An Experimental Investigation of the Control of Surge in Radial Compressors Using Close Coupled Resistances

Abstract

The aerodynamic characteristics of centrifugal compressors are examined with special attention given to the range of flows normally in the unstable region. They are examined for the intended purpose of extending the compressor’s useful stable range. Two such means are investigated, but a close coupled aerodynamic resistance designed to achieve negative combined slope showed the greater promise. A number of experiments are performed in which the geometry and location of the close coupled control devices are varied. It is shown that with adequate design, stable operation is possible down to 40 percent of the normal surge flow. This can be done with hardware the configuration of which is practical and with attendant additional losses which are not prohibitive. The rationale and the empirical work are devoted to the single stage case but an examination is made of the stability considerations for the case of multi-stage machines.

Centrifugal compressor surge and speed control

“…For turbomachines, applied torque equals the change in angular momentum of the fluid (5) where is the compressor torque, , and is the tangential component of the gas velocity Power delivered to the fluid is (6) where is the specific enthalpy delivered to the fluid without taking account for losses. Equation (6) is known as Euler's pump equation.…”

“…One drawback of CCV control is that the valve introduces a pressure drop in the compression system as discussed in [26]. When using the valve as a steady-state device, such as in [6], this loss may become unacceptably large. However, as pointed out in [25] and [26], a time varying valve will introduce considerably less pressure drop than a valve with constant pressure drop.…”

“…Of many possible actuation schemes, closed coupled valve (CCV) control is considered one of the most promising [6], [18], [21], [25], [27]. Experimental results of CCV control is reported in [6] and [21]. Surge in a compression system can be explained by the throttle line crossing the compressor characteristic in an area of positive compressor characteristic slope.…”

Two results on compressor surge control with disturbance rejection

“…The control law resulting from this approach i s g i v en by u = c 2 Here, passivity will be used to derive a stabilizing controller for (8) with all the disturbances set to zero.…”

Speed and surge control for a low order centrifugal compressor model

“…A recent review can be found in 2]. Of many possible actuation schemes, closed coupled valve (CCV) control is considered one of the most promising 4,11,12,14,16]. Experimental results of CCV control is reported in 4] and 12].…”