Direct numerical simulation of shock wave/boundary layer interaction controlled by steady microjet in a compression ramp

Shock wave/boundary layer interaction in a 24°turning angle of the compression ramp at Mach number 2.9 controlled by steady microjet is investigated using direct numerical simulation.Three different jet spacings which are termed as sparse,moderate and dense are considered,and the induced vortex system and shock structures are compared.A moderate jet spacing configuration is found to generate counter-rotating vortex pairs that transport high-momentum fluid towards the vicinity of wall and strengthen the boundary layer to resist separation,reducing the separation region.The dense jet spacing configuration creates a larger momentum deficit region,reducing the friction downstream of the corner.Analysis of pressure and pressure gradient reveals that dense jet spacing configuration reduces the intensity of separation shock.The impact of varying jet spacings on the turbulent kinetic energy transport mechanism is also investigated by decomposing the budget terms in the transport equation.Furthermore,the spectral characteristics of the separation region are studied using power spectral density and dynamic mode decomposition methods,revealing that moderate jet spacing configuration suppresses low-frequency fluctuations in the separation region.

A CLIMATOLOGY OF EXTRATROPICAL TRANSITION OF TROPICAL CYCLONES IN THE WESTERN NORTH PACIFIC

Based on best-track data and JRA-25 reanalysis,a climatology of western North Pacific extratropical transition (ET) of tropical cyclone (TC) is presented in this paper. It was found that 35% (318 out of 912) of all TCs underwent ET during 1979-2008. The warm-season (June through September) ETs account for 64% of all ET events with the most occurrence in September. The area 120°E-150°E and 20°N-40°N is the most favorable region for ET onsets in western North Pacific. The TCs experiencing ET at latitudes 30°N-40°N have the greatest intensity in contrast to those at other latitude bands. The distribution of ET onset locations shows obviously meridional migration in different seasons. A cyclone phase space (CPS) method was used to analyze the TC evolution during ET. Except for some cases of abnormal ET at relatively high latitudes,typical phase evolution paths-along which TC firstly showed thermal asymmetry and an upper-level cold core and then lost its low-level warm core-can be used to describe the main features of ET processes in western North Pacific. Some seasonal variations of ET evolution paths in CPS were also found at low latitudes south of 15°N,which suggests different ET onset mechanisms there. Further composite analysis concluded that warm-season ETs have generally two types of evolutions,but only one type in cold season (October through next May). The first type of warm-season ETs has less baroclinicity due to long distance between the TC and upper-level mid-latitude system. However,significant interactions between a mid-latitude upper-level trough and TC,which either approaches or is absorbed into the trough,and TC's relations with downstream and upstream upper-level jets,are the fingerprints for both a second type of warm-season ETs and almost all the cold-season ETs. For each type of ETs,detailed structural characteristics as well as precipitation distribution are illustrated by latitude.

GUE via Frobenius Manifolds.I.From Matrix Gravity to Topological Gravity and Back

Dubrovin establishes a certain relationship between the GUE partition function and the partition function of Gromov-Witten invariants of the complex projective line.In this paper,we give a direct proof of Dubrovin’s result.We also present in a diagram the recent progress on topological gravity and matrix gravity.