The bluff body cut from a small circular cylinder that is cut at both sides parallel to the y-axis was used as passive control to reduce the drag of a larger circular cylinder. The small bluff body cut is called an I-type bluff body, which interacts with a larger one downstream. I-type bluff bodies with different cutting angles of θ s = 0 • (circular), 10 • , 20 • , 30 • , 45 • , 53 • , and 65 • were located in front and at the line axis of the circular cylinder at a spacing S/d = 1.375, where their cutting surfaces are perpendicular to the free stream velocity vector. The tandem arrangement was tested in a subsonic wind tunnel at a Reynolds number (based on the diameter d of the circular cylinder and free stream velocity) of Re = 5.3 × 10 4 . The results show that installing the bluff bodies (circular or sliced) as a passive control in front of the large circular cylinder effectively reduces the drag of the large cylinder. The passive control with cutting angle θ s = 65 • gives the highest drag reduction on the large circular cylinder situated downstream. It gives about 0.52 times the drag of a single cylinder.

No abstract

The present studies investigate the performance of a small Savonius vertical axis wind turbine equipped with an upstream obstacle to guide the wind direction. The wind tunnel measurement was carried out in a test facility at the Mechanical Engineering Department, Institut Teknologi Sepuluh Nopember (ITS). The dynamic torque was measured using the brake dynamometer. Several variations of the obstacle orientations were investigated. Two different wind speeds of 2.48 m/s and 7.45 m/s were considered, that correspond to the Reynolds numbers of 30,000 and 90,000, respectively, according to the rotor diameter. It is found from the studies that the mechanical torque and power generated by the rotor are strongly affected by the obstacle. On the other hand, the Reynolds number has no significant impact on the rotor performance.

We consider two-dimensional numerical simulation of a tandem configuration of both I-shape cylinder and circular cylinder. Diameter of circular cylinder is D as the bluff body and I-shaped cylinder has diameter of d with a cutting angle 53 o as passive control, that is located in front of the bluff body. Navier Stokes equations are used to solve this problem and solved with a finite difference method. When we put the Reynolds number of R e = 7 × 10 3 , the domain distance between bluff body and passive control is a 0.6 ≤ S/D ≤ 3.0 and X/D = 2.0 then we obtain profile streamline around the bluff body, pressure distribution, separation point on the top around the 65 o and on the bottom around 285 o , wake and mathematics models of drag coefficient.

Nine existing mixture viscosity models were tested for predicting a two-phase pressure drop for oil-water flow and refrigerant (R.134a) flow. The predicted data calculated by using these mixture viscosity models were compared with experimental data. Predicted data from using one group of mixture viscosity models had a good agreement with the experimental data for oil-water two-phase flow. Another group of viscosity models was preferable for gas-liquid flow, but these models gave underestimated values with an error of about 50%. A new and more reliable mixture viscosity model was proposed for use in the prediction of pressure drop in gas-liquid two-phase flow.