Current state-of-the-art of TsAGI studies in the area of helicopter

(

TWEN

T

Y FIRST EUROPEAN ROTORCRAFT FORUM

D

N

I

'

'

7

,

cper

i

·o

i.l

CCRRE:\T STATE-OF-THE-A

.

RT OF TsAGI STCDIES

IN THE AREA OF HELICOP

TER AERODYl\"A\IICS

BY

Eugene

S

.

Vozhdaev and

Vladimir A. Golovkine

CE::ITRAL .~RODYN.A.:'vfiC L\'STITL1E (TsAGI)

ZHUKO'WSKY, MOSCO\\i REGIO~, RuSSIA

August 30- September

l,

1995

SAINT-

PETERSBURG, RUSSIA

Paper nr.:

II.17

Current state

-

of-the-art of TsAGI Studies in the Area

of Helicopter Aerodynamics.

E.S.

Vozhdaev;

V.A.

Golovkin

TWENTY FIRST EUROPEAN ROTORCRAFT FORUM

August 30 - S

e

ptember 1, 1995 Saint-Petersburg

,

Russia

(

[

@

Current State-of-the-Art of TsAGI Studies in the Area

of Helicopter Aerodynamics.

Central Aerodynamic Institute

(TsA.GI)

Zhukovsky, Moscow Region, Russia.

Abstract.

The paper reviews the basic works of Ts.A.GI aimed at providing high-level aerodynamic perfection of helicopters.

I

n

t

r o d u c

t

i

o n.

Traditionally the activities of TsAGI in the area of helicopters, as it is know, include:

-calculational/theoretical and ex]Jerimental studies of l1elicopter aerodynamics; -calculationaljtheoretical and ex]Jerimental studies of helicopter flight dynamics using flight simulators;

-calculational and ewerimental studies of helicopter strength and

structure dynamics;

-studies of markets and prospects of helicopter development.

In the area of helicopter aerodynamics the following basic trends are

developing (Fig.!):

-investigation and development of aerodynamic and aeroelastic

configurations of main rotor blades;

-investigation and finishing of aerodynamic configurations of helicopter

bodies:

-investigation and developrnent 0f aerodyn~nnic coEfigura.tions of controL

devices for helicopter of various configurations:

-examination of problems of helicopter units and elements interference.

Helicopter aerodynamic design system

Evolution and practical use of a helicopter aerodynamic design system as a constituent of a more general system of helicopter development has become one of the major trends of TsAGI's activities.

The aerodynamic design system \Vas first used in the

of development of the heavy transport helicopter Mi-26. The results of venture of Ts.""-Gl and the M.L Mil Design Bureau turned out considerable value. The :Vfi-26 flight tests have shown that the highest

process the joint to be of

level of

l·o ..

lift-to-drag ratio (L/De=4.3) and the highest level of fuel efficiency (0.75

;,o·;''' )

l ·.<in

were achieved at cn1ise flight mode. There are still record features for

transport helicopters with rear fuselage cargo doors.

The aerodynamic design at Ts.A.GI is presently performed on the basis of an interactive hierarcl:tical system of theoretical and ex]Jerimental methods of

structures, etc., enabling with the use of a stmctured successio;1 of iterative procedures to find optimized solutions in compliance with the hdicopter objecti\'e function and the resulting objective functions of its elements (rotor, fuselage, etc.).

The objective function contains criteria of efiectiveness and constraints

that correspond to the helicopter purpose and conditions of its practical use.

Rotor aerodynamic design system

An important element of the helicopter design system is th~ rotor

aerodynamic design system. Tilis system comprises blocks of prograiiJ.S w compute flow> over blade airfoils and rotor aerodynamic, aeroelastisiti.c and acoustic characteristics (Fig. 2).

The block of the programs to compute the rotor performance uses theories of various level of complexity:

-vortex disk theory with a "rigid" vortex wake using simple analytical algorithiiJ.S;

-blade theory \l:'ith a "rigid" vortex \Vake \Vith non-deforn1able or

elastic blades for any type of fasteni.rlg the blade to the hub: -blade theory with a free vortex wake.

In developing the algorithms of computation great attention was focused on the issue of reducing the computer-consumed time. Thus, for example, it became-possible to establish a linear relation between circulation along Jilting vortex iine and eiastic deformations in the theory of a rotor with a "rigid'" vortex wake on the basis of the analysis of full non-linear equations of blade motion enabling to provide the labour consummation close to the one of calculating the rotor with non-deformable blades.

The. rotor computation based on the full non-linear e.quations of elastic

blade motion is used at the stage of deveioping aeroelastic blade conligurations.

In the blade theory of a rotor with a free vortex wake an effective

iteration procedure with an original approximation in the form of "rigid'" vortex wake is used instead of an ordinary calculation of motion of dements of free vortices in time that enabled to solve this problem using an ordinary PC (Fig. ~

and 4).

One of the objectives of using this theory is investigation of complicated processes of flow around the blade tip part.

Consideration of unsteadiness cfiects on the aerodynamic loading of blade airfoils is an important and dillicult issue of the rotor aerodynamics.

Special experimental equipment has been used for a number of years to

investigate

this problem in the wind and water humels of TsAGI. Tilis equipment consisted of systems of measuring the distribution of pressure over the bbde surface and also forces and moments on narrow blade segments with the use of strain-gauge balances.

Apart from that JS a system of exciting the blade oscillations from

complex polyharmon.ic laws by summmg any three from the eight

harmonics of the oscillations. Visualization of the unsteady flow over an airfoil

is made using various te.chniques, including a high accuracy waccr tunnel

optical method. Investigations of unsteady flow around oscillating airfoiis are performed at TsAGI at M<=0.8.

Analysis of the result has revealed that the use of only

expcrirnental characteristics of oscillati.I1g airfoils at a constant velocity of the

undisturbed 11ow is not sullicient for the complete description of complex

processes of a real Dow round a blade airfoil under conditions of a dynamic stall.

Therefore TsAGI has concentrated on the study of unsteady feature of airfoils on the basis of measuring the ir1stantaneous pressure on the blade of rotor models in wind tunnels.

The studies have shown that the primary factors deEning the change of blade characteristics at a dynamic stall are:

-blade loading CT/6; -advance ratio ;.t;

-rotor effective angle of attack

a,

(over the plane of blade tip). -relative radius of the blade section F.

Further on, approximate relation betw~en airfoil lift coet1icients and its longitudinal moment was built using these parameter (Fig. 5-6).

The flight tests at the Flight Research Institute (LII) in regard to measuring the instantaneous pressures on a full-scale rotor blade of a Mi-6 have shown that the above relation is realistic of the dynamic stall processes occurring on the full- scale rotor despite essential differenc·es in the numbers of

?11

and Re and the airfoil geometry (Fig. 7 -8).

The reason of this phenomenon lies i..Cl the fact that tile decisive atTect on the airfoil at a dynamic stall is produced by a system of vortices formed near the airfoil in the transonic Dow, i.e. dynamic component of the fluid motion equations. The role and the Mach number effect is weakened due to a considerable change of the airfoil's liquid contour shape. The approach proposed gave a simple algorithm to estimate the values to be added to the static characteristics CL and Cm in order to approximately account for the dynamic stall effects.

The block of the programs to design the blade airfoils conmins:

-a method to calculate an unsteady potential Jlow round an airfoil under arbitrary laws of variation in time of angle of attack and velocity of the undisturbed flow at small number of M:

-a method to calculate a transonic How about an airfoil with a simultaneous calculation of elastic deformations of the airfoil's tail part;

-a method to optimize the airfoil geometry m accordance with its objective function.

Consideration of elastic defonnations appeared to be of iinportance: f')r in a transonic How small elastic deformations are capable to mongly afl'ect the airfoil performance.

An element of the procedure of optimizing the airfoil's contour in accordance with its objective function is shown in. It is seen that an airfoil with a wave. shock is transformed into a shockless low drag airfoil.

The rotor aerodynamic design system contains procedures of optimizi.Ilg the blade aeroelastic configuration taking into account the fuselage inductive elTect on the Dow over the blade. This account leads to some correction of the geometric parameters of the blade stem part.

The rotor aerodynamic design system also includes:

1 )test of airfoils in the T -106 wind tunnel;

2)test of oscillating airfoils in the SVS-2 wind tunnel at ?liacb number up to

0.8;

3)test of rotor models (\vith rotor diameters up to 2.5m) of one-rotor and any

two-rotor helicopters as well as any type of steering systems:

4)tests of large-scale 4-5m diameter rotor modes at full-scale ?v1ach numbers in the T-104 wind tunnel (Fig.9);

5)tests of full-scale rotors with diameters up to 17m in the T-101 wind tunnel (Fig.l 0).

The e;.;perimental facilities is equipped with up-to-date equipment, measuring and computation systems allowing for an automated definition of aerodynamic,

aeroelastic and acoustic characteristics of rotors. The full-scale rotors of Ka-50 and Ka-62 helicopters have gone through complete set of such tests.

The current state-of-art of works to develop aerodynamic airfoils is presented in Fig.ll. Correctness of comparison of various airfoils if due to the standard methodology of tests in the T -106 wind tunnel of TsAGI. A peculiar feature of Ts.A.Gl's airfoils is a smaller value of the longitudinal moment in the transonic f1ow zone what is extremely important to minimize the variable part of the hinge moment (Fig.l2).

The progress in ;-otor :o-.c:rodynamics is demomtrated in Fig.l3-14

sho-,ying ,.:;st results of large-scale rotor models.

The latest Russian helicopters Ka-50, Mi-28, Ka-62. :vli-38 and others

have improved aerodynamic rotor configurations.

Fuselage aerodynamics.

The fuselage aerodynamic design if based on caicutatmg the potent!3i

unseparated flow and separated flow with present streamlines of se.paration.

/IJ1 important tool of developing improved fuselage configuration at TsAGI is experiment, that is usually realized with design bureau. These o:periments are carried out both on isolated fuselage models and on models with operating rotors.

Fig. 15 shows progress in the fuselage drag of hem·y transport

helicopters with a rear cargo door. The fuselage drag of the :.1i-38 is twice lower than that of the .Mi-8, its prototype.

To achieve this an ex1ensive program of e:qJerime.ntal studies has been fulfilled investigating a number of alternative of solutions.

Considerable progress in the direction has been obtained for the Ka-62

heiicopter (Fig.l6). Comparison test of fuselage models of the helicopter and the Sikorsky S-76 . (as prototype) have shown that the fuselage drag of the Ka-62 may be 25% less than of the S-76. This result was obtained also on the basis of a great number of tests of various alternative variants of the fuselage aerodynamic configurations.

Of special attention at Ts,A.GI is the problem of local 8ercc\ynarnics of

fusciages. As an example of this activity may serve investigations on drag reduction of fuselages of the .Mi-8. Mi-38 helicopters by aerodynamic improvements of the body near the exhaust manifolds (Fig.17).

A noticeable effect is achieved by a method of suppressing the

diffuser-induced separations by air bleeding from the engine cooling system into the

separc.tion area (Fig.18). The fuselage drag m this case is reduced

considerably (Fig.19).

Of great use for the investigations on fuselage ae.rodynamic improvements 3re full-scale tests offuselages in the T-!01 wind t1mnel ofTs,A.Gl.

Great attention was paid to the issue of studying the TsA.Gfs most recent jet system with an adjustable thrust vector of the tail nozzie and a slotted system of super circulation where efficie.nt progress had also been made in the 2rea of drag reduction (Fig.20).

C

o n c

1

u s

i

o n s.

TsAGI possesses a multi-year expenence of studies in the field of

aerodynamics and dynamics of helicopters that had found its implementation in national helicopters and in some joint design with foreign countries.

@

I

Helicopter aerodynamics

I

' '

Investigation Investigation Investigat~on Exa.'Ilination

and and and of

development finishing devdo;:l!nen: problems

of of oi of

aerodynamic aerodynamic aerodynamic helicopter and configuration configurarion units

aeroelastic of of and

configuration helicopter control elements

of bodies de\'ices interference

rotor blades

Fig. 1

~---·.

Helicopter CAD

·-··-··-··-··l··-··-··-··-

-~

I

Rotor CAD

_I

I

l

Forming limi:ation syst-:'::~ _2.ild efficiency c:·~eLia for main rmor

I

'

Disk theory with ((rigid'' Potentia! fiow theory

von ex wake of eiastic ai~oil

Blade theory with "rigid'~ ' '

I

_{Tbeory Yiscou_s-i:Jviscid}

l

wa..'<e and elastic blades ' _' m~era.c~:on

Blade theory v:ith \Vind-Iunnd inYestigation free vortex w2ke of air!O~l c .b 3.f2.'2 ~e. ris tics

I

I

Determination of aerodync.mic and ae.rodastic cof1guration ofmai.;1 rotor

I

Experimental studies of aerodyna..rnic and ae.roelastic performances of main rotor

I

Recommendations for rotor co:::Ilguration

_Fig.

₂

>

N

Tip vortexes of rotor blades.

':' • < ,. ~:.... y•' I _{. /:_.,I} I _{'t ·: y} I _{'\ -~ II} I -1 I ; : I r I ' I _1.' ' I I I I :I I I I I I I

·'

I I I I ;I I· _:; c. I ,. 1: I 1: I I ; I I I

;I

I : .I I

\ '

,I

'i

I I _I -~ I

i

I -4· I. _{I I} 12 _I I I I' I

i

I I I I I I I I I I ' _I I XV

Distribution of induced velocity along rotor blade.

' _'· ' ... : ... '

'

\ I I \ I I

'

_: I ; I I ·4.00E-02

r---c

1- - . 3.00E-02 l.OOE-02 l.OOE02 -O.OOE '"00 t----+----+---l----+----;---;..---.;----;--"'-0.1 0.2 0.3 0.4 0.5 0.6 0. 7 0.8: I II I; I· II I; I.

"

~

'

..

··r

I I

I

I I

-+---1

oy

r :;.. . i.OOE-02 I -... . ... ... --···

/

. : rn::.-oz l I

i

r

L ________ _

_ _ _ _ _ _ _ _ _ _j

i

i

II.I7-6 --blad' I ----bbdc2 · · · ·· · · bUdc 3 -·-··blade 4 Fig. 3

---·

~---'!':::-"C.' ~----'1-':: 1 s-:~ I Fig.L

Rotor model ,D=2.656m

~

....

I

. . -.-.!. ...

ol!----~~~----~~---L---~

0

'-0.5

+---· !

!

1

Cm I ! • ' 100 100

I

l

200 300 200 300 'll

...

..

. •.- .. I < •• 0

l:~===========t,==~~~~/.~-~-~-_-·j·r

______________

-=~~~~

1\)0 2\)0 300 airioil NACA -0012 k=3. b=0.12m, CT1rr=0.1 0. a=· 4.5~ wR"'90.4mlsec Re=s.2·:o' r =0. 717. ].!=0.352 ---wind tunnel · · · ·steady( calc) -·-·-approximation ----wind tunne( · · · ·steady( calc/ - · - · - appcx!tnaticn airioii NACA 230-12f.~ C!!co =0.077. c:= ,_,~.,=?3~·...,.,/sc.r- H=3300::) \JJo\ _ Vo•• VV • ~ i Mo=0.725 - - ilight te" ···steady( calc) - · - ·- apprcximatio• [:__ _ _ _ _ _ _ _ _ _ _ _ ---'-'8.:.!...._ _ _ _ _ _ _ _:...:._ _______ , -0.25

Cm

0 \()0 200 . _,

_,

_.. . ... " ..

IL17-7

· - -fl{;;:h~ tes~ · · s_:eady(caic:) -apprcx~maf:or.

Fig. 9

Fi2,· 10

HELICOPTER AIRFOIL EFFICIENCY

e

TsAGI

RA£9845 @OA313 ""

OA

O

@ ~ ~ VR-12 '<Y

6 DM-H·

~

1.50

OA213

0oA312~0

DM-H4

TsAGI- 4

. 0 RAE

!;;; . NACA-23012

0

KA .

~

u""' OA 212 BFY '<>'

0 SC

,_. RA£9648 0

o

o~

0

NACA

~

1 25

]'sAGi-2~-H3 -~--.

~ ~

VR r;: Q RAE96 4 OA209 [j

sc

1095 ' \ o · VR-15/ ®OA207

~

l.

NACA-0012

0

TsAGI-3

\ \

KTM

~

LOO

.

1,----T---r---~--~--. 01,----T---r---~--~--.75

::: t

0.03 -0.02

om

0.00

t

0.6 -0.01 -·0.02 -0.03 -0,0~ Cm₀

0.8

. 0.85

DRAG DIVERGENCE MACH NA.l,ffiER

•

Fig. 1 i

AIRFOILS FOR BLADE TIP

; ! TsAGI:_4 OA-209 DMH 1 YR-15

'

0.7

•

s

0.9 Mctct 0.9 !.!

~-

\'-\

fig.)£. II.17-9

Fig

;.ere

of ·

mer it ~0 0.8 0.75

""

TsAGI WIND TUNNEl DATA

t

0.8

~TsAGI-3

0.75

, Tip speed

wR=215

m/s

ROTOR

DIAMETER D=4r:-c

SOU

DITY

v=O.f

Ts!,GJ ·

.3

7'ip sreed

wR=233

m/s

l_;~L.r

--->---~-I

I

'

'·Jv-.--~--+---C,

/u

C: /G 0.1 0.15 0 .. ? 0.15 0.2 Blade loading L/De

10

-5

2

u. F'ig.J:;

WIND TUNNEL DATA

D=4

m,

CJ

R=215

m/s

s

'fsAGI-3

..

NACA-23012

"1

_,r----200

_L----~:::'-;,:----~4~o;:;-o ---;;\'~.

₃₀₀

kkm/h

fig .14

IU7-10

... ... ...

o,_

\ \ \

""

b

\ \ . \

q

LD

I

-"" u I ~

"'

"'

I 0 ~

c3

~-

q-

c<) c\J 0 ~

o-

a

_9-

0-

_w

.,

1:

9

~

<

I _.

..,

0 LO 00 I

"

I

'

I

-~~

')::

p

~ "---, _c c

"'

I (_. > :..:: ~ ₀ I ~-" ~ I Z'G

""

I

I

/ L") / ..., / / lC1 biJ ._..--~ I 11.17-11

..

\

."t'

_~

:::1

2

VI

=

0 II l ;

_?

\

I= I II.l7-13

\

~I

=

··II =-,

.::wl~~:::~

·

::~llij~

..

-..._. E Ln c-....1 II

;::::,

0.2

--rt:sdGse · ·· : · ·

1

..

----"'-11us~ta?'

"SHd tandlno

neac+keet~sLatita.to-2·-L

-(j & ;J ' ' . '

,.,!,.,, _{., 1U>ccO.~e}

+r·.o'·n;•l•m

_{. ,,,,~}

_{9, ,ys}

_{u . ., ·: , ... -}

'.

--~

. • ~ ~! >

-20 -!0 •- 5 0 . 5' 10' 15'

Ang,ie. of

aituk

Fig.

18

The model o( Mi-34

Flg.

19