Skin friction reduction characteristics of variable ovoid non-smooth surfaces

The use of bionic non-smooth surfaces is a popular approach for saving energy because of their drag reduction property. Conventional non-smooth structures include riblets and dimples. Inspired by sand dunes, a novel variable ovoid non-smooth structure is proposed in this study. The body of the variable ovoid dimple was designed based on three size parameters, the radius, semimajor, and depth, and a 3D model was created based on UG software. The constructed variable dimples were placed in a rectangular array on the bottom of a square tube model. Following ANSYS meshing, the grid model was imported into FLUENT, where the flow characteristics were calculated. Results of skin friction reduction were achieved and the effect of the design parameters on different variable ovoid dimples was obtained by orthogonal testing. Various aspects of the skin friction reduction mechanism were discussed including the distribution of velocity vectors, variation in boundary layer thickness, and pressure distribution.

The effect of surgical skin tension reduction combined with early electronic line irradiation on keloid treatment after median sternotomy

Background Median sternotomy remains the preferred technique in open heart surgery. The middle part of the chest is a predilection site for keloids. Keloids are often accompanied by itching and pain, and seriously affect the beauty and quality of life. The main treatments of keloids include surgical resection, local injection of drugs, laser, cryotherapy, compression therapy, and topical application of silica gel. Unfortunately, there is no way to achieve superior results. Therefore, there is a need to find an effective way to treat keloid after median sternoto- my. Our study was designed to investigate the effect of reducing the tension of the skin and the early electronic line irradiation on the treatment of keloid after median sternotomy. Methods A retrospective analysis was per- formed in 54 patients with keloid after median sternotomy treated by reducing the tension of the skin and remov- ing the keloid, followed with electron beam irradiation treatment 24 hours after the operation. For each patient, 5 Gy electron beam irradiation was used every day after the operation for 4 days with the total dose of 20 Gy. The patients were followed up at 6 months and 12 months after surgery. Results Fifty-four cases of patients were followed up for at least 6 months. In 6 months follow-up, there were significant effects in 34 cases with a total effective rate of 98.1%. In 12 months follow-up, 33 cases were cured with the total effective rate was 96.3%. Conclusion The treatment of keloid after median sternotomy can be achieved by the combination of tension re- duction surgery and early electronic line irradiation.

Characteristics of array of distributed synthetic jets and effect on turbulent boundary layer

An array of distributed round synthetic jets was used to control a fully developed turbulent boundary layer.The study focused on the related skin friction drag reduction and mechanisms involved.The control effects were analyzed by measuring the streamwise velocities using a hot-wire anemometer downstream of the array.A reduction in the skin friction was observed both in the regions downstream of the orifices and in the regions between two adjacent orifices.A statistical analysis with the variable-interval time-averaging(VITA)technique demonstrated a weakened bursting intensity with synthetic jet in the near-wall region.The streamwise vortices were lifted by the upwash effect caused by synthetic jet and induced less low-speed streaks.The control mechanism acted in a way to suppress the dynamic interaction between the streamwise vortices and low-speed streaks and to attenuate the turbulence production in the near-wall region.The forcing frequency was found to be a more relevant parameter when synthetic jet was applied in turbulent boundary layer flow control.A higher forcing frequency induced a higher reduction in the skin friction.The power spectral density and autocorrelation of the fluctuating velocities showed that the synthetic jets gradually decayed in the streamwise direction,having an effect as far as 34.5 times the displacement thickness that was on the trailing edge of the distributed synthetic jets array.