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Engineering, Technology & Applied Science Research Vol. 8, No. 5, 2018, 3316-3320 3316

www.etasr.com Abbasi et al.: Impact of a Single Spoiler on Scouring Depth Status beneath a River Crossing Inclined …

Impact of a Single Spoiler on Scouring Depth Status

Beneath a River Crossing Inclined Pipeline

Saeed Abbasi

Department of Civil Engineering

University of Zanjan

Zanjan, Iran

abbasi.saeed@znu.ac.ir

Maryam Masoomi

Department of Civil Engineering

University of Zanjan

Zanjan, Iran

m.masoomi@znu.ac.ir

Seyyed Aliasghar Arjmandi

Department of Civil Engineering

University of Zanjan

Zanjan, Iran

arjmandi@znu.ac.ir

Abstract—Deep river crossing pipelines utilized to carry fluids

are often placed upon the sand bed. Placement of pipe on the

non-smooth bed would result in the production of some local gaps

beneath the pipe. Asymmetric scouring is one of the main reasons

for pipe underwater failures which are significant in pipeline

management. So, in designing pipelines, knowing the interaction

between pipelines and bed, and predicting the scour depth with

respect to the pipe distance from the bed is significant to ensure

that the pipe will finally deposit on the bed. Numerical models

have been developed for predicting the balance depth of scouring

beneath the pipelines. In this paper, the impact of pipe

orientation on maximum scour depth beneath the pipelines is

investigated. To do this, a pipe is modeled with various angles

with the flow. To manage the local scouring, some spoilers are

placed and modeled upon some pipes too. Also, in order to know

the effects of placement of a pipe at various distances from the

bed, the impact of placement of each pipe at a distance of 0.2D,

0.4D and 0.6D is investigated as well. To model the pipe with and

without a spoiler, the finite element model Flow-3D is utilized and

the results show good accordance with previous experimental

studies and proof the current model’s precision in predicting the

scour depth. Results show that in the placement of the pipe in

angles not investigated before and also with the installing of a

spoiler, the scour process has a reverse ratio with the distance

which would result in full deposition of the pipe on the bed. The

least scour depth belongs to the condition in which the pipe has a

130° angle with the side wall.

Keywords-Flow-3D; pipeline; pipe orientation; pipe with

spoiler; scouring

I. INTRODUCTION

Submerged pipes are significant parts of water conveying
systems, wastewater networks, and oil transmitting lines.
Sediment movement under the pipes is very important because
failure of these pipes would cause huge costs and damages on
the environment. The local scouring at the river is investigated
in [1]. During the water transmission around a pipe situated at
the flow path, collide of the streamlines to an obstacle would
produce several vortices around the pipe. The vortices move
the sediment particles until a small void is produced beneath
the pipe which causes tunnel erosion [2]. Scouring of the soil
under the pipe might suspend a part of the pipe in the water and
if the free span of the pipe is big enough, it would result to

vibration resonance and might lead to pipe failure. So it is
essential to assess the scouring depth to be able to make an
exact and secure design. Preparing a spoiler on the pipe is a
method to accelerate the pipe self-interring (Figure 1).

Fig. 1. Pipe on the flow path: up: with spoiler, down: without spoiler

Several researches have been performed on scouring
phenomena around a pipeline. In these studies, the pipe is
placed perpendicular to the flow path, while it is not always
possible to install the pipe perpendicular to the flow path.
Authors in [3] showed that for the pipe with a spoiler the self-
interring process is ten times faster than that for a pipe with no
spoiler. Author in [4] investigated the scouring around a
horizontal cylinder under various Reynolds numbers (Re),
various Shields parameters (θ) and various distances from the
bed and introduced two small vortices on pipe upstream and
downstream. Author in [5] showed that the scour depth could
be considered as a function of Froude number and the free
distance between the pipe and the bed. Author in [6, 7],
experimentally investigated the impact of spoiler and its
orientation on a pipe subjected to wave and a one-way flow. He
showed that the installation of spoiler would accelerate the
under pipe scouring (tunnel erosion) and also increase the
erosion on downstream and its depth. Authors in [8]
investigated the scouring under the pipe experimentally and
studied the impact of Froude and Reynolds numbers on it.
Author in [9] studied the flow and scouring beneath the pipe

Engineering, Technology & Applied Science Research Vol. 8, No. 5, 2018, 3316-3320 3317

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utilizing K-ε turbulence model using Taylor-Galerkin FEM
method. Authors in [10] showed that a standing spoiler
considerably increases the upstream pressure, reduces the
downstream pressure and causes a downward force. Authors in
[11, 12] showed that the K-ω turbulence model is more
adaptive than K-ε and a special case of LES turbulence models.
Authors in [13] investigated numerically the scouring beneath
the pipe under one-way flow and wave. Authors in [14, 15]
investigated numerically the scouring under the pipe with
spoiler and its impact on flow characteristics. Authors in [16]
studied the hydrodynamic effects of a horizontal spoiler on the
flow around a pipe and concluded that the length of 1-1.5 times
the pipe diameter for the spoiler is optimum. Authors in [1]
investigated a river crossing inclined pipeline experimentally
and authors in [17] modeled the flow around a cylinder over a
scoured bed. Despite that experimental models are accurate and
suitable for scour depth estimation, some limitations such as
costs, scaling, data acquiring and also some benefits of the
numerical methods such as flexibility and considerable
improvement of their potentials, have expanded the use of
numerical simulations. In this paper, the impact of spoiler
installation on an inclined river crossing pipeline on local scour
depth is numerically investigated. Also, in addition to the
spoiler presence, effects of bed-pipeline distance are included
in this paper which was not studied in [1].

II. GOVERNING EQUATIONS

The governing equations are continuity and momentum
equations. To include the sediment effects, some changes are
applied to these equations. The continuity and momentum
equations are presented in (1)-(5):

( ) ( ) ( ) xF x y z DIF SOR
uA

V uA R uA uA R R
t x y z x

ρρ
ρ ρ ρ ξ

∂ ∂ ∂ ∂
+ + + + = +

∂ ∂ ∂ ∂
(1)

yx x SORF z
vAuA uA RV wA

R
t x y z xc

ρ
ξ

ρρ

∂∂ ∂∂
+ + + + =

∂ ∂ ∂ ∂
(2)

2
1

1
( )

x y z

F F

SOR

x x x w s

A vu u u u
uA vA R wA

t V x y z xV

p R
G f b u u u

x V

δ
ρ ρ

 ∂ ∂ ∂ ∂
+ + + − 

∂ ∂ ∂ ∂ 
∂

= − + + + − − − −
∂
�

(3)

1
( ) ( )

x y z

F F

SOR
y y y w s

A uvu v v v
uA vA R wA

t V x y z xV

Rp
R G f b u u u
y V

δ
ρ ρ

 ∂ ∂ ∂ ∂
+ + + − 

∂ ∂ ∂ ∂ 
∂

= − + + + − − − −
∂

�

(4)

1
( )

x y z

SOR
z z z w s

u w w w
uA vA R wA

t V x y z

Rp
G f b u u u

z V
δ

ρ ρ

 ∂ ∂ ∂ ∂
+ + + 

∂ ∂ ∂ ∂ 
∂

= − + + + − − − −
∂

�

(5)

.( ) 0
F

F
V AUF

∂
+ ∇ =

∂
(6)

where VF is the proportion of open volume to the flow, ρ is the
fluid density and RSOR is the spring function. The fluid particle
movement equations in three directions are Navier-Stocks
equations with an additional term. Also, Ax, Ay, and Az are

volume ratios, Gx, Gy and Gz are gravitational accelerations, fx,
fy and fz are viscosity accelerations and bx, by and bz are
dissipations in porous media in x, y and z directions
respectively. Equation (6) is the VOF equation in which A is
mean flow cross-sectional area, U is mean flow velocity in x, y
and z directions and F is fluid volume function. In Flow-3D,
two methods, VOF (to model the performance of the fluid at
the open boundary with air) and FAVOR (to model the rigid
volumes and surfaces such as geometric boundaries) are used
to model the interactions [18].

A. The K-ω Model

The K-ω turbulence model is a two-equation model which
uses two partial differential equations with two variables of K
and ω. The first variable (K) is turbulent kinetic energy and the
second one (ω) is dispersion characteristic velocity [19, 20].
The related equations of this model are presented in (7-9).

k
ν

ω
= (7)

( )* *ij ij T
j j j j

Uk k k
U k

t x x x x
τ β ω ν σ ν

 ∂∂ ∂ ∂ ∂
+ = − + + 

∂ ∂ ∂ ∂ ∂  
(8)

( )2ij ij T
j j j j

U
U

t x k x x x

ω ω ω ω
α τ βω ν σν

 ∂∂ ∂ ∂ ∂
+ = − + + 

∂ ∂ ∂ ∂ ∂  
(9)

where * * *
5 3 9 1 1
, , , , ,

9 40 100 2 2
kα β β σ σ ε β ω= = = = = =

B. Dimensional Analysis

The effective parameters in local scouring beneath the
pipeline in a channel are flow conditions, sediments
characteristics and pipe shape [1, 8]. The relation between the
mentioned parameters can be written as:

50
( , , , , , , , , , )

s s f
d f v y g d S D e sρ ρ= (10)

where ds is scouring balance depth, ρ is flow density, ρs is
sediment density, ν is kinematic viscosity, y is flow depth, g is
gravitational acceleration, d50 is mean particle size, Sf is energy
line slope, D is pipe diameter, e is bed-pipe distance and s is
the spoiler length. Utilizing the Buckingham’s Π theorem and
neglecting the Reynolds number effects, we get:

*50( , , , , , , )s
d d D e s

Fr
y y y y y

ψ τ θ= (11)

in which Fr is Froude number, τ* is Shields parameter and θ is
the angle of pipe orientation.

III. THE NUMERICAL SOLUTION, ANALYTICAL DOMAIN

In this paper, the experimental work of [21] for a fixed pipe
is used to validate the model. In the experimental work, the
width of the flume is 0.5m, the pipe diameter is 0.032m, the
flow velocity is 0.255m/s, sediment particle mean size is
0.38mm and the Shields parameter is evaluated as 0.039. In the
numerical model, the K-ω turbulence model is used; the pipe is
placed at a distance of 10D from the beginning and at various
distances from the bed. The depth of flow is 0.40m and two
nested mesh of 10mm and 5mm are utilized for the outer and

Engineering, Technology & Applied Science Research Vol. 8, No. 5, 2018, 3316-3320 3318

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inner domain (around the pipe) respectively. Figure 2 shows
the analytical domain.

Fig. 2. Analytical domain

With respect to the orientation angle, the pipe and flow can
be at three situations: 1) perpendicular to the river, 2) parallel
to the flow, and 3) inclined crossing [22]. In this paper, an
inclined pipe with angles of 90°, 100°, 110°, 120° and 130° at
various bed-pipe distances is investigated. Figure 3 shows the
inclined pipe and Table I represents the numerical model's
layout.

Fig. 3. Inclined pipe on the flow path

TABLE I. NUMERICAL MODELS LAYOUT

Pipe angle θ (Deg.)
Bed-Pipe distance

0.2D 0.4D 0.6D

Pipe without spoiler

90° A1 B1 C1

100° A2 B2 C2

110° A3 B3 C3

120° A4 B4 C4

130° A5 B5 C5

Pipe with spoiler

90° A6 B6 C6

100° A7 B7 C7

110° A8 B8 C8

120° A9 B9 C9

130° A10 B10 C10

A. Boundary Conditions

Nested mesh was used to model the flow in this study. To
apply the boundary conditions, the specified velocity was
applied to the inlet boundary. The Outflow is used for the outlet
boundary and the Symmetry is applied to the upper boundary.
For the other borders, the Wall boundary condition was
utilized. These boundary conditions are shown in Figure 4.

B. Validation

The results of an experimental work in [21] show that the
balance depth of scouring beneath a pipe was 1.34cm. The
result of numerical simulation was 1.39cm which shows a good
accordance with the experimental work. The relative error is
3.73% which shows a good precision of numerical simulation
under a submerged pipe. Comparison of numerical and
experimental work and balance reaching process for the
numerical model are shown in Table II and Figure 5
respectively.

Fig. 4. The boundary conditions

TABLE II. NUMERICAL AND EXPERIMENTAL RESULT COMPARISON

Error % Scouring depth (cm)

3.73%
1.34 Experimental [21]

1.39 Numerical (Flow-3D)

Fig. 5. Balance reaching process for the scouring under the pipe,

numerical model validation

IV. RESULTS AND DISCUSSION

A. Results for Pipe Placement without Spoiler at Various

Bed-Pipe Distances

To investigate the impact of pipe inclined placement on the
flow path, the following characteristics were applied to the
numerical model: Pipe diameter=0.032m, water velocity
=0.255m/s, sediment particle mean size d50=0.38mm, channel
width=0.5m and Shields parameter=0.039. The pipe was
oriented at 90°, 100°, 110°, 120° and 130° measured from the
side wall (Figure 3). To investigate the bed-pipe distance
effects, the pipe was placed at distances of 0.2D, 0.4D and
0.6D of the bed.

TABLE III. MAXIMUM DEPTH OF SCOURING BENEATH THE PIPE W/O
SPOILER

Bed-pipe distance (cm)
Pipe Angle

Ys=0.6D Ys=0.4D Ys=0.2D

0.88 1.29 1.39 90°

1.06 1.34 1.40 100°

1.03 1.34 1.41 110°

0.84 1.29 1.34 120°

0.75 1.02 1.15 130°

Figures 7-9 show the simulation results for various
distances and orientations. The asymmetric scouring under the
pipe in Figure 6 is caused by flow turn, affecting the flow by
the walls, vortex pattern change and their expansion path
deviation. This asymmetry scouring decreases by increasing
the bed-pipe distance because of bed-pipe interaction reduction.

Engineering, Technology & Applied Science Research Vol. 8, No. 5, 2018, 3316-3320 3319

www.etasr.com Abbasi et al.: Impact of a Single Spoiler on Scouring Depth Status beneath a River Crossing Inclined …

Fig. 6. Numerical simulation sample result, scouring hole beneath inclined

pipe, θ=130°

Fig. 7. Scouring beneath the inclined pipe, e/D=0.2

Fig. 8. Scouring beneath the inclined pipe, e/D=0.4

Fig. 9. Scouring beneath the inclined pipe, e/D=0.6

B. With Spoiler

To investigate the impact of spoiler installation around the
pipe [23], an 1cm length spoiler was installed on top of the pipe
and the pipe and spoiler were subjected to the flow. The
scouring results of this configuration on orientations of 90°,
100°, 110°, 120° and 130° are presented in Figures 7-9 and
Table IV. These results show that installation of the spoilers
has increased the depth of scouring compared to a similar
situation without spoiler. The spoiler changes the flow and
pressure distribution around the pipe and increases the pressure
at the rear [10]. Also, results indicate that the scouring depth
decreases as the bed-pipe distances increase. Figure 10 shows
the scouring progress for the submerged pipe with and without
spoiler for e/D=0.2. It is evident that the scouring progress in
case of utilizing a spoiler is more consistent and continuous
which helps the pipe in the self-interring process.

TABLE IV. MAXIMUM SCOURING DEPTH WITH SPOILER

Bed-pipe distance (cm)
Pipe Angle

Ys=0.6D Ys=0.4D Ys=0.2D

1.73 1.84 1.95 90°

1.60 1.85 1.92 100°

1.80 1.89 2.03 110°

1.77 1.89 2.00 120°

1.35 1.66 1.91 130°

Fig. 10. Scouring progress beneath the inclined pipes, e/D=0.2

V. SUMMARY AND CONCLUSIONS

In this paper, the effectiveness of a single spoiler on
scouring depth reduction beneath a river crossing inclined
pipeline at various bed-pipe distances was investigated
numerically. Main conclusions are:

• As the scouring depth at the validation model has a balance
time of 140s, the simulation time was selected to be 350s
for all models.

• Considering the results, the least scouring belongs to the
pipe in 130° orientation and the depth of scouring in
orientations of 90°, 100°, 110° and 120° is more by 2.09%,
0.52%, 6.28% and 7% respectively. The scouring hole is
symmetric when the pipes angle is 90° while the scouring
hole for the pipe at 100°, 110°, 120° and 130° is
asymmetric. According to the results, the maximum depth
of scouring occurs next to the wall in which the pipe angle
deflects the flow and the pressure varies upstream and
downstream. Sediment transport to the pipes downstream is
because of the uplift pressure beneath the pipe and also the
pipe orientation. The scouring starts somewhere upstream
and slightly travels towards the pipe.

• Maximum scouring depth occurs at the first stages of
scouring process. Also, when the bed-pipe distance is more
than zero, the scouring starts immediately after the
simulation starts, because no time is needed for the piping
phenomenon. So the sediment particles under the pipe start
their travel immediately after the flow beginning. For
angles of 120° and 130°, the scouring depth balance occurs

Engineering, Technology & Applied Science Research Vol. 8, No. 5, 2018, 3316-3320 3320

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more rapidly and the variation chart extends with fewer
slopes. Also, the scouring depth is less than in other
orientations. This is because of less resistance of pipe
against the flow.

• Placement of the pipe at distances of 0.2D, 0.4D and 0.6D
from the bed increases the horizontal distance of deepest
scouring hole location from the pipe center. According to
Tables III and IV, the bed-pipe distance at five distinct
states of orientations has a similar impact on all pipes which
proofs the reverse relation of bed-pipe distance with
scouring depth. It is seen that the scouring depth decreases
with increase in the bed-pipe distance which happens
because of the pipe influence reduction on the bed at greater
bed-pipe distances.

• Spoiler installation increases the scour depth and extension.
The flow rate increases between the pipe and river bed
which results to increasing scour depth under the pipe with
a spoiler.

• The influence of pipe on the bed scouring depth reduces
with an increment of bed-pipe distance at the case of pipe
with spoiler and the maximum scouring depths reduce.

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