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European Scientific Journal ISSN: 1857 - 7881 (Print) e - ISSN 1857- 7431
Aerodynamic properties for high performance sports
textiles
Hasan Mahmud(N-20141026),monour khan(N-20141002), Zahid hasan
(N-20141026) (B.Sc in textile eng.)
Textile engineering college, Noakhali
Goal: To analyze the essential aerodynamic properties and desiginig
process of a sportswear to make it perform more effectively.
Abstract: Generally, the surface textures of the sport fabrics influence the
aerodynamic properties of the athletes in motion. On the other hand, the
surface texture of sports garments largely depends on the applied stress while
wearing. Therefore, the design and fitting of garments on athlete bodies can
make the aerodynamic behaviour more complex. Additionally, the fabric at
an appropriate level of stretching can provide an aerodynamic advantage.
keywords: texture,design,fitting,aerodynamic.
Introduction: whenever we are thinking about about sports textile the first
thing that come to our mind is speed which tends to conflict with air and so
to minimize the friction between air and garments the aerodynamic
properties need to take in consideration . The use of textile materials in high
performance sports can play a pivotal role in the outcome of the event and/or
game. It is no doubt that the understanding of aerodynamic effects of sports
garments on sporting performance is becoming an important criterion of
sports technology and product design. The demands on garment design
associated with the aerodynamics require a quantitative understanding of
materials performance, textile construction and surface texture. Therefore,
the garment design requires detailed information on the textile and surface
morphology as well as systematic evaluation of the aerodynamic behaviour
using wind tunnel experimentation and/ or Computational Fluid Dynamics
(CFD) modelling. (Harun Chowdhury*, 21 march 2010)
European Scientific Journal ISSN: 1857 - 7881 (Print) e - ISSN 1857- 7431
Main topic:
Factors Contributing to the Aerodynamic Performance of Sports
Garments:
A number of factors have been identified that may contribute to the
aerodynamic efficiency of athletes in high-speed sports (Barelle, Ruby, &
Tavernier, 2004; Grappe, Candau, Belli, & Rouillon, 1997; Lukes, Chin, &
Haake, 2005). Some major factors are:
Athlete’s body position during the activity
Sport equipment and/or accessories
Sports garments
As sports garments have direct impact on athletic performance in high-speed
sports, it is necessary to identify the important factors that may influence the
aerodynamic properties of sports garments. There are several factors that can
affect these aerodynamic characteristics of sports garments. These factors
are:
Speed
Body position
Fabric properties
Garment construction
Time contribution
Now we will discuss about the surface properties and do some test of the
sports textiles.
Material Composition:
Three commercially available knitted fabrics with different material
composition were selected for this study. Table 1 shows the material
composition of the fabrics tested.
Table 1. Material composition of sport fabrics studied
Fabric Material Composition Material Thickness, mm
European Scientific Journal ISSN: 1857 - 7881 (Print) e - ISSN 1857- 7431
Sample- 1 92 % Polyester and 8 % Spandex 0.4
Sample- 2 80 % Polyester and 20 % Spandex 0.5
Sample- 3 50 % Nylon, 45 % Polyester and 5 % Spandex 0.7
Measurement of fabric tension:
An Instron universal test machine (Model 4466) with the maximum load
rating 10 kN was used to conduct the tensile strength test of fabric samples.
Two adapters (grips made of aluminium) weredesigned to hold the two ends
of fabric uniformly. One attachment was used for the upper end of the fabric
sample connected to the moving part of Instron loading arm while the other
attachment was used to hold the base. The rubber slabs were used on the
interior side of the aluminium adapter pales to make surethat the fabric
would not slab out of the grip. The dimensions of the plate are 250 mm
width, 60 mm length and 10 mm thickness which are bigger than the sample.
The samples were prepared withdimensions of 220 mm width and 280 mm
length. The thickness of the three samples is shown in Table 1.The
experimental setup is shown in Figure 1. The fabric sample was stretched till
it reached 100 mm extension from zero. The data measurement sampling rate
was 4 Hz. The tension applied in the weft direction of the three samples
.
Measurement of aerodynamic properties:A standard cylinder methodology
was used to measure the drag generated by the fabric under different stretched
conditions. Figure 2 shows the CAD model of the experimental setup. More
European Scientific Journal ISSN: 1857 - 7881 (Print) e - ISSN 1857- 7431
details about the methodology can be found in Moria et al. [4, 5] and
Chaowdhury et al. [2, 8].
Test Cylinder
220 Wind Direction
6 Component Force Sensor
75
Fig. 2. Schematic CAD model of the test cylinder (All dimensions are in mm)
In order to obtain aerodynamic properties of the fabric samples
experimentally, a 90 mm diameter and 220 mm length cylinder was
manufactured. The cylinder was made of PVC material and used some filler
to make it structurally rigid. The cylinder was vertically supported on a six
component force sensor (type JR3) that had a sensitivity of 0.05% over a
range of 0 to 200 N. The aerodynamic forces and their moments were
measured over a range of Reynolds numbers (Re) based on cylinder diameter
and varied wind speeds (from 30 km/h to 140 km/h with an increment of 10
km/h). Material to be tested was wrapped onto the cylinder at different
tension level and joined together by creating a seam which was placed at the
rear of the cylinder (e.g., 180° orientation) to minimise the effect of seam on
aerodynamic properties (see Moria et al [4,5]). Based on the stretch
measured by Instron, the sample length was determined. Each sample was
tested with different tension but made of the same material. The drag of the
cylinder support was measured and subtracted from the drag of the cylinder
and support. Figure 3 shows the cylinder fitted with three test fabrics for the
wind tunnel testing. The RMIT Industrial Wind Tunnel was used for this
study. Details about the tunnel can be found in Alam et al. [9].
European Scientific Journal ISSN: 1857 - 7881 (Print) e - ISSN 1857- 7431
Fig. 3. Experimental arrangement in the wind tunnel test section: (a) sample-1; (b) sample-2; (c) sample-3
Model Design With cylinder: After the fabric analylis comes the
design of the garments.The body configuration of human is extremely
complex due to varied shapes and sizes. Although several researchers have
studied the aerodynamic characteristics of human bodies, their studies were
mainly based on over simplified human body (Hoerner 1965; Brownlie,
1992). Brownlie (1992) used a simplified human analogous model for wind
tunnel study of different fabrics. He developed the model with 11 separate
components of uniform circular cylinders of different dimensions. Oggiano
et al. (2009) tested several fabric samples in the wind tunnel using both the
cylinder and leg models. The study showed that the aerodynamic behaviour
was similar with the cylinder and the leg models. Chowdhury et al. (2010)
demonstrated that athlete body parts can be represented as multiple cylinders
for aerodynamic evaluation in wind tunnel experimentations. The study
showed that the number of the cylinders representing the body parts can be
simplified according to the body positions in different sports. The simplified
human body represented with multiple cylindrical segments is illustrated in
Figure 1(a). The body parts covered with fabrics can influence the
aerodynamic behaviour by altering the air flow characteristics without
affecting the body position. The airflow characteristics can also be
influenced by varying angles of attack. Figure 1(b) shows the segmentation
of a sprinter in running position. The breakdown of individual body parts
clearly show that these parts can be treated as multiple cylinders with varied
dimensions and positions (Chowdhury et al., 2009, 2010).
wind
Fig. 1. Simplified model with cylindrical segments (Chowdhury et al., 2010) Thus,
European Scientific Journal ISSN: 1857 - 7881 (Print) e - ISSN 1857- 7431
the aerodynamic characteristics of these cylindrical body parts can easily be
evaluated in wind tunnel testing under a range of angles of attacks and yaw
angles representing real life body position in sporting actions using the
articulating cylindrical methodology developed by Chowdhury et al. (2009,
2010). The study demonstrated that the cylindrical arrangements can be used
to evaluate the aerodynamic properties of fabric features such as seam
position, wale orientation and surface roughness with standard cylindrical
geometry to quantify the aerodynamic properties more accurately. In this
study, the drag and lift characteristics of a number of sports fabrics were
evaluated in various configurations together with the implications of this
behaviour for the design of garments in such higher speed sports. Two sports
were selected based on their speed ranges and characteristics. One is ski
jumping where the speed is about 90 to 100 km/h. Another one is cycling
where the speed is relatively lower, ranges from 30 to 60 km/h. For ski
jumping, both lift and drag optimisation are important as the ski jumper
become airborne during the in-flight phase. On the other hand, in cycling, the
minimisation of aerodynamic drag is paramount. Full scale evaluation for ski
jumping and cycling were also conducted. Full scale mannequin or human
athlete test results were correlated with the standardised cylinder test data.
Therefore, the focus of the research is on the comprehensive evaluation of
aerodynamic behaviour of sports garments used in ski jumping and cycling
sports to determine aerodynamic efficiency. No such study has been reported
in the literature. This chapter will describe a systematic methodology to
design aerodynamically optimised sports garments starting from the wind
tunnel experimentations of fabric sleeves with cylinder models to the full
scale evaluation of prototype suits. Details studies were carried out for
cycling and ski jumping suits, although this methodology can be applied to
other higher speed sports based on their characteristics.
Full scale evaluation of sports garments:
Two ski-jumping suits were tested for the full scale aerodynamic evaluation
at two different positions. Frontal areas of the ski jumping experimental
arrangement including the ski jumper at both positions were measured using
the projected frontal area measurement system described in Chowdhury et
al., 2011a. Drag and lift forces were measured at a range of wind speeds
from 80 to 110 km/h. Drag and lift forces were converted to their non
dimensional drag and lift coefficient. Figure 18 shows the full scale testing
of ski jumping suits for the CD, CL and L/D variations with speed with error
bars indicating the standard deviation of the experimental data
European Scientific Journal ISSN: 1857 - 7881 (Print) e - ISSN 1857- 7431
Fig. 18. Full scale testing of ski jumping suits
Results show that there is little variation in CD values between two suits in
both positions within the speed range from 90 to 100 km/h. Suit-B exhibits
more CL value in both positions than Suit-A. Also L/D values of Suit-B are
higher than that of Suit-A. Thus a little aerodynamic benefit is noted with
Suit-B. With Suit-B, the Drag is decreased by 0.4% but the lift is increased
by 2.2% with respect to Suit-A. The resultant jump length can be increased
by about 4.44 m by using the simulation approach formulated by Muller &
Schmolzer (2002).
Two cycling suits were manufactured for the full scale testing. Suits were
tested at two widely used cycling positions: road racing and time trial.
Projected frontal areas of the cyclist at different positions were measured
using the projected frontal area measurement system described by
Chowdhury et al., 2011b. Drag forces were measured under a range of wind
speeds starting from 20 to 70 km/h with an increment of 10 km/h. Drag
forces were converted to non dimensional drag coefficient (CD). Figure 19
shows the CD variation with speed at road racing and time trial position.
European Scientific Journal ISSN: 1857 - 7881 (Print) e - ISSN 1857- 7431
The road racing (upright) position is used by the cyclist generally during
long distance road racing. In this position, the frontal area is comparatively
higher than time trial positions. As a result, the cyclist experiences more
aerodynamic drag. The speed range for upright position is from 30 to 40
km/h. Suit-2 is made of relatively rough fabric (Sample#05) and has lowest
CD values from 30 to 50 km/h as shown in Figure 19(a). Therefore, Suit-2
provides more aerodynamic benefits at this cycling position and speed range
compared to Suit-1 which is made of relatively smooth fabric (Sample#04).
Results show that around 2.1% drag reduction is possible with Suit-2 at
upright position between 30 to 40 km/h.
On the other hand, in time trial position is used by the cyclist generally
during the time trial cycling event. At this position, the cyclist tries to
achieve the minimum projection frontal area in order to minimise the
aerodynamic drag. This is the most streamlined position used by the cyclist.
Figure 19(b) shows the CD variation with speed at time trial position. The
speed range for the time trial position is generally 50 to 60 km/h. Suit-1 has
lowest CD value within this speed range.
Comparison of results:
In ski jumping, it was predicted earlier with the cylinder results that Suit-B
would be more aerodynamically efficient than Suit-A. Cylinder results
indicate an increase of L/D ratio approximately 30% for the leg segment and
8% for the arm segment compared to the base configuration (Sample #01).
Full scale results shows that Suit-B has approximately 3% increase of L/D
compared to Suit-A which is made according to base configuration.
Therefore, it is evident that cylinder results has similar trend with full scale
results. However, the magnitude of the aerodynamic benefit is different.
Cylinder test results are more specific to the fabric properties. Full scale
testing is more complicated compared to simplified cylindrical
methodology.
In cycling, the average drag reduction was calculated by taking Suit-1 as the
base for comparison. The average drag reduction with Suit-2 was found at
road racing (upright) position by 2.1% approximately. But the drag
increased by 1.5% at the time trial position at low speed (below 50 km/h).
The average reduction of drag for the time trial positions was around 21%
compared to the upright position. Suit-2 has the highest reduction of drag in
road racing (upright) position where generally the cyclist’s body is not very
streamlined.
European Scientific Journal ISSN: 1857 - 7881 (Print) e - ISSN 1857- 7431
Suit-1 performs better than Suit-2 at time trial position at high speeds (over
50 km/h).
Cylinder test results indicate that the smooth fabric possesses 5% less drag
than rough fabric at low angle of attack (α < 45 ) at speed ranges from 50 to
60 km/h. Full scale results indicate 2.1% drag reduction with Suit-1 at time
trial position compared to Suit-2. Cylinder results also showed that the rough
fabric undergoes the flow transition earlier than the smooth fabric when
angle of attack is more than 45 . Therefore, at low speeds (from 40 to 50
km/h), CD values of the rough fabric are lower than that of the smooth fabric.
The average drag reduction was calculated around 3.3% with Suit-2
compared to Suit-1. Therefore, it is evident that full scale test results
compared well with cylinder results.
However, the magnitudes of the aerodynamic forces are less in cylinder
testing. Cylinder results are more specific to fabric features (e.g., surface
profile) of the suit compare to the full scale testing. The full scale testing is
less sensitive as the high magnitude of force is measured and also the
aerodynamic interference is more. Therefore, the cylinder test is more
appropriate as the flow transition due to the surface roughness can be
observed with cylinder testing. On the other hand, no flow transition was
observed in the full scale testing for ski jumping and cycling which agreed
well with published data (Brownlie, 1992). Brownlie tested several fabrics
with cylinder model and garments with full scale models for cycling and
sprint. The study showed that flow transition was only observed with
cylinder model but no flow transition was noted with full scale model.
Brownlie (1992) suggested that peripheral parts (arm, leg, etc.) of human
athlete prevented the flow separation. In this study, complex flow structures
were observed around the ski jumping and cycling using the flow
visualisation technique which is not included in this study. However, on field
test can be another way for further verification of cylinder test results.
Result:
Cylinder results have good agreement with the full scale testing both for ski
jumping and cycling garments. In this study, it was estimated about 4.44 m
increase of the jump length which could be a decisive advantage for a ski
jumper. The results also demonstrated that the cycling suit should be selected
depending on the cycling position and speed range in order to take the
aerodynamic advantage. As the position in the world class competitions are
decided with a fraction of time difference, apart from the athletic
European Scientific Journal ISSN: 1857 - 7881 (Print) e - ISSN 1857- 7431
performance, an efficient sport garment can enhance the overall performance
of the athlete. Depending on the nature of the sport, this methodology can be
used as a basic design tool to optimise or select proper parameters for the
betterment of the outcome. Prior to making a full-scale suit, this
methodology can be an essential tool to investigate the performance of
individual parts of the body. Thus, it will be easier to manufacture the
aerodynamic prototype suit. The practical implementation of knowledge
from this study can be applied not only in ski jumping and cycling but also
other speed sports.
Conclusion:
The following conclusions were drawn from the work presented here:
 The surface texture of the fabric was changed under different
stretched level causing a notable effect on the aerodynamic
drag.
 The fabric with higher stretches can provide an aerodynamic
advantage by reducing drag at lower speeds.
 The early flow transition caused by the surface texture under
tension reduced the aerodynamic drag up to 30% for fabrics
used in this study.
References:
Harun Chowdhury*, F. A. (21 march 2010). Aerodynamic Performance Evaluation
of Sports Textile . Melbourne,Australia: Elsevier Ltd.
European Scientific Journal ISSN: 1857 - 7881 (Print) e - ISSN 1857- 7431

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Aero Dynamic Properties on Sports wear

  • 1. European Scientific Journal ISSN: 1857 - 7881 (Print) e - ISSN 1857- 7431 Aerodynamic properties for high performance sports textiles Hasan Mahmud(N-20141026),monour khan(N-20141002), Zahid hasan (N-20141026) (B.Sc in textile eng.) Textile engineering college, Noakhali Goal: To analyze the essential aerodynamic properties and desiginig process of a sportswear to make it perform more effectively. Abstract: Generally, the surface textures of the sport fabrics influence the aerodynamic properties of the athletes in motion. On the other hand, the surface texture of sports garments largely depends on the applied stress while wearing. Therefore, the design and fitting of garments on athlete bodies can make the aerodynamic behaviour more complex. Additionally, the fabric at an appropriate level of stretching can provide an aerodynamic advantage. keywords: texture,design,fitting,aerodynamic. Introduction: whenever we are thinking about about sports textile the first thing that come to our mind is speed which tends to conflict with air and so to minimize the friction between air and garments the aerodynamic properties need to take in consideration . The use of textile materials in high performance sports can play a pivotal role in the outcome of the event and/or game. It is no doubt that the understanding of aerodynamic effects of sports garments on sporting performance is becoming an important criterion of sports technology and product design. The demands on garment design associated with the aerodynamics require a quantitative understanding of materials performance, textile construction and surface texture. Therefore, the garment design requires detailed information on the textile and surface morphology as well as systematic evaluation of the aerodynamic behaviour using wind tunnel experimentation and/ or Computational Fluid Dynamics (CFD) modelling. (Harun Chowdhury*, 21 march 2010)
  • 2. European Scientific Journal ISSN: 1857 - 7881 (Print) e - ISSN 1857- 7431 Main topic: Factors Contributing to the Aerodynamic Performance of Sports Garments: A number of factors have been identified that may contribute to the aerodynamic efficiency of athletes in high-speed sports (Barelle, Ruby, & Tavernier, 2004; Grappe, Candau, Belli, & Rouillon, 1997; Lukes, Chin, & Haake, 2005). Some major factors are: Athlete’s body position during the activity Sport equipment and/or accessories Sports garments As sports garments have direct impact on athletic performance in high-speed sports, it is necessary to identify the important factors that may influence the aerodynamic properties of sports garments. There are several factors that can affect these aerodynamic characteristics of sports garments. These factors are: Speed Body position Fabric properties Garment construction Time contribution Now we will discuss about the surface properties and do some test of the sports textiles. Material Composition: Three commercially available knitted fabrics with different material composition were selected for this study. Table 1 shows the material composition of the fabrics tested. Table 1. Material composition of sport fabrics studied Fabric Material Composition Material Thickness, mm
  • 3. European Scientific Journal ISSN: 1857 - 7881 (Print) e - ISSN 1857- 7431 Sample- 1 92 % Polyester and 8 % Spandex 0.4 Sample- 2 80 % Polyester and 20 % Spandex 0.5 Sample- 3 50 % Nylon, 45 % Polyester and 5 % Spandex 0.7 Measurement of fabric tension: An Instron universal test machine (Model 4466) with the maximum load rating 10 kN was used to conduct the tensile strength test of fabric samples. Two adapters (grips made of aluminium) weredesigned to hold the two ends of fabric uniformly. One attachment was used for the upper end of the fabric sample connected to the moving part of Instron loading arm while the other attachment was used to hold the base. The rubber slabs were used on the interior side of the aluminium adapter pales to make surethat the fabric would not slab out of the grip. The dimensions of the plate are 250 mm width, 60 mm length and 10 mm thickness which are bigger than the sample. The samples were prepared withdimensions of 220 mm width and 280 mm length. The thickness of the three samples is shown in Table 1.The experimental setup is shown in Figure 1. The fabric sample was stretched till it reached 100 mm extension from zero. The data measurement sampling rate was 4 Hz. The tension applied in the weft direction of the three samples . Measurement of aerodynamic properties:A standard cylinder methodology was used to measure the drag generated by the fabric under different stretched conditions. Figure 2 shows the CAD model of the experimental setup. More
  • 4. European Scientific Journal ISSN: 1857 - 7881 (Print) e - ISSN 1857- 7431 details about the methodology can be found in Moria et al. [4, 5] and Chaowdhury et al. [2, 8]. Test Cylinder 220 Wind Direction 6 Component Force Sensor 75 Fig. 2. Schematic CAD model of the test cylinder (All dimensions are in mm) In order to obtain aerodynamic properties of the fabric samples experimentally, a 90 mm diameter and 220 mm length cylinder was manufactured. The cylinder was made of PVC material and used some filler to make it structurally rigid. The cylinder was vertically supported on a six component force sensor (type JR3) that had a sensitivity of 0.05% over a range of 0 to 200 N. The aerodynamic forces and their moments were measured over a range of Reynolds numbers (Re) based on cylinder diameter and varied wind speeds (from 30 km/h to 140 km/h with an increment of 10 km/h). Material to be tested was wrapped onto the cylinder at different tension level and joined together by creating a seam which was placed at the rear of the cylinder (e.g., 180° orientation) to minimise the effect of seam on aerodynamic properties (see Moria et al [4,5]). Based on the stretch measured by Instron, the sample length was determined. Each sample was tested with different tension but made of the same material. The drag of the cylinder support was measured and subtracted from the drag of the cylinder and support. Figure 3 shows the cylinder fitted with three test fabrics for the wind tunnel testing. The RMIT Industrial Wind Tunnel was used for this study. Details about the tunnel can be found in Alam et al. [9].
  • 5. European Scientific Journal ISSN: 1857 - 7881 (Print) e - ISSN 1857- 7431 Fig. 3. Experimental arrangement in the wind tunnel test section: (a) sample-1; (b) sample-2; (c) sample-3 Model Design With cylinder: After the fabric analylis comes the design of the garments.The body configuration of human is extremely complex due to varied shapes and sizes. Although several researchers have studied the aerodynamic characteristics of human bodies, their studies were mainly based on over simplified human body (Hoerner 1965; Brownlie, 1992). Brownlie (1992) used a simplified human analogous model for wind tunnel study of different fabrics. He developed the model with 11 separate components of uniform circular cylinders of different dimensions. Oggiano et al. (2009) tested several fabric samples in the wind tunnel using both the cylinder and leg models. The study showed that the aerodynamic behaviour was similar with the cylinder and the leg models. Chowdhury et al. (2010) demonstrated that athlete body parts can be represented as multiple cylinders for aerodynamic evaluation in wind tunnel experimentations. The study showed that the number of the cylinders representing the body parts can be simplified according to the body positions in different sports. The simplified human body represented with multiple cylindrical segments is illustrated in Figure 1(a). The body parts covered with fabrics can influence the aerodynamic behaviour by altering the air flow characteristics without affecting the body position. The airflow characteristics can also be influenced by varying angles of attack. Figure 1(b) shows the segmentation of a sprinter in running position. The breakdown of individual body parts clearly show that these parts can be treated as multiple cylinders with varied dimensions and positions (Chowdhury et al., 2009, 2010). wind Fig. 1. Simplified model with cylindrical segments (Chowdhury et al., 2010) Thus,
  • 6. European Scientific Journal ISSN: 1857 - 7881 (Print) e - ISSN 1857- 7431 the aerodynamic characteristics of these cylindrical body parts can easily be evaluated in wind tunnel testing under a range of angles of attacks and yaw angles representing real life body position in sporting actions using the articulating cylindrical methodology developed by Chowdhury et al. (2009, 2010). The study demonstrated that the cylindrical arrangements can be used to evaluate the aerodynamic properties of fabric features such as seam position, wale orientation and surface roughness with standard cylindrical geometry to quantify the aerodynamic properties more accurately. In this study, the drag and lift characteristics of a number of sports fabrics were evaluated in various configurations together with the implications of this behaviour for the design of garments in such higher speed sports. Two sports were selected based on their speed ranges and characteristics. One is ski jumping where the speed is about 90 to 100 km/h. Another one is cycling where the speed is relatively lower, ranges from 30 to 60 km/h. For ski jumping, both lift and drag optimisation are important as the ski jumper become airborne during the in-flight phase. On the other hand, in cycling, the minimisation of aerodynamic drag is paramount. Full scale evaluation for ski jumping and cycling were also conducted. Full scale mannequin or human athlete test results were correlated with the standardised cylinder test data. Therefore, the focus of the research is on the comprehensive evaluation of aerodynamic behaviour of sports garments used in ski jumping and cycling sports to determine aerodynamic efficiency. No such study has been reported in the literature. This chapter will describe a systematic methodology to design aerodynamically optimised sports garments starting from the wind tunnel experimentations of fabric sleeves with cylinder models to the full scale evaluation of prototype suits. Details studies were carried out for cycling and ski jumping suits, although this methodology can be applied to other higher speed sports based on their characteristics. Full scale evaluation of sports garments: Two ski-jumping suits were tested for the full scale aerodynamic evaluation at two different positions. Frontal areas of the ski jumping experimental arrangement including the ski jumper at both positions were measured using the projected frontal area measurement system described in Chowdhury et al., 2011a. Drag and lift forces were measured at a range of wind speeds from 80 to 110 km/h. Drag and lift forces were converted to their non dimensional drag and lift coefficient. Figure 18 shows the full scale testing of ski jumping suits for the CD, CL and L/D variations with speed with error bars indicating the standard deviation of the experimental data
  • 7. European Scientific Journal ISSN: 1857 - 7881 (Print) e - ISSN 1857- 7431 Fig. 18. Full scale testing of ski jumping suits Results show that there is little variation in CD values between two suits in both positions within the speed range from 90 to 100 km/h. Suit-B exhibits more CL value in both positions than Suit-A. Also L/D values of Suit-B are higher than that of Suit-A. Thus a little aerodynamic benefit is noted with Suit-B. With Suit-B, the Drag is decreased by 0.4% but the lift is increased by 2.2% with respect to Suit-A. The resultant jump length can be increased by about 4.44 m by using the simulation approach formulated by Muller & Schmolzer (2002). Two cycling suits were manufactured for the full scale testing. Suits were tested at two widely used cycling positions: road racing and time trial. Projected frontal areas of the cyclist at different positions were measured using the projected frontal area measurement system described by Chowdhury et al., 2011b. Drag forces were measured under a range of wind speeds starting from 20 to 70 km/h with an increment of 10 km/h. Drag forces were converted to non dimensional drag coefficient (CD). Figure 19 shows the CD variation with speed at road racing and time trial position.
  • 8. European Scientific Journal ISSN: 1857 - 7881 (Print) e - ISSN 1857- 7431 The road racing (upright) position is used by the cyclist generally during long distance road racing. In this position, the frontal area is comparatively higher than time trial positions. As a result, the cyclist experiences more aerodynamic drag. The speed range for upright position is from 30 to 40 km/h. Suit-2 is made of relatively rough fabric (Sample#05) and has lowest CD values from 30 to 50 km/h as shown in Figure 19(a). Therefore, Suit-2 provides more aerodynamic benefits at this cycling position and speed range compared to Suit-1 which is made of relatively smooth fabric (Sample#04). Results show that around 2.1% drag reduction is possible with Suit-2 at upright position between 30 to 40 km/h. On the other hand, in time trial position is used by the cyclist generally during the time trial cycling event. At this position, the cyclist tries to achieve the minimum projection frontal area in order to minimise the aerodynamic drag. This is the most streamlined position used by the cyclist. Figure 19(b) shows the CD variation with speed at time trial position. The speed range for the time trial position is generally 50 to 60 km/h. Suit-1 has lowest CD value within this speed range. Comparison of results: In ski jumping, it was predicted earlier with the cylinder results that Suit-B would be more aerodynamically efficient than Suit-A. Cylinder results indicate an increase of L/D ratio approximately 30% for the leg segment and 8% for the arm segment compared to the base configuration (Sample #01). Full scale results shows that Suit-B has approximately 3% increase of L/D compared to Suit-A which is made according to base configuration. Therefore, it is evident that cylinder results has similar trend with full scale results. However, the magnitude of the aerodynamic benefit is different. Cylinder test results are more specific to the fabric properties. Full scale testing is more complicated compared to simplified cylindrical methodology. In cycling, the average drag reduction was calculated by taking Suit-1 as the base for comparison. The average drag reduction with Suit-2 was found at road racing (upright) position by 2.1% approximately. But the drag increased by 1.5% at the time trial position at low speed (below 50 km/h). The average reduction of drag for the time trial positions was around 21% compared to the upright position. Suit-2 has the highest reduction of drag in road racing (upright) position where generally the cyclist’s body is not very streamlined.
  • 9. European Scientific Journal ISSN: 1857 - 7881 (Print) e - ISSN 1857- 7431 Suit-1 performs better than Suit-2 at time trial position at high speeds (over 50 km/h). Cylinder test results indicate that the smooth fabric possesses 5% less drag than rough fabric at low angle of attack (α < 45 ) at speed ranges from 50 to 60 km/h. Full scale results indicate 2.1% drag reduction with Suit-1 at time trial position compared to Suit-2. Cylinder results also showed that the rough fabric undergoes the flow transition earlier than the smooth fabric when angle of attack is more than 45 . Therefore, at low speeds (from 40 to 50 km/h), CD values of the rough fabric are lower than that of the smooth fabric. The average drag reduction was calculated around 3.3% with Suit-2 compared to Suit-1. Therefore, it is evident that full scale test results compared well with cylinder results. However, the magnitudes of the aerodynamic forces are less in cylinder testing. Cylinder results are more specific to fabric features (e.g., surface profile) of the suit compare to the full scale testing. The full scale testing is less sensitive as the high magnitude of force is measured and also the aerodynamic interference is more. Therefore, the cylinder test is more appropriate as the flow transition due to the surface roughness can be observed with cylinder testing. On the other hand, no flow transition was observed in the full scale testing for ski jumping and cycling which agreed well with published data (Brownlie, 1992). Brownlie tested several fabrics with cylinder model and garments with full scale models for cycling and sprint. The study showed that flow transition was only observed with cylinder model but no flow transition was noted with full scale model. Brownlie (1992) suggested that peripheral parts (arm, leg, etc.) of human athlete prevented the flow separation. In this study, complex flow structures were observed around the ski jumping and cycling using the flow visualisation technique which is not included in this study. However, on field test can be another way for further verification of cylinder test results. Result: Cylinder results have good agreement with the full scale testing both for ski jumping and cycling garments. In this study, it was estimated about 4.44 m increase of the jump length which could be a decisive advantage for a ski jumper. The results also demonstrated that the cycling suit should be selected depending on the cycling position and speed range in order to take the aerodynamic advantage. As the position in the world class competitions are decided with a fraction of time difference, apart from the athletic
  • 10. European Scientific Journal ISSN: 1857 - 7881 (Print) e - ISSN 1857- 7431 performance, an efficient sport garment can enhance the overall performance of the athlete. Depending on the nature of the sport, this methodology can be used as a basic design tool to optimise or select proper parameters for the betterment of the outcome. Prior to making a full-scale suit, this methodology can be an essential tool to investigate the performance of individual parts of the body. Thus, it will be easier to manufacture the aerodynamic prototype suit. The practical implementation of knowledge from this study can be applied not only in ski jumping and cycling but also other speed sports. Conclusion: The following conclusions were drawn from the work presented here:  The surface texture of the fabric was changed under different stretched level causing a notable effect on the aerodynamic drag.  The fabric with higher stretches can provide an aerodynamic advantage by reducing drag at lower speeds.  The early flow transition caused by the surface texture under tension reduced the aerodynamic drag up to 30% for fabrics used in this study. References: Harun Chowdhury*, F. A. (21 march 2010). Aerodynamic Performance Evaluation of Sports Textile . Melbourne,Australia: Elsevier Ltd.
  • 11. European Scientific Journal ISSN: 1857 - 7881 (Print) e - ISSN 1857- 7431