The interaction of flow and film-cooling effectiveness between jets of double-jet film-cooling (DJFC) holes on a flat plate is studied experimentally. The time-averaged flow field in several axial positions (X/d = −2.0, 1.0, and 5.0) is obtained through a seven-hole probe. The downstream film-cooling effectiveness on the flat plate is measured by pressure sensitive paint (PSP). The inclination angle (θ) of all the holes is 35 deg, and the compound angle (β) is ±45 deg. Effects of the spanwise distance (p = 0, 0.5d, 1.0d, 1.5d, and 2.0d) between the two interacting jets of DJFC holes are studied, while the streamwise distance (s) is kept as 3d. The blowing ratio (M) varies as 0.5, 1.0, 1.5, and 2.0. The density ratio (DR) is maintained at 1.0. Results show that the interaction between the two jets of DJFC holes has different effects at different spanwise distances. For a small spanwise distance (p/d = 0), the interaction between the jets presents a pressing effect. The downstream jet is pressed down and kept attached to the surface by the upstream one. The effectiveness is not sensitive to blowing ratios. For mid-spanwise distances (p/d = 0.5 and 1.0), the antikidney vortex pair dominates the interaction and pushes both of the jets down, thus leading to better coolant coverage and higher effectiveness. As the spanwise distance becomes larger (p/d ≥ 1.5), the pressing effect almost disappears, and the antikidney vortex pair effect is weaker. The jets separate from each other and the coolant coverage decreases. At a higher blowing ratio, the interaction between the jets of DJFC holes happens later.

This paper is focused on the heat transfer augment ability and friction factor of different cross-section pin fins. An experimental study is conducted in a wide rectangular channel. The steady-state thermochromic liquid crystals (TLC) method is applied to measure the tested surface temperature. Nine sets of pin fins are employed in the experiment. The nominal diameter of all pin fins is the same value. Nine sets of pin fins have three roundness shapes (Circle, Ellipse and Oblong), three streamline shapes (Dropform, NACA and Lancet) and three quadrangle shapes (Diamond, Diamond-s and Square), respectively. The arrangement parameters of all nine shapes are kept the same. As they have the same nominal diameter and arrangement, the channel blockage ratio is the same for each pin fin set. Reynolds numbers range from 10,000 to 60,000. The pressure losses of pin fin arrays are measured to obtain friction factor. Meanwhile, the overall thermal performances of all nine sets are also considered and compared. The results show heat transfer enhancement abilities of quadrangle shape pin fins are relatively higher than the roundness and streamline shapes. Diamond-s pin fins present the largest averaged Nusselt number and overall thermal performance on the endwall for all the nine pin fins under different Re. Concerning overall thermal performance, the traditional Circle pin fin is the second best. The pressure loss of streamline shape pin fins is the lowest in these three shape types. Moreover, the characteristic of local heat transfer distribution varies substantially for different pin shapes at low Re.

The film cooling effectiveness distribution and its uniformity downstream of a row of film cooling holes on a flat plate are investigated by pressure sensitive paint (PSP) under different density ratios. Several hole geometries are studied, including streamwise cylindrical holes, compound-angled cylindrical holes, streamwise fan-shape holes, compound-angled fan-shape holes, and double-jet film-cooling (DJFC) holes. All of them have an inclination angle (θ) of 35 deg. The compound angle (β) is 45 deg. The fan-shape holes have a 10 deg expansion in the spanwise direction. For a fair comparison, the pitch is kept as 4d for the cylindrical and the fan-shape holes, and 8d for the DJFC holes. The uniformity of effectiveness distribution is described by a new parameter (Lateral-Uniformity, LU) defined in this paper. The effects of density ratios (DR = 1.0, 1.5 and 2.5) on the film-cooling effectiveness and its uniformity are focused. Differences among geometries and effects of blowing ratios (M = 0.5, 1.0, 1.5, and 2.0) are also considered. The results show that at higher density ratios, the lateral spread of the discrete-hole geometries (i.e., the cylindrical and the fan-shape holes) is enhanced, while the DJFC holes is more advantageous in film-cooling effectiveness. Mostly, a higher lateral-uniformity is obtained at DR = 2.5 due to better coolant coverage and enhanced lateral spread, but the effects of the density ratio on the lateral-uniformity are not monotonic in some cases. Utilizing the compound angle configuration leads to an increased lateral-uniformity due to a stronger spanwise motion of the jet. Generally, with a higher blowing ratio, the lateral-uniformity of the discrete-hole geometries decreases due to narrower traces, while that of the DJFC holes increases due to a stronger spanwise movement.

Flow statistic in the mid-plane of a rectangular channel with diamond-s pin fins was obtained by means of particle imaging velocimetry at Re = 10,000. Large-scale and small-scale fluctuations were separated using proper orthogonal decomposition. The flow characteristics were compared to the Nusselt number distribution on the endwall acquired by thermochromic liquid crystal to reveal the flow mechanism driving heat transfer enhancement. Results indicate that local vorticity plays an important role in strengthening Nu on both sides of leading point (Zone 1). Downstream of the two sharp edges on both sides (Zone 2), small size disturbances from shear layer eddies drive local heat transfer. The flow characteristics and heat transfer distribution downstream of the first row (Zone 3) present alternated feature along Y direction due to the interaction between shear layers of neighboring pin fins. Lateral velocity fluctuation induced by large vortex shedding drives the heat transfer augmentation in Zone 3 where there is violent large vortex shedding. Meanwhile, small size disturbances of the shear layer drive local heat transfer enhancement in Zone 3 downstream of pin fins where large vortex shedding is suppressed. For the second and third rows, there is no difference in the flow characteristics downstream of neighboring pin fins. Small-size fluctuations distributed uniformly downstream of large vortex shedding (Zone 4) resulting in a uniformly distributed Nu.

Rotating significantly alters the internal cooling of turbine rotor blades by induced Coriolis force and buoyancy force, whose effects are characterized by the nondimensional rotation number (Ro) and buoyancy parameter (Bo). The present work was carried out in a new experimental rig of rotor blade internal cooling to obtain detailed heat transfer distributions when the three nondimensional criterion numbers (i.e., Re, Ro, and Bo) are similar to aero-engine operating conditions. Smooth and ribbed two-pass internal cooling channels with a 180-deg tip turn are investigated. The hydraulic diameter is 25.4 mm (1 in.), and the aspect ratio is 2:1. The Reynolds number is fixed at 25,000, with the maximum Ro and Bo of 0.316 and 0.272, respectively. The steady-state thermochromic liquid crystal (TLC) technique is used to measure detailed heat transfer distributions in the channel. Steady-state RANS simulations are also employed to resolve the flow characteristics. The effects of rotation on the flow and heat transfer characteristics are studied in this paper. The results show effects of rotation on the heat transfer distribution present apparent spatial discrepancy, especially around the bend region. The significant difference in the influence of rotation is witnessed in the smooth and the ribbed channels.

In many machines and mechanical components, there is a need for new bearing technologies to reduce friction and wear, and provide precision control of motion when the load is varied. This can be provided by electronically controlled actuators and sensors on the surfaces, but then the system reliability can be an issue. In contrast, biomimetic surfaces can be created that adapt mechanically to variations in load. This work uses numerical methods to research the use of self-adapting surfaces for bearings that are based on the deformable nature of biological materials such as articular cartilage. These surfaces are designed to change their profiles to achieve a desired behavior, without any external control. The surfaces change their profile to control the film height and tilt of the bearing to a near constant value for different loads. If the surfaces are tilted, the grooved self-adapting surfaces will also react with a larger restoring moment than a conventional grooved surface. These surfaces could be beneficial to applications where electrical systems and controls are not feasible.