Abstract
The ability to predict the nature of instabilities is highly important from the compressor design point of view since their consequences could result in widely varying difficulties with the fluid dynamic performance of the systems. Even though the behavior of surge and rotating stall is reported in many literatures, it is noticed that an in-depth analysis is not undertaken. Hence in view of the importance for a deeper understanding, the present paper is aimed at tracking the chaos of these instabilities in a more detailed manner. Primarily the influence of geometric parameters on the nature of surge and rotating stall is investigated. The effect of each of the major geometric parameters such as compressor effective length, annulus area, and plenum volume is discussed. The physical reason for the onset of instabilities is also explained in each case, and the well-accepted Moore-Greitzer model has been used for the present study. The combined effect of physical parameters is determined through the Greitzer <svg style="vertical-align:-0.0pt;width:10.6125px;" id="M1" height="11.175" version="1.1" viewBox="0 0 10.6125 11.175" width="10.6125" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns="http://www.w3.org/2000/svg"> <g transform="matrix(.017,-0,0,-.017,.062,11.113)"><path id="x1D435" d="M594 511q0 -122 -171 -157l1 -2q158 -33 158 -159q0 -52 -34.5 -95t-90.5 -65q-76 -33 -217 -33h-223l8 28q63 5 79.5 19t26.5 72l83 426q9 48 -2.5 60t-77.5 17l6 28h259q195 0 195 -139zM499 509q0 59 -37 83t-91 24q-36 0 -51 -9q-17 -9 -22 -44l-35 -195h62
q82 0 128 37t46 104zM481 199q0 71 -48 102.5t-121 31.5h-56l-37 -201q-11 -58 7.5 -77t80.5 -19q76 0 125 44.5t49 118.5z" /></g> </svg> parameter. The results shown in this paper clearly elucidate the dominating effect of the geometric parameters on the development of flow instabilities like rotating stall and surge and hence can serve as a design guideline to avoid such instabilities.
Highlights
The operability of compression systems is limited at low mass flow rates by fluid dynamic instabilities leading to rotating stall or surge
The general result that emerges is that the system will be dynamically unstable near the peak of the pressure rise/mass flow characteristic at some slight positively sloped operating point [7]
A basic conclusion of this model is that at the same value of B, the compression system will exhibit the same transient behavior, independent of whether this value is obtained with a larger plenum volume and low speed or vice versa
Summary
The operability of compression systems is limited at low mass flow rates by fluid dynamic instabilities leading to rotating stall or surge. Based on the work of Moore [13], Moore and Greitzer developed an approximate theory [14, 15] capable of predicting the poststall transients in multistage axial compression systems This model explains the coupling between rotating stall-like and surge-like motions and gives the nature of the operating point motion during a transient stall phenomenon. In the present study by using the Moore-Greitzer theoretical model [14, 15], the effect of change in geometric parameters on axial compression systems is examined to describe the nature of poststall transients that could be expected as the instantaneous operating point of the compressor crosses the peak point in the compressor performance curve
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