Comparison between fiber bragg gratings and conventional pressure sensor in surface pressure analysis of generic transport aircraft

Abstract

UTM-LST model is a semi span model of aircraft wing which is scaled as 9% of generic transport. This model is important in investigating aircraft wing aerodynamic performance such as lift, drag and shear forces acting on the wing in various conditions. These forces affect an important aircraft flight parameter which is pressure coefficient, Cp and flight performance due to air vortex formation. The established technique for measuring Cp is using conventional static pressure sensors embedded into the wing model. This work focuses on measurement of Cp and locating air vortex formation on the UTM-LST half model surface. Two techniques, namely, fiber Bragg gratings (FBGs) strain sensor and static pressure sensors were employed for these purposes and measurement were performed inside a low speed wind tunnel. The FBGs strain sensor was placed as close as possible to the pressure sensor taps to allow more accurate comparison of Cp measurement between these two techniques. The wind tunnel test was conducted at the wind speed, v in the range of 20 m s -1 to 40 m s -1 and the angle of attack, a in the range of 0° to 20°. The results revealed that FBGs sensors are capable in measuring Cp and to locate the air vortex formation on the wing. The Cp values obtained using FBGs were well in agreement with Cp values obtained using conventional static pressure sensors except the Cp obtained at separation region. The Cp measured using FBGs experiences strain due to air pressure from all directions is not only from wind flow but from vortices as well. The Cp obtained by pressure sensor is only affected by pressure difference. Thus, Cp measured using FBGs is higher than the one measured by pressure sensors. The formation of air vortex using FBGs can then be determined based on the location on wing that has a higher Cp from FBGs sensor compared to the one measured using conventional pressure sensors. In conclusion, the FBG strain sensor can be used as an alternative technique to determine Cp and to locate air vortex formation.