Simulation of air jets for controlling stall in a centrifugal fan

Abstract

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.

Bio-inspired variable structural color materials

“…Similar to the polymer NIPAM that could respond to the temperature, many hydrogels with functional groups could show volume changes in response to their corresponding ions or molecules. [172][173][174] When the photonic nanostructures are constructed using these hydrogels, their stop bands could be shifted by using the ions or molecules stimulus. For this research, Lowe fabricated the holographic multilayer PhCs using poly-hydroxyethylmethacrylate (poly-HEMA) hydrogel with the ions or molecules-responsive groups.…”

Thermal Switching of the Reflection in Chiral Nematic Mesoporous Organosilica Films Infiltrated with Liquid Crystals

“…The ability to reversibly control the optical properties of photonic crystals is attractive for many applications including reflective displays and sensors. − Band structures of photonic crystals depend on both their periodicity and the refractive index contrast between their constituent dielectric materials; it is therefore possible to modulate the optical properties of photonic crystals by addressing either of these structural parameters. The refractive index contrast of porous photonic crystals (e.g., inverse opals) is readily varied by infiltrating the pores with different substances, such as vapors and liquids. − Further control over the optical properties of porous photonic crystals can be achieved through loading the pores with stimuli-responsive materials. Liquid crystals (LCs), which can show large changes in orientation and refractive index in response to different stimuli, have been studied in this regard. , A number of photonic crystals infiltrated with LCs are known and show interesting properties upon phase transition of the mesogens inside the periodic structure. − Neubert et al prepared photonic crystals infiltrated with 4-cyano-4′-pentylbiphenyl (5CB) showing polarization-dependent optical properties due to the orientation of the LC in its liquid crystalline phase .…”

Experimental and numerical study on the influence of flow passages in centrifugal fan using computational fluid dynamics

“…This is because seriously distorted inflows can affect the onset of flow instability, such as rotating stall and surge, in centrifugal fans. Lei et al [9] stated that when the flow rate is 4.30 m3/s, the original fan experiences a rotating stall, with the onset of the stall occurring initially in three impeller passages near the volute tongue and front disc. The influence of various blowing speeds (50, 70, 90, 110, and 130 m s −1 ) was analyzed during the stall's initiation.…”