Calculations and measurements of heat transfer in a square duct with inclined ribs

37th Aerospace Sciences Meeting and Exhibit

1999

Computations were performed to investigate the three-dimensional flow and heat transfer about a flat, a convex, and a concave surface cooled by jets, injected from a plenum through one row of film-cooling holes inclined at 35' with a density ratio of 1.6 and mass flux ratio of 0.5. The focus is on understanding how the mainflow distorts the jets issuing from the film-cooling holes and how the resulting interactions affect film cooling effectiveness and temperature distribution. Results are presented for the surface effectiveness, normalized temperature, velocity vector field, and contours of the vorticity magnitude. The computed results for the surface effectiveness on a flat plate were compared with experimental data, and reasonably good agreements were obtained.This computational study is based on the ensemble-averaged conservation equations of mass, momentum (compressible NavierStokes), and energy closed by a low Reynolds number k-o/SST turbulence model (i.e., wall functions were not used). Solutions were generated by a cell-centered finite-volume method that uses secondorder accurate flux-difference splitting of Roe, multigrid acceleration of a diagonalized AD1 scheme with local time stepping, and patched/overlapped structured grids. In the computations, the flow is resolved not just in the cooling-jet/mainflow interaction region, but also inside the film-cooling holes and in the plenum. NOMENCLATURE D diameter of film-cooling hole DR density ratio of coolant to mainflow (p&ph) I momentum-flux ratio of coolant to mainflow (M?

Section: Numerical Methods Of Solutionmentioning

confidence: 99%

Film cooling over flat, convex, and concave surfaces

Lin

37th Aerospace Sciences Meeting and Exhibit

1999

“…Other rules include aligning grid lines with flow direction as much as possible and keeping grid-aspect ratio near unity in regions with recirculating flow. For further details on "rules of thumb," see Stephens, et al (1996). As a further test, grids were refined by a factor of 25% in each direction.…”

Section: Numerical Methods Of Solutionmentioning

confidence: 99%

Computations of Film Cooling From Holes With Struts

Volume 3: Heat Transfer; Electric Power; Industrial and Cogeneration

Lin

Chyu

et al. 1999

Computations were performed to study the three-dimensional flow and heat transfer on a flat plate cooled by jets, injected from a plenum through one row of film-cooling holes in which each hole is fitted with a strut in the form of a circular cylinder. Three different configurations of the film-cooling hole were investigated: without strut, with strearnwise strut, and with spanwise strut For all configurations, the film-cooling holes are inclined at 35°, and the coolant-to-mainflow density and mass-flux ratios are 1.6 and 0.5, respectively. The focus of this study is to understand how struts in holes affect film cooling jets and their interactions with the mainflow in forming a protective layer of cooler fluid over the plate.This computational study is based on the ensemble-averaged conservation equations of mass, momentum (compressible Navier-Stokes), and energy. Effects of turbulence was modeled by a low Reynolds number k-co closure known as the shear-stress-transport (SST) model. Solutions were generated by a cell-centered finitevolume method that uses third-order accurate flux-difference splitting of Roe with limiters, multigrid acceleration of a diagonalized ADI scheme with local time stepping, and patched/overlapped structured grids. In the computations, the flow is resolved not just in the cooling-jet/mainflow interaction region, but also inside the filmcooling holes and in the plenum. Computed results for adiabatic effectiveness for the case without struts were compared with experimental data, and reasonably good agreements were obtained.

“…The grid system used was arrived by satisfying a set of "rules of thumb" needed to obtain grid independent solutions such as having five grid points within y+ of 5. The rules and the process can be found in Stephens, et al (1996a), and will not be repeated here.…”

Section: Numerical Methods Of Solutionmentioning

confidence: 99%

“…In that problem, the geometry of the duct and rib is identical to that studied here for the up-leg portion of the U-duct. The computed heat-transfer enhancement for that problem was compared with measurements obtained by using liquid crystal thermography (see Stephens, et al (1996a)). The comparisons showed that the code used can predict the qualitative features very well.…”

Section: Numerical Methods Of Solutionmentioning

confidence: 99%

“…Unlike the temperature profile, the velocity profile at the inlet was not uniform but taken to be "fully developed" in the sense that any changes in the profile are due to pressure changes needed to overcome drag. The process used to generate the velocity profile is given in Stephens, et al (1996a). The Reynolds number at the inlet was Re = piViDh/g; = 25,000.…”

Section: Description Of Problemmentioning

confidence: 99%

See 1 more Smart Citation

Computation of Compressible Flow and Heat Transfer in a Rotating Duct With Inclined Ribs and a 180-Degree Bend

Stephens

Volume 3: Heat Transfer; Electric Power; Industrial and Cogeneration

1997

Computations were performed to study the three-dimensional flow and heat transfer in a U-shaped duct of square cross section with and without ribs under rotating and staggered inclined ribs of rounded cross sections on the leading and trailing walls. Parameters investigated include: two rotation numbers (0, 0.24), two density ratios (0.13, 0.22), and smooth versus ribbed walls at a Reynolds number of 25,000 and an inlet Mach number of 0.05. For the conditions of the present study, rib-induced secondary flows were found to dominate over those induced by the Coriolis force in terms of flow pattern. This shifted tendency for flow separation induced by centrifugal buoyancy from the leading wall to the outer-side wall for radially outward flow. The secondary flows induced by the 180-degree bend were found to be comparable to that induced by the ribs, creating very complex interactions in flow and surface heat transfer characteristics. The computations are based on the ensemble-averaged conservation equations of mass, momentum (compressible Navier-Stokes), and energy closed by a low Reynolds number k-ω model of turbulence. Solutions were generated by using a cell-centered finite-volume method based on flux-difference splitting and a diagonalized alternating-direction implicit scheme with multigrid.