Effects of blade sweep on the performance characteristics of axial flow turbomachinery rotors

Abstract

Experimental studies were carried out in order to survey the performance and efficiency aspects of spanwise constant forward and backward sweep in axial flow rotors of low aspect ratio (AR) blading for incompressible flow, for part-load, near-design, and overload operational ranges. The experiments involved overall performance tests, laser Doppler velocimetry, and stationary total pressure probe measurements. The overall performance data and pitchwise averaged and resolved flow characteristics were evaluated in detail. For moderate and high flow rates, it was pointed out that positive or negative sweep tends to reduce or increase the blade load in the vicinity of the endwalls, respectively. It has been concluded that the loss-modifying effect of sweep can be judged by considering the three-dimensional viscous phenomena, and the influence of sweep on local blade efficiency depends on the balance of changes in blade load and losses. For low flow rates, forward sweep was found beneficial over the entire span from the aspect of improved stall margin and efficiency. The influence of AR on the performance reducing effect of sweep was studied on the basis of literature data.

Correlation of flow path length to total pressure loss in diffuser flows

“…C L opt relates implicitly to a maximum lift-to-drag ratio (LDR), as a function of inlet and outlet angles. As discussed in reference [21], the increase -or decrease -of LDR leads to the gain -or deterioration -of cascade efficiency. The above imply the following:…”

Aerodynamic effects of forward blade skew in axial flow rotors of controlled vortex design

“…The open literature suggests a general consensus that forward sweep/skew gives potential for the following advantages in the part load operational range (flow rates lower than design): improvement of efficiency, increase of total pressure peak, and extension of stallfree operating range by improving the stall margin [3,[7][8][9][10][11][12]. Nevertheless, the research results are rather diversified regarding the judgment of performance and loss modifying effects of forward sweep/skew at flow rates near the design point.…”

“…However, forward sweep reported in references [10] and [11] and FSK in reference [4] were found to cause the deterioration of efficiency near the design point. In reference [12], the reduction of efficiency was established for a forward-swept rotor over the dominant part of the entire stall-free operational range. Backward sweep was reported to be optimal in reference [13] from the viewpoint of efficiency improvement.…”

On loading corrections and loss distributions in low-speed forward swept axial compressor rotors

“…Since the effect of aspect ratio (AR) also contributes to the deviation of the actual behaviour from the one predicted by theory of infinitely long airfoils, Vad et al [13] extended the study on the above estimations to include the effects of the blade AR. On the basis of five case studies reported in the literature [10,11,[14][15][16], they sought the following correlations between the sweep angle and the ratio of pressure coefficients of comparative swept and unswept rotors by modifying the equations (1) and (2), respectively, as follows: Figure 1 presents the corresponding 1/AR as well as A and B data pairs calculated from the literature data.…”

“…Next to the data points, the literature source and the actual λ value are specified. Note that the reference numbers in the figure were the ones mentioned in the original article [13]. Wherever λ was not shown, the data point refers to entire sweep angle range.…”