Yingzi Jin

Effect of Inlet Geometry on Fan Performance and Inlet Flow Fields in a Semi-opened Axial Fan

Abstract In order to clarify the effect of inlet bellmouth size of semi-opened type axial fan on its performance and flow fields around rotor, fan test and flow field measurements using hotwire anemometer were carried out for 6 kinds of bellmouth size. As results of fan test, the shaft power curve hardly changed, even if the bellmouth size changed. On the other hand, the pressure-rise near best efficiency point became small with the bellmouth size decreasing. Therefore, the value of maximum efficiency became small as the bellmouth size decreased. As results of flow field measurements at fan inlet, the main flow region with large meridional velocity existed near blade tip when the bellmouth size was large. As bellmouth size became smaller, the meridional velocity at fan inlet became smaller and the one at outside of blade tip became larger. As results of flow field measurements at fan outlet, the main flow region existed near rotor hub side.

Numerical Study on the Characteristics of Dual-Mode Scramjet Isolator

As one of the most promising propulsive systems in the future, the dual-mode scramjet engine has drawn the attention of many researches. Detailed flow features concerned with the isolator play an important role in the dual-mode scramjet system. The 2D numerical method has been used for the dual-mode scramjet with wind tunnel. To validate the ability of the numerical model, numerical results have been compared with the experimental results. Overall pressure distributions show quite good match with the experimental results. Back pressure has been studied for maximum pressure rising. According to the results, pressure distribution of supersonic inlet section is not influenced by back pressure. The shock train is pushed towards upstream as the back pressure increases. The maximum value of back pressure without inlet unstart goes up rapidly and then keeps constant when the isolator length increases. The optimal length of isolator section (L/H th ) is 8.7 in this model.

Effect of Inlet Geometry on Fan Performance and Flow Field in a Half-Ducted Propeller Fan

In order to clarify the effect of rotor inlet geometry of half-ducted propeller fan on performance and velocity fields at rotor outlet, the experimental investigation was carried out using a hotwire anemometer. Three types of inlet geometry were tested. The first type is the one that the rotor blade tip is fully covered by a casing. The second is that the front one-third part of blade tip is opened and the rest is covered. The third is that the front two-thirds are opened and the rest is covered. Fan test and internal flow measurement at rotor outlet were conducted about three types of inlet geometry. At the internal flow measurement, a single slant hotwire probe was used and a periodical multisampling technique was adopted to obtain the three-dimensional velocity distributions. From the results of fan test, the pressure-rise characteristic drops at high flowrate region and the stall point shifts to high flowrate region, when the opened area of blade tip increases. From the results of velocity distributions at rotor outlet, the region with high axial velocity moves to radial inwards, the circumferential velocity near blade tip becomes high, and the flow field turns to radial outward, when the opened area increases.

Experimental Investigation on Separated Flows of Axial Flow Stator and Diagonal Flow Rotor

Experimental investigations were conducted for the internal flows of the axial flow stator and diagonal flow rotor. Corner separation near the hub surface and the suction surface of stator blade are mainly focused on. For the design flow rate, the values of the axial velocity and the total pressure at stator outlet decrease between near the suction surface and near the hub surface by the influence of corner wall. For the flow rate of 80-90% of the design flow rate, the corner separation of the stator between the suction surface and the hub surface is observed, which becomes widely spread for 80% of the design flow rate. At rotor outlet for 81% of the design flow rate, the low axial velocity region grows between near the suction surface of rotor and the casing surface because of the tip leakage flow of the rotor.

Fluidic thrust vector control based on counter-flow concept

Computational studies are conducted on the supersonic nozzle to investigate the possibility of utilizing counter-flow in fluidic thrust vector control. In this work, the design Mach number of the symmetric supersonic nozzle is set to be 2.5. For the validation of methodology, numerical results are compared with experimental data referred from the literature. Two-dimensional numerical simulations are based on well-assessed standard k–ɛ turbulence model with standard wall functions. Second-order accuracy is ensured to reveal more details of flow field. The system thrust ratio, deflection angle, and secondary mass flow ratio were studied for a wide range of nozzle pressure ratios and secondary pressure ratios. The results indicate that deflection angle and secondary mass flow ratio are found to be decreased with increasing nozzle pressure ratio as well as system thrust ratio. The secondary mass flow ratio and deflection angle decrease with the increase of secondary pressure ratio, and system thrust ratio increases with the increasing of secondary pressure ratio. The secondary mass flow rate remains under 2.4% of the primary flow to obtain efficient thrust vector control at high Mach number.

Characteristics of intersecting airflows in the narrow flow channel

Abstract Air-jet loom is a kind of shuttleless loom, which is widely used in textile industries. The weft insertion system is composed of main nozzle, auxiliary nozzles, and profiled dent groove. The jets from the main and auxiliary nozzles intersect in the profiled dent groove. The velocity and stability of the intersecting airflows have a direct impact on the yarn’s motion. In this paper, the commercial software is adopted to simulate the intersecting airflows in the profiled dent groove. The result shows it is reasonable that the distance from the main nozzle to the first dent is 15 mm. The optimal distance from the main nozzle to the first auxiliary nozzle is between 45 and 50 mm based on the criteria of the utilization efficiency of the airflow. According to the standard of airflow stability, when the spray angle of auxiliary nozzle is about 7°, the standard deviation of the radical airflow velocity is the smallest in different cross sections. Therefore, the intersecting airflows are the most stable when the spray angle of auxiliary nozzle is about 7°. The velocity distribution of intersecting airflows in the profiled dent groove is measured using Particle Image Velocimetry (PIV) technique. The research results can provide some useful references for the optimization of the weft insertion system of the air-jet loom.

Numerical Visualization of the Pseudo-Shock Waves using LES

The interaction between a normal shock wave and a boundary layer along a wall surface in internal compressible flows causes a very complicated flow. This interaction region containing shock train and mixing region is called as pseudo-shock waves. Pseudo-shock waves in the divergent part of a rectangular nozzle have been investigated by using large-eddy simulation (LES). LES studies have been done for the complex flow phenomena of three-dimensional pseudo-shock waves. The LES results have been validated against experimental wall-pressure measurements. The LES results are in good agreement with experimental results. Pseudo-shock length and corner separation have been studied in three-dimensional LES model. Comparison of centerline pressure measurement and 3D visualization measurement has been discussed for the corner separation position. It has been concluded that the pseudo-shock length should be measured by using 3D visualization measurement.

Experimental and Numerical Investigation of Blades Effect on Aerodynamic Performance of Small Axial Flow Fan

To explore the effect of blade numbers on aerodynamic performance and noise of small axial flow fan, the steady flow field and the unsteady flow field of fan models with 6 different blade numbers (such as 5, 7, 9, 11, 13, 15) are numerically calculated. Then the internal flow distribution, static characteristic and aerodynamic noise are analyzed among six different fan models. The analysis results show: (1)Total pressure and efficiency generally maintain the trend of first increasing and then decreasing with increasing blade numbers, and it is the maximum when fan blade number is 11. The flow rate coupled with the maximum efficiency has never changed with increasing the blade numbers. (2)With increasing blade numbers, overall sound pressure level of the aerodynamic noise is gradually decreasing near the outlet of fan tip, while it is first decreasing and then increasing before decreasing again at 1 meter away from the central axis of the impeller along the outlet. When fan blade number is 11, overall sound pressure level of the aerodynamic noise is the greatest. Furthermore, the aerodynamic performance tests of fan models with 6 different blade numbers are carried out, the results of between the tests and the numerical calculations are roughly consistent. The research results will provide the proof of the parameter optimization and the structure design for high performance and low noise small axial fans.Copyright

Study on the Aerodynamic Performance of Small Axial Flow Counter-Rotating Fans

Small axial flow fans are used as cooling components for computers, electronic equipments and other electronic components. With the increasing power of electrical equipment, the demand for lower noise and higher ventilation of cooling fans to improve heat transfer effects is also increasing. Traditional methods of improving ventilation by raising the fan’s rotation speed causes a decrease in efficiency and an increase in noise. The researchers have found that higher pressure, ventilation and efficiency can be achieved in a small space by counter-rotating fans than single fans. In this paper, 3D simulation has been done on flow field of counter-rotating fans for heat exchange, and the method of large eddy simulation (LES) and FW-H acoustic model have been used to simulate the distribution of noise field. The frequency spectrum from different sound sources has been analyzed, and the optimal ranges of the distance and gap between rotors have been determined. All that will provide a theoretical basis for researches on their characteristics and structure design.Copyright

Numerical Investigation on the Separated Flow of Axial Flow Stator in Diagonal Flow Fan

Experimental and numerical investigations were conducted for the internal flow of the stator of the diagonal flow fan. Corner separation near the hub surface and the suction surface of the stator blade are focused on. At low flow rate of 80% of the design flow rate, the corner separation between the suction surface and the hub surface can be found in both experimental and numerical results. Separation vortices are found in the computed oil flow on both suction and hub surfaces at 80% of the design flow rate in the three‐dimensional numerical simulation.