CFD analysis of gas labyrinth seal
![Picture](/uploads/8/8/8/3/8883295/6189552.jpg)
Fig. 1 Velocity vector of flow in labyrinth seal
I have performed CFD simulation of straight labyrinth seal for more than one year. My B.E. thesis is about rotordynamic coefficient of labyrinth seal. Using commerical software-FLUENT, many essential features of seal flow can be captured, such as the pressure gap between each cavity and leakage. However, There are still many tricks in using FLUENT for labyrinth seal simulation, which, if not being handled properly, can lead to divergent or incorrect result. One trick is about the set of inlet boundary. Usually, the pressure boundary in FLUENT is selected. However, FLUENT chooses the total pressure including static and dynamic pressure as the boundary value. With different inlet velocity, the static pressure in the inlet is not uniform. It is still unknown whether this non-uniform static pressure boundary is reasonable for simulating labyrinth seal. Anyway, choosing narrow inlet can reduce this boundary influence.
I am interested in transient simulation of labyrinth seal. That is, the rotor in the seal is not only rotating, but also whirling along certain orbit. This orbit includes linear, circle and ellipse track around certain eccentric position. Dynamic mesh method is required to realize this kind of simulation. Some valuable results are found through this transient simulation. See more >>
I am interested in transient simulation of labyrinth seal. That is, the rotor in the seal is not only rotating, but also whirling along certain orbit. This orbit includes linear, circle and ellipse track around certain eccentric position. Dynamic mesh method is required to realize this kind of simulation. Some valuable results are found through this transient simulation. See more >>
CFD analysis of liquid annular seal
![Picture](/uploads/8/8/8/3/8883295/138796.jpg)
Fig. 2 Pressure distribtuion in annular seal
Annular seal is widely used in multistage pump to reduce second leakage flow. Another important function of annular seal is to increase natural frequency of rotor in pump. Although annular seal has little influence on pump when the pump doesn't operate, it can become some kind of bearing when the pump is running. This is because the sealing annulus shifts off-center and the so-called Lomakin Effect occurs. For rotor in the pump, there is a large difference between the actual wet critical speeds and modal damping versus the dry critical speeds and modal damping without accounting for the influence of liquid annular seal. Force due to the annular seals are mainly responsible for the large difference.
I have performed CFD analysis of liquid annular seal to calculate its dynamic coefficient. That is, finding to what extent annular seal will influence the rotor dynamics of pump rotor. It is important to accurately calculate stiffness and damping of annular seal in different situation. Stiffness is easy to figure out, while damping or added mass is hard to get, because the later ones involve with speed perturbation. Steady simulation will not perform such speed perturbation. Using dynamic mesh method, I have successfully realized the calculation of damping in annular seal and the simulation result fits theory prediction well. See more >>
I have performed CFD analysis of liquid annular seal to calculate its dynamic coefficient. That is, finding to what extent annular seal will influence the rotor dynamics of pump rotor. It is important to accurately calculate stiffness and damping of annular seal in different situation. Stiffness is easy to figure out, while damping or added mass is hard to get, because the later ones involve with speed perturbation. Steady simulation will not perform such speed perturbation. Using dynamic mesh method, I have successfully realized the calculation of damping in annular seal and the simulation result fits theory prediction well. See more >>
Natural frequency measurement by electromagnetical exciter
![Picture](/uploads/8/8/8/3/8883295/6509350.jpg)
Fig. 3 Magnetic flux density in exciter
Natural frequency is always an important consideration for rotating machinery designer.This is because when the running speed of machinery is close to natural frequency, vibration will increase significantly because of resonance, which may cause severe damage to the whole system. There are already several methods to measure system natural frequency such as sine excitation method, random excitation method and impulse excitation method. Impulse excitation method has merit of saving time and requiring not complicated device, while its main drawback is the low signal to noise ratio (SNR).
I have developed a new-type electromagnetic exciter, using periodical impulse excitation method to measure natural frequency. The periodical impulse is realized and controlled by output function of a DAQ card. This periodical impulse effectively avoid the drawback of low SNR of ordinary impulse method. Experiment shows that the natural frequency can be accuratedly recoganized through this new-type excitation method. See more >>
I have developed a new-type electromagnetic exciter, using periodical impulse excitation method to measure natural frequency. The periodical impulse is realized and controlled by output function of a DAQ card. This periodical impulse effectively avoid the drawback of low SNR of ordinary impulse method. Experiment shows that the natural frequency can be accuratedly recoganized through this new-type excitation method. See more >>
Developed Vibration Test System
![Picture](/uploads/8/8/8/3/8883295/2678490.jpg)
Fig. 4 Weclome screen of VibTest system
Vibration is an interesting phenomenon and worth of consideration in both industrial and research field. Nowadays, there are already matured commercial hardware and software to help research sample vibration signal. However, developing a vibration test system is always helpful when you want to realize specific functions, and easily manipulate sampling data without paying for expensive commercial software. Most importantly, dealing with signal is an exciting journey, where you can see how signal can be analyzed to provide useful information.
I have developed one Vibration Test System (VibTest1.0) for a pump group, combining VC++ with DAQ card. This system covers most frequent used features of signal sampling, such as sampling frequency options, channel options, trigger options and display options, etc. I also added many specific features, such as output function, dynamic balance function and data post-process function including time domain analysis, frequency domain analysis and time-frequency domain analysis, signal filtering, etc. The VibTest1.0 has already received software copyright in China. Registration Number: 2011SR048123.
I have developed one Vibration Test System (VibTest1.0) for a pump group, combining VC++ with DAQ card. This system covers most frequent used features of signal sampling, such as sampling frequency options, channel options, trigger options and display options, etc. I also added many specific features, such as output function, dynamic balance function and data post-process function including time domain analysis, frequency domain analysis and time-frequency domain analysis, signal filtering, etc. The VibTest1.0 has already received software copyright in China. Registration Number: 2011SR048123.