cases:case086

# Surface Pressure in Normal Triangular Tube Arrays

The experimental facility consists of a draw-down wind tunnel which has a tube array installed in the test section. The test-section is 750mm long with a cross-section of 300mm x 300mm. Three tube arrays were investigated in this study. The configurations tested were five row, normal triangular tube arrays with pitch ratios of 1.32, 1.58 and 1.97 subject to air cross-flow. A schematic of the test-section is shown in figure 1. The flow velocity in the wind tunnel test-section ranged from 2 to 18 m/s with a free stream turbulence intensity of less than 1%. The tubes in the array (38mm diameter) were rigidly fixed, except for one tube in the third row (shaded in the figure) which will be referred to as the instrumented cylinder, which could be displaced slightly in the $y$ direction in order to study the effect of tube displacement.

Fig. 1: Flow configuration and geometry

The instrumented cylinder had 36 pressure taps with a diameter of 1mm and located at the mid-span around the circumference of the cylinder. The instrumented tube was connected to pressure transducers with short lengths of 2mm internal diameter silicone tubing. Each pressure tap was monitored with a Senotec differential pressure transducer (24 PC Series). The other port of the pressure transducer was vented to atmosphere. In effect the gauge pressure was measured. The signal from the pressure transducer was acquired at a sample frequency of 64 Hz and the signal was averaged to give a mean value. No dynamic measurements or high frequency sample rates were used. Hence, only a simple static calibration procedure was necessary. The readings from the pressure transducers were digitised and logged using an NI 8 channel, 24 bit data acquisition frame. Each channel was simultaneously sampled and automatically low-pass filtered to avoid aliasing.

The instrumented tube was mounted on a bidirectional traverse (located outside the wind tunnel) allowing a specific static displacement to be applied to the cylinder. The traverse facilitated fine displacements and the displacement was monitored with a clock gauge with an accuracy of 0.01mm.

The mean surface pressure distributions for the instrumented cylinder were measured for a range of Reynolds numbers for all three array pitch ratios. The free stream flow velocities ($U$), the gap velocities ($U_g$) and Reynolds numbers ($Re$) tested are outlined in the following table:

$U$ (m/s) $P/d=1.32$ $P/d=1.58$ $P/d=1.97$
$U_g$ (m/s) $Re$ ($\times 10^4$) $U_g$ (m/s) $Re$ ($\times 10^4$) $U_g$ (m/s) $Re$ ($\times 10^4$)
2 8.3 2.23 - - - -
3 12.5 3.34 8.2 2.19 - -
4 16.7 4.46 10.9 2.92 8.1 2.17
5 20.8 5.58 13.6 3.65 10.1 2.72
6 25.0 6.7 16.4 4.38 12.2 3.26
7 29.2 7.82 19.1 5.12 14.2 3.80
8 33.3 8.93 21.8 5.85 16.2 4.35
9 37.5 10.05 24.5 6.58 18.2 4.89
10 41.7 11.16 27.3 7.31 20.3 5.43
11 - - 30.0 8.04 22.3 5.98
12 - - 32.7 8.77 24.3 6.52
13 - - 35.4 9.50 26.4 7.06
14 - - 38.2 10.23 28.4 7.60
15 - - - - 30.4 8.15
16 - - - - 32.4 8.69
17 - - - - 34.5 9.23
18 - - - - 36.5 9.78

For each Reynolds number a range of static tube displacements was examined, with the instrumented tube displaced in the $y$ direction by distances of $y/d=0$, $1$, $2$, $3$, $4$, $5$, $7$ and $10$%.

For the pitch ratios of 1.32 and 1.97, the data is presented in terms of the surface pressure coefficient (defined as $C_P=1-(P_{\theta max}-P_{\theta})/(0.5\rho U_g^2)$ where $P_{\theta max}$ is the stagnation pressure on the cylinder and $U_g$ the gap velocity (defined as $U_g=U[P/(P-d)]$ where $P$ is the pitch, and $d$ the tube diameter). For the pitch ratio of 1.58 the pressure data is presented in dimensional form.

The data available consists of surface pressure distribution around the instrumented cylinder for each Reynolds number, tube array configuration (pitch ratio) and displacement of the instrumented tube.

Sample plots of selected quantities are available.

The data files can be downloaded as compressed archives, or individually from the tables below.

The data is also available in three Excel (.xls) files, corresponding to the three $P/d$ ratios:

The experimental work has emanated from research conducted with the financial support of Science Foundation of Ireland.

1. Mahon, J., Meskell,C. (2009). Surface pressure distribution survey in normal triangular tube arrays. Journal of Fluids and Structures, Vol. 25(8), pp. 1348-1368.
2. Mahon, J. (2008), Interaction between acoustic resonance and fluidelastic instability in normal triangular tube arrays. PhD Thesis, Trinity College, Dublin.

Indexed data:

case086 (dbcase, flow_around_body, confined_flow)
case086
titleSurface pressure in normal triangular tube arrays
authorMahon, Meskell
year2009
typeEXP
flow_tag2d, separated, bluff_body, tube_array