The simultaneous measurement of temperature and velocity plays an important role in research on turbulent combustion which is a complex problem coupled of fluid dynamics and chemical reaction dynamics.With the rapid development of laser combustion diagnosis technology, researchers have studied many schemes of simultaneous measurement of multi-parameters, such as temperature and velocity, by means of multi-technology combination and extending the multi-parameter measurement function of measurement technology. The principle of hydroxyl tagging velocimetry (HTV) is to dissociate with water molecules in the flow by lasers which produce ion OH^- as tagging particles (OH_P). Combined with the technique, plane laser-induced fluorescence (PLIF), OH_P can be displayed in certain positions at different time. It is unnecessary to inject extra tracer particles into the flow field without a particle-following problem. OH_P, the tagging molecule, is of long life in a high-temperature environment, which has the advantage of measuring velocity in flow with high temperature and velocity. The technique has been widely applied to obtain the velocity of various flows such as super-combustion ramjet engines. The technique of temperature acquiring through double-color PLIF and fluorescence intensity of OH_P is configured based on OH_P on the basis of HTV, making it possible to accomplish simultaneous measurement of temperature and velocity of flows. In this paper, the principle and the configuration of the set-up are fully illustrated, while an experiment to verify the technique used in the flow of temperature is conducted.

The key to simultaneously measuring velocity and temperature based on HTV is how to realize temperature measurement based on OH_P. In this paper, two methods of temperature measurement are studied, one of which is the two-line PLIF temperature measurement method. On the basis of the PLIF device used to display the image of OH_P in HTV technology, another set of PLIF devices is added to build the double-color PLIF, realizing the temperature measurement. The variation of OH_P fluorescence intensity with laser dissociation and fluorescence excitation time delay under different excitation lines (Fig. 1) is obtained by experiments. It can be concluded that OH_P has reached the state of thermal equilibrium with the surrounding environment when the delay time is more than 500 ns, and OH_P can be used as a probe to monitor temperatures in the flow. It is proven to be probable that temperature and velocity can be simultaneously acquired by OH_P. The other method is using OH_P fluorescence intensity to measure temperature. Analyzing the relationship among OH_P fluorescence intensity, temperature, and intensity of fluorescence is monotonically changeable as the temperature of the objects changes when appropriate fluorescence excitation is selected (Fig. 3). Therefore, temperature can be observed by fluorescence intensity.

The simultaneous measurement of velocity and temperature is tested and verified in the electric heating flow field and the flow field of the super-combustion ramjet engine. Compared with results obtained by thermocouple, in the range from room temperature to 900 K, the average standard deviation of temperature measurement based on PLIF is 12.1 K (Fig. 6). The maximum deviation of temperature measurement based on photolysis OH_P fluorescence intensity is 16.8 K, with the uncertainty of velocity measurement less than 1% (Fig. 10). In the flow of super-combustion ramjet engine, data of temperature measured by CARS serve as baseline to acquire the results of temperature and velocity on the tagging line simultaneously. The maximum deviation between them is 44 K (Fig. 11).

In this paper, simultaneous measurement of velocity and temperature based on HTV technology is presented, which extends the function of HTV technology and provides a new scheme for simultaneous measurement of temperature and velocity in flow fields with high speed and high temperature.