Boundary layer measurements were carried out on a glider under natural conditions. Two effects are investigated: the effect of inconstancy of the development of static pressure within the boundary layer and the effect of the negative pressure difference in a sublaminar boundary layer. The results obtained by means of an ion probe in parallel connection confirm those results obtained by means of a pressure probe. Additional effects which have occurred during these measurements are briefly dealt with

Nes, W. V.

English

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ASA TECHNICAL "EMORANDUM
	
NASA T14 75294
	 1
"-	 "THODS AND RESULT OF BOUNDARY LAYER MEASUREMENTS ON A GLIDER
1	 Wilhelm: Van Iles
t,
(` ASA-Trl-75294)	 METHnBs AND FESULTS OF	 1178-24085
BOUNDARY LAYER MEASUREMENTS CN A GLIDER
(National Aeronautics and Space
Administraticn)	 12 p EiC A02/MF A01 CSC'- 01A	 Uricla,
	
G3/02	 21225
Transl at.inn of "Beri cht 11her Messmethnc:en tend Messergebenisse
bei F1urmessungen in der Grenzschicht,"
Der Wissenschaftiichen Gesellschaft fti.- Luftfahrt E.V.,
Jahrbucl-., 1961, pp. 255 - 259.
I
^"^ 611S I
	
'_	 P'E sty ^ ac^v^^ ,tit
	
cs^	 Np$A	 ^^
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
WASITINGTON, D.C. 20546	 MAY 1978
I
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a^	
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STANDARD TITLE PAGE 	 1.
NASA-HQ
1.	 Report No.
	
2. Governm.nr Accession No. 	 7,	 Recipient's
NASA TM 79294
4	 Title
	 nd Subtitle	 S.	 Re o
METH DS AND RESULTS OF BOUNDARY LAYER
	
I^ay 1978
MEASUREMENTS ON A GLIDER
	 6. Performing Organisation Cod.
r7,	 Authos)	 8.	 Performing Organization Report No.
Wilhelm Van Nes
Leichtbau and Flugtechnik GmbH,	 10. Work Unit No,
Duisburg
11.	 Contract ar Grant No.
9.	 Psrlarmin9 Organisation Name and Address 	 ATA$1v -279G
Leo	 Kanner	 Associates	 13, Type of Report and Period Cov.r.d
Redwood City, California
1.	 Translation
1 12,	 Sponsoring Agency Nam• and Address
National Aeronautics and Space Adminis- u, Sponsoring Agency Code
Creation, Washington, D.C.
	 20546
15.	 Supplementary Notre
Translation of "Bericht Uber Messmethoden raid Messergebeniss
bei •Flugmessungen in der Grenzschicht,°
Der Wissenschaftlichen Gesellsehaft fir LuftfhartE.V.,
Jahrbuch, 1961, pp. 255 - 259•	 (A63-21852)
16.	 Abstract
This paper deals with methods and results of boundary layer
measurements.	 These measurements were carries] out in a
glider, i.e. under natural conditions.
	 The paper continues
the survey presented at the WGL Meeting in Essen in 1957.
Two effects are investigated: the effect of inconstancy of
the development of static pressure within the boundary layer
(8p/9y ¢ 0) and the effect of the negative pressure dif-
ference in a tr sublaminar 1l boundary layer.
The results obtained by means of an ion probe in parallel
connection confirm those results obtained by means of a
pressure probe.	 Additional effects which have occurred
during these measurements are briefly dealt with.
17.	 Key Words (Selected by Author(&)) 	 18.	 Distribution Statement
Unclassified-Unlimited
19.	 Security Classil. (of this report)	 20.	 Security Clossif. (of. this page) 	 21• No. of Pages	 22.	 Price
Unclassified	 Unclassified	 11 -
 Catalog No,	 f
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	 ^^s>a»w.+„wrn._nsew4tx.^at_3+^/ktt*+x.+l..^.x^
METHODS AND RESULTS OF BOUNDARY LAYER MEASUREMENTS ON A GLIDER
Wilhelm Van Nes
Leiehtbau and Flugteehnik GmbH, Duisburg
At the 1957 WGL Meeting in Essen I reported on boundary 	 /255*
layer measurements made on a glider [1]. Today I would like
to discuss refinements in measuring methods which we have made
in the meantime and the new results these have yielded.
Two effects, in particular, are puzzling:
The first is that the results on the static pressure
-- -- curve within the boundary layer, which. according to the theory
is supposed to be constant and equal to the static pressure of
the outer flow, do not confirm this simplifying assumption of
the theory. I have already briefly referred to this in the paper
I gave in Essen.
In order to detect
the pressure difference
with a manometer and on
adding the measured par
r.	 Z)Y..,
this effect we proceeded as follows:
was on the one hand determined directly
the other hand it was calculated by
Lial pressures:
Ih,	 lhn
	 Puo
	 Pui,
A PI `91 Ann,
I P,	 S.	 91
flYq< _ 4P:	 The measurements clearly
-7
I
showed the following:
Lmm	 ^	 i
j	 With a turbulent boundary
layer the first summandp p
= _^o
	
0- 04
is approximately zero and maintains
	Basic diagra:;,.	 this value over the entire velocity
* Numbers in the margin indicate pagination in the foreign text
1
1
i
4
l^
4	 M
range with a laminar boundary layer, however, the difference
changes more or less linearly with the air speed.
)
Fig. 1 snows the curve of partial pressures as a function of
the air speed.	 In this graph the solid lines represent the
partial pressures and their 	 sum in the case of a laminar boundary
?:':r layer.	 The broken lines show
^n the partial pressures for a
turbulent boundary layer.	 The
turbulence was caused by a trip
':Sf wire on the nose.	 The measurement
point was the same for both
a•; flights.	 The tendency of the
ce
shape of the pressure curves
e
,.. was always the same. 	 The results
were clearly reproducible.
's*	 u
The result is actually not
-id-
U	 :P	 40	 60 0/3	 BU	 BU
surprising: the transition of the
boundary layer into the outer flow
Fig.	 1.	 Flight no.	 5, Sept. Ill occurs asymptotically.
	 At this(—),	 boundary1959	 laminar
layer, Sk.(4140; and flight point, which is not exactly
no.	 9,	 Sept.	 14, ',959
	 (---),
turbulent boundary layer, defined in physical terms, there
Sk.^4)40 with trip wire at must be a discontinuity in the
2.55.
Curve 1(1): difference in static pressure curve if Op /O,y
static pressures at y = 0 and were equal to zero in the region
y = 4 mm;
Curve 2 (;\) :	 curve 1 + dynamic of the boundary layer.
pressure at y = 0 min;
Curve 3 (C)) : curves 1 + 2 +
difference in total pressures The measurements were
at y = m and y = 4 imn. expanded in the summer of 1961
Sk.(4)40 denotes probe adjust-
ment in position 4 on the 	 _ so that the static pressure
test surface, probe at scale curve in the vertical direction
division 40.	 the x/1 location
of the probe is indicated. was determined by 5 static probes.
Abeissa:	 local pressures; Evaluations up to that time had
ordinate: pressur:ss in the
clearly shown the difference inboundary layer.
	 Lp are the
measured pressure differences.
2
M	 AaAxVWA -
^.
	
1
ry^	
V
^ t
/256
t he curve in the turbi d cnt and , mi^ar rc, icn. .
4
^i
a
is
Fig. 2. Manometer panel photo- rig. 3. Manometer panel photc-
graph of flight no. 4, 9/10/59, graph of flight no. 4, 9/10/59•
The second puzzling effect,
namely the pressure reversal in
layers close to the wall, was
'+	 - ^^ I'	 t I I '
of course already known at the time
of the Essen WGL Meeting, but at
that time we still had too little
an publishdata t0	 results. I
I
h
i
s 
P	 Y
first referred to t 	 effect at
a VIGL discussion meetinc; in Duisburg
in 1959 and showed a number of
manometer panel photogra phs. Some
of these photographs are shown
 below. Note the variation in
^w.
	
__	 manometers 1-4 and 5 -8 and also
that of manometer 12 (Figs. 2-4).
Fig. 4. Manometer panel photo-
graph of flight no. 4, 9/10/59.
Manometers 1-4 were connected
to four pitot tubes which were arranged at a distance of abcut
4 mm from the surface and at intervals of 15 mm in the wing -op.'n
direction. The right leg of the U-tube is connected to the total
RI PR(JDUCIBI. ffy OF THE
(JIjIUI.,Al, PAGE 15 POOR
1
	
3
-f
9
-I
_fps
I'
e
y
^w
to the total pressure and the left leg to the static probe
lying on the surface,
{	 The right legs of manometers 5-8 are also connected to the
{	 surface pitot tubes and the left leg is connected to the same
static probe. Thus under normal oncoming flow conditions the
tendency of the reading must be the same in all cases; the right
leg must be lower than the left leg.
Manometer 12 measures the pressure difference between the
total pressure at infinity and the total pressure at a distance
of 4 mm from the surface. There it moves if the boundary layer
thickness is greater than 4 mm; if it is less than this, then the
response is zero.
Manometer 11 serves as a control. It measures the total
pressure of a pair of pitot tubes at a height of 4 mm separated
in the chord direction by 35 mm. Thus a significant movement in
this manometer may only occur when the transtion takes place
,just between these two probes.
It is clear from the photographs that during a transition
of flow from the turbulent to the laminar state an undeniable
pressure reversal can be detected on manometers 5-8.
Fig. 5 shows a graphical representation. In this graph the
boundary layer velocity at a distance of 4 mm from the wall and
the velocity in the layer next to the wall are plotted over the
local outer velocity. The pressure curves for manometers 11 and
12 are also indicated. The graph shows the suddenness of the
pressure reversal with the transition from turbulent to laminar
flow.
This effect was detected in hundreds of test flights, even
with different surface materials and different profiles. For
a physical interpretation of this effect we have set up a
4
1	
0'
^ ^_.j._ 1 _^1.^^^ 	---' swcer^aae^.	 L,srw.mexerMUi:9.113^N'!Y1^6'f9^iW".s..w^.d1^:
hypothesis, namely that it
perhaps involves the overlapping
of a normal boundary layer
profile by a vortex street rolling
-r in the chord direction over the
surface.
30
M&C
	
50	 20
40 u, 4
1P 11112 _.
fI	 10
20
	
0	 0
1'	 -70
—10
-4a _:
	
-50	 -20
30	 40	 50
Fig. 5. Flight no. 4, 9/10/59,
Sk(4)^5.
0,56, caPU = O,OCS24, ''ront == 0,0143, c, r .r, `= 0,00606,
cr,.r,lC40, = 0,42.1.
c au is the ca value at which
the transition occurs.
cwpu is the drag coefficient
pertaining to this ca value.
cwpt is the corresponding drag
coefficient at full tur-
bulence.
Lp values are the measured
pressure differences.
Abcissa: local velocity,
Ordinate: velocities in the
boundary layer
MnnO1nL`Ltlf
und5
2 and 6
Q	 7 and 7
®	 4 and S
II
V	 12
Key: and and
From our manometer obser-
vations we found that this
effect started in the vicinity
of the leading edge of the
wing where strong unstabilizing
effects are to be expected
because of the concave curvature
of the flow filameni.s. There-	 /257
fore at a surface depth of 2.5%,
where the manometers showed the
greatest fluctuation, we placed
a small perforated tape and,
applied suction. The result was
amazing in two respects. A very
small amount of suction was
sufficient to considerably influence
the development of the boundary
layer over the entire measurement
range, i.e. from x/1 = 0.075 to
x/1 = 0.375. However, we also
found that an increase in the
amount of suction had no noticeable
effect. This is shown in Figs. 6
and 7.
The question then arose as
to whether this measured effect
was real or a trick of our
-30
10
REPRODUCMLy,frY OF THE
MI TC'T`:t.T. T-,Ajl T;' T, pnr17.	 5
115	 35	 45
40	 30 .__
	 (.	 -II	 40	 -...
i
^	 I	 /
m/sec m/sec
30	 10 -
	
)^
	 JO
eI•'	
U, t
	
VI J
	
3
20	 10	
—	
_lam!'	 20
10	 to
^	 r
I	 l
F i
t
.,- -
	
a i	 L	 I
10	 30	 1,0 m/sec
	
50
M,
Fig. 6. Flight no. 8, 11/30/58, 4	 I
Sk. 33))10, 6h = 4.0 mm; without	 —10 ----
lea3ing edge suction (0), and
flight no. 9, 3/24/59, Sk.(q)10 	 -15 --	 -
Ah = 4.0 mm, with leading edge	 20	 30	 40 m/see 50
Un
suction, suction velocity =
40 m/sec O	 Fig. 7. Flight no. 14, 11/30/58,
Sk. (3 40, Ah = 4.0 mm, withoutleading edge suction (0) , and
flight no. 7, 3/25/59, Sk.(3)40,
Ah = 4.0 mm, with leading edge
suction, suction velocity
40 m/sec (L)
measurement apparatus. It was now suggested by ministerial
advisor Wahl to measure this effect again using a quite different
method, namely by means of the ion probe developed by Prof. Fucks,
Prof. Schmitz and Dr. Franzen [2,3].
i
We performed experiments using this new measurement 	 /25 8
arrangement. It is based on the following principle: if a
voltage is applied to the anode and the cathode of the probe in
a normal atmosphere, then either the air acts as an insulator or
L	 an arc-over occurs. However, between these two limit states there
RL`1 RODUOM11,Ny OP TIC
^T^* .n r n.tiF IS POOR
6
Iis an intermediate state, the so—called corona discharge. A
positive ion cloud forms at the anode and migrates to the
cathode. In this situation the anode consists of a platinum
point measuring 5 u in diameter and the cathode consists of a
platinum spear measuring 0.3 mm in diameter. In the course of
the measurements the applied voltage was reduced from 2800 V
to 1450 v, and in so doing the distance between the electrodes
was reduced to about 1.2 mm.
If the electrodes are now exposed to a flow of air, then
the amount of ion transport increases if the flow is in the
anode—cathode direction. If the flow direction is reversed, the
transport is slowed down, i.e. the ion flow is velocity
dependent.
Thus we have a d.c. circuit with a constant load resistor
and a variable resistor between anode and cathode. Between
these two resistors the voltage is conducted to the grid of an
amplifier tube and the anode flow of the tube controlled by the
grid is measured on a milliammeter.
In addition, a low—frequency pickup connected to the anode
circuit through a capacitor so that it was possible to record
the corona fluctuations on tape and retain them in an
oscillogram. There is not enough room here to go into details.
This method turned out to be practical and it confirmed the /259
back streaming effects -- no longer called "pressure reversal"
(Figs. S and 9). It should still be mentioned that considerations
were necessary, for example to eliminate, by means of connecting
a bridge, distrubances caused by air pressure, air humidity and
proximity to the surface. Ultimately we used a double probe
with two cathodes and one anode in the center. Our studies are
continuing along this line.
7
RUI PR.ODUCIIITUIY OF rIIL ^?
ORIGLNAL PAGL IS POOR
C
a
40	 ?	 mA
y.
` m4	 50
Y,
70
i;.
.,	
u
A	 40	 ;.
'r Rubes tromA
. 
Ruhes,,orn
70	 30	 40	 g0	 m/sec	 50
70
4
Fig. 8a. Reprod.ucibility of
results.
Flight no.	 1, 5/9/60,	 Sk.(4)16,
	 0
A hk
 = x2 	 ' (0) ,	 lR b
Flight no.	 2,	 5/9/60,	 Sk. ( 4)16,	 m/sect	 c
Ahk = x 2 	 (Lj) ,	 u	 IIL'
_	
I- Flight no.	 3, 5/9/60 1 Ek.	 4)16	
_'	
u	 _I! JG
Ahk = x2-1 (C9
	
^^	
t
Ahk is the distance from the
)surface of the corona
	
probe.
-lR
Key:	 A)	 quiescent current	 0	 00	 40	 m/sec	 50 { $. U
l5p
 - -	 1°Runestram?	 Fig.	 9a.	 Flight no	 8,	 5/12/60,
mA	 A	 1	 Slt. (3)22, Ahk = x5-5.625	 = 0.2mm
Ruhestram III 	 (^) ;I•
Key: A) quiescent current;
y
Fig. 9b. Flight no. 14•	 	 9/12/60
s( .I^
GU	 ^	 (0)	 Flight no 27,
	
9/12/60 (Q). i ljn
100 —
	 70--	 -	 --,
Ruhestram	 _	 __ ^
' Q
,1	
A
40	 _..	 ^
I	 00	 ${ Anllamperemeter
l	
_..	 } s '^	 l70	 — h 	 045mm'1	 !	 ^ I
TO
^.`	 _._____ aullregende Pitetsonde70
V ^.	 ,	 she-0,7mm
70	 00	 40 m/sec	 50	 r
^^ I
ab	 (
1
Fig.	 8b.	 Sensitivity and repro-	 5	 t 
1
ducibility of the results.
Direction
anode.
0 m/sec	 50  
-10 2D 	
o	 ab	
4L.
(	 )j	 Ahk = 0.7 mm	 (L7)	 Fig.	 9c.	 Flight no.	 9,	 9/17/60,
Flight no.	 4, 10/17/60	 Sk,^6)20Sk.(2)20, Ahk = 0.45 mm, direction,
of wind flow: cathode-anode..
I	 Ahk - 0'7 mm	 (®) Key: B) milliammeter 6
C) surface pitot tube " iy
1	
	
We also came up with some other interesting findings in our
measurements. In the summer of 1960 in Freiburg we recorded a
number of tapes with corona fluctuations. Khen listening to
these tapes it turned out that the corona noise was super-
imposed by the reception of a foreign transmitter, as was
obvious from the different languages. Although this d:W not
have anything directly to do with the boundary layer
investigations, naturally it interested us and so we investigated
the arrangement in place using a test transmitter. The result,
of course, was negative. Over the entire frequency range of
the test transmitter from 160 kHz to 2 110 MHz we did not get any
modulation. The experiment was repeated in the Physical Institute
of the Aachen Tenhnische Hochsr.Nule with their equipment, but
even here no pronounced resonance point could be detected. Only
very broad resonance ranges appeared.
By using two synchronized tape recorders, one of which
was connected to the microphone probe and the other to tY,e
corona probe, we tried to make a comparison between the pressure
variations and the migration of the ion cloud. liowever, these
investigations are not yet completed. As for the resolution of
the oscillograms, by using primitive means we succeeded in
increasing this to the extent that a length along the abeissa
of I mm corresponds to a time of 1/50,000 second.
Figs. 10 and 11 give some
indication of the large pos-
sibilities offerred by this
method. Each of these figures
involves two different tape
recordings which were made under
identical conditions. ,lust as
with these examples, all of the
oscillation pictures are clearly
reproducible.
Y1 lPPPsrc'
Fig. 10. Comparison of two
tape recordings with corona
probe under identical con-
ditions.
9
4,f
^s.e.cmnX=«^aa.^+..w^^swa xYn+w.p.^uMSawr
	 ^+,x.0 ,X =^.L^^!+.^°. ^.: _" .^L-3^'
VVVYA*
^rer^o5^.
Note: We are very grateful
to Dr. Raspet fox' his valuable
advice and enthusiastic help
in 1952 and 1953.
Fig. 11. Comparison of two
tape recordings with corona
probe under identical con-
ditions.
Discussion
cr.v
	
aaai:inuaiiri^ rii. v. r.ti^;. \vvxtuc^ti)	 nPpai=Iluly ttv.
transition occurred at a small Reynolds number. Presumably what
is involved, therefore, is a laminar bubble. That this occurs
may be due to the fact that an American NACA profile was used.
With similar profiles which were checked in England, a jagged
pattern showed up in the pressure distribution which was missing
in the American data. It was not noticed since fewer points were
calculated. It may be that in his investigations Mr. van Nes
was in the range of this zigzag pattern.
W. van Nes, M.S. Eng.: Measurements were made over the
profile chord which showed the same effect everywhere.
Prof. A. Naumann, Ph.D. (Aachen): What was the surface
S'
	 material used?
W. van Nes, M.S. Eng.: Conducting and nonconducting
material, aluminum and sprayed wood. The effect is independent
of the surface material.
10
3l^A'}NaeKteel^'^ .	 .:b.MK^4. +mas.f^l+m,..w.wr.+..e.,w.s.«Aartae^t
__•; ,n.._.f^a..s:S.,y ^#va.u_..^,k.s	 h.__ .^+._.' ___:_.^ _	 1_. 1
REFERENCES
i. Van Nes, W., "Boundary layer measurements inn a k°lide.r,°
Jahrbuoh 1951 der WGL, pp. 481-286
Franzen, B., W. Fucks.. I G. Gchmitx, "Ccmpar9son of
1 -.. and hot—wire anemometers by measuring turbulence
spectra," Research Report no. 760 of Nerdrhein—Wastfalen,
Westdeutscller Verlafi, Cologne and Opladeh, lctrcl
3. Franzen, B. , tJ. Fueks and G. Schmit z , " ..^.	 ,anemome ter r  f. r
measuring turbulence components," Z. Flugwiss. 9,
(1961)
a
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i
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i	 z


Methods and results of boundary layer measurements on a glider

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