Active control of flow structure and unsteady aerodynamic force of box girder with leading-edge suction and trailing-edge jet
EXPERIMENTAL THERMAL AND FLUID SCIENCE
Authors: Chen, Guan-Bin; Chen, Wen-Li; Gao, Dong-Lai; Yang, Zi-Feng
An experimental study was conducted to investigate the control effectiveness and underlying mechanism of the leading-edge suction and trailing-edge jet (LSTJ) for a box girder at a Reynolds number of 2.0810(4). Four circular holes were machined in the leading edge and the trailing edge of the box girder to induce steady LSTJ flow. The strength of the LSTJ is described by a dimensionless suction/jet momentum coefficient. Pressure taps around the surface associated were used with a digital sensor array system to acquire the pressure distribution of the test model. The aerodynamic forces, which macroscopically represent the control abilities of the LSTJ, were calculated based on the surface pressure distribution. The pressure measurements indicate that the fluctuating pressure on the surface near the trailing edge was attenuated and the root-mean-square value of the lift, drag, and moment forces reduced with LSTJ control. In addition to the surface pressure measurements, particle image velocimetry (PIV) was used to obtain the flow fields of the box girder model with and without LSTJ control. Both the pressure measurement and PIV results show that a certain value of the suction/jet momentum coefficient can ensure optimum control effectiveness of the LSTJ. Moreover, the LSTJ was found to push the unsteady flow structure further downstream in the model wake. A data-processing method of dynamic mode decomposition was used to illustrate the LSTJ mechanism. The energy and Strouhal number of the main mode of the LSTJ controlled case were found to differ from the uncontrolled case. The topological structure of the main mode extracted from the flow field also showed a significant variation. Linear stability analysis of the wake flow field indicates that the control method of LSTJ changes the region of unstable flow notably. Moreover, the control effectiveness of the LSTJ at various wind angles of attack was confirmed in the present study.
Does abnormal ductus venosus pulsatility index at the first-trimester effect on adverse pregnancy outcomes?
JOURNAL OF GYNECOLOGY OBSTETRICS AND HUMAN REPRODUCTION
Authors: Baran, Safak Yilmaz; Kalayci, Hakan; Durdag, Gulsen Dogan; Yetkinel, Selcuk; Arslan, Alev; Kilicdag, Esra Bulgan
Aim: The ductus venosus pulsatility index for veins (DV PIV) has become a popular marker of the first-trimester scan. The aim of this study is to search for any difference between groups with normal and abnormal DV PIV values in terms of adverse pregnancy outcomes. Methods: We retrospectively evaluated 556 women whose first-trimester scan was performed. The ductus venosus pulsatility indices were examined at singleton pregnancies between 11 and 14 weeks of gestation. Patients were categorized as Group-I with normal DV PIV (DV PIV >= 0.73, <= 1.22) and as Group-II with abnormal DV PIV. Group-II was subgrouped as Group-IIA which composed of patients with DV PIV < 0.73 and as Group-IIB with DV PIV > 1.22. Results: There were 451 subjects in Group-I and 105 subjects in Group-II (Group-IIA = 32 and Group-IIB 73). The comparisons between major groups revealed a statistically significant increase about miscarriage (p = 0.002), stillbirth (p < 0.001), small for gestational age (p = 0.033), low birth weight (p < 0.001), fetal growth restriction (p = 0.048), and major congenital heart defect (p=<0.001) in Group-II. This difference is mainly due to Group-IIB. There is no difference in preterm delivery, preeclampsia and gestational diabetes between Group I and II. Conclusion: Routinely monitoring DIV PIV as a first-trimester screening should provide valuable information regarding adverse pregnancy outcomes such as miscarriage, stillbirth, small for gestational age, low birth weight, fetal growth restriction and major congenital heart defect. (C) 2020 Elsevier Masson SAS. All rights reserved.