Session: 32-08 Flow Control 1

Paper Number: 127998

127998 - Performance of Rough-Ribbed Low-Pressure Turbine Blades Under Varying Loading and Operating Conditions 

The low-pressure turbines (LPTs) in modern aircraft engines typically operate at low Reynolds numbers of O(10⁵). Consequently, the suction surface boundary layer of the ultra-high-lift blades of LPTs is prone to separation under strong local adverse pressure gradients. Intermittent free-stream turbulence, periodic wakes shed by the moving upstream blades, and surface roughness due to in-service degradation can suppress the separation bubble, however at the cost of an increased turbulent wetted area. Recent investigations employing surface roughness and/or riblets [1-3] have shown promise in reducing the profile loss of blade surface boundary layers. To simulate the suction surface of an LPT blade, we adopt the configuration of a boundary layer developing over a flat surface with a streamwise varying pressure gradient imposed by a contoured inviscid top wall [4]. It was found that by employing a combination of roughness and riblets over this flat surface, both the trailing edge momentum thickness and turbulent wetted area can be reduced considerably. Specifically, it was demonstrated that by employing two-dimensional scalloped riblets, a riblet spacing of s⁺=17 and height of h⁺=22 resulted in a reduction of skin-friction drag and momentum thickness of 7.3% and 14.5%, respectively, compared to the baseline case [1]. In the current investigation, in the presence of free-stream turbulence, this ‘rough-ribbed’ blade surface will be tested for a range of Reynolds numbers and adverse pressure gradients to assess its performance under varying operating conditions. To this end, we perform a series of high-fidelity scale-resolving simulations to study the transitional and turbulent boundary layer development over this surface. An in-house, high-order structured compressible flow solver (COMP-SQUARE) is used for this numerical study. The Boundary Data Immersion Method is used to represent the surface roughness and riblet geometries, and a Synthetic Eddy Method is used to impose free-stream-turbulence at the inlet. Flow statistics for various test cases will be compared based on the time-averaged flow quantities, boundary layer integral parameters, and Reynolds stresses, and the boundary layer losses will be analyzed in detail. It is expected that this study will demonstrate the robustness of the ‘rough-ribbed’ LPT blade design proposed in our previous works and its operational efficiency under off-design conditions.

References:

1] Ananth, S.M., Nardini, M., Vaid, A., Vadlamani, N.R. and Sandberg, R.D., 2023, “Effects of Riblet Dimensions on the Transitional Boundary Layers Over High-Lift Turbine Blades,” Turbo Expo: Power for Land, Sea, and Air 87097, V13BT30A036.

2] Dellacasagrande, M., Lengani, D., Simoni, D., Ubaldi, M., and Bertini, F., 2023, “Effects of Ribbed Surfaces on Profile Losses of Low-Pressure Turbine Blades,”  ASME J. Turbomach., 145(10), 101009.

3] Ananth, S.M., Nardini, M., Vaid, A., Vadlamani, N.R. and Sandberg, R.D., 2023, “Profile Loss Reduction of High Lift Turbine Blades With Rough and Ribbed Surfaces,” ASME J. Turbomach., 145(2), 021001.

4] Rao, V. N., Tucker, P., Jefferson-Loveday, R., and Coull, J., 2013, “Large Eddy Simulations in Low-Pressure Turbines: Effect of Wakes at Elevated Free-Stream Turbulence,” Int. J. Heat Fluid Flow, 43, pp. 85–95.

Presenting Author: Ananth S M Indian Institute of Technology Madras

Presenting Author Biography: Ananth is a post-doctoral researcher at IIT Madras. He has pursued his PhD jointly from IIT Madras and the University of Melbourne. His research interests include transitional flows in low pressure turbines, passive flow control using roughness and riblets, high performance computing and high order methods.

Authors:

Ananth S M Indian Institute of Technology Madras
Massimiliano Nardini University of Melbourne
Melissa Kozul University of Melbourne
Nagabhushana Rao Vadlamani Indian Institute of Technology Madras
Richard Sandberg University of Melbourne