Study On A New Type Reversible Axial Flow Fan With Skewed And Combined Blades

Reversible ventilation is crucial to the security of mines and tunnels. The inverse ventilation of axial flow fan by simply reverse motor has been proved excellent in the inverse ventilation fields. Designing axial flow turbomachinery such as fans, propellers, propfans, and compressors with skewed blades has several advantages. The noise emission is mostly lower and the aerodynamic performance can be widely improved. In this paper, detailed experimental and computational investigation has been carried on to a reversible fan with combined blades and two other fans with skewed blades. After that, a new-type reversible axial flow fan with skewed and combined blades is firstly invented.Detail contents are listed as bellows,1. Impeller designIn this paper, four different impellers, namely forward skewed impeller, backward skewed impeller, reversible combined impeller, and reversible combined&skewed impeller respectively, are designed and investigated. So far, to the best of our knowledge, no design method of skewed blade is available. This paper has developed a reverse engineering design (RED) process of skewed blade. In order to apply the optimal circumferential combine parameters from plain cascade experiment to actual impeller designation, a non-dimensional coefficient named relative pitch T’is defined and used as a criterion of combine parameters.2. The test rig and measurement methodAn aerodynamic&aeroacoustic test rig is designed and constructed in this thesis. Five hole probe and hot-wire (CTA) is employed to measure the three-dimensional velocity and pressure distribution downstream of each impeller. A rotating single slanted hot-wire technique and a periodic multi-sampling measurement system has been developed, with the use of a infrared probe as pulse generator. Typical experimental results of different rotating times and mass-average times are presented to investigate the measurement accuracy.3. Study on the impellers with skewed bladesExperimental and computational results show that the aerodynamic and aeroacoustic perfonnance of the impellers with skewed blades can be widely influenced due to the transformation of passage vortex and the movement of low energy fluids in blade boudery layer. Performance of impeller with forward skewed blades is improved because of the lower passage vortex loss and the weaken boundary layer thickness at the impeller tip region. On the contrary, performances of impeller with backward skewed blades become worsen. Numerical flow simulation results give some details on the distributions of fluid field parameters. In the theory aspect, the so called Diactuator Disc Theory (DDT) is finally consummated and adopted to optimize the skew angle. It shows that appropriate forward skew angle may decrease the total pressure loss, improve aerodynamic efficiency, lower the aerodynamic noise, and enlarge the steady flow range. In this paper, impeller with forward-skew angle from2to4degree may get the best performance. The efficiency may be improved by1.5%-2.0%compared to impeller with straight blades.4. Study on the reversible impellers with combined and skewed bladesFirst, a so called combined-impeller is investigated, which is composed of two rows of T35archetype blades, namely normal and reverse blades respectively. It shows the merits of fully reversible ventilation and direct re-rotating. However, the aerodynamic and aeroacoustic performance is not satisfied due to the negative pressure induced by the reverse blade. With the use of skewed blade technique, the new type reversible impeller with combined and skewed blades shows a great performance improvement. The flow rate coefficient is increased of7.97%, the total pressure coefficient is increased of9.69%, the static pressure coefficient is increased of5.88%, the efficiency is increased of11.78%, and the sound pressure level is decreased of4.97dB.5. Conclusion and expectationAt the end of this thesis, research conclusions are presented and farther research expectations on skewed blade technique and the combined blade technique is also listed for reference.