Sehjin Park

Effect of Manufacturing Tolerances on the Cooling Performance of Internal Rib Turbulated Passages

ABSTRACT The manufacturing tolerances of rib turbulators lead to variations in the cooling of internal ribbed passages because the manufacturing tolerances cause the actual geometry to differ some from the design which affects the flow structure as well as the coolant mass flow rate. Such variations may significantly affect the system cooling performance, and may lead to the failure of hot components. Thus, it is necessary to determine the effects of manufacturing tolerances on the cooling performance for such variations in rib turbulators in internal passages. This study numerically investigates the cooling of internal rib turbulated passages using the relationship between the geometric parameters and the coolant mass flow rate using the three-dimensional Reynolds-averaged Navier–Stokes equations for various rib heights, rib widths, wall thicknesses, and coolant mass flow rates. Correlations are developed to predict the cooling performance in response to geometric variations of the internal passages due to manufacturing tolerances. The variations in the design parameters of the internal rib turbulated cooling system has differing effects on the cooling performance, even within the same range of manufacturing tolerances.

Enhancement of Film Cooling Effectiveness Using Backward Injection Holes

Film cooling is a cooling method used to protect the hot components of a gas turbine from high temperature conditions. For this purpose, high and uniform film cooling effectiveness is required to protect the vanes/blades from excessive thermal stress. Backward injection is proposed as one of the methods for the improvement of film cooling effectiveness. In this study, experiments were performed to investigate the effect of backward injection on film cooling effectiveness, using pressure sensitive paint (PSP) method. Four experimental configurations were composed of forward and backward injection cylindrical holes. The cylindrical holes were aligned in two staggered rows with pitch (p) of 6d and row spacing (s) of 3d. The injection angles (α) of the cylindrical holes were 35° and 145° for forward and backward injection, respectively. The blowing ratios (M) ranged from 0.5 to 2.0 and the density ratio (DR) was about 1. The results indicate that backward injection enhanced not only film cooling effectiveness but also the lateral cooling uniformity. At a high blowing ratio, all configurations demonstrated higher film cooling effectiveness with backward injection than with only forward injection; thus, the dispersion of the backward injection jets enhanced the lateral coverage over wide areas. Configuration, in particular, arranged with forward injection in the first row and backward injection in the second row, obtained the highest film cooling effectiveness among the four cases studied, due to the dispersion of the backward injection jets and the coolant supply from the forward injection jets at a high blowing ratio.Copyright

Augmented Heat Transfer for Angled Rib With Intersecting Rib in Rectangular Channels of Different Aspect Ratios

This study was an experimental investigation of the effect of an intersecting rib on heat/mass transfer performance in rectangular channels with angled ribs and different aspect ratios. In a rib-roughened channel with angled ribs, heat/mass transfer performance deteriorates as the channel aspect ratio increases, since the vortices induced by angled ribs diminish with increasing aspect ratio. A longitudinal rib that bisects the angled ribs is suggested to overcome this disadvantage. The heat transfer performance of angled rib configurations with a 60° attack angle were tested with and without an intersecting rib using naphthalene sublimation method. The channel aspect ratio is varied from 1 to 4. When the intersecting rib was present, additional vortices were generated at every point of intersection with the angled ribs. Thus the heat/mass transfer performance was significantly enhanced for all channel aspect ratios when an intersecting rib was added to an ordinary angled rib configuration.Copyright

Effect of Secondary Flow Direction on Film Cooling Effectiveness

Key Words: Double-jet Film Cooling(이중분사 막냉각), Secondary Flow Channel(이차유로), Film CoolingEffectiveness(막냉각효율), Anti-Kidney Vortex(안티키드니와류), Numerical Analysis(수치해석)초록: 막냉각에관한많은연구들은주유동과이차유로가평행한형태로연구가이루어졌다. 하지만실제터빈블레이드에서이차유로의방향은일반적으로주유동의방향에수직한형태이다. 그래서본연구에서는이차유동의방향이이중분사막냉각의효율에미치는영향을수치해석을통해알아보고자한다. 분사율은1, 2이고횡방향분사각은22.5°이다. 분사율이1일때평행형상에서는안티키드니와류가잘형성되어막냉각효율이수직형상의경우보다더높다. 반면에분사율이2일때수직형상의막냉각효율은평행형상보다향상되었다. 많은유량의제트가서로반대방향으로분사되기때문에두형상모두막냉각효율이높게나타난다. 하지만안티키드니와류의영향은다른분사율보다상대적으로작다.Abstract: Several studies of film cooling were accomplished with a secondary flow channel parallel to themain flow. In real turbine blades, however, the direction of the secondary flow channel is generally normalto the main flow. Thus, this study performs a numerical analysis to investigate the effects of the direction ofsecondary flow on the effectiveness of double-jet film cooling. The blowing ratio is 1 and 2, and the lateralinjection angle is 22.5°. The parallel channel case creates a well-developed anti-kidney vortex with a blowingratio of 1, and the laterally averaged film cooling effectiveness of the parallel channel is enhanced comparedto the normal channel. The normal channel shows higher performance with a blowing ratio of 2. Both casesshow high film cooling effectiveness. These phenomena can be attributed to a high blowing ratio and flowrate rather than an anti-kidney vortex.