Sixteenth International Symposium on Air Breathing EnginesAugust 31- September 5, 2003, Cleveland, Ohio, USA

1

FLOW INVESTIGATION IN A TWO-PASS COOLANT CHANNELWITH/WITHOUT RIBBED WALLS

Dr.-Ing. Marc P. JARIUS and Dipl.-Ing. Martin ELFERTGerman Aerospace Center

Institute of Propulsion TechnologyD-51170 Köln, Germany

Fax Number: +49 2203 64395,E-mail address: marc.jarius@dlr.de, martin.elfert@dlr.de

KEY WORDS: MULTI-PASS COOLANT CHANNEL, PARTICLE-IMAGE VELOCIMETRY, CFD

VALIDATION, WALL FLOW VISUALIZATION.

ABSTRACT

The aero-engine industry and the power generation industry operate in a highly competitive market.

Therefore high requirements in terms of high technology development as well as cost and development

times reduction are constant major objectives. On the other hand, environmental and safety constraints are

an increasingly stringent necessity, which enforces the demand for new technologies. Currently, the

industry relies on expensive and time consuming rig test programs, whereas the existing numerical design

tools have a number of deficiencies in accurately describing the complex multi-pass coolant channel flow.

Under these conditions the Institute of Propulsion Technology at DLR is involved in national and European

research programs aimed to provide the industry with high quality experimental data from the flow field for

CFD validation.

In past projects the flow behaviour in rotating passages was analysed at DLR using wall pressure

measurements to obtain the pressure drop. In addition, Laser-2-Focus velocimetry (L2F) was used to obtain

flow velocity components and fluctuations. Although time-consuming, this non-intrusive, single-point

measurement technique worked very well within straight and smooth duct flows, which generally have a

moderate degree of turbulence. However, state of the art, serpentine shaped, multi-pass systems (Figure A)

are equipped with ribbed walls, in order to improve heat exchange which is typical in realistic

configurations. In this case L2F velocimetry was not able to measure accurate flow properties due to the

increased turbulence intensities in the vicinity of the ribs as in the bend region and further downstream. The

dividing wall separating the two passages forces the flow into a sharp turn which generally results in a flow

separation. The flow within the separation bubble itself is very unsteady.

Modern planar measurement techniques such as particle image velocimetry (PIV) are capable of obtaining

complete maps of flows even at high turbulence. As a first step toward applying this technique, a multi-

pass cooling system is investigated in stationary (e.g. non-rotating) mode using two-component PIV. Two

types of models were investigated: model (a) with smooth walls, model (b) with ribbed walls. The PIV

2

results are compared to some visualisation results of wall streamlines and throughflow as secondary flow

development and 3D NS CFD results.

The high quality of the obtained results encourage the application of the two-component PIV to the rotating

system. As a logical consequence, the application of three-component PIV will be necessary to obtain the

complete flow field information within the complex flow passages.

Figure A. Schematic and transparent view of the test model geometry without ribbed walls

25°

20°

35°

8°

30° axis of rotation

1.0d

0.3d

dh = hydraulic diameter of the first pass

3∗

4

2

4∗

2∗

31∗

1

1.3d

Inlet Outlet

7.1

d0.

8 d 0.1 d

8 d

0.3d2 d

3

RESULTS

With regard to PIV processing, standard cross correlation algorithms were used with an interrogation

window size of 32 x 32 pixel and a 50 % overlap. The velocity of the intake flow into the first pass

amounts to v0 = 30.5 m/s, and consequently the REYNOLDS number is about 50.000 for the PIV

measurements. The measured flow field of the secondary flow within the second pass in four cuts for a

REYNOLDS number of 25.000 are shown in Figure B.

Figure B. Secondary flow velocity distribution in four cross cuts of the second pass measured with PIV(Re=25.000)

Figure C shows the streamline patterns and the velocity distribution on the leading wall of the duct,

obtained from oil flow visualization experiments, in comparison with a numerical solution and a PIV

measurement close to the wall.

x in mm

yin

mm

0 5 10 15 20 25 30 350

5

10

15

x in mm

yin

mm

0 5 10 15 20 25 30 350

5

10

15

x in mmy

inm

m0 5 10 15 20 25 30 35

0

5

10

15

x in mm

yin

mm

0 5 10 15 20 25 30 350

5

10

15

4

Figure C. Comparison between PIV, calculated and visualized wall velocities and streamlines on leadingwall, non-rotating

SUMMARY

This paper describes experimental investigations of a typical two-pass cooling channel system of a turbine

blade with and without ribbed walls with respect to fluid flow phenomena affected by geometry effects. A

complex flow situation is present showing several kinds of separation and vortices. In order to give an

accurate value of the turbulence level more than 2000 instantaneous PIV images will to be taken and

evaluated. To collect such a relatively high number of images it requires relatively high storage capacity.

The performed flow visualization and simulation are very helpful in that case to understand the interaction

of all apparent effects. The presented experiments were mainly intended to assess the feasibility of applying

PIV in a multi-pass cooling channel used for applied cooling research. The results will show that it is

possible to apply PIV at a multi-pass cooling channel also with ribs. The application of PIV is approved

and will be adopted to the rotating system in the near future.

x in mm5 10 15 20 25 30 35

50

55

60

65

70

75

80

85

zin

mm

210

215

220

225

230

235

240

245

v in m/s: 2 4 6 8 10 12 14 16 18 20 22 24

170

175

180

185

190

195

200

205

130

135

140

145

150

155

160

165

90

95

100

105

110

115

120

125