Models for Estimation of Lift and Drag Coefficients for Low-Reynolds-Number Cambered Plates

Abstract

Empirical models capable of predicting the lift and drag coefficients of circular-arc cambered plate blades are presented, together with the detailed documentation of the related wind-tunnel technique and data evaluation. The blade profiles are equipped with rounded leading and trailing edges. The empirical models offer an easy-to-use tool for preliminary design of low-solidity low-speed blade cascades. By means of the models, the lift-coefficient range of 0–1.3 is covered, associated with the drag coefficient varying between 0.02 and 0.14. The validity ranges of the empirical models are as follows: Reynolds-number between $4\times {10}^4$ and $1.4\times {10}^5$ , relative camber ranging from 0 to 8%, and angle of attack between 0 and 8 deg. The force coefficients are expressed as a function of relative camber, angle of attack, and Reynolds-number. The models assume linear relationships between the Reynolds-number and the force coefficients, as inspired by the literature and justified by statistical means. The dependence of the force coefficients on the angle of attack and the relative camber is expressed by incorporating second-order polynomials. The trends of force changes with Reynolds-number are analyzed. The cases of apparently extraordinary trends in the Reynolds-number dependence (i.e., increasing drag and decreasing lift with increasing Reynolds-number) are discussed in detail. A method for the determination of the confidence intervals related to the models is presented, and a detailed uncertainty analysis is provided. On this basis, the relative errors of the force coefficients can be quantified in a case-specific, empirical manner.