Korea-Japan Joint Workshop on Rotorcraft
Feb. 10, 2023

Rotorcraft Aeromechanics Research Activities
at Konkuk University
Prof. Sung Nam Jung
Konkuk University, Seoul, Republic of Korea
02/09/2023

Part I

Introduction to Konkuk IRT GroupKonkuk University (KU)
❖ Dept. of Aerospace Eng.
▪ Established in Mar. 1990
Konkuk Univ., Seoul▪ Currently 12 faculty members▪ About 160 undergraduate students &70 graduate students enrolled▪ Home of BK21 ST-IT fusion program
sponsored by MOE (2006 – 2013)• Konkuk University (KU):- Founded in 1946; One of the leading private universities in Korea- Located in the northeastern region of Seoul- About 25k students enrolled, including 3k graduate students- Over 700 faculty members

Subsonic wind tunnel

High speed shock tube
(M = 2.5)

KU Int. Rotorcraft Technology (IRT) Group❖ IRT group members of Int. R&D Hub program sponsored by KRF (2006 – 2013)

Prof. Yung Yu(retired)

Prof. S. Park

Prof. S. Jung

Prof. S. Sung
Prof. C. Moon
Prof. C. Kim➢ All IRT members joinedon or after BK-21

KU Int. Rotorcraft Technology (IRT) Group Activities❖ Major research activites of KU IRT group- Home of national BK21 & IRH programs sponsored by NRF Korea (2006- 2013)- German DLR - Konkuk MoU research (2008 - 2013)- Active participants of Int. HART II Workshop (2008 - 2012)- One of STAR (Smart Twisting Active Rotor) int. consortium project members (since 2008)- Founding member of international meetings such as Rotor Korea (2007, 2008) and ARF- Development of various rotorcraft software tools: KFLOW, HETLAS, Ksec2D, etc.
- Establishment of high precision numerical schemes such as CFD/CSD coupling for
HART I/II validation

2D FE cross-sectional analysis S/W Ksec2D
3D compressible RANS flow solver KFLOW

Rotorcraft flight dynamics simulation S/W HETLASPart II

Summary of Rotorcraft Aeromechanics
Research Outcomes at KU

HART I Blade Property Test
Motivation:
HART I rotor test conducted in 1994
▪ No systematic measured blade
property data available so far▪ All blades damaged at a follow-on test▪

Approaches:
In collaboration with NASA, DLR, KU▪ Use the original blade set tested inDNW (1994)▪ Well-established test techniques
employed▪ Destructive-type of test techniques
adopted▪

HART I blades used for structural test

Mirror method for flap bending

Outcomes:

Property table completed for HART I
blades and documented as NASA techreport (NASA/CR-2012-216039)▪ Property data released in JAHS 2013▪

3 point bending for chord stiffness
Trifillar pendulum for section
MOI

Result: HART I Blade Property Test

-1-2-3-4-50

Blade tip elastic torsion, deg

Elastic torsion
motion:

90

180

270

20-2090

180

270

Azimuth angle, deg(a) BL••-1-2-3-4-5036090

180

270

20-20901802700-1-2-3-4-50360

90180

270360Azimuth angle, deg

4Measured
Present
Lim et al. (2003)-4

MeasuredPresent
Lim et al. (2003)

1-6360Azimuth angle, deg

4Measured
Present
Lim et al. (2003)

-4

0-6

360

Azimuth angle, deg

41

Blade tip flap deflection, cm

0Measured
Present
Lim et al. (2003)

Blade tip elastic torsion, deg

1Blade tip flap deflection, cm

MeasuredPresent
Lim et al. (2003)

Blade tip elastic torsion, deg

Blade tip flap deflection, cm

Elastic flap
motion:222Measured
Present
Lim et al. (2003)
20-2-4090180270

Azimuth angle, deg

Azimuth angle, deg(b) MN(c) MV360

Jung, S. N., You, Y. H., Lau, B., Johnson, W., and Lim, J. W., "Evaluation of Rotor Structural and Aerodynamic Loads Using Measured Blade Properties,"
Journal of the American Helicopter Society, Vol. 58, No. 4, Oct. 2013
Jung, S. N., and Lau, B., “Determination of HART I Rotor Blade Structural Properties by Laboratory Testing," NASA CR-2012-216039, Aug. 2012.

HART II Blade Property Test
Motivation:

No measured properties availablefor HART II blades▪ Reliable measured properties
needed for accurate predictions
▪

#2
#1

#3

#4

Approaches:
In collaboration with NASA, DLR, KU▪ Use the original set of HART IIblades tested in DNW (2001)▪ Non-destructive test techniques (xray CT-scan plus 2D FE section
analysis system Ksec2D) adopted▪ Assess measurement quality▪

Outcomes:
Updated structural property data ofHART II blades released▪ Documented in journal papers:
AIAA J & Comp Str (2015)▪

FlapbendingResult: HART II Blade Property TestN-m

Flap bending

Torsion stiffness

25.2% at 0.17R••

Jung, S. N., You, Y. H., Dhadwal, M., Riemenschneider, J., and Hagerty, B., "Study on Blade Property Measurement and Its Influence on Air/StructuralLoads," AIAA Journal, Vol. 53, No. 11, 2015
Jung, S. N., M. Dhadwal, Kim, Y. W., Kim, J. H., and Riemenschneider, J., "Cross-section Constants of Composite Blades Using Computed Tomography
Technique and Finite Element Analysis," Composite Structures, Vol. 129, Oct. 2015

Validation of HART I Rotor
Summary:HART I test performed at DNW in 1994
▪ First international joint effort to apply HHCtechnology to reduce rotor noise/vibration▪ Measured blade properties available due to therecent measurement campaign▪

Approaches:
Modern CFD/CSD coupling used
▪ Both isolated rotor & rotor-fuselage modelsused▪ In CFD, up-to-date space/time marching
schemes adopted for high precision results▪

HART I

HART II

No. of air stations

3 (0.75, 0.87, 0.97R)

1 (0.87R)

No. of strain gages

34 → 32!

6CFD/CSD coupled airloads results showed
excellent correlation with the test data
▪ BVI characteristic of HART I data captured
precisely▪ Structural loads correlation showed slight
improvements

20.9M cells

Rotor-fuselage:

37.5M cells

STARTCSD TrimFindings:▪

Isolated rotor:

F/M iCSD  F/M iLL  F/M i
Output: control angles &blade motions

HART I

CFD Airloads

HART II

Compute F/MiCFD
1. 25 to 3 rev. run required

Delta airloads
F/M i Ouput: M2 Cn , M2 Cx , M2 Cm

LL
F/M iCFD1  F/M i 1Converged?

NOF/M iCSD  F/MiCFD
YES

Shank models

Post Processing

END

Loose CFD/CSD
coupling algorithm

Validation of HART I Test Data
Measured (75%R)
CAMRAD II with free wake
CAMRAD II/KFLOW (isolated rotor)
CAMRAD II/KFLOW (rotor-fuselage)

0.15

Measured (87%R)
CAMRAD II with free wake
CAMRAD II/KFLOW (isolated rotor)
CAMRAD II/KFLOW (rotor-fuselage)

0.15

0.1

M 2C nM 2C n
0.05

0.05

0.05

0000.75R
-0.05

090

180

270

360

0. 87R
-0.05

090

180

2700.97R
360

-0.05

090

180

360

0.04

0.2
Measured (87% R)
CAMRAD II with free wake
CAMRAD II/KFLOW (isolated rotor)
CAMRAD II/KFLOW (rotor-fuselage)

0.15

Isolatedrotor model

Measured (87% R)
CAMRAD II with free wake
CAMRAD II/KFLOW (isolated rotor)
CAMRAD II/KFLOW (rotor-fuselage)
0.02

M 2C nM 2C n

0.1

00.05

-0.02
0-0.05270

Azimuth anlge, deg

Azimuth anlge, deg

Azimuth anlge, deg

Harmonicanalysis on
M2Cn(at 0.87R):

Measured (97%R)
CAMRAD II with free wake
CAMRAD II/KFLOW (isolated rotor)
CAMRAD II/KFLOW (rotor-fuselage)

0.15

0.1

0.1

M 2C nSection
airloads:

0.2

0.2

0.2090

180

270

360

-0.04

090

180

270

Azimuth angle, deg

Azimuth angle, deg

Low harmonic (0 to 10P)

High harmonic (11P and higher)

360

R-F modelValidation of HART I Test Data
0-1-2-3-4-5090

180

270

Measured
CAMRAD II with free wake
CAMRAD II/KFLOW (isolated rotor)
CAMRAD II/KFLOW (rotor-fuselage)
10-1-2360

0Azimuth angle, deg

2700-490

180

270

Azimuth angle, deg

0-20360

180

270

360

100. 45R

Measured (0.45R)
CAMRAD II with freewake
CAMRAD II/KFLOW (isolated rotor)
CAMRAD II/KFLOW (rotor-fuselage)

200-4090

Azimuth angle, deg-20

Measured (0.45R)
CAMRAD II with freewake
CAMRAD II/KFLOW (isolated rotor)
CAMRAD II/KFLOW (rotor-fuselage)

02-4

360

090

180

270

Azimuth angle, deg

0.4R

Torsion moment, N-m

4

Chord bending moment, N-m

Flap bending moment, N-m

180

400.45R-890

Measured
CAMRAD II with free wake
CAMRAD II/KFLOW (isolated rotor)
CAMRAD II/KFLOW (rotor-fuselage)

Azimuth angle, deg

8Bladestructuralloads:

Blade tip elastic torsion, deg

1-642Measured
CAMRAD II with free wake
CAMRAD II/KFLOW (isolated rotor)
CAMRAD II/KFLOW (rotor-fuselage)

Blade tip lag deflection, cm

Blade tipmotions:

Blade tip flap deflection, cm

2360

Measured (0.4R)
CAMRAD II with freewake
CAMRAD II/KFLOW (isolated rotor)
CAMRAD II/KFLOW (rotor-fuselage)

50-5-10090

180

270

Azimuth angle, deg

360• "Improved Rotor Aeromechanics Predictions using a Fluid-Structure Interaction Approach," Aerospace Science and Technology, Vol. 73, No. 2, Feb. 2018
• "Data Transfer Schemes in Rotorcraft Fluid-Structure Interaction Predictions," International Journal of Aerospace Engineering, Vol. 2018, Mar. 2018
• "Comprehensive Aeromechanics Predictions on Air and Structural Loads of HART I Rotor," Int. J. of Aeronautical and Space Sciences, Vol. 18, No. 1, 2017

Validation of HART II Rotor
Isolated Rotor Model

Motivation:
HART II test performed at DNW in 2001
▪ Wind tunnel test data open to public in 2006
▪ High resolution test data used to demonstrate
the prediction capability▪

Approaches:

Rotor-Fuselage ModelStep-by-step approaches taken for the validationof measured data
CAMRAD II
aero model

Outcomes:

Code-to-code validation proved efficient forimproved correlation of HART II data
▪ Mechanism of BVI noise reduction via HHC
inputs explained▪ Loose CFD/CSD coupling algorithm shown to behighly reliable for aeromechanics predictions

4000

0.2

600

iter 0iter 1iter 2iter 3iter 4iter 5iter 6

ThrustRolling moment
Pitching moment

▪

400
3500

Thrust, N

20003000

Trim iteration
history:0.15

M 2Cn1) CSD approach: CAMRAD II alone or with prescribed(CFD or measured) airloads
2) CFD approach: KFLOW with measured blade motions
3) Loose CFD/CSD coupled approachRoll/Pitch Moment, N-m▪

87% span

0.1

0.05

-200

M2Cn

Rotor thrust and moments
2500

01

2

3

Trim Cycles

456-400

0090

180

270

Azimuth angle, deg360

Validation of Section Airloads❖ Validation of section normal forces M2Cn
0.2

0.25
Measured
Isolated rotor
Rotor + fuselage

87% span
0.2

0.15

87% spanBL case
M 2Cn

Measured
Isolated rotor
Rotor + fuselage

0.15

87% span

Measured
Rotor + fuselage

M 2Cn

0.2

0.3

0.15

0.1

0.1

0.05

0MN case

0.1

Advancing side

Enlarged 00view
0.2
0.05

-0.05

306090Measured
Isolated rotor
Rotor + fuselage

090

180

270

360

Azimuth angle, deg

90

180

270

Azimuth angle, deg

120

Measured
Rotor + fuselage

Azimuth angle, deg
87% span360

87% span

0.2

0.15

M 2Cn

00

0.25

0.15

M 2Cn

M 2Cn

0.05

0.1

0.1

0.05

➢ Good correlation (BVI peaks, phase)obtained, particularly with R-F model

0.05

0MV case

Retreating side
0240

-0.05
270

300

330

Azimuth angle, deg

360

090

180

270

Azimuth angle, deg360

Validation of Blade Elastic Motions
1+0++++++++++-1+++++++++++-2-3

2+1++++++++-1+

180

270+-2+360

02++++++++++++++-2+++++++-3

1+++-1-2++++++++++++++++++++-3-5090

180

270

Azimuth angle, deg

360++++++-1+++++++++-2+0+90180

420+270360(c) MV
Measured - blade #1
Measured - blade #3
Measured - blade #4
Isolated rotor
Rotor + fuselage+32+1++0++++++++-1+++++++-2+++-3++-4-4-4-5

3+++5++++

Azimuth angle, deg

Measured - blade #1
Measured - blade #3
Measured - blade #4
Isolated rotor
Rotor + fuselage

40+0-3

360

51-1

270

1

Azimuth angle, deg

Tip elastic torsion, deg

Tip elastic torsion, deg

Torsionmotion:31802(b) MN

Measured - blade #1
Measured - blade #2
Measured - blade #3
Measured - blade #4
Isolated rotor
Rotor + fuselage++90(a) BL
4+++

Azimuth angle, deg

5+++-390+++0+0+

Measured - blade #1
Measured - blade #4
Isolated rotor
Rotor + fuselage+

Tip flap deflection, 100 z/R+

Measured - blade #1
Measured - blade #2
Measured - blade #3
Measured - blade #4
Isolated rotorRotor + fuselage

Tip elastic torsion, deg

2

Measured - blade #1
Measured - blade #2
Measured - blade #3
Measured - blade #4
Isolated rotor
Rotor + fuselage

Tip flap deflection, 100 z/R

Tip flap deflection, 100 z/R

Flap
motion:

3

33-5

090

180

270

Azimuth angle, deg

360

090

180

270

Azimuth angle, deg

360

Validation of Tip Vortex Trajectories
0.8

0.8
Measured Data
Isolated Rotor
Rotor + Fuselage

freestream

Ref. blade( = 70)

mxh

0.4

0.4
P19P18

P17P20

P22P18

 = 70-2-1 = 70

Advancing side

0-0.4
2 -2

1xh(m)-1

Measured Data
Isolated Rotor
Rotor + Fuselage

P44

P45
P46
P47+
 = 20

••••

1

2

Measured Data
Rotor + Fuselage

freestream

-2

-1

P44

P43

P45xh(m)+ = 20

Retreating side
1

P46
P470 = 70
0zh(m)

zh(m)

P43

Ref.
blade (= 20) 0-0.4

0xh(m)

0.4

0.4xh

 = 20

0.8
freestream

mP22(b) MN case

0.8yh

P21+0 = 20

P20

P23(a) BL caseyh/R = 0.7P19P17+0-0.4

P21zh(m)yhzh(m)yh/R = 0.7

Measured DataRotor + Fuselage

freestream-0.4
2 -2-1

 = 70
0xh(m)

1"Modern Computational Fluid Dynamics/Structural Dynamics Simulation for a Helicopter in Descent," Journal of Aircraft, Vol. 50, No. 5, 2013
"Loose Fluid-Structure Coupled Approach for a Rotor in Descent Incorporating Fuselage Effects," Journal of Aircraft, Vol. 50, No. 4, 2013
"Correlation of Aeroelastic Responses and Structural Loads for a Rotor in Descending Flight," Journal of Aircraft, Vol. 49, No. 2, 2012
"Comprehensive Code Validation on Airloads and Aeroelastic Responses of the HART II Rotor," Int. J. of Aeronautical and Space Sciences, Vol. 11, No. 2, 2010

2International HART II Workshop▪ 1st Int. HART II Workshop started: Sept. 2005
▪ HART II test data opened to public: 3 test points indescending flight

Participatingorganizations forjoint workshop:- Test data points: BL, MN, MV (at m = 0.15)

OVERFLOW- Data released: Blade motions, Airloads, Rotor trim,Acoustics, PIV wake, Flow visualization for descendingflight▪ Workshop held biannually at AHS & ERF until 2012

GENCAS

Correlation
results:

Joint workshop held in AHS Forum, Fort Worth, TX, May 1-3, 2012

DLR-KU MoU ResearchGoals:▪ To establish an int. collaboration▪ To broaden the technology base byincreasing fundamental knowledge onhelicopter aeromechanics area

Summary:▪ MoU began in Apr. 2008 for 6 years▪ Consisted of 2+ tasks: rotor
aeromechanics, dynamic stall, andinformation exchange (rotary UAV)
▪ Meetings held twice per year at the otherorganization▪ Points of contact: Sung N. Jung (KU),
Berend G. van der Wall (DLR)

Outcomes:▪ S4-KFLOW coupling attempted▪ Bound meeting minutes (11 meeting volumes)▪ 1 journal papers and 7 conference papers

Reduce noise/vibration withimproved performance via ATR
concept (post-decessor of HART II)▪ Realize active rotor technology▪

German DLR / French ONERA▪ US Army AFDD & NASA Ames
▪ Korea Konkuk Univ. & KARI
▪ Japan JAXA
▪ UK DSTL & Univ. of Glasgow

FlightConditions▪

▪

ScheduleMembers

Goals

STAR (Smart Twisting Active Rotor) Int. Consortium Project▪

STAR hover test, 2013

Hover, Low speed descent▪ Cruise/high speed▪ High load, High m (at 50% RPM)
▪ Speed/thrust/phase sweep
Phase I: Launched at May 2009
▪ Phase II: Resumed in 2018
▪ Wind tunnel test planned: Sept. 2024
at DNW, Netherlands• Ahn, J. H., Hwang, H. J., Jang, S., Jung, S. N., Kalow, S., and Keimer, R., "X-ray Computed Tomography Method for Macroscopic
Structural Property Evaluation of Active Twist Composite Blades," Aerospace, Vol. 8, Nov. 2021

Q&A

Thank you!
Contact: snjung@konkuk.ac.kr