The Transient Measurement Of Film Heating Effectiveness And Heat Transfer Coefficient Of The Discrete Slots By The Liquid Crystal

The structure of disorder discrete slots have been applied to anti-icing system of aircraft. Amount of all anti-icing methods, hot air anti-icing system has been widely applied to the modern aircraft. The hot air source came from the compressor will be sent to the anti-icing surface through the anti-icing structures. One of these structures is the disorder discrete slots. The hot air source will inject to the surface through the discrete slots and form an hot air film to heat the surface, so that the temperature of surface will be above zero and prevent the upwind surface of aircraft accreting ice. The discharge coefficient, film heated effectiveness and heat transfer coefficient of the discrete slots will be study in this paper.The structure of disorder discrete slots will be applied to the guide vane of the engine practically. The length from the leading edge of the guide vane to the slots are 10mm and 15.2mm. The length of the slot is 13mm and the short edge is a semicircle, the diameter is 0.7mm. All of the slots incline 45° to the surface. The model was configured in similar condition according 1:2 scale. And nine experiment condition were conducted including three velocities of the mainstream and three blow ratio. When the densities variety of the mainstream and injection is negative, the blow ratio just the velocity ratio.Compared with the steady heat transfer experiment with the thermocouple in the pass time, a new technique was used in this experiment the first time, it is the transient liquid crystal technique. Because the color change of the liquid crystal has a correlation with the temperature change, so we use this characteristic to measure the distribution of temperature on the model surface.According to the practical condition in this experiment, a new condition will be considered. The mainstream and injection temperature are vary along with time compared with the step change of the mainstream temperature. Then a new measurement correlation is built up. And this condition makes the device of the experiment simple compared with the step change of mainstream temperature but the process is more complex.Except for the experiment, the numerical simulation is also used. The result ofthe numerical simulation indicates that this new measurement technique are right and can applied to this experiment.The transient liquid crystal technique had been applied to this experiment to measure the heated effectiveness and heat transfer coefficient. The major conclusion of this study are followed:Flow resistance:(l)When the velocity of mainstream is lower, the higher the blow ratio is the higher the discharge coefficient is. But when the velocity of mainstream is higher, the discharge coefficient keep a constant trend in high blow ratio.(2)The higher the velocity of mainstream is the higher the discharge coefficient is. But there is not significant difference in the maximum discharge coefficients between different mainstream velocities.Heated effectiveness:(l)The average heated effectiveness has two district, one is the roll district and another is the overlay district in the flow direction. In the roll district, the more far away from the slots the higher the average heated effectiveness is;but in the overlay district, the more far away from the slots the lower the average heated effectiveness is. And the descending trend of average heated effectiveness is slower when the mainstream velocity is higher in the flow direction of overlay district.(2)In the same blow ratio, the higher the mainstream velocity is the higher the average heated effectiveness in the overlay district is.(3)The heated effectiveness in the centerline of the slots is higher than that between slots, which indicates the distribution of heated effectiveness is not uniform in the spanwise direction.Heat transfer coefficient(l)The average heat transfer coefficient has a descending trend in the flow direction. In the same velocity of mainstream, the higher the blow ratio is the higher the average heat transfer coefficient is and in the same blow ratio, the higher velocity of mainstream is the higher the average heat transfer coefficient is.(2)The distribution of heat transfer coefficient in the spanwise direction is not uniform. The heat transfer coefficient between slots is higher than that in the centerline of slots. The nearer the slots the location is the more obviously the phenomena of disuniform is.