A Model for Stall and Surge in Low-Speed Contra-Rotating Fans

Abstract

This paper reports on a theory for poststall transients in contra-rotating fans, which is developed from the basic Moore–Greitzer theory. A second-order hysteresis term is assumed for the fan pressure rise, which gives the theory more capabilities in predicting the fan instabilities. The effect of the rotational speed ratio of the two counter rotating rotors on the fan performance during the occurrence of surge and rotating stall are studied (the rotational speed of the front rotor is assumed to be kept constant whereas the speed of the rear rotor is variable). One of the new capabilities of the current model is the possibility of investigating the effect of the initial slope on the fan characteristic. Results reveal that unlike the conventional fans and compressors, in the current contra-rotating fan stall cannot be initiated from the negative slope portion of the fan pressure rise characteristic curve. One of the important advantages of the developed model is that it enables investigation of the effect of the rate of throttling on the instabilities. Results show that more the rotational speed of the rear rotor, the more robust to surge (caused by throttling) the fan is.

Adaptive Variable-speed Control for Enhancing the Performance of a Mine Counter-rotating Fan System

“…In summary, to solve the overload problem, we adopted the traditional method with different loads (e.g., by reducing the load) or raised the power margin for R2. (25)(26)(27)(28) By comparing our proposed method of AVS control with traditional methods, we observed that our novel method is more comprehensive and has higher performance.…”

“…(20)(21)(22)(23)(24) To solve the overload problem encountered in R2 under small-flow conditions, a common solution is to adopt different loads (e.g., by reducing the load) or raise the power margin for R2. (25)(26)(27)(28) Nevertheless, these measures usually reduce the overall performance for other flow conditions. Some studies showed that adaptively changing the load distribution by adjusting the impeller velocity of the rotor may effectively and optimally enhance the overall performance for all flow conditions.…”

A Model for Predicting Post-Stall Behavior of Axial Compressors

“…In the recent work done by Khaleghi et al (2020) and Shahriyari et al (2019), the compressor pressure rise function which was used by Moore (1984a) and Moore and Greitzer (1986) was modified to include a second order derivative term, which enabled the investigation of the stall cell transient behavior. The same hypothesized function is used in the current study:…”

The Effect of Load Control on the Performance of Contra-Rotating Fans

“…By measuring and comparing the flow characteristics and unsteady characteristics of the three sets of CRFs, they concluded that, under the condition of keeping the rotor angular velocity of two stages approximately equal, redistributing the load of the FR to 60% and the RR to 40% could reduce the loss of the RR. Shahriyari et al [9] reported a CRF post-stall transient theory, which could better predict the instability of a CRF. Besides, by studying the effect of different rotating speeds between rotors, which matched the stall and surge pattern, they concluded that, the higher the RR speed, the stronger the fan resistance to a surge caused by throttling.…”