Detailed Flow Investigation Using PIV in a Rotating Square-Sectioned Two-Pass Cooling System With Ribbed Walls

Abstract

In a 2-pass cooling system the pressure driven air flow distribution is investigated experimentally using the non-intrusive PIV Technique. The generic model as part of a complex and sophisticated cooling system consists of two square-sectioned ducts with a length of 20 diameters and an inherent 180 degree bend. The system has been investigated basically with smooth walls (case 0) and, later on, with two different kinds of ribbed walls in both legs. Ribs are applied to enhance the cooling performance; they are placed on two opposite walls of both legs in a symmetric (case A) and an asymmetric manner (case B), respectively. The ribs are inclined with an angle of 45 degrees versus the duct axis (i.e. main flow direction). The applied rib lay-out is well-proved and optimized with respect to heat transfer improvement and the inherent pressure drop increase. The system rotates about an axis orthogonal to the centreline of the straight passes. The configuration was analyzed with the planar the two-component Particle Image Velocimetry (2C PIV), which is capable of obtaining complete maps of the instantaneous as well as the averaged flow field even at high turbulence levels, which are typically present within duct turns, near ribs and, above all, during rotation. The presented investigations were conducted in stationary and rotating mode. Especially in the bend region separation phenomena and vortices with high local turbulence are apparent. The presence of ribs changes the fluid motion by generating additional vortices impinging the side walls. Flow visualization with injected oil smoke using the laser light sheet visualization technique was helpful to detect vortex structures and separations. Especially in the bend area separation regions and vortices with high local turbulence are apparent. The results shown in this paper demonstrate the effect of the 180 degree bend in combination with the two rib turbulator geometries for isothermal flow conditions excluding any buoyancy with and without rotation. Turbulent channel flow was investigated at a Reynolds number of 50,000, derived with the hydraulic diameter of the pass, non-rotating and at a rotation number of 0.02 which was chosen still moderate. Engine relevant rotation numbers are in order of .1 or higher. A reconstruction of model mountings will allow higher values for the next tests. Future work will expand to higher rotational speed and, also, will include buoyancy effects. This investigation shall help to clarify the complex flow phenomena due to the interaction of several vortices, present in two-pass cooling systems. The flow maps obtained with PIV are of good quality and high spatial resolution and therefore provide a test case for the development and validation of numerical simulation tools like the DLR flow solver TRACE which is not a topic of this paper.

Heat Transfer Augmentation Technologies for Internal Cooling of Turbine Components of Gas Turbine Engines

“…As a result, local surface heat transfer and friction factor augmentation levels are often altered because of the presence of rotation. Figure 21 shows a typical turbine blade cooling passage arrangement from Elfert et al [50]. Here, a two-pass system is employed, which is rotating in an orthogonal mode, such that the flat surface which comprises the 180 ∘ bend between the two passes is parallel to the axis of rotation.…”

“…Such vortex pairs are illustrated in Figure 21. Experimental evidence of Coriolis vortex pairs in rotating channels is provided by Elfert et al [50] and Bons and Kerrebrock [178] from Particle Image Velocimetry (PIV) experiments, as well as by Chen and Liou [101] from Laser-Doppler Velocimetry (LDV) experiments.…”

“…Another important event associated with turning ducts is formation of a separation flow region on the inner wall of the channel immediately following the bend, as shown in Figure 24. According to Elfert et al [50], the characteristics and extent of such a separation region depend upon flow characteristics, such as flow speed, channel geometry, and channel surface condition.…”

“…Figure 27 from Huh et al [104] shows that local area-averaged Nusselt number ratios are affected by variations of the buoyancy parameter in the same approximate qualitative manner as when the rotation number changes. Note that the buoyancy parameter Acharya et al [238] Acharya et al [180] Acharya et al [129] Agarwal et al [239] Al-Hadhrami and Han [184] Azad et al [58] Bons and Kerrebrock [178] Chang et al [231] Chang and Morris [220] Chang et al [221] Chang et al [222] Chang et al [236] Chen and Liou [101] Chiang and Li [185] Cho et al [240] Cho et al [241] Cho et al [242] Dutta and Han [64] Dutta et al [232] Dutta et al [65] Dutta et al [223] Elfert et al [50] Shin et al [66] Fu et al [186] Fu et al [128] Fu et al [187] Griffith et al [208] Griffith et al [209] Hajek and Higgins [188] Hajek et al [189] Hajek et al [263] Han and Zhang [210] Han et al [190] Han et al [211] Harasgama and Morris [224] Hsieh and Hong [225] Hsieh and Liu [191] Hsieh et al [192] Huh et al [104] Huh et al…”

Particle Image Velocimetry Measurements in a Two-Pass 90 Degree Ribbed-Wall Parallelogram Channel

“…PIV measured turbulent fluid flow in smooth-wall and 90 deg ribbed square channels with a 180 deg sharp turn for Re ¼ 30,000 was reported by Son et al [31]. Elfert et al [32] reported PIV measurements in a rotating square-sectioned two-pass cooling channel with inline and staggered 45 deg ribs at Re ¼ 50,000 under isothermal flow condition. They found that rotation influenced the 3D extension of turn induced separation bubble in the second pass.…”