Large eddy simulation of compound angle hole film cooling with hole length-to-diameter ratio and internal crossflow orientation effects

Unsteady analysis of adiabatic film cooling effectiveness behind circular, shaped, and sand-dune–inspired film cooling holes: Measurement using fast-response pressure-sensitive paint

On the flow structure of an inclined jet in crossflow at low velocity ratios

We study experimentally a round Jet In CrossFlow (JICF) at low values of the jet-to-crossflow velocity ratio R using instantaneous and time-averaged three-dimensions three-components velocimetry. The difference between instantaneous and time-averaged swirling structures of the JICF is emphasized. Through the analysis of spatial distribution of instantaneous transverse and longitudinal vortices the main transitions of the JICF are characterized for 0.15 1.25), the classic JICF topology is recovered. In between, a deformation of the classical JICF topology is observed consisting in a progressive disappearance of the leading-edge vortices, a bending of the jet trajectory toward the wall and thus a strengthened interaction with the boundary layer. Thanks to a state-of-the-art review on the JICF topology and using visualizations of the flow structures extracted from our experimental volumetric velocimetry mea...

Transition scenario of the round jet in crossflow topology at low velocity ratios

The present experimental and numerical study focuses on the vortical structures encountered in steady and pulsed low-blowing-ratio transverse jets ( ), a configuration hardly discussed in the literature. Under unforced conditions at low blowing ratio, a stable leading-edge shear-layer rollup is identified inside the jet pipe. As the blowing ratio is increased, the destabilization and evolution of this structure sheds light on the formation mechanisms of the well-known transverse jet vortical system. A discussion on the nature of the counter-rotating vortex pair in low-blowing-ratio transverse jets is also provided. Under forced conditions, the experimental observations support and extend numerical results of previous fully modulated jet studies. Large-eddy simulation results provide scaling parameters for the classification of starting vortices for partly modulated jets, as well as information on their three-dimensional dynamics. The counter-rotating vortex pair initiation is observed and detailed in both Mie scattering visualizations and simulations. The observations support a mechanism based on stretching of the starting vortical structures because of inviscid induction and partial leapfrogging. Two modes of cross-flow ingestion inside the jet pipe are described as the pulsed jet cycles from high to low values of blowing ratio.

On steady and pulsed low-blowing-ratio transverse jets

The effects of jet flow-rate modulation were investigated in the case of a 35° inclined jet in cross-flow over a flat plate using Mie scattering visualizations, time-resolved flow rate records and large eddy simulations (LES). In forced experiments, average blowing ratios of 0.3 and 0.4 were investigated with a duty cycle of 50% and pulsing frequencies of St = 0.016 and 0.159. Time-resolved flow rate measurements during the experiments provided precise knowledge of the instantaneous jet blowing ratio and adequate inlet boundary conditions for large eddy simulations. The dynamics of the vortical structures generated during the transient parts of the forcing cycle as well as their impact on film cooling performance were investigated with respect of the forcing parameters. At the considered blowing ratios, a starting ring vortex was consistently generated at the transition from low to high blowing ratio. Ingestion of cross-flow fluid at the transition from high to low blowing ratio was also observed and had a negative impact on film cooling performance. All studied cases exhibited an overall decrease in coverage regardless of pulsing parameters over their corresponding steady jet cases at fixed mass flow rate. Comparisons between pulsed and steady jets at constant pressure supply (same high blowing ratio) did exhibit some film-cooling improvement with pulsing. 3D Proper orthogonal decomposition was performed on LES results at distinct forcing frequencies to provide an analysis of dominant modes in the velocity and temperature fields. Significantly different results were obtained depending on the forcing frequency.Copyright © 2011 by ASME

Study of Unforced and Modulated Inclined Film-Cooling Jets Using Proper Orthogonal Decomposition: Part I—Unforced Jets

The effects of jet flow pulsation on a vertical jet in crossflow over a flat plate were investigated using Mie scattering visualizations, hot-wire anemometry, and large eddy simulations. An unforced-jet study was conducted over a wide range of blowing ratios to provide a baseline comparison with pulsed results and exhibited two distinct transverse jet regimes with characteristic vortical-structure dynamics, separated by a transitional region responsible for a significant drop in film-cooling performance. The influence of the forcing parameters such as blowing ratio, forcing frequency, and duty cycle on pulsed jets was investigated in terms of the vortical structures generated during the transient parts of the forcing cycle, as well as their impact on wall coverage and adiabatic effectiveness. Although jet forcing led to a global decrease in film-cooling performance when compared with relevant unforced results in most cases, instantaneous quantifications revealed improvements associated with the jet-pulse onset that, if correctly exploited by proper alteration of the forcing signal, could lead to overall improved pulsed-jet film-cooling metrics.

Fundamental Study of Modulated Transverse Jets from a Film-Cooling Perspective

Film cooling jets were simulated using Large Eddy Simulation (LES) at blowing ratios of 0.150, 0.50 and 1.0. The results were analyzed using Proper Orthogonal Decomposition (POD) and Dynamic Mode Decomposition (DMD) as a statistical analysis tool and the first step toward reduced order modeling. The results of both decompositions are presented and put in perspective with dominant vortical structures and heat transfer mechanisms observed in the instantaneous velocity and temperature fields. Assessment of the performance of the decompositions is provided in terms of energy content and rendered dominant frequencies. Evolution of the dominant modes and decomposition metrics are discussed as the blowing ratio is increased.

Film-Cooling Jets Analyzed with Proper Orthogonal Decomposition and Dynamic Mode Decomposition

A new cascade wind tunnel has been designed and constructed at the LSU Wind Tunnel Laboratory. The objective was to develop a versatile test facility, suitable for a wide range of experimental studies and measurements on turbine airfoils, especially with regards to film-cooling incorporating realistic unsteady effects due to passing wakes. The test section consists of a four passage linear cascade composed of three full blades and two shaped wall blades. The 2D blade shape profile of the cascade is a high-lift, low-pressure turbine L1A profile provided by the US Air Force Research Laboratories (AFRL), with a 152-mm axial chord. The Reynolds number based on the axial chord length at the nominal freestream velocity of 50 ms−1 is 500,000. A conveyor-based system was designed and fabricated to simulate the passing wakes of the upstream vanes (or blades) on the test blades (or vanes) depending on which airfoil types are put on the stationary frame and the moving frame of the conveyor. The original implementation uses blade profiles on the stationary frame and thick plate wake generators on the translating frame. Results are presented from hot-wire surveys conducted to characterize and qualify the velocity and turbulence intensity distributions and associated spectral characteristics at the cascade test section inlet, in the wake of the vanes and in the wake of the test blade. A blade instrumented with 123 pressure taps was used to acquire static pressure profiles of the cascade central blade, which were compared to the ones from the nominal airfoil design as well as to those obtained from a CFD simulation of the cascade flow. Incoming velocity and temperature profiles were found to be uniform to within a few percentage points, and the pressure coefficient distribution was found to be in good agreement with design values. The passage periodicity of the conveyor-belt-driven, flat-plates was verified and their wake was characterized. These results verified that the cascade wind tunnel operates according to design, thus proving to be a reliable test-bed for film cooling studies with and without unsteady wake effects. The design also incorporates an in-house-designed, miniature periscopic and adjustable laser sheet generating system integrated within the “dummy” blades to enable Particle Image Velocimetry measurements in the intra-blade domain.© 2015 ASME

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Guillaume Bidan

Papers

On steady and pulsed low-blowing-ratio transverse jets

Study of Unforced and Modulated Inclined Film-Cooling Jets Using Proper Orthogonal Decomposition: Part I—Unforced Jets

Fundamental Study of Modulated Transverse Jets from a Film-Cooling Perspective

Film-Cooling Jets Analyzed with Proper Orthogonal Decomposition and Dynamic Mode Decomposition

Design, Characterization, and Verification of a Closed Loop Wind Tunnel With Linear Cascade and Upstream Wake Generator