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ANALYSIS OF DRAG AND LIFT FORCES IN DIFFERENT TAILED GROUND EFFECT VEHICLES

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International Journal of Mechanical Engineering and Technology (IJMET)
Volume 10, Issue 01, January 2019, pp. 1399-1412, Article ID: IJMET_10_01_142
Available online at http://www.iaeme.com/ijmet/issues.asp?JType=IJMET&VType=10&IType=1
ISSN Print: 0976-6340 and ISSN Online: 0976-6359
© IAEME Publication
Scopus Indexed
ANALYSIS OF DRAG AND LIFT FORCES IN
DIFFERENT TAILED GROUND EFFECT
VEHICLES
Pavan Hiremath, Manjunath Shettar, Suhas Kowshik C S*, Rajath J and Sukhesh P D
Department of Mechanical and Manufacturing Engineering, Manipal Institute of Technology,
Manipal Academy of Higher Education, Manipal – 576104, Karnataka, India.
* Corresponding author
ABSTRACT
In recent days people are dependent highly on transportation and the demand for
quicker modes of transportation are increasing day by day. Technological advances in
the areas of roadways, airways and waterways have led to development of faster and
efficient vehicles which has largely contributed in connecting people across the globe.
This study deals with finding the effect of different forces acting on Ground Effect
Vehicles. Initially three different tail models were considered and modeled in CATIA
and then imported to ANSYS for further analysis. It was observed that the higher
pressure at tips is a result of the shape of the GEV and it causes drag, since it is
opposing the inlet flow. Lift is generated due to difference in pressures between top
and bottom surfaces of the wing, which is a consequence of velocity difference. The
pressure at top is much lesser that than bottom of the GEV, so lift is also generated.
However, it was found from L/D ratio that V tail displayed higher response for the
considered process parameters and boundary conditions.
Keywords Lift, Drag, Ground effect, tail, bounding.
Cite this Article: Pavan Hiremath, Manjunath Shettar, Suhas Kowshik C S, Rajath J
and Sukhesh P D, Analysis of Drag And Lift Forces in Different Tailed Ground Effect
Vehicles, International Journal of Mechanical Engineering and Technology, 10(1),
2019, pp. 1399-1412.
http://www.iaeme.com/IJMET/issues.asp?JType=IJMET&VType=10&IType=1
1. INTRODUCTION
Transportation has always been a need for the growth of civilization and mankind. Traveling
larger distances with minimum time has been a subject to interest for centuries [1]. Faster and
Improved modes & means of transport have been a subject of interest in the field of science
and technology [2]. Technological advances in the areas of roadways, airways and waterways
have led to development of faster and efficient vehicles which has largely contributed in
connecting people across the globe [3-5]. One such technologically advanced vehicle which
can be listed under both waterway and airway is the ‘Ground Effect Vehicle’ (GEV). Ground
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Analysis of Drag And Lift Forces in Different Tailed Ground Effect Vehicles
Effect Vehicles (GEVs) are designed to fly like airplanes and glide on water like boats but
they can neither completely fly at higher altitudes nor can they maneuver high tides in rough
seas. However, GEVs are designed to transport people and goods at a high speed to areas
which are incapable of harboring big boats or land airplanes. These can be effectively used for
transportation over calm seas or lakes to reach smaller islands[6-8].
Lift is the force generated under the wings of an airplane due to the aerodynamic pressure
built up that acts in the upward direction and is responsible for the countering the pressure
above the wing. Lift helps during take-off of airplanes [9]. Drag is force generated behind any
vehicle as the vehicle against the direction of the wind or other aerodynamic or fluid forces.
Vehicles are required to spend additional energy to work against the drag forces [10]. Boats
need to overcome a huge drag force while traveling on sea due to large drag co-efficient of
water which leads to high fuel consumption and reduced efficiencies in addition to the
reduced speed [11]. The operating principle of a GEV is comparable to an airplane and a boat
in terms of its aerodynamic forces viz. lift and drag. The principle that explains the same is
called the ‘Ground Effect’ [12]. The principle of Ground Effect is the key to understanding
GEVs. An airfoil is a cross section of the wing of an airplane. The airfoil is designed to
provide and maintain the necessary lift force that helps in flying an airplane. As the altitude
increases, the lift force reduces as the area under the wings increase [13-14]. If the distance
between the underside of the wing and the ground is less, the lift increases. This phenomenon
is called as Ground effect. GEVs operate close to the water surface by utilizing the air cushion
of relatively highly pressurized air created between the airfoil and the water surface. The air
cushion augments lift and reduces drag considerably. This phenomena further enhance the
lift-to drag ratio. Hence, GEVs can cruise safely at higher speeds owing to the phenomenon of
Ground Effect which not only increases lift force but also reduces the drag forces.
2. EXPERIMENTAL METHOD
Initially the models were developed using CATIA and are shown in figures 1 2 and 3. Sketch
Tracer is used to position two dimensional images in workspace so that projection of the
model in a plane can be viewed. 3-D Curve was used extensively in modelling to generate
many key curves like cockpits, wings, ailerons, tails etc. After modelling the surface models
‘Closed Surface’ command was used to convert them into solid form, after ensuring that there
are no open curves or surfaces. Later these models were imported to ANSYS software for
further analysis.
Figure 1 3-D model of GEV having T tail
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Figure 2 3-D model of GEV having V tail
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Figure 3 3-D model of GEV having High Boom tail
After importing to ANSYS, creation of bounding box is an important step as it decides the
space in which the boundary conditions act. The box created here is not a rectangular cuboid
but a hexahedron with front face 24m x 24.5m and rear rectangular being 30m x 34.5m. The
way it is arranged has been shown in Figure 4. This helps in knowing the effect of air at the
inlet and the effect of boundary conditions at outlet. Along with that, this shape ensures that
optimal number of elements are formed for calculations. Symmetry has been applied so that
the number of elements and time for calculation gets reduced by half.
Figure 4 Bounding box with symmetry
It is always desirable do divide the bounding box such that highest number of elements
are near the surface of the plane. If the bounding box domain is divided in the same way
everywhere, it would result in a large number of elements and increases the time for
calculation and is undesirable. Hence, slicing (Figure 5) was done to divide the bounding box,
which in turn helps to decide where more precise elements have to be generated. The GEV
surface remains untouched (Figure 6) and results in getting less errors during meshing.
Figure 5 Slicing of the box
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Figure 6 Close up of slicing near GEV surface
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From Figure 7, it can be seen that hexahedral mesh can be used in the sliced boxes as the
geometry of boxes is simple, but for more complexly designed surfaces, the usage of
tetrahedral mesh is preferred. Tetrahedral mesh also ensures low skewness and gives out
better quality mesh. All three GEVs have been tested using zero angle of attack. The analysis
of all models have common conditions to ensure simple comparison. The maximum speed of
the aircraft chosen to be 50 m/s (180 kmph) since this is the speed closest to maximum speeds
of the aircraft [8]. The analysis parameters for all models were same and are shown in the
table 1. The inlet velocity values have been applied to Inlet, Side Inlet and Top Inlet surfaces.
Later a 3-D curve was generated using points and a surface Was created using concept
surfaces. A bounding surface with radius of 10 M and a rectangle of dimension 19 M X 20 M
and they were combined as shown in figure 8. Later aero foil was subtracted from the
bounding surface. The inlet and outlet wall edges which are done for bench marking is shown
in figure 8 and the mesh bounding surface is shown in figure 9. A Bias Size and Factor of
0.02m and 50 has been used in Horizontal lines, and 0.02m and 10 has been used in Vertical
lines as shown in figure 9. For applying the boundary conditions, the
Figure 7 Meshed bounding box and GEV surface
parameters have been taken from literature survey [3,8] as shown in Table 2. The
calculation was done for 2000 iterations along with refining the mesh near the wall in post
processing in order to get better results.
Figure 8 Inlet, Outlet and Wall edges
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.
Figure 9 Meshed bounding surface
Table 1 Parameters of GEV analysis
Solver
Pressure Based Steady State
Viscosity Model
SST k-Omega
Density (kg/m3)
1.225
Viscosity (kg/m-s)
1.79E-05
Turbulent Intensity (%)
500
Turbulent Viscosity Ratio
10
Inlet Velocity (m/s)
50
Table 2 Analysis parameters for benchmarking test
Solver
Pressure Based Steady State
Viscosity Model
Spalart-Allmaras
Density (kg/m3)
1.225
Viscosity (kg/m-s)
1.7894
Turbulent Viscosity Ratio
10
Inlet Velocity (m/s)
18
Chord Length (m)
0.1
Momentum
Second Order Upwind
Pressure Velocity Coupling
Simple
The grid independence test was conducted as a means for verification as well as validation
of results. Care must be taken for the mesh and quality should remain high by considering
some key parameters. The following points show the process for grid independence test:
 The model of the GEV after slicing and naming the boundaries for boundary
conditions, was duplicated three more times.
 In meshing: Under ‘Mesh’ – ‘Sizing’, the ‘Min Size’, ‘Proximity Min Size’, ‘Max
Face Size’, and ‘Max Tet Size’ were changed. Under ‘Mesh’ – ‘Face Sizing’, the
‘Element Size’ were changed.
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
The mesh quality was kept in check by checking the Skewness and ensuring that
Maximum Skewness and Average Skewness were low. This ensured that results were
as accurate as possible.
Details of mesh models are shown in tables 3, 4 and 5 for three different tail types. The
second row in tables 3, 4 and 5 meshed models’ analysis are shown in the results.
Table 3 Details of the meshed T tail model
Sl. No. Number of Elements Orthogonal Quality Average Skewness Maximum Skewness
1
6957859
0.92144
0.15004
0.97131
2
4664740
0.92998
0.13994
0.94057
3
2105398
0.95331
0.11276
0.9371
4
511171
0.96529
9.88E-02
0.98043
Table 4 Details of the meshed V tail model
Sl. No. Number of Elements Orthogonal Quality Average Skewness Maximum Skewness
1
6398341
0.91427
0.15899
0.8659
2
4238718
0.93839
0.13063
0.8856
3
2293134
0.9345
0.13714
0.89317
4
1957591
0.94663
0.12325
0.8484
Table 5 Details of the meshed High Boom tail model
Sl. No. Number of Elements Orthogonal Quality Average Skewness Maximum Skewness
1
7044436
0.9183
0.14907
0.84008
2
4873734
0.93174
0.13243
0.84892
3
3620716
0.93698
0.12533
0.836
4
2474694
0.9512
0.10737
0.84655
3. RESULTS AND DISCUSSION
3.1. High Boom tail
From the Pressure Contour (Figure 10), Velocity Contour (Figure 11) and Velocity
Streamlines (Figure 12) at the mid-section, we can see that due to difference in velocities of
air particles between top surface and bottom surface, due to Bernoulli’s principle, lift is
generated. However, the lift is not much in comparison to the one generated by the wing. The
higher pressure at tips is a result of the shape of the GEV and it causes drag, since it is
opposing the inlet flow. From the Pressure and Velocity Contours shown in Figures 13 and
14, it is observed that there is a large difference in velocities of air between the top and
bottom of the wing. Hence due to Bernoulli’s principle, there is a pressure gradient and lift is
generated. As expected, lift is generated due to difference in pressures between top and
bottom surfaces of the wing, which is a consequence of velocity difference. This has been
shown in Figures 15 and 16. Also, it was found from the whole model that the drag is
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generated at the front of the GEV due to boundary layer formation. The pressure at top is
much lesser that than bottom of the GEV, so lift is also generated.
Figure 10 Pressure Contour in Mid-Section
Figure 11 Velocity Contour in Mid-Section
Figure 12 Velocity Streamline in Mid-Section
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Figure 13 Pressure Contour at Tail Section
Figure 14 Velocity Contour at Tail Section
Figure 15 Pressure Contour at Wing Section
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Figure 16 Velocity Contour at Wing Section
3.2. V tail
As discussed earlier the Pressure Contour (Figure 17), Velocity Contour (Figure 18) and
Velocity Streamlines (Figure 19) at the mid-section for V tail model exhibit similar contour.
From the Pressure and Velocity Contours shown in Figures 20 and 21, we can see that there is
a large difference in velocities of air between the top and bottom of the wing. As expected, lift
is generated due to difference in pressures between top and bottom surfaces of the wing,
which is a consequence of velocity difference. This has been shown in Figures 22 and 23.
Figure 17 Pressure Contour in Mid-Section
Figure 18 Velocity Contour in Mid-Section
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Figure 19 Velocity Streamline in Mid-Section
Figure 20 Pressure Contour at Tail Section
Figure 21 Velocity Contour at Tail Section
Figure 22 Pressure Contour at Wing Section
Figure 23 Velocity Contour at Wing Section
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3.3. T tail
The contours for T tail exhibit similar results and helps the GEV to lift and maintain
velocities and pressure which is required for the motion of the GEV with T tail. Figures 24 to
30 shows the different velocities and pressures at wing and tail as discussed earlier.
Figure 24 Pressure Contour in Mid-Section
Figure 25 Velocity Contour in Mid-Section
Figure 26 Velocity Streamline in Mid-Section
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Figure 27 Pressure Contour at Tail Section
Figure 28 Velocity Contour at Tail Section
Figure 29 Pressure Contour at Wing Section
Figure 30: Velocity Contour at Wing Section
Table 6 Grid independence test performed for T Tail
Number of
Static
Elements
Pressure
Lift Coeff
Lift
Force
Drag Coeff
Drag
Force
L/D Ratio
6957859
-159.90941 0.007775994 6693.4927 0.000611943 539.73355 12.70706
4664740
-159.82428 0.00774813 6833.8506 0.000639526 564.06204 12.115424
2105398
-158.3226 0.007726367 6841.9977 0.000722505 637.24973 10.693854
1511171
-156.88149 0.007688026 6780.8389 0.000844833 745.14241 9.1000576
Table 7 Grid independence test performed for V Tail
Number of
Static
Elements
Pressure
6398341
-219.6574 0.027060231 24066.016 0.00175547 1561.2274 15.414805
4238718
-218.70027 0.026853761 23882.392 0.001886879 1678.0956 14.231842
2293134
-215.8773 0.026594353 23651.687 0.002026989 1802.7023 13.12013
1957591
-209.97034 0.025551887 22724.57 0.002170858 1930.6525 11.770409
Lift Coeff
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Lift
Force
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Drag Coeff
Drag
Force
L/D Ratio
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Table 8 Grid independence test performed for High Boom Tail
Number of
Static
Elements
Pressure
7044436
-266.4308
0.12198794 109834.9 0.009081712 8176.9463 13.432263
4873734
-266.0306
0.12141599 109319.92 0.009562855 8610.1558 12.696625
3620716
-264.0284
0.12024085 108261.86 0.010075893 9072.0819 11.933518
2474694
-257.0927
0.11712327 105454.87 0.012538186 11289.069 9.341325
Lift Coeff
Lift
Force
Drag Coeff
Drag
Force
L/D Ratio
Tables 6, 7 and 8 shows the results of grid independence done for T tail, V tail and High
Boom tail respectively. It is observed that that the difference between maximum and
minimum values of coefficient of lift and drag are very small even though there is difference
of elements by a high number. The closeness of pressure values is further proof that the value
does not vary much even though there is significant difference in mesh size and quality if the
mesh. This proves that the analysis is valid, and the mesh and conditions are accurate.
4. CONCLUSION
In this study a comparison was made between three different tail that could be seen in the
Ground Effect Vehicles. Initially all the three models were made using CATIA and then
analyzed in ANSYS. It was observed that the higher pressure at tips is a result of the shape of
the GEV and it causes drag, since it is opposing the inlet flow. Lift is generated due to
difference in pressures between top and bottom surfaces of the wing, which is a consequence
of velocity difference. The pressure at top is much lesser that than bottom of the GEV, so lift
is also generated. Since each of tails are different and have different dimensions, it was difficult
to compare their Lift Force and Drag Force. However, it was possible to compare their
Coefficients of Lift and Drag. A better method of comparison is by using the L/D ratio, and this
shows that the order V tail > High Boom tail > T tail.
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Analysis of Drag And Lift Forces in Different Tailed Ground Effect Vehicles
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