Numerical Investigation on Sand Particles Deposition in a U-Bend Ribbed Internal Cooling Passage of Turbine Blade

Sand particles impinge the internal cooling passage of the turbine blade and easily deposit, which lead to the decrease of cooling efficiency of the turbine blade and the increase of turbine blade temperature. In order to explore sand particles deposition mechanism in the internal cooling passage of turbine blades, the numerical simulation was performed in a U-bend passage with rib turbulators by means of a commercial CFD code. The fluid phase was modelled employing Reynolds-averaged Navier-Stokes approach. The discrete phase was solved using Lagrangian particle tracking method and a continuous random walk model. A particle deposition model was implemented using user-defined functions. The Reynolds numbers of 30000, 23000 and 15500 are considered. Particles sizes in the range 1–20 microns are considered. Results show that the particles deposition flux decreases gradually along the flow direction. The particles significantly deposit on the rib wall and the bend wall, especially on the windward rib wall and the upstream wall of the bend, with less deposition on the leeward rib wall. This is because the rib wall hinders the movement of fluid and sand particles impact the wall due to inertia, which lead to the energy loss. The particles deposition flux on the windward rib wall increases with the increase of Reynolds number and particles diameter, while the deposition flux on the leeward rib wall decreases. With the increase of the particles diameter, the particles deposition flux increases. The deposition rate increases with the increase of Reynolds number and particles diameter.

Experimental and Numerical Investigation of the Flow in a Trailing Edge Ribbed Internal Cooling Passage

The flow field in a ribbed triangular channel representing the trailing edge internal cooling passage of a gas turbine high-pressure turbine blade is investigated via magnetic resonance velocimetry (MRV) and large eddy simulation (LES). The results are compared to a baseline channel with no ribs. LES predictions of the mean velocity fields are validated by the MRV results. In the case of the baseline triangular channel with no ribs, the mean flow and turbulence level at the sharp corner are small, which would correspond to poor heat transfer in an actual trailing edge. For the staggered ribbed channel, turbulent mixing is enhanced, and flow velocity and turbulence intensity at the sharp edge increase. This is due to secondary flow induced by the ribs moving toward the sharp edge in the center of the channel. This effect is expected to enhance internal convective heat transfer for the turbine blade trailing edge.

Numerical Investigation on the Modified Bend Geometry of a Rotating Multipass Internal Cooling Passage in a Gas Turbine Blade

The present work is aimed to investigate whether the modification to the bend geometry of a multipass internal cooling passage in a gas turbine blade can enhance heat transfer and reduce pressure drop. The two-pass channel and the four-pass channel are modified at the bend from the U shape to the bulb and bow shape. The first objective of the work is to investigate whether the modified design will still improve heat transfer with reduced pressure drop in a four-pass channel as in the case of a two-pass channel. It is found out that, unlike the two-pass channel, the heat transfer is not improved but the pressure drop is still reduced for the four-pass channel. The second objective is to investigate the rotating effect on heat transfer and pressure drop in the cases of two-pass and four-pass channels for both original and modified designs. It is found out that heat transfer is improved with reduced pressure drop for all cases. However, the modified design results in the less improvement on heat transfer and lower reduced pressure drop as the rotation number increases. It can be concluded from the present work that the modification can solve the problem of pressure drop without causing the degradation of heat transfer for all cases. The two-pass channel with modified bend results in the highest heat transfer and the lowest pressure drop for rotating cases.

Experimental and Numerical Investigation of the Flow in a Trailing Edge Ribbed Internal Cooling Passage

The flow field in a ribbed triangular channel representing the trailing edge internal cooling passage of a gas turbine high pressure turbine blade is investigated via Magnetic Resonance Velocimetry (MRV) and Large Eddy Simulation (LES). Results are compared to a baseline channel with no ribs. LES predictions of the mean velocity fields are validated by the MRV results. In the case of the baseline triangular channel with no ribs, the mean flow and turbulence level at the sharp corner are small, which would correspond to poor heat transfer in an actual trailing edge. For the staggered ribbed channel, turbulent mixing is enhanced, and flow velocity and turbulence intensity at the sharp edge increase. This is due to secondary flow induced by the ribs moving toward the sharp edge in the center of the channel. This effect is expected to enhance internal convective heat transfer for the turbine blade trailing edge.

Effect of Rib Density on Flow and Heat Transfer in an Internal Cooling Passage

Effect of rib density on mechanism of flow and heat transfer enhancement in an internally-cooled channel with rib turbulators have been investigated numerically. Based on the experimental setup in the previous study [32], flowfield and heat transfer coefficient distributions were predicted with LES approach. The rib pitch-to-height ratios were 3 and 11, and Reynolds number based on the channel hydraulic diameter and bulk velocity was set at 30,000. Comparison of time-averaged flow and heat transfer characteristics between numerical and experimental results showed that prediction accuracy of the present numerical setup was reasonable. The previous study [33] suggested that, for higher rib density, low-frequency velocity fluctuation characterizes heat transfer. To investigate its flow and heat transfer mechanism, instantaneous velocity and temperature fields were compared. For smaller rib density, small vortices constantly occurred from each rib and were dissipated into the mainstream before reaching the next rib. On the other hand, for higher rib density, relatively large vortex occurs above the ribs in addition to smaller vortices inside the cavity between the ribs. The large vortex occurs intermittently behind the second rib of the channel, and increases its size by interacting with smaller vortex downstream. For each rib pitch, similar trend was observed in the measured result obtained using Particle Image Velocimetry. This unsteady vortex structure would contribute to enhancing the heat transfer of a cooling channel with densely-arranged rib turbulators.

Effects of Crossflow in an Internal-Cooling Channel on Film Cooling of a Flat Plate Through Compound-Angle Holes

CFD simulations were performed to study the film cooling of a flat plate from one row of compound-angles holes fed by an internal-cooling passage that is perpendicular to the hot-gas flow. Parameters examined include direction of flow in the internal cooling passage and blowing ratios of 0.5, 1.0, and 1.5 with the coolant-to-hot-gas density ratio kept at 1.5. This CFD study is based on steady RANS with the shear-stress transport (SST) and realizable k-ε turbulence models. To understand the effects of unsteadiness in the flow, one case was studied by using large-eddy simulation (LES). Results obtained showed an unsteady vortical structure forms inside the hole, causing a side-to-side shedding of the coolant jet. Values of adiabatic effectiveness predicted by CFD simulations were compared with the experimentally measured values. Steady RANS was found to be inconsistent in its ability to predict adiabatic effectiveness with relative error ranging for 10% to over 100%. LES was able to predict adiabatic effectiveness with reasonable accuracy.