Recent progress on the study of asymmetric vortex flow over slender bodies

The investigations of forebody vortex flow and its flow control have great importance in both academic field and engineering application areas. A large number of papers and many review papers have been published. However in this research field of forebody asymmetric vortices, three problems such as tip perturbation effect, Reynolds number effect and flow instability are less studied and thus not understood completely. So many researches are still working on the issues in recent years. The present paper attempts to provide a review of recent research progress on first two problems. The first problem is mainly concerned with how the vortex flow evolves after tip perturbation; how to solve the problem of repeatability and reproducibility of wind tunnel testing data; how to develop a conception of active flow control technique with tip perturbation based on the study of vortex flow response to tip perturbation. For the second problem one is mainly concerned that how the asymmetric vortices are developed with the increase of Reynolds number; how to classify the vortex flow patterns in different Reynolds number regimes; how to develop an appropriate boundary layer transition technique to simulate flows at high Reynolds number in the convention wind tunnels. Finally, some important ques- tions that deserve answers are proposed in the concluding remarks.

Investigation of Possible Half-Metallic Antiferromagnets on Double Perovskites A_(2)BB′O_(6)(A=Ca,Sr Ba;B,B′=Transition Metal Elements)

A search was made for possible half-metallic(HM)antiferromagnet(AFM)in all the(C_(2)^(92)=406)double perovskites structures of Sr2BB′O6 where BB′pairs are any combination of 3d,4d or 5d transition elements with the exception of La.Sr can also be replaced by Ca or Ba whenever HM-AFM was found and similar calculations were then performed in order to probe further possibilities.It was found that A_(2)MoOsO_(6),A_(2)TcReO_(6),A_(2)CrRuO_(6),where A=Ca,Sr,Ba,are all potential candidates for HM-AFM.The AFM of A2BB′O6 comes from both the superexchange mechanism and the generalized double exchange mechanism via the B(t2g)-O2pp-B′(t2g)coupling,With the latter also being the origin of their HM.Also considered were the effects of spin-orbit coupling(SOC)and correlation(+U)by introducing+SOC and+U corrections.It is found that the SOC effect has much less influence than the correlation effect on the HMproperty of the compounds.For A_(2)TcReO_(6)and A_(2)CrRuO_(6),after+U,they become nearlyMott-Insulators.In the future,it is hoped that therewill be further experimental confirmation for these possible HM-AFMcandidates.

First-Principle Calculations of Half-Metallic Double Perovskite La_(2)BB'O_(6)(B,B'=3d transition metal)

In this paper,we present calculations based on density functional theory using generalized gradient approximation(GGA)in double perovskite structure La_(2)BB'O_(6)(B,B'=3d transition metal)out of 45(C_(2)^(10))combinational possibilities.Considering 4 types of magnetic states,namely,ferromagnetic(FM),ferrimagnetic(FiM),antiferromagnetics(AF),and nonmagnetic(NM)with full structure optimization,13 possible surviving,stable FM/FiM-HM materials containing 6 FM-HM materials(La_(2)ScNiO_(6),La_(2)CrCoO_(6),La_(2)CrNiO_(6),La_(2)VScO_(6),La_(2)VZnO_(6),and La_(2)VNiO_(6))and 7 FiM-HM materials(La_(2)VFeO_(6),La_(2)ZnCoO_(6),La_(2)TiCoO_(6),La_(2)CrZnO_(6),La_(2)CrMnO_(6),La_(2)ScFeO_(6),and La_(2)TiMnO_(6))are found.Considering the correlation effect(GGA+U),there are 6 possible half-metallic stable,surviving(HM)materials containing 3 FMHM materials(La_(2)ScNiO_(6),La_(2)CrCoO_(6),and La_(2)CrNiO_(6))and 3 FiM-HM materials(La_(2)VFeO_(6),La_(2)ZnCoO_(6),and La_(2)TiCoO_(6)).