TY - JOUR
T1 - Flow over periodic hills
T2 - An experimental study
AU - Rapp, Ch
AU - Manhart, M.
N1 - Funding Information:
We would like to thank the Deutsche Forschungsgemeinschaft (DFG) for the generous support of the PIV system and the funding of the research position (MA-2062-6).
PY - 2011/7
Y1 - 2011/7
N2 - Two-dimensional flow over periodically arranged hills was investigated experimentally in a water channel. Two-dimensional particle image velocimetry (PIV) and one-dimensional laser Doppler anemometry (LDA) measurements were undertaken at four Reynolds numbers (5,600 ≤ Re ≤ 37,000). Two-dimensional PIV field measurements were thoroughly validated by means of point-by-point 1D LDA measurements at certain positions of the flow. A detailed study of the periodicity and the homogeneity was undertaken, which demonstrates that the flow can be regarded as two-dimensional and periodic for Re ≥ 10,000. We found a decreasing reattachment length with increasing Reynolds number. This is connected to a higher momentum in the near-wall zone close to flow separation which comes from the velocity speed up above the obstacle. This leads to a velocity overshoot directly above the hill crest which increases with Reynolds number as the inner layer depth decreases. The flow speed up above that layer is independent of the Reynolds number which supports the assumption of inviscid flow disturbance in the outer layer usually made in asymptotic theory for flow over small hills.
AB - Two-dimensional flow over periodically arranged hills was investigated experimentally in a water channel. Two-dimensional particle image velocimetry (PIV) and one-dimensional laser Doppler anemometry (LDA) measurements were undertaken at four Reynolds numbers (5,600 ≤ Re ≤ 37,000). Two-dimensional PIV field measurements were thoroughly validated by means of point-by-point 1D LDA measurements at certain positions of the flow. A detailed study of the periodicity and the homogeneity was undertaken, which demonstrates that the flow can be regarded as two-dimensional and periodic for Re ≥ 10,000. We found a decreasing reattachment length with increasing Reynolds number. This is connected to a higher momentum in the near-wall zone close to flow separation which comes from the velocity speed up above the obstacle. This leads to a velocity overshoot directly above the hill crest which increases with Reynolds number as the inner layer depth decreases. The flow speed up above that layer is independent of the Reynolds number which supports the assumption of inviscid flow disturbance in the outer layer usually made in asymptotic theory for flow over small hills.
UR - http://www.scopus.com/inward/record.url?scp=79959513725&partnerID=8YFLogxK
U2 - 10.1007/s00348-011-1045-y
DO - 10.1007/s00348-011-1045-y
M3 - Article
AN - SCOPUS:79959513725
SN - 0723-4864
VL - 51
SP - 247
EP - 269
JO - Experiments in Fluids
JF - Experiments in Fluids
IS - 1
ER -