A method for the speed matching of the second rotor (R2) with equal power for two rotors was proposed to avoid the overload of the second motor under low flow rate and the rapid decrease in pressure-rise and efficiency of R2 under high flow rate. The speed matching of two-stage rotors is proposed and analyzed to improve the stability margin of the counter-rotating fan (CRF). The fan performances during constant speed operating and during the speed matching operating are presented and discussed using experimental research. The results show that, the speed matching of R2 operating decreases the load of R2 under low flow rate and increases the pressure-rise and efficiency of R2 under high flow rate. Thus, the efficient working range and the blocking condition margin are increased. Reducing n 1 and increasing n 2 under low flow rate can regulate the position of unstable working line leftward without reducing the pressure-rise of the fan. Thus, the stability margin of the CRF is expanded.

A method for speed matching of the second rotor (R2) with equal power for two rotors was proposed to improve the performance of the counter-rotating fan under off-design conditions. In this method, the speed of R2 is adjusted until the power of R2 is equal to the power of the first rotor (R1). The fan performance during constant speed operation and during R2 speed matching operation is presented and discussed using theoretical analysis, numerical simulation, and experimental research. The results show that R2 speed matching improves the power and efficiency characteristics of R2. Thus, the pressure rise and power characteristics of the fan were improved. The load of R2 under low flow rates condition was decreased, and the pressure rise and efficiency of R2 under high flow rates condition were increased. The blocking condition margin increased from 37.2% to 48.0%, and the high-efficiency working range of the fan increased from 33.2% to 37.9%.

Enhancing compressor stall and surge has a great importance for the development of turbo compressors. The application of casing treatment is an effective measure to expand the stall margin and stable operation range. Numerical investigations were conducted to predict the performance of a low flow rate centrifugal compressor with circumferential groove casing treatment in diffuser. Numerical cases with different radial location, radial width and axial depth of a circumferential single groove in different types of diffusers (vaned diffuser, half-vaned diffuser, vaneless diffuser) were carried out to compare the results. The computational fluid dynamics analyses results show that the centrifugal compressor with circumferential groove in vaned diffuser can extend stable range by about 9.1% while the efficiency over the whole operating range decreases by 0.2 to 1.7%; the results with half-vaned diffuser and vaneless diffuser can improve stable range less and the efficiency decreases more. Efforts were made to study blade level flow mechanisms to determine how the circumferential groove impacts the compressor’s stall margin and performance. The flow structures in the passage, the tip gap, and the grooves as well as their mutual interactions were plotted and analyzed. The flow transport across the tip gap in the smooth wall and the circumferential grooves were compared.

Ionic Polymer-Metal Composite (IPMC) material is capable of producing electrical current signal closely correlated to its mechanical movement due to redistribution of the free ions inside the IPMC material. Motivated by the potential applications of this intrinsic characteristic of IPMC beams to automotive engines for flow property measurements, such as fuel flow viscosity, this paper presents a finite-element dynamic model of an IPMC beam and uses it to estimate the fluid properties based upon the measured IPMC signal using the least squares minimization approach. The results show that with the distinct output signals of the IPMC beam under different fluid media, the identified flow properties (such as drag coefficient) have a good agreement with the actual fluid properties. This is very important for automotive applications when the characteristics of the fuel blend (such as gasoline and ethanol) need to be identified.