Investigation On Pumping Performance Of Multi-nozzles Supersonic Ejector In A Radiator Passage

For the most modern turbo-prop aircrafts,the lubricant oil radiator air-cooled passage is commonly located at the bottom of the turbo-prop engine,where the radiator is cooled by air or propeller slipstream.When the aircraft is in the cruising state,there is enough cooling air in the radiator passage due to the great dynamic pressure of air.However,little propeller slipstream can get through the passage in the state of taking off,especially under ground idle state.In these situations,the air flow capacity in the radiator passage is very little due to nearly zero dynamic pressure of air,thus can not satisfy the cooling requirement of radiator.In addition,there is a great flow resistance in the passage because of the existence of radiator,which makes the flowing of cooling air difficult.All of these causes would make lubricant oil get an over limited temperature.Aimed at a specific lubricant oil radiator air-cooled passage used in a turbo-prop aircraft,the pumping performance of a multi-nozzles supersonic ejector is numerically and experimentally investigated in the current study,in order to improve the air flow mass in the radiator passage.The porous medium model is introduced for modeling the pressure drop across the radiator on the basis of pressure drop-velocity relationship which is derived from experimental test.And then the effects of flow resistance across radiator,multi-nozzles arrangement,nozzle exit shape and propeller slipstream on the pumping performance are numerically analyzed.The results indicate that in the idle state the additional pressure drop across the porous medium matrix has a very significant influence on the pumping performance.The pumping ratio of ejector decreases with the increase of flow resistance across radiator.For a specified porous medium model used in the passage,the pumping ratio decreases as the rise of pressure ratio between the primary flow and second flow.Given the same parameters of porous model and total throat area of multi-nozzles,the multi-nozzles ejector of single piccolo tube achieves a better pumping performance than the double piccolo tubes.With regard to the single piccolo tube,the pumping ratio increases firstly and then decreases with the increase of multi-nozzles arrangement parameter ?.Under the same ?,it is found that the circular nozzle exit shape produces a bigger pumping ratio than the chevron nozzle or lobe nozzle.In the state of taking off,the propeller slipstream brings a significant influence on the flow field of the secondary flow.In comparison with the condition that the radiator is cooled by the pure slipstream,the use of ejector in the radiator passage is capable of increasing the mass flow rate of secondary flow and making the secondary flow field more uniform.Besides the numerically analysis,experimental tests are performed for some typical experimental models.The effects of flow resistance across porous medium matrix,multi-nozzles arrangement,and nozzle exit shape on the pumping performance are experimentally analyzed.The results indicate that the factors mentioned above have similar influences on the pumping performance of ejector with the results from CFD simulations.