“…It was also found the emergence of the low dominating frequency components linked to the rotating stall cells. 29,30 From the analyses in the following section, there exists a periodical spillage of the interface in rotor 2 due to the unsteady of TLF at near stall condition. According to the research by Vo et al., such an interface may cause spike-type stall inception if it spills out of the blade LE.…”
Section: Numerical Results and Discussionmentioning
Unsteady numerical simulations of a counter-rotating axial compressor are performed to investigate the unsteady effects of rotor-rotor interaction process and the tip flow unsteady behavior near the stall operating condition. The results show that potential effects from the rear rotor have a more pronounced influence on the front rotor. Because of the interaction between the two rotors and the unsteady flow behaviors, the strongest fluctuant regions are different for the two rotors. Additionally, the oscillation on the pressure side is generally much stronger than that on the suction side. Frequency analyses show that self-unsteadiness occurs with the frequency of 0.76 blade passing frequency due to the impingement of the tip leakage flow on the pressure side near leading edge of the adjacent blade. An interesting phenomenon, i.e., the emergence of a local high pressure spot, is observed in the tip region. As a whole, it is concluded that there are two key effects of the emergence of the local high pressure zone in the tip region: (a) more leading edge spillage of tip leakage flow and increasing the risk to trigger stall; and (b) a decrease in blockage associated with doubleleakage of tip clearance flow within the influenced region of the local high pressure zone.
“…It was also found the emergence of the low dominating frequency components linked to the rotating stall cells. 29,30 From the analyses in the following section, there exists a periodical spillage of the interface in rotor 2 due to the unsteady of TLF at near stall condition. According to the research by Vo et al., such an interface may cause spike-type stall inception if it spills out of the blade LE.…”
Section: Numerical Results and Discussionmentioning
Unsteady numerical simulations of a counter-rotating axial compressor are performed to investigate the unsteady effects of rotor-rotor interaction process and the tip flow unsteady behavior near the stall operating condition. The results show that potential effects from the rear rotor have a more pronounced influence on the front rotor. Because of the interaction between the two rotors and the unsteady flow behaviors, the strongest fluctuant regions are different for the two rotors. Additionally, the oscillation on the pressure side is generally much stronger than that on the suction side. Frequency analyses show that self-unsteadiness occurs with the frequency of 0.76 blade passing frequency due to the impingement of the tip leakage flow on the pressure side near leading edge of the adjacent blade. An interesting phenomenon, i.e., the emergence of a local high pressure spot, is observed in the tip region. As a whole, it is concluded that there are two key effects of the emergence of the local high pressure zone in the tip region: (a) more leading edge spillage of tip leakage flow and increasing the risk to trigger stall; and (b) a decrease in blockage associated with doubleleakage of tip clearance flow within the influenced region of the local high pressure zone.
“…In addition, the Fast Fourier transformation (FFT) results of the instantaneous signals are often used to observe the flow characteristics. 19,39,47,48 Therefore, first, the method of FFT was used to explore the variation of unsteady fluctuation and the stall inception in the compressor in this section. Iterating histories of the outlet mass flow under three different conditions are recorded and analyzed, and the FFT results are shown in Figure 11.…”
Section: Numerical Results and Discussionmentioning
confidence: 99%
“…It was also found the emergence of the low dominating frequency components linked to the rotating stall cells. 47,48 Figure 11.FFT results for outlet mass flow history records at three different operating points.…”
Section: Numerical Results and Discussionmentioning
Unsteady computations of a counter-rotating axial compressor are performed and analyzed to investigate the unsteady behaviors in the compressor and the role of the tip leakage flow together with the rotating stall inception process. The results show that the oscillation on the pressure side is much stronger than that on the suction surface for both rotors, especially near the tip region where the trajectory of the tip leakage vortex (TLV) interacts with the blades most often. There exists a periodical leading edge spillage of the interface in rotor2 due to the unsteadiness of tip leakage flow (TLF) at near-stall condition. The blockage generated by the TLV increases dramatically due to the increasing strength of the TLV and the backflow phenomenon as the mass flow decreased. The appearance of the frequency components of 0.5 blade passing frequency (BPF) and 1.5BPF from 0.64BPF can be viewed as the rotating stall inception warning. The fluctuation strength of oscillation frequencies of 0.5BPF and 1.5BPF decreases rapidly from leading edge to trailing edge in rotor2, which indicates that the unsteady fluctuation of TLF at the leading edge in rotor2 is responsible for the stall inception of the compressor. Additionally, both the leading edge spillage and trailing edge backflow phenomena are observed for spike initiated rotating stall at stall point.
“…In recent years, the study of rotating stall has mainly focused on the compressor field. 9–14 Sano et al. 15 conducted detailed research on the rotating stall phenomena inside a vaned diffuser pump.…”
The main goal of the present work is to analyze the three-dimensional unsteady flow field of a centrifugal fan by solving Navier–Stokes equations, coupled with the throttle condition. The results show that rotating stall occurs in the original fan when the flow rate is 4.30 m3/s, and the stall inception first appears at three impeller passages near the volute tongue and front disc. An active control method is proposed to inhibit the stall inception, which involves blowing air at the inlets of the three impeller passages. This blowing control method cannot inhibit the stall inception when the blowing speed is lower than 50 m/s. The stability margin of the centrifugal fan is extended when the blowing speed is increased from 50 to 110 m/s, while no further effect is obvious with a further increase in the blowing speed. At a blowing speed of 110 m/s, rotating stall occurs again when the fan flow reaches 3.46 m3/s. After the application of the nozzle blowing, the safety margin of the centrifugal fan is extended by 13%, and an obvious stability enhancement effect is achieved. From an engineering standpoint, this new active control method for rotating stall offers a valuable means to ensure the safe operation of a centrifugal fan.
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