5 Experimental Fluid Mechanics
373
Fig. 5.31 Six-component force balance
in the wind tunnel and the determination of acceleration by means of a
high-speed camera. The aerodynamic forces and aerodynamic moments are
calculated according to Newton’s second law. In order to make the aircraft
have good stability and maneuverability, it is also necessary to know the
derivative of the angular change rate of aerodynamic forces and aerodynamic
moments acting on the model, that is, the dynamic derivative. In a wind
tunnel, the dynamic derivative can be measured by a balance that is freely
vibrating or forced to vibrate, or it can be reversed by a free-flight test.
(5) Surface friction measurement method
It is often required to measure the surface shear stress when studying viscous
flow. In addition to the indirect method, the friction balance can be directly
measured. The friction balance often uses a differential transformer or a strain
sensor, a thermal film, and a Prius tube.
5.7 Test Error Analysis
Measurement and analysis are indispensable means and ways for human
beings to understand the laws governing the development of things. Through
experimentation and measurement, people can obtain qualitative concepts
and quantitative relationships with things, and rise to rationality through
processing analysis, and discover the general regularity of things development. Many new discoveries and breakthroughs in science are done on the
basis of experiments. An important purpose of the test is to obtain the quantitative relationship between the physical quantities through measurement,
so it is necessary to carefully examine the accuracy of the physical quantity measurement, which inevitably leads to the measurement error and its
analysis.
373
Fig. 5.31 Six-component force balance
in the wind tunnel and the determination of acceleration by means of a
high-speed camera. The aerodynamic forces and aerodynamic moments are
calculated according to Newton’s second law. In order to make the aircraft
have good stability and maneuverability, it is also necessary to know the
derivative of the angular change rate of aerodynamic forces and aerodynamic
moments acting on the model, that is, the dynamic derivative. In a wind
tunnel, the dynamic derivative can be measured by a balance that is freely
vibrating or forced to vibrate, or it can be reversed by a free-flight test.
(5) Surface friction measurement method
It is often required to measure the surface shear stress when studying viscous
flow. In addition to the indirect method, the friction balance can be directly
measured. The friction balance often uses a differential transformer or a strain
sensor, a thermal film, and a Prius tube.
5.7 Test Error Analysis
Measurement and analysis are indispensable means and ways for human
beings to understand the laws governing the development of things. Through
experimentation and measurement, people can obtain qualitative concepts
and quantitative relationships with things, and rise to rationality through
processing analysis, and discover the general regularity of things development. Many new discoveries and breakthroughs in science are done on the
basis of experiments. An important purpose of the test is to obtain the quantitative relationship between the physical quantities through measurement,
so it is necessary to carefully examine the accuracy of the physical quantity measurement, which inevitably leads to the measurement error and its
analysis.