Aerothermal Characteristics of a Mixing Layer on a Multiperforated Plate

In the aeronautics field, engine manufacturers are continually confronted with the cooling problems associated with walls in contact with overheating gases. In such situations, full coverage film cooling techniques are commonly used to protect aeronautic engine walls. For example, the first stage of gas turbine rotor or stator as well as the combustion wall chamber need to be protected from the ever-increasing temperature of combustion products. The present experimental work is an attempt to both better understand the behaviour of the flow obtained on several rows of 30° inclined staggered jets and to control heat transfers. When the ambient temperature injected flow meets the hot main flow (its temperature ranges from ambient temperature to 60°C), it should protect the wall from the main flow. The wall is heated by electric dissipated power and maintained at constant heat flux. The number of injection rows may vary from 0 to 9. So, we can observe cold layer formation in function of the successive opening rows. Experiments are carried out for different injection rates (M = 3 to 5) as well. Injection flow velocity is maintained constant and equal to 7.5m/s. Association of temperature profile measurement by thermocouples and wall temperature measurement with infrared thermography allows us to describe the behaviour of the flows and to propose the injection leading to the most satisfactory cooling of the plate. Using wall temperature measurement with infrared thermography, we write the heat balance at the wall and present the results in form of heat transfer coefficient h variations and film cooling effectiveness η variations. The analysis of these results suggests an optimal number of injection rows and may enable researchers to determine the topology of the mixing layer and to thereby more effectively control their use of wall cooling techniques.