The turbulent flow inside a rotating channel provided with transverse ribs along one wall is studied by means of two-dimensional time-resolved particle image velocimetry. The measurement set-up is mounted on the same rotating disk with the test section, allowing to obtain the same accuracy and resolution as in a non-rotating rig. The Reynolds number is 15 000, and the rotation number is 0.38. As the ribbed wall is heated, both the Coriolis force and the centrifugal force play a role in the fluid dynamics. The mean velocity fields highlight the major impact of the rotational buoyancy (characterized by a buoyancy number of 0.31) on the flow along the leading side of the duct. In particular, since the flow is directed radially outward, the near-wall layers experience significant centripetal buoyancy. The recirculation area behind the obstacles is enlarged to the point of spanning the whole inter-rib space. Also the turbulent fluctuations are significantly altered, and overall augmented, with respect to the non-buoyant case, resulting in higher turbulence levels far from the rib. On the other hand the centrifugal force has little or no impact on the flow along the trailing wall. Vortex identification, proper orthogonal decomposition, and two-point correlations are used to highlight rotational effects, and in particular to determine the dominant scales of the turbulent unsteady flow, the time-dependent behavior of the shear layer and of the recirculation bubble behind the wall-mounted obstacles, the lifetime and advection velocity of the coherent structures.

The continuous demand from the airlines for reduced jet engine fuel consumption results in increasingly challenging high pressure turbine nozzle guide vane (NGV) working conditions. The capability to reproduce realistic boundary conditions in a rig at the combustor-turbine interaction plane is a key feature when testing NGVs in an engine-representative environment. A large scale linear cascade rig to investigate NGV leading edge cooling systems has been designed with particular attention being paid to creating engine representative conditions at the inlet to the NGVs. The combustor simulator replicates the main features of a rich-burn design including large dilution jets and extensive endwall film cooling. A three-dimensional computational domain including the entire combustor simulator has been created and RANS CFD simulations have been run in order to match Reynolds number and mainstream-to-coolant momentum flux ratio; velocity and turbulence measurements have been acquired at the NGV inlet plane at ambient temperature. In this engine-representative environment the authors focused their attention on the flow field downstream of different endwall film cooling holes configurations: three arrangements of a double row of staggered cylindrical holes (lateral pitch-to-diameter ratio of 2–3–6) and one with intersecting holes (intersecting angle of 90°) are experimentally and numerically analyzed. Velocity, turbulence intensity and integral length scales are predicted and measured for a density ratio of 1 and coolant-to-mainstream momentum flux of 6. A hot wire sensor was mounted on a two-axis traverse mechanism able to move the probe in the spanwise and lateral directions. Three slots allowed to reposition the traverse and take measurements at three downstream locations (stream-wise distance-to-diameter ratio of 4.2–9.2–14.2). The research confirmed the strong influence of the endwall coolant on the flow field at the NGV inlet plane and the hole spacing results a key parameter in managing the film development. Closer-spaced hole configurations can assure an effective film coverage. The integral length scales are strongly connected to the hole diameter and spacing. Intersecting holes can potentially reduce the amount of required coolant at a fixed pressure ratio, but they offer worst film performance than cylindrical holes. RANS simulations proved to be able to get the main trends shown by the measurements.

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To ensure adequate cooling and avoidance of hot gas ingestion, a high pressure turbine nozzle guide vane must maintain a safe pressure margin by which the film coolant static feed pressure exceeds the hot gas total pressure. This pressure margin is lowest for cooling holes near the stagnation region, especially near the coolant inlet. This study investigates an insert device which increases the pressure margin in these ingestion risk regions by altering the coolant passage geometry, potentially allowing engine performance gains via reduced combustor pressure loss requirements. Seven parametrically varied inserts are compared within a pressure-tapped, cooled vane model, and design rules are suggested. For correctly designed inserts, pressure margin results show significant improvement in the ingestion risk region, without causing ingestion risks elsewhere. An analytical model of combined converging, diverging and prismatic coolant channels is validated by experimental data to be capable of accurately predicting coolant pressure margins.

The present contribution addresses the effect of Coriolis and buoyancy forces in a rotating rectangular channel having one wall provided with ribs perpendicular to the flow direction. Time-resolved PIV measurements are performed in a rotating facility where both the channel model and the measurement system rotate on a turntable at 134 rpm. Air is used as working fluid. The Reynolds number defined by the bulk velocity and the hydraulic diameter is 15000, and a rotation number of 0.38 is obtained both in clockwise and counter-clockwise sense. The ribbed wall, machined out of copper, is heated to a uniform temperature of about 100°C by means of electrical resistances. This allows to obtain a centrifugal buoyancy number of 0.31. Velocity fields are measured along the channel symmetry plane using a continuous laser diode and a high-speed camera. Both ensemble-averaged and time-resolved measurements are performed. In the latter case the realizations are acquired at 3.3 KHz, allowing to resolve the fine temporal flow scales. The effects of the rotational buoyancy with respect to the action of the Coriolis forces alone are highlighted. Particular attention is drawn to the extension of the separated area behind the rib, as well as to the length scales and time scales of the structures generated on the separated shear layer behind the ribs. Vortical structures are identified as regions of strong swirl having both spatial and temporal coherence. The rotational buoyancy near the heated wall affects strongly the physical characteristics, distribution and trajectory of such structures, which are critical for the turbulent transport and heat transfer.