Research For Enhanced Heat Transfer Of Jet Impingement On A Confined Concave Surface

Jet impingement is an effective means for heat transfer enhancement,which has been widely used in a variety of engineering applications such as drying of textile and paper products,cooling of turbine blades and electronic components,as well as the anti-icing of aircraft wings and engine inlets,etc.With regard to the influence of target surface orientation on the jet impingement heat transfer characteristics,a great majority of the previous investigations were involved in semi-circular or hemi-spherical target configurations.In practice,the impingement surfaces with curvatures are not generally regular,i.e.the leading edge of the engine inlet strut heated by hot air impingement for anti-icing application generally has a more complex curvature than the semicircular and hemispherical concave surfaces.The jet impingement heat transfer on the complex concave surface is not well understood in details.The objective of present paper is to investigate the convective heat transfer of jet impingement on a confined concave surface.For this purpose,the present paper focusing on following aspects:With regards to the structure feature of wedge-shaped cavity,the jet-offset arrangement and corrugated orifice plate with a front-extended port inside the wedge-shaped concave cavity are proposed for the purpose of heat transfer enhancement.The results show that the jet-offset arrangement introduces a stronger complex vortex flow inside the concave cavity.As the jet-offset distance increases,the recirculation zone moves far away from the leading edge of concave cavity,which is capable to enlarge the jet impingement influence area.For the corrugated impinging plate,the presence of front-extended port plays two roles by reducing the jet impinging distance on one hand and aggravating the jet confinement on the other.Experimental and numerical investigations are conducted to study the flow and convective heat transfer characteristics of the jet-offset and corrugated orifice plate.The results show that for the jet-offset arrangement,the local Nusselt number at the stagnation in increased significantly in relative to the baseline(non-offset)case,with the increase of the jet-offset distances,the peak of laterally-averaged Nusselt number move to the wedge-shaped downstream region.In addition,the jet-offset plays a little effect on the pressure loss.Under the given conditions,it seems that the optimum non-dimensional jet-offset distance is about 1.5,which is capable to improve the heat transfer performance of the wedge-shaped surface.The corrugated impinging plate shows a significant impact on improving the conjugated heat transfer performance in the vicinity of concave wall leading edge.The enhancement of heating effectiveness related to the baseline case is more behaved under a smaller jet Reynolds number.In generally,the corrugation with larger length and width seems to perform the better heating effectiveness over the entire concave surface.The corrugated impinging plate cause high jet total pressure loss.However,increases the width of the front-extend port is helpful to decrease the pressure loss.Investigations are conducted to investigate the flow and convective heat transfer characteristics by a chevron-excited jet and satellite-hole jets on a conical-shaped concave surface.The results show that the chevron jet is proved to be capable of improving the convective heat transfer in the vicinity of the conical surface leading edge.Two main factors associated with the enhancement mechanism on the jet impingement heat transfer are illustrated.Firstly,the tilted-inward chevrons make a convergent flow of the impinging jet after issuing from the nozzle base,resulting in a larger normal velocity in the jet core and a stronger wall jet flow along the inner surface of concave cavity.Secondly,array pairs of vortices are introduced downstream the chevrons,producing more intensive jet fluctuation.As well as the satellite arrangement is proved to be capable of improving the convective heat transfer of the conical surface leading edge.At first,the presence of satellite-hole makes the center jet hole diameter decrease and jet velocity increases,which is capable of enhancing the convective heat transfer of the concave surface leading edge.Secondly,the satellite-hole jet could improve the corresponding area convective heat transfer.In addition,center jet and satellite jets introduce a complex vortex,resulting in a stronger mixing among the center jet and satellite jets.Experimental and numerical investigations are conducted to study the flow and convective heat transfer characteristics of the chevron-excited jet and satellite-hole jets.The results indicate that for a fixed chevron length,the jet impingement heat transfer as well as the heating effectiveness in the vicinity of the conical leading edge is enhanced wit the increase o the chevron penetration depth.For a fixed chevron penetration depth,the jet impingement heat transfer as well as the heating effectiveness is improved with the decrease of the chevron length.The influence of chevron penetration depth or the chevron length on the pressure loss becomes weaker gradually as the chevron penetration depth increases or the length decreases.For the satellite-hole jets impingement,under the fixed center jet diameter,the second peak heat transfer coefficiency move to the back with the satellite-hole distance increases.For a fixed satellite-hole distance,the concavity leading edge heat transfer as well as the second peak heat transfer coefficiency is improved with the decrease of the center jet diameter.The pressure loss of satellite-hole jets is higher than the conventional jet.For the composite construction of wedge-shaped and conical-shaped,the effect of geometric and inlet mass flow are experimentally and numerically investigated.The results present that for the wedge-shaped structure,the corrugated orifice plate makes a stronger influence on convective heat transfer than jet-offsert arrangement.With regards to the conical-shaped concave cavity,both of the chevron-excited jet and jet satellite-hole jets are proved to be capable of improving the convective heat transfer.However,the satellite-hole jets play a more important role with a large mass flow.Numerical investigations are fininally performed to study the water droplet particle flow and heat transfer characteristics in the wedge-shaped and conical-shaped outer channel.An obviously separate point is appeared in the position of wedge-shaped curvature becomes smaller,while the separate point is not observed in the conical-shaped outer channel flow filed.The effect of water droplet particle on the concave surface leading edge region is improved with the increase of water droplet particle content,resulting in the concave surface leading edge temperature has a significant reduction.The concave surface tail region temperature is decreased as well,however,the reduction of temperature in the tail region is evident smaller than the leading edge region.