Abstract
This paper presents the results of an experimental study on the developing pulsatile flow in curved pipes with a long, straight pipe upstream. In order to examine the dependence of flow-field development on the governing parameters, LDV measurements were conducted systematically for six cases of flow, where the Womersley number α was varied from 5.5 to 18, the mean Dean number D m was 200 and 300, the flow rate ratio η was 0.5 and 1, and the curvature radius ratio Rc was 10 and 30. Peculiar flow phenomena, such as flow reversal for all values of α and a depression in the axial velocity profile for α = 10, were analyzed by decomposing the axial velocity into a time-mean and a varying component, as well as by obtaining the bias of their profiles. The velocity distributions abruptly change with the phase at turn angles Ω of 15–30°, corresponding to the nondimensional axial length z′ ≅ 1–2 from the bend entrance, and their development along the pipe axis is the most complicated for the flow at a moderate α of 10 and large η of 1. The entrance length in the case of pulsatile flow is shorter than that for steady flow with the same flow rate as the maximum pulsatile flow rate.
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Abbreviations
- a :
-
radius of pipe, a = d/2
- C p :
-
pressure coefficient, C p = (P − P ref)/(ρW 2 m /2)
- D :
-
Dean number, D = Re Rc −1/2
- P :
-
static pressure at pipe wall
- P ref :
-
reference value of P, i.e., P at z/d = −2
- R :
-
curvature radius of pipe
- R c :
-
curvature radius ratio, R c = R/a
- Re :
-
Reynolds number, Re = W m d/ν
- u, w :
-
velocities in x and z directions, respectively
- W :
-
axial velocity averaged over cross section
- x, y, z :
-
coordinate system, see Fig. 2
- z′:
-
nondimensional axial length, z′ = z/(aR)1/2
- α :
-
Womersley number, α = a(ω/ν)1/2
- β :
- ϕ :
-
phase difference, see Eq. (2)
- η :
-
flow rate ratio, η = W o /W m
- Θ :
-
phase angle, Θ = ωt (t: time, ω: angular frequency)
- ν :
-
kinematic viscosity of fluid
- ρ :
-
density of fluid
- Ω :
-
turn angle, see Fig. 2
- m, o :
-
time-mean and amplitude values, respectively
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Acknowledgment
The author would like to thank Professor Emeritus K. Sudo of Hiroshima University for his useful and helpful suggestions.
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Sumida, M. Pulsatile entrance flow in curved pipes: effect of various parameters. Exp Fluids 43, 949–958 (2007). https://doi.org/10.1007/s00348-007-0365-4
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DOI: https://doi.org/10.1007/s00348-007-0365-4