372
P. Liu
(3) Measurement method of density
Optical methods are generally used to measure the density of the gas stream.
The shadow method, the schlieren method, the interference method, etc., can
only be used for qualitative measurement of density, and the laser hologram
can quantitatively measure the three-dimensional density distribution of the
wind tunnel flow field. In the holography method, an interference pattern
formed by two columns of interfering light waves (signal wave and reference
wave) is recorded by a photographic method, and the light wave of the “flow
field” can be reproduced by appropriately illuminating the hologram afterwards. The holographic method records all the information of the flow field
(including phase difference, direction difference, and optical path difference),
so the reproduced light wave can be quantitatively measured afterwards (as
shown in Fig. 5.30).
(4) Measurement methods of force and moment
The aerodynamic forces and aerodynamic moments acting on the model
can usually be measured directly using a wind tunnel balance (as shown in
Fig. 5.31) and by measuring the motion of the free flying tunnel model. Freeflight force measurement is the calculation of the trajectory of free flight
Fig. 5.30 Schlieren technique
P. Liu
(3) Measurement method of density
Optical methods are generally used to measure the density of the gas stream.
The shadow method, the schlieren method, the interference method, etc., can
only be used for qualitative measurement of density, and the laser hologram
can quantitatively measure the three-dimensional density distribution of the
wind tunnel flow field. In the holography method, an interference pattern
formed by two columns of interfering light waves (signal wave and reference
wave) is recorded by a photographic method, and the light wave of the “flow
field” can be reproduced by appropriately illuminating the hologram afterwards. The holographic method records all the information of the flow field
(including phase difference, direction difference, and optical path difference),
so the reproduced light wave can be quantitatively measured afterwards (as
shown in Fig. 5.30).
(4) Measurement methods of force and moment
The aerodynamic forces and aerodynamic moments acting on the model
can usually be measured directly using a wind tunnel balance (as shown in
Fig. 5.31) and by measuring the motion of the free flying tunnel model. Freeflight force measurement is the calculation of the trajectory of free flight
Fig. 5.30 Schlieren technique