Development of a new tandem cascade for axial flow fan/compressor applications

With the inception of low aspect ratio blades in high pressure ratio axial compressors of modem day jet engines, there has been a renewed interest in tandem blading where high flow deflection could be exhibited. The objective is to maximize the blade loading beyond the present limits and to maintain the off-design performance range. The hypothesis that a tandem blade may offer higher deflection characteristics than a single blade is based on the consideration that its overall camber should be of the order of 45 degrees and above, below which it may not contribute any special advantage over well designed single blade rows. The authors' earlier experimental efforts in Low speed cascade studies with single and tandem airfoils showed interesting capabilities of the latter. In the present investigation, flow deflection of 48 degrees has been attempted with a newly developed tandem cascade in comparison to the single cascade of 43 degrees camber. The study includes blade surface pressure distribution, diffusion factor and loss coefficient of the cascades at a fixed stagger angle with similar solidity and aspect ratio. Experimental evidence shows sustained flow attachment on the rear airfoil suction surface over a wide range of angle of attack indicating high deflection capability of the tandem cascade