The Effects of Freestream Turbulence, Turbulence Length Scale, and Exit Reynolds Number on Turbine Blade Heat Transfer in a Transonic Cascade

Abstract

This paper experimentally investigates the effect of high freestream turbulence intensity, turbulence length scale, and exit Reynolds number on the surface heat transfer distribution of a turbine blade at realistic engine Mach numbers. Passive turbulence grids were used to generate freestream turbulence levels of 2%, 12%, and 14% at the cascade inlet. The turbulence grids produced length scales normalized by the blade pitches of 0.02, 0.26, and 0.41, respectively. Surface heat transfer measurements were made at the midspan of the blade using thin film gauges. Experiments were performed at the exit Mach numbers of 0.55, 0.78, and 1.03, which represent flow conditions below, near, and above nominal conditions. The exit Mach numbers tested correspond to exit Reynolds numbers of 6×105, 8×105, and 11×105, based on true chord. The experimental results showed that the high freestream turbulence augmented the heat transfer on both the pressure and suction sides of the blade as compared with the low freestream turbulence case. At nominal conditions, exit Mach 0.78, average heat transfer augmentations of 23% and 35% were observed on the pressure side and suction side of the blade, respectively.

Continuous Closed-Loop Transonic Linear Cascade for Aerothermal Performance Studies in Microturbomachinery

“…The schematic layout of the closed test facility and its components are presented in Fig. 1, comprising of the two-stage oil $3.5 0.9-1.12 University of German Armed Forces, Munich, Germany [8] 0.7-11 0.2-1.05 University of North Dakota, Grand Forks, ND [9] 0.5-10 0.5-0.9 University of Oxford, Oxford, UK [10] 8-30 0-1.6 Virginia Tech, Blacksburg, VA [11] 6-11 0.55-1.05 Von Karman Institute (VKI), Rhode-Saint-Genèse, Belgium [12] 5-34 0.3-1.25 Transactions of the ASME free screw compressor, small 6 m 3 pressure equalization tank to damp out transients, electric 350 kW heater, test section, pressure drop valves, large 24 m 3 dump tank, and aftercooler, which reduces the compressor inlet temperature to 300 K. Considering the aerodynamic similarity parameters, the volumetric flow rate (and therefore M) is predominantly set by the compressor rotational speed, whereas the total mass in the isolated system defines the Reynolds number. The air retained in the cycle is coarsely adjusted during start-up by a blow-off valve, and finetuned during operation.…”

“…Addressing these issues, there are a limited number of continuous transonic turbine research rigs, capable of operating in various Reynolds conditions. Regardless of operational principle, a noninclusive list of existing transonic linear cascade facilities in academic institutions is provided in Table 1 [1][2][3][4][5][6][7][8][9][10][11][12]. The only heated test rigs among them are in Ecole Polytechnique Federal de Lausanne and Virginia Tech [2,11].…”

“…For the typical microgas turbine Reynolds and Mach numbers, Re $ Oð10 4 À 10 5 Þ and M $ Oð1:05 À 1:35Þ, the aerodynamic and thermal performance is highly sensitive to the particular flow conditions, Refs. [13] and [11], respectively. Although the operational principles of some existing facilities (located in Munich and North Dakota [8,9]) can partially address this range, the lower Reynolds and the upper Mach boundaries of the operation envelope have not received much attention.…”

On the Influence of High Turbulence on the Convective Heat Flux on the High-Pressure Turbine Vane LS89

“…Nix et al [10] developed a turbulence generator reaching 10-12% turbulence intensity with large scale of 2 cm where heat transfer results indicate an increase of 8% for the suction side with respect to the low turbulence case [11]. Further heat transfer measurements by Carullo et al [12] report an effect of length scale on the stagnation heat transfer: at similar turbulence levels, a higher heating is observed when the integral length scale is smaller (reduced from 24 mm to 15 mm).…”

A characteristic inlet boundary condition for compressible, turbulent, multispecies turbomachinery flows

“…• Aside from adequately prescribing the total quantities while treating acoustic, an inlet turbomachinery boundary condition must be able to handle vorticity injection. Indeed turbulence may have a significant impact on turbomachinery flows (Choi et al [5] , Carullo et al [4] ). For a fan or a compressor computation, the level of turbulence is likely to modify the suction side transition mode, which will influence losses predictions (Jahanmiri [20] , Wissink et al [50] , Michelassi et al [27] , Scillitoe et al [43] ).…”