An Investigtion Into The Aerodynamic Behaviour of A Compressor Cascade In A Droplet Laden Flow

Abstract

The injection of water droplets during the compression process is a well- accepted technique for augmenting the power output from a gas turbine engine. Several researches have been carrying out in this area of ‘wet compression (overspray)’ in order to understand its impact on the aerodynamic performance of the compressor since it is a newly introduced concept in this field. Other hand boundary layer suction cavity on the blades is already a well-established technique in the field of turbo machines. The suction cavity helps to minimize boundary layer growth and helps to delay the flow separation. Hence the overall aerodynamic performance of the system would be increased. However the concept of incorporation of boundary layer suction with wet compression technology would be a new method. The first part of this study analyzes the effect of water injection on the aerodynamic performance of a linear compressor cascade. Studies have been conducted to investigate the impact of incidence angles, water droplet size, and injection ratios (IR) on the stalling characteristics of the compressor blade. Comparative analyses have been made with the dry case. Primarily, the studies have been carried out numerically using RANS simulations. The experimental analysis has also been carried out using flow visualization techniques. The study reveals notable flow modifications in the separated flow region under wet compression. For positive incidence angles, the total loss coefficient considerably decreases at the compressor’s downstream side whereas, wet compression increases the overall pressure losses inside the blade pathway at negative incidence angles. Studies with droplet size and injection ratio reveal the possibility of an optimum value for these parameters for wet compression. The flow visualization studies help to understand the water film formation and its propagation over the blades at negative and positive incidence angles. In the second part of the study, an active flow control mechanism (suction slots) is used to stabilize the boundary layer flow. Suction slots are provided to control the corner separation of the axial compressor cascade. Studies are carried out in a droplet laden flow, and comparisons are made with dry air conditions. Numerical simulations have been carried out to investigate the effect of different suction slot configurations on the iloss coefficient of the cascade. Four different slot configurations are tested near endwall slot (NES), near midspan slot (NMS), full span slot (FSS), and combined full span- endwall slot (FEWS). It was observed that the suction slot placed on the suction surface of the blade could successfully reduce the flow separation. However, the flow field at other portions of the span deteriorated as a result of this. Full-span suction (FSS) scheme on the suction surface removed boundary layer separation in the middle of the blade while greatly enhancing flow uniformity close to the end wall. Despite the improvement in flow uniformity using the full span suction scheme, a three- dimensional corner separation still existed due to the strong cross-passage pressure gradient. The combined FEWS configuration could further reduce the separation, and the total pressure loss coefficient was reduced significantly by 26 %.