Film Cooling From a Row of Holes Supplemented With Anti Vortex Holes

Abstract

The primary focus of this paper is to study the film cooling performance for a row of cylindrical holes each supplemented with two symmetrical anti vortex holes which branch out from the main holes. The anti-vortex design was originally developed at NASA-Glenn Research Center by Dr. James Heidmann, co-author of this paper. This “anti-vortex” design is unique in that it requires only easily machinable round holes, unlike shaped film cooling holes and other advanced concepts. The hole design is intended to counteract the detrimental vorticity associated with standard circular cross-section film cooling holes. The geometry and orientation of the anti vortex holes greatly affect the cooling performance downstream, which is thoroughly investigated. By performing experiments at a single mainstream Reynolds number of 9683 based on the free stream velocity and film hole diameter at four different coolant-to-mainstream blowing ratio of 0.5, 1, 1.5, 2 and using the transient IR thermography technique, detailed film cooling effectiveness and heat transfer coefficients are obtained simultaneously from a single test. When the anti vortex holes are nearer to the primary film cooling holes and are developing from the base of the primary holes, better film cooling is accomplished as compared to other anti vortex hole orientations. When the anti vortex holes are laid back in the upstream region, film cooling diminishes considerably. Although an enhancement in heat transfer coefficient is seen in cases with high film cooling effectiveness, the overall heat flux ratio as compared to standard cylindrical holes is much lower. Thus cases with anti vortex holes placed near the main holes certainly show promising results.

Flow Visualization of Multi-Hole Film-Cooling Flow under Varying Freestream Turbulence Levels

“…The hole diameter and Reynolds number and the plenum condition from this past study are consistent with the current work. It can be seen that there is a large amount of area downstream of a hole that is not covered at all by the coolant, which is typical of straight cooling holes and has been studied extensively in previous work [7] [10]- [16]. The hole spacing is three hole diameters as is consistent with practice in real engines for cylindrical holes.…”

“…Dhungel et al [7] reported that for a single hole geometry case, similar to that shown in Figure 6, the cooling hole effectiveness reduces as the blowing ratio is increased from 1.0 to 2.0. A study conducted by Kim and Hassan [1] with a single hole geometry by using RANS and URANS simulations with blowing ratio 1.0 showed that the predicted maximum cooling effectiveness along the centerline was less than 0.5 and this occurs only at a limited x/d region.…”

“…The current study presents the results of numerical study to visualize a multi-hole concept, the anti-vortex hole (AVH) that has been documented in previous studies [5]- [7]. The anti-vortex hole concept is shown in the current study as well as the previous studies to have its performance enhanced with elevated mainstream turbulence levels.…”

“…The geometry examined in this study was selected from the study by Dhungel et al [7] that compared six different anti-vortex hole geometries. The geometry for this study was selected as the best performing cooling geometry as well as the most practically machined geometry from the six cases previously tested.…”

Parametric Study on Anti-Vortex Film Cooling Hole Arrangements

“…Consequently, it improves the film effectiveness compared to a standard hole case for the same blowing ratios. Dhungel et al [7] further confirm the superiority of the anti-vortex cooling hole by investigating it performance four different blowing ratios. The results indicate better downstream and lateral film coverage leads to improved overall film cooling effectiveness.…”