Flow structure and surface heat transfer from numerical predictions for a double wall effusion plate with impingement jet array cooling

Abstract

To provide additional understanding of double wall cooling arrangements, especially local distributions of flow properties which are responsible for hot-side surface and cold-side surface heat transfer variations, investigated are numerically-simulated distributions of turbulent flow structural characteristics. Also considered are numerically-simulated surface heat transfer characteristics, including comparisons with experimentally-measured distributions. The numerical results are obtained using the ANSYS FLUENT Version 19.1 numerical code, with a k-ω SST turbulence model. The present arrangement includes a full-coverage effusion cooling plate, with coolant initially supplied by an impingement jet array. Considered are the effects of effusion blowing ratio, impingement jet Reynolds number, and streamwise development on flow structure, and on hot-side and cold-side surface heat transfer characteristics. Data are obtained for an approximately constant main flow Reynolds number of 138000 to 159000, with blowing ratios from 2.2 to 8.5, which correspond to impingement jet Reynolds numbers from 7360 to 25200. Of particular importance are horseshoe-shaped vortices, which form upstream and around each effusion jet, which then result in two horseshoe-originated vortex legs which advect downstream along coolant trajectories. Also important are secondary flows, local flow separation regions, and local velocity regions, which are evident within the effusion hole passages near entrance locations. Within the cross flow passage, locally increased flow velocities, associated with impingement jet locations, are apparent, especially near the lower surface of the cross flow passage. These are associated with regions of augmented streamwise vorticity, which are present around the circumference of each impingement jet.

Introduction

Considered is the simultaneous use of full coverage effusion cooling and impingement jet array cooling, as employed for thermal protection of combustor liner components of gas turbine engines. Only a few papers are available within the literature, which describe the simultaneous use of effusion and impingement cooling. Recent past investigations, which utilize such an arrangement, include Andrews, et al. [1], Al Dabagh, et al. [2], Andrews, et al. [3], and Andrews and Nazari [4]. Cho and Rhee [5] present spatially-resolved, local mass transfer coefficients for the impingement target surface of an effusion plate. The impingement perforated plate and effusion perforated plate are located such that holes within the two plates are either staggered or shifted relative to each other. A more recent investigation by Hong et al. [6] addresses the influences of fin shape and arrangement on surface heat transfer characteristics for an impingement/effusion cooling configuration with cross flow. Cho et al. [7] consider effects of hole arrangements on local surface heat transfer characteristics for a similar impingement/effusion cooling arrangement, with relatively small hole spacing, where hole pitch to diameter ratio is 3.0, and distances between perforated plates varies from 1 to 3 hole diameters. Shi et al. [8] examine mainstream-side, cooling effectiveness for an arrangement, wherein the same streamwise spacing and spanwise spacing are employed for both the effusion and impingement holes, such that one impingement hole is present for each effusion hole. El-Jummah et al. [9] consider the influences of wall conjugate heat transfer on impingement/effusion cooling arrangements using computational fluid dynamics numerical predictions. El-Jummah et al. [10] investigate the effects of a reduced number of impingement jet holes, relative to the number of effusion holes, in regard to magnitudes of surface heat transfer characteristics for internal walls within impingement/effusion configurations. Oguntade et al. [11] discuss data which are obtained using conjugate heat transfer, computational fluid dynamics predictions. For a range of coolant mass flux values, the investigators indicate that overall cooling effectiveness for impingement/effusion cooling is superior, compared to effusion cooling alone, especially near upstream locations within the effusion cooling array.

Of interest within the present investigation are numerically-simulated distributions of flow structural characteristics for a double wall cooling configuration, especially local distributions of flow properties which are responsible for hot-side surface and cold-side surface heat transfer variations. The originality of the present study is provided by detailed, numerically-predicted flow structural characteristics (and the insight into physical behavior provided by these characteristics), which are difficult or impossible to measure within an experimental environment. As such, the present investigation is unique and novel, with results that are different from the data which are given in recent, previous investigations [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11]. Also considered are numerically-simulated surface heat transfer characteristics, including comparisons with experimentally-measured distributions [12,13]. The numerical results are obtained using the ANSYS FLUENT Version 19.1 numerical code, with a k-ω SST turbulence model. The present arrangement includes a full-coverage effusion cooling plate, with coolant initially supplied by an impingement jet array. Considered are the effects of effusion blowing ratio, impingement jet Reynolds number, and streamwise development on turbulent flow structure, and on hot-side and cold-side surface heat transfer characteristics. Data are obtained for an approximately constant main flow Reynolds number of 138,000 to 159,000, with blowing ratios from 2.2 to 8.5, which correspond to impingement jet Reynolds numbers from 7360 to 25,200. Here, blowing ratio is coolant mass flux divided by local main flow freestream mass flux.

The advantage of the present combustor liner cooling configuration is a result of the double wall arrangement. As such, thermal protection is provided on both the hot side and the cold side of the liner plate. Cold side protection is provided by heat transfer augmentation, resulting from the impact of an array of impingement cooling jets. Hot side protection is provided by surface heat transfer reductions, produced by a layer of effusion coolant produced by an array of angled holes.