Wind tunnel test for BVI noise and vibration reduction using blade active control

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Wind tunnel test for BVI noise and vibration reduction

using Blade Active Control

Kenta Masaki, Keisuke Hattori, Minoru Yoshimoto, Naoki Uchiyama, Masahiro Nakao Mitsubishi Heavy Industries, LTD.

10 Oye-cho, Minato-ku, Nagoya 455-8515 Japan Shigeru Saito, Natsuki Kondo[i]

JAXA (Japan Aerospace Exploration Agency) 7-44-1, Jindaijihigashi-machi, Chofu, Tokyo182-8522 Japan

Abstract

Mitsubishi Heavy Industries, LTD. and JAXA (Japan Aerospace Exploration Agency) have been conducting a research on reduction of Blade-Vortex Interaction (BVI) noise and vibration of helicopter rotors using blade active control with trailing edge flaps(Ref 1, 2).

Last Year, we showed the result of BVI noise wind tunnel test with conventional rotor and our firstly applied active rotor with trailing edge flaps (Ref 3). This paper presents the result of following wind tunnel test and the examined mechanism of BVI noise reduction from the data acquired.

Nomenclature CT =Rotor thrust force coefficient

αs =Rotor shaft angle(positive nose up)

µ =Advance ratio

ψ =Blade azimuthal angle

δAFC =Active flap deflection angle

(positive trailing edge down)

δ0AFC =Active flap control amplitude

PAFC =Modulus of Active flap control

ψAFC =Active flap control phase angle

dCH =Fluctuation of drag force coefficient

dCT =Fluctuation of thrust force coefficient

dCM =Fluctuation of pitching moment coefficient

SPL =Sound Pressure Level Introduction

Helicopter is one of the most convenient transportation. It can take us almost everywhere if enough space exist for landing or sling off us. The noise problem, however, has barred wide spread use of helicopters. Most of the commercial use helicopters fly near the town. The aeronautics research on reducing noise have been conducted to make helicopters more acceptable to the public. Active blade control methods have been applied to reduce blade noise since 1970’s. The effectiveness has been confirmed but the practical applications of such methods are not realized yet. The difficulty exists on the blade control method. Several methods have been developed for this thirty years. HHC(Higher Harmonic Control) and IBC (Individual

Blade Control) are the famous blade control systems. HHC is the method to control a swash plate at high frequency to reduce vibration or rotor noise. IBC is the method to control each blade pitch angle individually. Active flap method can be called one sort of IBC method, however, conventional IBC methods use actuators between blade root and swash plate. High response and power are required for the IBC actuators. The merit of the active flap is that little force is required to control blade in comparison with conventional IBC methods. The problem of the active flap method is developing the actuator, which is small enough to be embedded in a narrow space of rotor blade, and has enough power to deflect flap to required angle at required frequency. Piezoelectric actuator and SMA(Shape Memory Alloy) have been applied for the active flap actuator. The former one can actuate with high frequency but has small displacement. The latter can actuate with large power and displacement but with low frequency. In this study, piezoelectric actuator was selected as an active flap actuator and flap angle amplification mechanism was newly developed.

This paper presents the study of BVI noise and vibration reduction using active flap control. The study consists of three steps.

The BVI noise for the conventional blade was measured in a wind tunnel as the first step. In this step, the BVI noise for the conventional blade was measured (Fig 1(a)). Sound pressure and blade surface pressure histories were obtained and the locations of the interaction were acquired (Fig 1(b)). As the second step, active flap model rotor was developed and its wind tunnel test was conducted to obtain data in order to estimate the noise reduction effect of the active flap method. In this step, the ability to reduce the BVI noise of the active flap model rotor was estimated, but the effect of the active flap was rather small (Fig 2). The accomplishments of these two steps were shown in the 30th European Rotorcraft Forum.

As for the third step, active flap model rotor was improved and its wind tunnel test was conducted to estimate improved BVI noise reduction effect. In addition, rotor vibration wind tunnel test was conducted to estimate the ability to reduce rotor

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vibration. This paper shows the result of this third step.

This study has been conducted under the joint research work between JAXA and Mitsubishi Heavy Industries, Ltd.

Active flap blade model description

A trailing edge active flap was installed on the each blade (Fig 3). The trailing edge flap system data is shown in Table 1. As shown in the table, flap chord and flap deflection amplitude was improved from old model. The flap chord of the old model was 25% blade chord in airfoil and the flap deflection amplitude was ±2degrees. The improved model was designed to have more influence on the BVI noise reduction than the old model.

Table 1 Active flap blade model description

Blade number 2

Rotor radius 1.0 m

Blade chord 0.065 m

Blade section airfoil NACA0015 Blade twist _{(linearly from hub to tip)}-8 deg. Flap chord* 40% blade chord (25% in airfoil,

15 % out of airfoil) Flap span 5% blade radius Flap location 75% blade radius Flap deflection

amplitude* ±3deg.

Flap control Frequency 40Hz(max) Flap actuator Piezoelectric Actuator *) improved from old model

Wind tunnel test description

This test was conducted in 6.5m x 5.5m Low speed wind tunnel at JAXA from November 1st to December 7th 2004. Two-bladed rotor helicopter model was located in the center of the wind tunnel facility (Fig 4). Two-bladed rotor of the helicopter model was driven and controlled by rotor rotation system shown in Fig 5. This system has “control and drive system”, “collective & cyclic control system”, and “active flap control system”. Control and drive system, which has electric power unit, control unit and lubrication/cooling unit, drives motor with specified rpm. Blade pitch angle is controlled with collective & cyclic control system. Active flap control system receives a blade azimuthal angle signal in every one cycle, and sends active flap deflection angle signal of one cycle. Steps of wind tunnel test

BVI wind tunnel test BVI wind tunnel test was conducted as follows.

1. Specification of advance ratio condition, in which BVI noise is significant.

2. Measurement of BVI noise in the wind tunnel without active flap control in various advance ratio and rotor shaft angle conditions.

3. BVI wind tunnel test with active flap control in significant BVI noise condition, which was determined from the result of the previous step. Rotor vibration wind tunnel test Rotor vibration wind tunnel test was conducted as follows.

1. Measurement of rotor vibration in the wind tunnel without active flap control in various advance ratio and rotor shaft angle conditions.

2. Rotor vibration wind tunnel test with active flap control in significant rotor vibration condition, which was determined from the result of the previous step.

Measurements

Measurement system description is shown in Fig 6. Steady data of the wind tunnel test data is written down, and unsteady data is recorded in real time to the data logger as digital data, which converted from analog data.

Data shown in table 2 was measured. Unsteady data of this table, NO.3 to No.15 and No.18 and No.19 were recorded to the data logger.

Three microphones (MIC1,2,3) were located in order to measure the sound pressure level (Data No.9 to 11). MIC1 was located about 1.5m ahead of the center of the rotor, MIC2 was located about 1.5m behind, and MIC3 was located 0.8m beside. MIC1 and MIC3 were located in order to measure advancing side BVI noise, and MIC2 located for retreating side BVI noise.

Table 2 Measurements

No. Measured data

1 temperature 2

Wind tunnel free

stream data static pressure

3 drag force 4 side force 5 thrust force 6 rolling moment 7 pitching moment 8 Rotor 6 component forces yawing moment 9 MIC1 output 10 MIC2 output 11 Microphone output MIC3 output 12 _{at 75% radius, 4% chord}lower surface pressure 13

Blade surface pressure

(No.1 blade) lower surface pressure at 90% radius, 4% chord

14 flapping angle

15 lead-lag angle

16 collective pitch angle

17

Blade angles

cyclic pitch angle (longitudinal, lateral)

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18 Active flap drive _signal

input signal to piezoelectric actuator

(No.1/No.2 blade) 19 _{deflection angle}Active flap

Active flap potentiometer output

(No.1/No.2 blade)

Test conditions

Test conditions are shown in Table 3. Table 3 Test Conditions Rotor revolution speed 800rpm Thrust coefficient (CT) 0.004

Rotor shaft angle(αs) 1.0, 4.0 degrees

(BVI test) -2.0, -5.0 degrees

(vibration test) Advance ratio (µ) 0.0 to 0.25

(BVI & vibration test without flap control) 0.12, 0.16

(BVI test with flap control)

0.07, 0.15

(vibration test with flap control)

Active flap actuation

As for the input waves for the active flap control actuation, both sine wave and rectangular wave were applied. Active flap deflection angle is defined as following equation and Fig 7 (positive trailing edge down).

(sine input wave)

δAFC=δ0AFC sin(PAFC x ψ + ψAFC)

(rectangular input wave)

δAFC=δ0AFC sin(PAFC x ψ + ψAFC) /

|sin(PAFC x ψ + ψAFC)|

Flap actuation parameters in above equations were as follows.

δ0AFC (Active flap control amplitude):about 3 degrees

PAFC (modulus of active flap control): 2/rev, 3/rev

ψAFC (Active flap control phase angle):

every 45 degrees from 0 to 315 degrees

(every 15 degrees from 210 to 330 degrees for some cases of BVI wind tunnel test)

Results and Discussions BVI wind tunnel test

BVI wind tunnel test result First, we specified advance ratio condition in which BVI noise was significant by simple analysis. An example of this analysis is shown in Fig 8. Free stream flows left to right and the rotor is rotating anticlockwise in these

figures, which are top view of rotor rotating. The tip vortex, shed from blade tip, flows left to right simply with the free stream velocity. BVI noise is considered to become significant, when the vortex interacts parallel with the blade at 90% radius as shown in Fig 8. By sweeping free stream velocity condition (advance ratio condition), advance ratio conditions in which BVI noise was significant were specified. BVI wind tunnel test was conducted without active flap control in condition of various rotor shaft angle and advance ratio. Significant spiky peaks of BVI noise were measured in specified advance ratio condition (Fig 9).

As a result of 1/3 octave band analysis for sound pressure data of the wind tunnel test, 600Hz to 2000Hz band sound pressure level was enlarged in significant BVI noise conditions (Fig 10). So, we named this band sound pressure level “BVI sound pressure level”. We used it as the index for quantitative BVI noise estimation.

In the condition of rotor shaft angle 1.0 degree and advance ratio 0.12, BVI wind tunnel test was conducted with active flap control. Active flap actuation was applied according to the equation described previously. The results of “BVI sound pressure level” reduction are shown in Fig 11. Vertical axis shows the difference of BVI sound pressure level between flap control on and off. Advancing side BVI was reduced Max 3dB with active flap control (modulus of control: 2/rev, control phase angle: 285deg.). Retreating side BVI was reduced Max 2dB with active flap control (modulus of control: 2/rev, control phase angle: 0deg.). Fig 12 shows the BVI sound pressure level data of max BVI noise reduction case in comparison with same condition without active flap control. Spiky peaks of BVI noise at blade azimuthal angle about 66 degrees and about 246 degrees were weakened.

BVI noise reduction mechanism It is known that BVI noise level has much correlation with miss-distance between the blade and the tip vortex at interaction. It is considered that flap actuation has influence on vertical position of the tip vortex and that the BVI noise is much reduced when miss-distance between the blade and the tip vortex is enlarged with flap actuation. So we specified vertical position of the tip vortex with two different approaches as follows.

A. The study with CAMRAD II The conditions of the CAMRAD II study were a little different from that of the wind tunnel test. The advance ratio condition was as same as the wind tunnel test, but the rotor shaft angle was set to more nose up condition than the wind tunnel test. It is because the CAMRAD II is considered to predict the tip vortex position lower. As the result of estimation by CAMRADII in the rotor shaft angle condition where significant BVI noise was measured in the wind tunnel test, specified

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vertical position of the tip vortex was too low and had too much distance from blade to induce significant BVI noise. The wake model of this study was single trailer model.

B. The “simple study” to predict vertical position of the tip vortex The other approach to predict vertical position of the tip vortex was the “simple study” as following. The blades and these trailing edge flaps are assumed to have effect on the tip vortex position at following 4 events before the blade and the tip vortex interaction in case of advancing side BVI in the conducted wind tunnel condition (Fig 13).

1. When the tip vortex generates.

2. When following blade crosses the tip vortex at first time

3. When following blade crosses the tip vortex at second time

4. When following blade crosses the tip vortex at third time

Active flap deflection angle at each event has influence on the tip vortex position. The active-flap- up makes the tip vortex upper than that of no active flap actuation and the active-flap-down makes lower than that of no active flap actuation at each event. Total effect of active flap at each event decides vertical position of the tip vortex at BVI.

Fig 14 shows trajectory of the tip vortex, which interacts parallel with the blade at 90% radius at azimuthal angle about 50degrees, estimated by CAMRAD II. The tip vortex, shed from a blade tip, is pushed down by the downwash when a blade crosses it. The tip vortex position changes upper or lower than that of no active flap actuation according to active flap position (up or down). The vertical position of the tip vortex changes by the active flap actuation at same situations where the active flaps are assumed to have effect on the tip vortex position in the “simple study”. Fig 15 shows the specified vertical position of the tip vortex with two approaches as a function of control phase angle. The trends of two approaches correspond to each other. Fig 15 also shows the comparison between the specified vertical position of the tip vortex and BVI noise reduction result of the wind tunnel test. These trends vs. control phase angle correspond to each other. We predict that the tip vortex position was at the lowest and the miss-distance between the tip vortex and the blade at interaction was enlarged with the active-flap-down position in every event at the tip vortex generation and at three crossing point of the blade and the tip vortex. In addition rectangular wave control input makes active flap always down with maximum deflection angle at every flap effective event, so the BVI noise with active flap control by rectangular wave input was more reduced than that by sine wave input.

Rotor vibration wind tunnel test

In addition to the BVI wind tunnel test, the rotor vibration wind tunnel test was conducted.

First, the wind tunnel test was conducted without active flap control in various conditions of advance ratio and rotor shaft angle. Fig 16 shows the result of this test. Fluctuation of thrust force coefficient (dCT)

was estimated as following equation (other fluctuations of coefficient were estimated by the same way).

]

))}

(

)

(

[{

_ψ

2 T T T

ave

C

ave

C

dC

=

−

, where ave(x) is the function of average

Advance ratio 0.07, 0.15 and rotor shaft angle -2.0 degrees were selected for the conditions of the rotor vibration wind tunnel test with active flap control, because the rotor vibration were locally maximum in these conditions.

Rotor vibration wind tunnel test with active rotor control was conducted. Active flap actuation was applied according to the equation described previously. Fig 17 shows the result of the test, significant rotor vibration reduction was achieved with 2/rev control and reduction of dCT(Fluctuation of

thrust force coefficient) was about 14%.

Fig 18 shows dCT reduction in relation to control

phase angle(ψAFC). Rotor vibration of dCT were

reduced when control phase angles were 270 degrees to 315 degrees. Control phase angle was estimated as an important parameter for rotor vibration reduction. This effective control phase angles for rotor vibration reduction corresponded to that for BVI noise reduction. It is different from the result of past studies (e.g. HART (Ref 4)). The reason is not clear in the present circumstance, but further investigation will be done in future.

Concluding Remarks

Active control rotor was improved and estimated the ability to reduce the BVI noise and vibration by the low speed wind tunnel test.

BVI Noise Reduction with Active Control Flaps

Advance ratio conditions with significant BVI noise level were estimated.

The maximum BVI noise reduction of 3dB was achieved by Active Control Flaps.

The mechanism of BVI noise reduction estimated with CAMRAD II and with other additional analysis has a correlation with the data of the wind tunnel test.

Vibration Reduction with Active Control Flaps

Advance ratio conditions with vibration level at local maximum were estimated.

The vibration level reduced about 14% (maximum) by Active Control Flaps.

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Effective control phase angles for vibration control corresponded to that for BVI noise reduction.

References

(1) Nakao, M., Uchiyama, N., Maeda, I., Hattori, K., Saito, S., Aoyama, T. and Kondo, N., “Research for the BVI noise reduction using the Blade Active Control,” Aircraft symposium 2003.

(2) Nakao, M., Uchiyama, N., Maeda, I., Saito, S., Aoyama, T. and Kondo, N., “On Helicopter BVI Noise Prediction,” NAL SP-57 2003.

(3) Hattori, K., Nakao M., Uchiyama, N., Yoshimoto, M., Saito, S. and Kondo, N., “Research for the BVI noise reduction using the Blade Active Control,” 30th_{European Rotorcraft Forum 2004.}

(4) Splettstoesser, W. R., Kube, R., Wagner, W., Seelhorst, U., Boutier, A., Micheli, F., Mercker, E. and Pengel, K. “Key results from a higher harmonic control aeroacoustic rotor test (HART),” J. of the American Helicopter Society, 42 (1), 1997

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Measured sound pressure signature

-10 -5 0 5 10 15 0 90 180 270 360 ψ[deg] P-P∞ [P a] Mic.1 Mic.2 Mic.3

Measured sound pressure signature

-10 -5 0 5 10 15 0 90 180 270 360 ψ[deg] P-P∞ [P a] Mic.1 Mic.2 Mic.3

Fig 1(a) Measured BVI sound pressure signature with conventional blade rotor

-1.0 -0.5 0.0 0.5 1.0 1.5 2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 Y [m] X [m] ② _{Free stream} rotation BVI

Azimuth angle ψ [deg] P-P _∞ [kPa] αs =4 °, µ =0.16 ② ③ ① Advancing blade -0.4 -0.3 -0.2 -0.1 0 30 60 90 ① ② ③ -5 0 5 10 0 30 60 90

Azimuth angle ψ [deg] Sound pressure [Pa]

Fig 1(b) Sound pressure and blade surface pressure histories under interaction

-1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 S oun d pr e ss ur e l ev el （ ac tiv e f lap on -off ） [d B ] 0 45 90 135 180 225 270 315 360 Phase angle [deg]

Sine wave Rectangular -1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 S oun d pr e ss ur e l ev el （ ac tiv e f lap on -off ） [d B ] -1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 S oun d pr e ss ur e l ev el （ ac tiv e f lap on -off ） [d B ] 0 45 90 135 180 225 270 315 360 Phase angle [deg] 0 45 90 135 180 225 270 315 360

Phase angle [deg]

Sine wave Rectangular Sine wave Rectangular

(advancing side BVI noise reduction(2/rev control))

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Fig 3 Active flap blade model

Fig 4 JAXA 6.5m x 5.5m Low speed wind tunnel

Active flap

Rotor center

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Electric power unit Control unit Drive signal Drive motor lubrication/cooling unit Control monitor Reducer lubrication Motor cooling Collective & Cyclic control system control

Two blades Rotor model

Azimuth angle signal

Flap deflection signal

Active flap control system Control unit

Electric power unit

Control and drive system

Electric power unit

Electric power unit Control unit

Electric power unit

Control and drive system

Fig 5 Rotor rotation system description

Collective & Cyclic control system

Electric power unit

Wind tunnel

Flap actuation signal

Free stream temperature static pressure

Display Collective pitch angle

Cyclic pitch angle _{Data logger}

Rotor 6 component forces, Blade flapping/lead-lag angle, Blade surface pressure, Flap deflection angle, Blade azimuthal angle, Microphones output 1560mm 1560mm 900mm 900mm 窓 800mm MIC1 MIC2 MIC3

Heights from ground Rotor head: 3,500mm MIC1 : 2,460mm MIC2 : 2,460mm MIC3 : 2,540mm 1000mm Free stream Collective & Cyclic control system

Electric power unit

Control unit

Electric power unit

Wind tunnel

Flap actuation signal

Free stream temperature static pressure

Display Collective pitch angle

Cyclic pitch angle _{Data logger}

Rotor 6 component forces, Blade flapping/lead-lag angle, Blade surface pressure, Flap deflection angle, Blade azimuthal angle, Microphones output 1560mm 1560mm 900mm 900mm 窓 800mm MIC1 MIC2 MIC3

Heights from ground Rotor head: 3,500mm MIC1 : 2,460mm MIC2 : 2,460mm MIC3 : 2,540mm 1000mm Free stream 1560mm 1560mm 900mm 900mm 窓 800mm MIC1 MIC2 MIC3

Heights from ground Rotor head: 3,500mm MIC1 : 2,460mm MIC2 : 2,460mm MIC3 : 2,540mm 1000mm Free stream

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-4 -3 -2 -1 0 1 2 3 4 0 45 90 135 180 225 270 315 360

No.1 blade azimuth angle ψ(deg)

ac ti ve f lap d e fl e c ti o n a n gl e (d e g) (p o sitiv e tr aili n g e dg e d o w n )

Sine wave input Rectangular wave input

-4 -3 -2 -1 0 1 2 3 4 0 45 90 135 180 225 270 315 360

No.1 blade azimuth angle ψ(deg)

ac ti ve f lap d e fl e c ti o n a n gl e (d e g) (p o sitiv e tr aili n g e dg e d o w n )

Sine wave input Rectangular wave input

example: PAFC=2/rev, ψAFC=45deg. example: PAFC=3/rev, ψAFC=45deg.

Fig 7 Input wave for active flap control actuation

-1.5 -1 -0.5 0 0.5 1 1.5 -1.5 -1 -0.5 0 0.5 1 1.5 2 2.5 3 x [m] y [m] blade #1 blade #2

tip path - blade #1 tip path - blade #2 72.5%R(blade #1) 72.5%R(blade #2) 77.5%R(blade #1) 77.5%R(blade #2) μ = 0.160 N = [rpm]800 V∞ = [m/s]13.4 αs = [deg]1 Ψ1 = [deg]50 Ψ2= [deg]230 -1.5 -1 -0.5 0 0.5 1 1.5 -1.5 -1 -0.5 0 0.5 1 1.5 2 2.5 3 x [m] y [m] blade #1_{tip path - blade #1} blade #2_{tip path - blade #2}

72.5%R(blade #1) 72.5%R(blade #2) 77.5%R(blade #1) 77.5%R(blade #2) μ = 0.121 N = [rpm]800 V∞ = [m/s]10.1 αs = [deg]4 Ψ1 = [deg]308 Ψ2 = [deg]128

µ=0.16, Advancing side BVI µ=0.12, Retreating side BVI Fig 8 Specification of advance ratio condition where BVI noise is significant

-8 -6 -4 -2 0 2 4 6 8 10 12 0 45 90 135 180 225 270 315 360 ψ [deg] SPL [ P a] MIC1 MIC2 MIC3 -8 -6 -4 -2 0 2 4 6 8 10 12 0 45 90 135 180 225 270 315 360 ψ [deg] SP L [ P a] MIC1 MIC2 MIC3 αs=1deg., µ=0.16, CT=4.0 x 10-3 αs =4deg., µ=0.12, CT=4.0 x 10-3

Fig 9 Measured BVI sound pressure Advancing side BVI

MIC1 MIC1 MIC3 MIC3

Advancing side BVI

MIC1 MIC1 MIC3 MIC3

Retreating side BVI MIC2

MIC2 MIC3

MIC3

Flap deflection angle changes from plus to minus at blade azimuthal angle ψ=180/ PAFC - ψAFC/PAFC

Flap deflection angle changes from minus to plus at blade azimuthal angle

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Thick solid line: Significant BVI case Thin solid line: Slight BVI case Dash line: no BVI case

70 80 90 100

1.0E+02 1.0E+03 1.0E+04

f [Hz] SP L [d B ] μ = 0.10 μ = 0.12 μ = 0.14 μ = 0.15 70 80 90 100

1.0E+02 1.0E+03 1.0E+04

f [Hz] SP L [d B ] μ = 0.10 μ = 0.12 μ = 0.14

Advancing side BVI (MIC3) Retreating side BVI (MIC2) Fig 10 1/3 octave band analysis of BVI [αs =4deg., µ=0.12, CT=4.0 x 10-3]

-4.0 -3.0 -2.0 -1.0 0.0 1.0 2.0 3.0 4.0 0 45 90 135 180 225 270 315 360

phase angle [deg]

ΔBV I so und p res sur e level [ dB] (f la p co nt ro l o n fl ap co n tr o l o ff )

Sine wave input［RunNo.014］ Rectangular wave input［RunNo.012］ Rectangular wave input［RunNo.026］ Rectangular wave input［RunNo.031］

-4.0 -3.0 -2.0 -1.0 0.0 1.0 2.0 3.0 4.0 0 45 90 135 180 225 270 315 360

phase angle [deg]

ΔBV I so und p ressure lev el [d B ] (f lap co nt ro l o n - fla p co n tro l o ff)

Fig 11(1) Reduction of BVI noise with active flap control(advancing side BVI) [αs =4deg., µ=0.12, CT=4.0 x 10-3] 600 to 2000Hz 600 to 2000Hz PAFC: 2/rev PAFC: 3/rev Max 3dB Reduction

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-4.0 -3.0 -2.0 -1.0 0.0 1.0 2.0 3.0 4.0 0 45 90 135 180 225 270 315 360

phase angle [deg]

Δ B V I s o und p res sur e l e vel [d B ] (flap co n tro l o n - flap co n tr o l o ff)

Sine wave input［RunNo.014］ Rectangular wave input[RunNo.012］ Rectangular wave input［RunNo.026］ Rectangular wave input［RunNo.031］

-4.0 -3.0 -2.0 -1.0 0.0 1.0 2.0 3.0 4.0 0 45 90 135 180 225 270 315 360

phase angle [deg]

ΔBVI so u nd p re ss ur e lev e l [d B ] (f lap co nt ro l on fla p c on tr ol o ff )

Fig 11(2) Reduction of BVI noise with active flap control (Retreating side BVI) [αs =4deg., µ=0.12, CT=4.0 x 10-3] -8 -6 -4 -2 0 2 4 6 8 10 12 0 45 90 135 180 225 270 315 360 ψ [deg] SP L [ P a] -1 0 1 2 3 4 5 6 7 8 9 A ct iv e fl ap d ri ve s ig nal [ V ] SPL(MIC3) Active flap drive signal

-8 -6 -4 -2 0 2 4 6 8 10 12 0 45 90 135 180 225 270 315 360 ψ [deg] SP L [ P a ] -1 0 1 2 3 4 5 6 7 8 9 A c ti v e f la p dr iv e si gn a l [ V ] SPL(MIC3) Active flap drive signal

without active flap control max BVI noise reduction case

with active flap control(PAFC: 2/rev, ψAFC: 285 deg.)

Fig 12 BVI sound pressure comparison [αs =4deg., µ=0.12, CT=4.0 x 10-3]

PAFC: 2/rev

PAFC: 3/rev

Max 2dB Reduction

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-1.5 -1 -0.5 0 0.5 1 1.5 -1.5 -1 -0.5 0 0.5 1 1.5 2 2.5 3 x [m] y [m] blade #1 blade #2

tip path - blade #1 tip path - blade #2 72.5%R(blade #1) 72.5%R(blade #2) 77.5%R(blade #1) 77.5%R(blade #2) μ = 0.121 N = [rpm]800 V∞ = [m/s]10.1 αs = [deg]4 Ψ1 = [deg]138 Ψ2= [deg]318 -1.5 -1 -0.5 0 0.5 1 1.5 -1.5 -1 -0.5 0 0.5 1 1.5 2 2.5 3 x [m] y [m] blade #1 blade #2

tip path - blade #1 tip path - blade #2 72.5%R(blade #1) 72.5%R(blade #2) 77.5%R(blade #1) 77.5%R(blade #2) μ = 0.121 N = [rpm]800 V∞ = [m/s]10.1 αs = [deg]4 Ψ1 = [deg]304 Ψ2 = [deg]124

1. The tip vortex generates 2. First encounter of the following blade and the tip vortex

-1.5 -1 -0.5 0 0.5 1 1.5 -1.5 -1 -0.5 0 0.5 1 1.5 2 2.5 3 x [m] y [m] blade #1 blade #2

tip path - blade #1 tip path - blade #2 72.5%R(blade #1) 72.5%R(blade #2) 77.5%R(blade #1) 77.5%R(blade #2) μ = 0.121 N = [rpm]800 V∞ = [m/s]10.1 αs = [deg]4 Ψ1 = [deg]97 Ψ2= [deg]277 -1.5 -1 -0.5 0 0.5 1 1.5 -1.5 -1 -0.5 0 0.5 1 1.5 2 2.5 3 x [m] y [m] blade #1 blade #2

3. Second encounter of the following blade 4. Third encounter of the following blade and the tip vortex and the tip vortex

-1.5 -1 -0.5 0 0.5 1 1.5 -1.5 -1 -0.5 0 0.5 1 1.5 2 2.5 3 x [m] y [m] blade #1 blade #2

5. blade and tip vortex interaction

Fig 13 The events where active flaps have effect the position of the tip vortex, which interacts with the blade of 90% radius (advancing side BVI).

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-0.1 -0.075 -0.05 -0.025 0 0.025 0.05 0.075 0.1 0.125 0.15 0.175 0.2 -0.8 -0.7 -0.6 -0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 X/R Z/ R

tip vortex position with active flap up at every event where the flap has effect the tip vortex position

(control phase angle 60deg.)

Free stream

tip vortex position without active flap control

blade path at BVI following blade path

at third encounter following blade path

at second encounter following blade path

at first encounter

Rotor shaft

tip vortex position with active flap down at every event where the flap has effect the tip vortex position

(control phase angle 255deg.)

Fig 14 Trajectory of the tip vortex (side view) (estimated with CAMRADII, advancing side, 2/rev control)

2/rev, advancing side

-8 -7 -6 -5 -4 -3 -2 -1 0 1 2 0 45 90 135 180 225 270 315 360 phase angle[deg] Δ B V I s ou nd p re ss ur e l ev el [d B ] (f la p c o nt ro l on fl ap c on tr ol o ff) CAMRADII Simple approach tip v o rt ex ver tic al posi tio n lo w e r < --> u pper

Fig 15 Specified tip vortex vertical position as function of phase angle, in comparison with BVI noise reduction result of the wind tunnel test

(14)

0 0.0005 0.001 0.0015 0.002 0.0025 0.00 0.05 0.10 0.15 0.20 0.25 μ dC T α=-2 α=-5 0 0.00002 0.00004 0.00006 0.00008 0.0001 0.00012 0.00014 0.00016 0.00018 0.00 0.05 0.10 0.15 0.20 0.25 μ dC M α=-2 α=-5

Fig 16 Result of Rotor vibration wind tunnel test without active flap control

(left: dCT(Fluctuation of thrust force coefficient), right: dCM(Fluctuation of pitching moment coefficient))

-16 -14 -12 -10 -8 -6 -4 -2 0 2 4 µ：0.07 µ：0.15 µ：0.07 µ：0.15 2/rev 3/rev re du ct io n ra tio [% ] dCH dCT dCM about 14% reduction 0.0E+00 2.0E-04 4.0E-04 6.0E-04 8.0E-04 1.0E-03 1.2E-03 1.4E-03 1.6E-03 0 45 90 135 180 225 270 315 360 phase angle［deg］ dC T

Rectangular wave input Sine wave input

without control

Fig 17 Reduction of vibration level with flap actuation

Fig 18 Relation between dCT and

control phase angle

µ:0.07 µ:0.15 µ:0.07 µ:0.15

µ:0.07 µ:0.15

T