Experimental Investigation of the Loss Coefficients in a Linear Cascade

Abstract

This paper reports results of experimental investigations on a linear cascade of axial compressor blades. Experiments were conducted in an open circuit subsonic wind tunnel of Aerodynamics Research Laboratory of the Iran University of Science and Technology. Different Reynolds numbers based on the blade chord length were examined, ranging from 80,000 to 500,000. Flow incidences were changed between −8 to +8 degrees with 2 degrees intervals. Freestream turbulence intensity was changed between 1.25 to 4 percent corresponding to different mesh screens mounted upstream of the test model. All the above flow conditions provided to establish various flow regimes, in terms of fully laminar and transitional flows, around the blades. At a specified range of Reynolds numbers laminar separation bubble/bubbles occurred over the blade solid walls. Surface pressure distributions were measured utilizing a computerized data acquisition system. Fluctuating velocities were also measured at various positions around the separation bubble zone, using hot film anemometry. Surface oil flow visualization was carried out for some selected flow conditions. Experimental results were used to study boundary layer characteristics and to determine variations of loss coefficient with each of Reynolds number, flow incidence and turbulence intensity parameters for the test model.

Experimental Investigations of Surface Roughness Effects on Aerodynamic Performance of Axial Compressor Blades

“…Continuous reduction in the pressure loss can be observed for the smooth case by increasing the Reynolds number. This type of variation has already been observed and reported by the present author 14 . In the low levels of roughness (i.e., TC1 test case), loss variations are similar to the smooth case.…”

The effects of free-stream turbulence intensity on the aerodynamic performance of compressor cascade

“…This is the major mechanism driving transition in separated flows. This finding is well-documented in the literature; see Gaster (1966), Watmuff (1999), McAuliffe and Yaras (2010), Simoni et al (2012), andTaghavi et al (2014). Lang et al (2004) and Marxen et al (2003) showed that the breakdown of these vortical structures forced transition close to the maximum bubble thickness location.…”

“…First, for all but the lowest Reynolds number considered, increasing turbulence intensity from 1.27% to 2.63% increases loss between 32% and 56% (depending on Reynolds number) while further raising it to 4.05% decreases loss between 20% and 47%. Second, at the lowest Reynolds number considered the loss increases monotonically with T u because the separation bubble never reattaches to the blade surface (Taghavi et al (2014)). It can also be seen that this trend is the same for the suction side profile loss in Figure 4(b).…”

“…Figure3: Fluctuating velocity on the suction surface at Re = 100, 000 and incoming turbulence intensity of 1.27%(Taghavi and Etemadi, 2014) …”