| 1. |
- Jia, Rongguang, et al.
(författare)
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A low-re RSTM model for computations of heat transfer and fluid flow for impingement and convective cooling
- 2004
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Ingår i: Proceedings of the ASME Turbo Expo 2004. ; 3, s. 429-438
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Konferensbidrag (refereegranskat)abstract
- A new Reynolds stress transport model (RSTM) aimed for engineering applications is proposed with consideration of near-wall turbulence. This model employs the SSG pressure strain term, the ω equation, and the SST model for the shear stresses at the near-wall region (say y+ less than or equal 30). The models are selected based on the following merits: The SSG RSTM model performs well in the fully turbulent region and does not need the wall normal vectors; the ω equation can be integrated down to the wall without damping functions; The SST model is a proper two-equation model that performs well for flows with adverse pressure gradient, while most two-equation models can have a good prediction of the shear stresses. A function is selected for the blending of the RSTM and SST. Three cases are presented to show the performance of the present model: (1) fully developed channel flow with Reτ = 395, (2) backward-facing step with an expansion ratio of 1.2 and Re = 5,200 base on the step height, (3) circular impingement with the nozzle-to-wall distance H = 4D and Re = 20,000.
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| 2. |
- Jia, Rongguang, et al.
(författare)
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A new low Reynolds stress transport model for heat transfer and fluid in engineering applications
- 2007
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Ingår i: Journal of Heat Transfer. - : ASME International. - 0022-1481 .- 1528-8943. ; 129:4, s. 434-440
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Tidskriftsartikel (refereegranskat)abstract
- A new Reynolds stress transport model (RSTM) aimed for engineering applications is proposed with consideration of near-wall turbulence. This model employs the Speziale, Sarkar and Gatski (SSG) pressure strain term, the omega equation, and the shear stress transport (SST) model for the shear stresses at the near-wall region (say, y(+) < 30). The models are selected based on the following merits: The SSG RSTM model performs well in the fully turbulent region and does not need the wall normal hectors; the omega equation can be integrated down to the wall without damping functions. The SST model is a proper two-equation model that performs wall for flows with adverse pressure gradient, while most two-equation models can have a good prediction of the shear stresses. A function is selected for the blending of the RSTM and SST Three cases are presented to show the performance of the present model: (i) fully developed channel flow with Re-tau=395, (ii) backward-facing step with an expansion* ratio of 1.2 and Re =5200 base on the step height, and (iii) circular impingement with the nozzle-to-wall distance H=4D and Re =20,000. It is believed that the new model has good applicability for complex flow fields.
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| 3. |
- Jia, Rongguang, et al.
(författare)
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A numerical,and experimental investigation of the slot film-cooling jet with various angles
- 2005
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Ingår i: Journal of Turbomachinery. - : ASME International. - 1528-8900 .- 0889-504X. ; 127:3, s. 635-645
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Tidskriftsartikel (refereegranskat)abstract
- Numerical simulations coupled with laser Doppler velocimetry (LDV) experiments were carried out to investigate a slot jet issued into a cross flow, which is relevant in the film cooling of gas turbine combustors. The film-cooling fluid injection from slots or holes into a cross flow produces highly complicated flow,fields. In this paper, the time-averaged Navier-Stokes equations were solved on a collocated body-fitted grid system with the shear stress transport k-omega, V2F k-epsilon, and stress-omega turbulence models. The fluid flow and turbulent Reynolds stress fields were compared to the LDV experiments for three jet angles, namely, 30, 60, and 90 deg, and the jet blowing ratio is ranging from 2 to 9. Good agreement was obtained. Therefore, the present solution procedure was also adopted to calculations of 15 and 40 deg jets. In addition, the temperature fields were computed with a simple eddy diffusivity model to obtain the film-cooling effectiveness, which, in turn, was used for evaluation of the various jet cross-flow arrangements. The results show that a recirculation bubble downstream of the jet exists for jet angles larger than 40 deg, but it vanishes when the angle is < 30 deg, which is in good accordance with the experiments. The blowing ratio has a large effect on the size of the recirculation bubble and, consequently, on the film cooling effectiveness. In addition, the influence of boundary conditions for the jet and cross flow are also addressed in the paper.
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| 4. |
- Jia, Rongguang, et al.
(författare)
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Computational analysis of heat transfer enhancement in square ducts with V-shaped ribs: Turbine blade cooling
- 2005
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Ingår i: Journal of Heat Transfer. - : ASME International. - 0022-1481 .- 1528-8943. ; 127:4, s. 425-433
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Tidskriftsartikel (refereegranskat)abstract
- Experimental studies have revealed that both downstream and upstream pointing V-shaped ribs result in more heat transfer enhancement than transverse straight ribs in ducts. However, based on the available experimental results, contradiction exists whether the upstream or the downstream pointing V-shaped ribs orientation is superior for better enhancement in heat transfer. Further investigations are thus needed concerning the heat transfer and fluid flow phenomena in ducts with V-shaped ribs to clarify this. In the present investigation a numerical approach is taken and the heat and fluid flow is numerically simulated by a multi-block parallel 3D solver For turbulence modeling, the (v(2)) over bar f-k epsilon model is employed but results from previous EASM calculations are also considered in analyzing and attempting to understand the various expert. mental data. Large eddy simulations (LES) are also carried to evaluate the accuracy and reliability of the results of Reynolds-averaged Navier-Stokes (RANS) methods and to understand the underlying physical phenomena. It is suggested that the discrepancy between the various experiments most probably is due to the measurement methods, or the number of sampling points. With the TC (thermocouples) technique, a few sampling points are not sufficient to represent the heat transfer behavior in V-shaped ribs, due to the uneven distribution of the heat transfer coefficients.
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| 5. |
- Jia, Rongguang, et al.
(författare)
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Heat transfer enhancement in square ducts with V-shaped ribs
- 2003
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Ingår i: Journal of Turbomachinery. - : ASME International. - 1528-8900 .- 0889-504X. ; 125:4, s. 788-791
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Tidskriftsartikel (refereegranskat)abstract
- This paper concerns a numerical investigation of the heat and fluid flow in V-shaped ribbed ducts. The Navier-Stokes equations and the energy equation are solved in conjunction with a low Reynolds number k-epsilon turbulence model. The Reynolds turbulent stresses are computed with an explicit algebraic stress model (EASM) while the turbulent heat fluxes are calculated with a simple eddy diffusivity model (SED). Detailed velocity and thermal field results have been used to explain the effects of the V-shaped ribs and the mechanisms of the heat transfer enhancement.
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| 6. |
- Jia, Rongguang, et al.
(författare)
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Heat transfer enhancement in square ducts with V-shaped ribs of various angles
- 2002
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Ingår i: American Society of Mechanical Engineers, International Gas Turbine Institute, Turbo Expo (Publication) IGTI. ; 3 A, s. 469-476
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Konferensbidrag (refereegranskat)abstract
- Experimental studies have revealed that both downstream and upstream pointing V-shaped ribs result in better heat transfer enhancement than transverse straight ribs of the same geometry. Secondary flows induced by the angled ribs are believed to be responsible for this higher heat transfer enhancement. Further investigations are needed to understand this. In the present study, the heat and fluid flow in V-shaped-ribbed ducts is numerically simulated by a multi-block 3D solver, which is based on solving the Navier-Stokes and energy equations in conjunction with a low-Reynolds number k-ε turbulence model. The Reynolds turbulent stresses are computed with an explicit algebraic stress model (EASM), while turbulent heat fluxes are calculated with a simple eddy diffusivity model (SED). Firstly, the simulation results of transverse straight ribs are validated against the experimental data, for both velocity and heat transfer coefficients. Then, the results of different rib angles (45° and 90°) and Reynolds number (15,000 - 30,000) are compared to determine the goodness of different rib orientations. Detailed velocity and thermal field results have been used to explain the effects of the inclined ribs and the mechanisms of heat transfer enhancement.
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| 7. |
- Jia, Rongguang, et al.
(författare)
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Impingement cooling in a rib-roughened channel with cross-flow
- 2001
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Ingår i: International Journal of Numerical Methods for Heat & Fluid Flow. - : Emerald. - 1758-6585 .- 0961-5539. ; 11:7, s. 642-662
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Tidskriftsartikel (refereegranskat)abstract
- A numerical investigation to determine the velocity and heat transfer characteristics of multiple impinging slot jets in rib-roughened channels in the presence of cross-flow has been carried out. Fluid flow is modeled using an explicit algebraic stress model. A simple eddy diffusivity and a generalized gradient diffusion hypothesis are applied for the modeling of turbulent heat fluxes. The computations are validated against available experimental fluid flow and heat transfer data. Different size and arrangement of jets and ribs are considered in detail, while the Reynolds numbers of a jet and the channel inlet are fixed at 6,000 and 14,000, respectively. Results show that the ratio (B/W) between the size of the jets and ribs is most important. An explanation is that the ribs inhibit the motion of eddies by preventing them from coming very close to the surface when B/W is low, e.g. B/W = 1, although the ribs will increase the turbulence intensity. This blockage limited the heat transfer enhancement effect of the ribs and impinging jets.
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| 8. |
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| 9. |
- Jia, Rongguang, et al.
(författare)
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Multiblock implementation strategy for a 3-D pressure-based flow and heat transfer solver
- 2003
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Ingår i: Numerical Heat Transfer Part B: Fundamentals. - : Informa UK Limited. - 1040-7790 .- 1521-0626. ; 44:5, s. 457-472
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Tidskriftsartikel (refereegranskat)abstract
- This article reports on a multiblock implementation of a general three-dimensional single-block computational fluid dynamics code, which is developed in a nonorthogonal, structured, collocated finite-volume grid system, and incorporates a range of turbulence models. The multiblock implementation is essentially block-unstructured, each block having its own local coordinate system unrelated to those of its neighbors. Any of the blocks may interface with more than one neighbor along any block face. Interblock communication is handled by inner-boundary connection information (receive and send point index arrays) and effected via two-layer dummy cells along interblock boundaries. This communication procedure is easy to extend to parallel computation. The implementation of the algorithm, which takes the advantage of Fortran 90, employs a method to keep most of the single-block code unchanged. Two cases are presented to validate the implementation, and another case with a block number ranging from 1 to 160 blocks is presented for test of the influence of the multiblocking on the convergence rate and execution time.
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| 10. |
- Jia, Rongguang, et al.
(författare)
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Numerical and experimental study of the slot film cooling jet with various angles
- 2003
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Ingår i: Proceedings of the ASME Summer Heat Transfer Conference. - 0791836959 ; 2003, s. 845-856
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Konferensbidrag (refereegranskat)abstract
- Numerical simulations coupled with LDV experiments were carried out to investigate a slot jet issued into a cross flow, which is relevant in the film cooling of gas turbine combustors. The film cooling fluid injection from slots or holes into a cross-flow produces highly complicated flow fields. In this paper, the time-averaged Navier-Stokes equations were solved on a collocated body-fitted grid system with the V2F turbulence model. The fluid flow and turbulent Reynolds stress fields were compared with the LDV experiments for three jet angles, namely, 30-deg, 60-deg, and 90-deg, and the jet blowing ratio is ranging from 2 to 9. Good agreement was obtained. Therefore, the present solution procedure was also adopted to calculations of 15-deg and 40-deg jets. In addition, the temperature fields, which were difficult to measure by experimental methods, were also computed with a simple eddy diffusivity model to obtain the film cooling effectiveness which was used for evaluation of the various jet-cross-flow arrangements. The results show that a recirculation bubble downstream the jet exists for jet angles larger than 40-deg, but it vanishes when the angle is less than 30-deg, which is in good accordance with the experiments. The blowing ratio has a large effect on the size of the recirculation bubble, and consequently on the film cooling effectiveness. In addition, the influence of boundary conditions for the jet and cross-flow are also addressed in the paper.
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