| Boundary Layer Ingestion is an efficient flow control method.Under the aircraft engine coupling configuration,the ducted fan can be used to extract and suck the upper boundary layer of the wing,increase the flow circulation to maintain the unseparated laminar boundary layer,and suppress the separation degree of the separated boundary layer to improve the aerodynamic performance of the aircraft.In order to make up for the shortcomings of the conventional wing in the lift characteristics and flow field control.In this paper,an experimental study on the coupled matching of ducted fan-wing was carried out in the low turbulence wind tunnel of Xihua University.The results of thrust and lift coefficient of ducted fan with and without BLI effect are compared.Verified that BLI effect of ducted fan can improve the lift of wing,and analyzed the flow mechanism of aerodynamic lift increase in combination with the effect of flow field control.Firstly,the thrust test of ducted fan with and without wing coupling was carried out to explore the influence of BLI effect on the thrust characteristics of ducted fan under the condition of wing and ducted fan coupling.The aerodynamic results showed that the thrust of the fan in the culvert did not change obviously in the range of 5° angle of attack when the wing was coupled with the culvert fan under the BLI effect.However,the uneven gas on the upper wing flows into the ducted fan,resulted in the increased inlet distortion of the ducted fan,which worsen the performance of the ducted fan and increases the thrust loss because of the certain flow separation when the angle of attack of the wing reaches 10°.Compared with the thrust of the isolated ducted fan at the same flow speed,the thrust loss of the coupling between the wing and the ducted fan decreases under BLI effect,moreover,the performance of the coupling configuration with a span of 0 mm is slightly worse than that of the coupling configuration with a span of 20 mm when the angle of attack is fixed.Compared with the isolated ducted fan,the maximum thrust of ducted fan generator coupling layout decreased by 13.15% under the condition of 20 m/s velocity and 15° angle of attack.After,the surface pressure distribution of the wing with and without ducted fan coupling was measured,and the results of the lift characteristic curve of the wing with angle of attack obtained by pressure integration and the surface pressure distribution of the single fan wing were compared.The influence of BLI effect on the aerodynamic characteristics of the wing with ducted fan coupling was obtained.The pressure distribution curve showed that BLI effect increased the pressure difference between the upper and lower wings,and the results were converted into lift characteristic curves.The results showed that BLI effect can greatly improve the aerodynamic performance of the wing and delay the range of stall angle of attack,which means that the flight envelope of the aircraft has been greatly improved.When the inlet velocity was 20m/s,the angle of attack of the wing was 15° and the fan speed was 7250 rpm,the lift coefficient increased by 228.4%,which was 17.4 times of the thrust loss,indicating that the gain was much greater than the loss.And as the increase of the speed of the ducted fan,the lift coefficient of the wing increased more obviously.With the increase of the angle of attack,the lift improvement performance was higher,but with the increase of the incoming flow velocity,the BLI effect weakened.At the same time,the aerodynamic performance of the wing with 20 mm distance coupling layout was better than that of the wing with 0mm distance coupling layout.Finally,particle image velocimetry technology was used to test the flow field with and without BLI effect,and the control mechanism of BLI effect improving wing aerodynamic performance was analyzed.The results of flow visualization indicate that BLI effect significantly increases the flow velocity of the upper wing.At low angles of attack,the lift increases with the increase of wing circulation;at high angle of attack,the lift increases with the decrease of flow separation,and the increase of fan speed will lead to the decrease of flow separation zone.However,with the increase of the incoming flow velocity,the flow separation zone become larger gradually.And the flow velocity on the wing with 20 mm distance from the ducted fan lip coupling layout was larger than that of the wing with 0mm distance from the ducted fan lip coupling layout,and the flow separation zone was smaller.These flow visualization results were consistent with the results of the wing lift characteristic curve,which verified the influence of BLI effect on the wing aerodynamics from the flow mechanism performance improvement. |
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