Modeling Unsteady Boundary Layer Transition on a Curved Plate Under Periodic Unsteady Flow Conditions: Aerodynamic and Heat Transfer Investigations

Abstract

A boundary layer transition model is developed that accounts for the effects of periodic unsteady wake flow on the boundary layer transition. To establish the model, comprehensive unsteady boundary layer and heat transfer experimental investigations are conducted. The experiments are performed on a curved plate at zero-streamwise pressure gradient under periodic unsteady wake flow, where the frequency of the periodic unsteady flow is varied. The analysis of the time-dependent velocities, turbulence intensities, and turbulence intermittencies has identified three distinct quantities as primarily responsible for the transition of an unsteady boundary layer. These quantities, which exhibit the basis of the transition model presented in this paper, are: (1) relative intermittency, (2) maximum intermittency, and (3) minimum intermittency. To validate the developed transition model, it is implemented in an existing boundary layer code, and the resulting velocity profiles and the heat transfer coefficients are compared with the experimental data.

Advances in Unsteady Boundary Layer Transition Research, Part I: Theory and Modeling

“…This facility has been described in several publications (Chakka and Schobeiri, 1999;Schobeiri and Radke, 1994;and Schobeiri et al, 1995), so only a brief description will be given here. The facility consists of a large centrifugal fan, a settling chamber, a nozzle, a wake generator, and a curved test section.…”

“…Implementing such a model in an unsteady Navier-Stokes code enables reliable prediction of the turbomachinery profile loss coefficients and, thus, of the efficiency. Based on the fundamental investigations of steady and unsteady wake flows by Schobeiri and his coworkers (1994Schobeiri and his coworkers ( , 1995Schobeiri and his coworkers ( , 1996, Chakka and Schobeiri (1999) established the first unsteady boundary transition model to account for the effect of periodic unsteady wakes on the boundary transition. This article briefly describes the experimental investigations that provided the basis for the inductive approach previously mentioned.…”

Intermittent Behavior of the Separated Boundary Layer Along the Suction Surface of a Low Pressure Turbine Blade Under Periodic Unsteady Flow Conditions

“…The current investigation attempts to extend the intermittency unsteady boundary layer transition model developed by Schobeiri and his coworkers ( [1], [2], [3]) to the LPT cases, where a massive separation occurs on the suction surface at a low Reynolds number at the design and off-design points. Furthermore, the experimental results are intended to serve as benchmark data for a comparison with numerical computation using DNS or RANS-codes.…”

“…Based on the fundamental investigations of the velocity and the turbulence structure of the impinging wakes and their interaction with the boundary layer, Chakka and Schobeiri [1] developed an intermittency based unsteady boundary layer transition model. The analysis revealed a universal pattern for the relative intermittency function for all the frequencies and pressure gradients investigated.…”

“…While the phenomenon of the unsteady boundary layer development and transition in the absence of the separation bubbles has been the subject of intensive research that has led to better understanding of the transition phenomenon, grasping the multiple effects of mutually interacting parameters on the LPT boundary layer separation and their physics still requires more research. To fully understand the basics involving the separation bubble phenomenon, an intermittency analysis has been employed to extend the intermittency unsteady boundary layer transition model developed in [1], [2], [3] to the LPT cases, where separation occurs on the suction surface at a low Reynolds number.…”