Effects of surface roughness and freestream turbulence on the wake turbulence structure of a symmetric airfoil

Abstract

The effects of surface roughness on the wake characteristics of a simulated turbine airfoil, operating in a compressible, high-speed environment, are studied at different freestream turbulence levels. The effects of these parameters on wake distributions of mean velocity, turbulence intensity, and turbulence length scale, as well as on power spectral density profiles and vortex shedding frequencies are quantified one chord length downstream of airfoil. All profile quantities broaden considerably, with lower peak values, as either the level of surface roughness of the turbulence intensity increases. Non-dimensional vortex shedding frequencies also decrease as either the level of surface roughness or the turbulence intensity increases.

Development of Turbulent Wakes Evolving from Asymmetric Shear Layers

“…When the upper BL was perturbed, the vortex shedding frequencies of the ATT wakes exhibited a slight shift towards lower frequencies corresponding to values of St v of about 0.21 and 0.20 for θ/θ 0 = 2.3 and θ/θ 0 = 3.1, respectively. The reduction in the von Kármán St v was attributed to the increased turbulence level in the wake of the ATT cases in agreement with [21]. A similar shift was also observed in the subharmonics of the vortex shedding frequency f v of the ATT wakes.…”

Aerodynamic Losses in Turbines with and without Film Cooling, as Influenced by Mainstream Turbulence, Surface Roughness, Airfoil Shape, and Mach Number

“…Within investigations which generally involve low-speed turbine cascades [3,[59][60][61][62][63], a total pressure loss coefficient Ω = (P oi − P oe )/(P oi − P se ) is employed, which is equivalent to the Y P quantity given by (6). Within this definition, each term is generally determined locally at a particular spatial location.…”

“…Figure 22 is also discussed in greater detail later in the present paper. The approach utilized by Kind et al is similar to methods employed by Friedrichs et al [65], where, instead of massaveraging, the P oe and P se quantities are determined as massaveraged, "mixed" quantities within total loss coefficients (6). These investigators also employ three different approaches for determination of the reference inlet stagnation pressure, each with a different means for inclusion of contributions from the film coolant supply.…”

“…Zhang et al [5][6][7], Zhang and Ligrani [8], Xu and Denton [9], Mee et al [10], Izsak and Chiang [11], Michelassi et al [12], Joe et al [13], and Bohn et al [14] present aerodynamic loss results for transonic turbine airfoils with no film cooling. Xu and Denton [9] investigate mixing losses from turbine blades with different trailing edge thicknesses, including the influences of blade boundary layers on downstream mixing.…”

Flow Characteristics of the Boundary Layer Developing over a Turbine Blade Suction Surface

“…(4) Volino (5) 는 유동방향 섭동성분의 차원 1 에너지스펙트럼 분포를 제시하였다 등 . Zhang (6,7) 은 터빈 흡입면을 모사한 대칭형 익형에 대하여 표면 거칠기가 압력손실과 난류구조에 미치는 영향에 대 하여 각각 연구하였다 최근 들어 등 . Dahnert (8) 은 저 압터빈 동익을 모사한 유동 조건 하에서 층류 박리 유동의 천이에 대하여 연구하였다 등 .…”