**3. Experimental method**

### **3.1 Experimental setup**

The test model was set in AF6116 (M = 0.1) subsonic wind tunnel located at the Hanoi University of Science and Technology, which was of a blowdown type with a closed test section (0.4 0.5 1.0 m<sup>3</sup> ). The wind speed could be arbitrarily varied up to 30 m/s, where the Reynolds number based on wing root chord was 10<sup>6</sup> , which was driven by an 8 kW electric motor.

**Wing 1 (non-structure) Wing 2 (with structure)**

Chord length 300 mm 300 mm Root chord length 500 mm 500 mm Tip chord length 100 mm 100 mm Profile NACA65A004 NACA65A004 Taper ratio 0.5 0.5

*Experimental models. (a) Wing model. (b) Wing with support. (c). Broken wing.*

*Research on Aeroelasticity Phenomenon in Aeronautical Engineering*

*DOI: http://dx.doi.org/10.5772/intechopen.91748*

Mass 5.1 g 11.6 g

**Table 4.** *Wing models.*

**Figure 10.**

**Table 5.**

**Figure 11.**

**65**

**Attack angle (0**

Material Balsa wood Balsa wood, carbon rod, hard wood

0 20 22 37.38 5 17.8 20.5 32.22 10 15.2 19.5 30.31

*Flutter characteristics at different attack angles—Non-structure wing.*

*Force at the wing root of the non-structure wing—Attack angle 10°.*

**) Velocity of first oscillation (m/s) Flutter velocity (m/s) Frequency (Hz)**

Flutter characteristics were determined with the help of the frequency meter and load cell, which allowed to specify the flutter frequency and root wing force, respectively. The oscillated frequency was measured by the DT-2234C+ frequency meter. The signal of measured frequency was averaged by five measurements. The force applied to the wing was measured by load cell system. In the experimental aeroelastic analysis, the flutter frequency and the flutter amplitude were measured at different velocities ranging from 10 to 30 m/s using an oscillator generator system.

### **3.2 Wing model**

Two wing models with the parameter and dimension are shown in **Figure 10** and **Table 4**. The non-structure wing had only balsa wood, while the structure wing had balsa wood for skin and carbon rod and hard wood for the inner parts.

#### **3.3 Results**

Experimental results showed that a flutter phenomenon appeared with the non-structure wing (broken wing in **Figure 10c**), but this phenomenon did not happen with the structure wing model. It could be explained by the more durability of structure wing than that of the non-structure wing with the testing range of velocity. Experiments also demonstrated that the combination of multiple materials to more durability of structure of wing could be highly effective in preventing flutter phenomenon [18].

The measurement results of the non-structure wing were shown in **Table 5**. When the attack angle increased, the velocity of first oscillation, flutter velocity, and frequency decreased.

**Figure 11** resumed the measurement of the force at the wing root in varying velocities from zero to flutter velocity and more by using the load cell system. After increasing the air velocity from zero to the limit of non-structure wing, the limit

*Research on Aeroelasticity Phenomenon in Aeronautical Engineering DOI: http://dx.doi.org/10.5772/intechopen.91748*

#### **Figure 10.**

This remark illustrated that the developed solution could be used to specify the

**Velocity (m/s) Density (kg/m<sup>3</sup>**

Baskut [6] 171.84 0.3987 21.67 Yates [13] 172.5 0.42770 20.39 Simulation 174.257 0.43164 18.87 Relative error with [13] 1% 1% 7%

The test model was set in AF6116 (M = 0.1) subsonic wind tunnel located at the Hanoi University of Science and Technology, which was of a blowdown type

varied up to 30 m/s, where the Reynolds number based on wing root chord was 10<sup>6</sup>

Flutter characteristics were determined with the help of the frequency meter and load cell, which allowed to specify the flutter frequency and root wing force, respectively. The oscillated frequency was measured by the DT-2234C+ frequency meter. The signal of measured frequency was averaged by five measurements. The force applied to the wing was measured by load cell system. In the experimental aeroelastic analysis, the flutter frequency and the flutter amplitude were measured at different velocities ranging from 10 to 30 m/s using an oscillator generator

Two wing models with the parameter and dimension are shown in **Figure 10** and **Table 4**. The non-structure wing had only balsa wood, while the structure wing

Experimental results showed that a flutter phenomenon appeared with the non-structure wing (broken wing in **Figure 10c**), but this phenomenon did not happen with the structure wing model. It could be explained by the more durability of structure wing than that of the non-structure wing with the testing range of velocity. Experiments also demonstrated that the combination of multiple materials to more durability of structure of wing could be highly effective in preventing

The measurement results of the non-structure wing were shown in **Table 5**. When the attack angle increased, the velocity of first oscillation, flutter velocity,

**Figure 11** resumed the measurement of the force at the wing root in varying velocities from zero to flutter velocity and more by using the load cell system. After increasing the air velocity from zero to the limit of non-structure wing, the limit

had balsa wood for skin and carbon rod and hard wood for the inner parts.

). The wind speed could be arbitrarily

**) Frequency at flutter (Hz)**

,

transonic flutter characteristics with errors less than 10%.

with a closed test section (0.4 0.5 1.0 m<sup>3</sup>

which was driven by an 8 kW electric motor.

**3. Experimental method**

*Flutter characteristics at M = 0.499.*

**3.1 Experimental setup**

system.

**Table 3.**

*Aerodynamics*

**3.2 Wing model**

**3.3 Results**

**64**

flutter phenomenon [18].

and frequency decreased.

*Experimental models. (a) Wing model. (b) Wing with support. (c). Broken wing.*


#### **Table 4.**

*Wing models.*


#### **Table 5.**

*Flutter characteristics at different attack angles—Non-structure wing.*

**Figure 11.**

*Force at the wing root of the non-structure wing—Attack angle 10°.*

velocity of non-structure wing was found at 19.5 m/s. The load at the wing root of this wing at flutter velocity is shown in **Figure 12**. The maximum force was 5.44 N, and the minimum force was 4.32 N.

The frequencies of the first and second modes of the non-structure wing were higher than those of the structure wing, while the frequencies of third and fourth mode of structure wing were higher than those of non-structure wing (**Table 6**). Considering both wings in the first mode of oscillation, when the force was applied to the wing, the amplitude of the non-structure wing was higher than that of the structure wing (**Figure 13**). In conclusion, the non-structure wing was easier to

Fluid flow and deformation of structure were governed by the following equa-

ð5Þ

ð6Þ

ð7Þ

ð8Þ

ð9Þ

ð10Þ

resonate than the structure wing.

*DOI: http://dx.doi.org/10.5772/intechopen.91748*

tions with assumption of linear elastic structure [11]:

*Research on Aeroelasticity Phenomenon in Aeronautical Engineering*

**4. IBM method**

**4.1 Methodology**

where:

**67**

u: fluid velocity vector p: fluid pressure

Re: Reynolds number Uc: displacement velocity ωp: angular velocity xc: center of gravity θp: rotation of wing r mp: mass of wing

f: force that affected on wing

Ip: inertial moment of wing

F: force created by fluid passing through the wing T: moment created by fluid passing through the wing

To solve out these equations using IBM method, the most important was that the

velocity of fluid at fluid-solid interface was equal to the velocity of the wing. It means that the interaction force (f) between the wing and fluid was calculated such that the boundary condition of fluid was satisfied on the surface of the wing. IBM method used the Cartesian grid and immersed boundary that were illus-

trated in **Figure 14**, in which the moving surface of wing was described by

With structure wing, different modes of vibration appeared depending on the characteristics of the structure as remarked in [8]. With the help of the oscillator generator system, the specific oscillation frequencies of the first four modes were estimated as shown in **Table 6**.

**Figure 12.**

*Force at the wing root of the non-structure wing—Attack angle 10° and velocity 19.5 m/s.*


#### **Table 6.**

*Specific oscillation frequency of the non-structure and structure wings.*

**Figure 13.** *Amplitude of oscillation of the structure wing—Mode 1.*

*Research on Aeroelasticity Phenomenon in Aeronautical Engineering DOI: http://dx.doi.org/10.5772/intechopen.91748*

The frequencies of the first and second modes of the non-structure wing were higher than those of the structure wing, while the frequencies of third and fourth mode of structure wing were higher than those of non-structure wing (**Table 6**). Considering both wings in the first mode of oscillation, when the force was applied to the wing, the amplitude of the non-structure wing was higher than that of the structure wing (**Figure 13**). In conclusion, the non-structure wing was easier to resonate than the structure wing.
