressure fluctuations at the blade passage frequency, regarding both amplitude and phase delay relative to the motion of the blades. Also, the experimental data obtained was used to adjust the parameters of a simple acoustic model for the volute of the pump. The results clearly show the leading role played by the tongue in the impeller-volute interaction and the strong increase in the magnitude of dynamic forces and dipole-like sound generation in off-design conditions.

Some Aspects of Wake-Wake Interactions Regarding Turbine Stator Clocking

2000 ◽  
Vol 123 (3) ◽  
pp. 526-533 ◽  
Author(s):  
Maik Tiedemann ◽  
Friedrich Kost
Keyword(s):  
Total Pressure ◽  
Guide Vane ◽  
Pressure Fluctuations ◽  
Fast Response ◽  
Turbine Stage ◽  
Flow Angle ◽  
Wake Interactions ◽  
Turbulence Data ◽  
Number Flow ◽  
Nozzle Guide

This investigation is aimed at an experimental determination of the unsteady flowfield downstream of a transonic high pressure turbine stage. The single stage measurements, which were part of a joined European project, were conducted in the windtunnel for rotating cascades of the DLR Go¨ttingen. Laser-2-focus (L2F) measurements were carried out in order to determine the Mach number, flow angle, and turbulence distributions. Furthermore, a fast response pitot probe was utilized to determine the total pressure distribution. The measurement position for both systems was 0.5 axial rotor chord downstream of the rotor trailing edge at midspan. While the measurement position remained fixed, the nozzle guide vane (NGV) was “clocked” to 12 positions covering one NGV pitch. The periodic fluctuations of the total pressure downstream of the turbine stage indicate that the NGV wake damps the total pressure fluctuations caused by the rotor wakes. Furthermore, the random fluctuations are significantly lower in the NGV wake affected region. Similar conclusions were drawn from the L2F turbulence data. Since the location of the interaction between NGV wake and rotor wake is determined by the NGV position, the described effects are potential causes for the benefits of “stator clocking” which have been observed by many researchers.

A Fast Response Surface Thermocouple

1974 ◽  
Vol 16 (3) ◽  
pp. 174-177 ◽  
Author(s):  
I. S. Donaldson ◽  
R. A. Haslett
Keyword(s):  
Response Surface ◽  
Rise Time ◽  
Fast Response ◽  
Experimental Results ◽  
Fabrication Technique ◽  
Surface Thermocouple

A fabrication technique is described for a cheap, robust surface thermocouple having a rise time of the order of 5 μs. Experimental results using the thermocouple are also presented.

Effects of inlet radial distortion on the type of stall precursor in low-speed axial compressor

2016 ◽  
Vol 232 (1) ◽  
pp. 55-67 ◽  
Author(s):  
Ali Arshad ◽  
Qiushi Li ◽  
Simin Li ◽  
Tianyu Pan
Keyword(s):  
Pressure Fluctuations ◽  
Axial Compressor ◽  
Rotating Stall ◽  
Experimental Investigations ◽  
Inlet Flow ◽  
Blade Loading ◽  
Stall Inception ◽  
Low Speed ◽  
Modal Type ◽  
Stall Precursor

Experimental investigations of the effect of inlet blade loading on the rotating stall inception process are carried out on a single-stage low-speed axial compressor. Temporal pressure signals from the six high response pressure transducers are used for the analysis. Pressure variations at the hub are especially recorded during the stall inception process. Inlet blade loading is altered by installing metallic meshed distortion screens at the rotor upstream. Three sets of experiments are performed for the comparison of results, i.e. uniform inlet flow, tip, and hub distortions, respectively. Regardless of the type of distortion introduced to the inflow, the compressor undergoes a performance drop, which is more severe in the hub distortion case. Under the uniform inlet flow condition, stall inception is caused by the modal type disturbance while the stall precursor switched to spike type due to the highly loaded blade tip. In the presence of high blade loading at the hub, spike disappeared and the compressor once again witnessed a modal type disturbance. Hub pressure fluctuations are observed throughout the process when the stall is caused by a modal wave while no disturbance is noticed at the hub in spike type stall inception. It is believed that the hub flow separation contributes to the modal type of stall inception phenomenon. Results are also supported by the recently developed signal processing techniques for the stall inception study.

scholarly journals Rotating Stall in Centrifugal Compressor Vaneless Diffuser: Experimental Analysis of Geometrical Parameters Influence on Phenomenon Evolution

2004 ◽  
Vol 10 (6) ◽  
pp. 433-442 ◽  
Author(s):  
Giovanni Ferrara ◽  
Lorenzo Ferrari ◽  
Leonardo Baldassarre
Keyword(s):  
Centrifugal Compressor ◽  
Dynamic Pressure ◽  
Pressure Sensors ◽  
Experimental Tests ◽  
Fast Response ◽  
Rotating Stall ◽  
Geometrical Parameters ◽  
Vaneless Diffuser ◽  
Response Dynamic ◽  
Frequency Domains

The rotating stall is a key problem for achieving a good working range of a centrifugal compressor and a detailed understanding of the phenomenon is very important to anticipate and avoid it. Many experimental tests have been planned by the authors to investigate the influence on stall behavior of different geometrical configurations. A stage with a backward channel upstream, a 2-D impeller with a vaneless diffuser and a constant cross-section volute downstream, constitute the basic configuration. Several diffuser types with different widths, pinch shapes, and diffusion ratios were tested. The stage was instrumented with many fast response dynamic pressure sensors so as to characterize inception and evolution of the rotating stall. This kind of analysis was carried out both in time and in frequency domains. The methodology used and the results on phenomenon evolution will be presented and discussed in this article.

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