Abstract:This paper presents wall shear stress measurements obtained with a new type of wall-mounted probe based on the thermal electrical principle. The sensor consists of three single surface hot wires arranged in a delta configuration. This allows for measuring wall shear stress magnitude and direction simultaneously. Each probe has to be calibrated in a flat plate experiment for a number of wall shear values and flow directions before applying it to the relevant flow situation. To assess the full potential of the n… Show more
“…The shear stress transport turbulence model (SST) with Gamma-Theta transition model is selected for simulation due to its superiority in the predictions of the onset and the amount of flow separation under adverse pressure gradients. 28 Although some quantitative variations exist, the predicted trends and the control mechanisms of the CFC are basically in consistent with the previous findings. Taking the outlet loss distribution as an example, as can be seen from Figure 21 that, similar to the Figure 12, the endwall loss is also reduced with the increased incidence due to the enhanced gap flow (note that no large-scale corner stall is detected in the passage either), and the control effect of the gap flow seems more prominent for the results predicted by CFX (the inflection point close to the endwall is more evident).…”
Section: Discussion On the Cfc And Future Worksupporting
Aspirated compressor is a promising design concept to enhance the power density of the compression system; however, with regard to the rear stages of multistage aspirated compressor, the blade is fairly thin. Limited by the mechanical constraints, it seems impractical to implement the boundary layer suction on the blade suction surface. So the question arising is can we replace the blade suction surface with other feasible flow control methods without implementing extra device on the blade? To address this issue, a compound flow control method, composed of the endwall boundary layer suction and tandem blade, is proposed. The design philosophy is to utilize the EBLS to suppress the three-dimensional corner stall while to use the tandem blade to control the two-dimensional airfoil flow separation. The endwall boundary layer suction is barely implemented in the forward blade, whereas the corner flow in the rear blade is restrained by the flow through the gap between the forward and rear blades. The preliminary implement strategy of the compound flow control was presented and then applied in the design of a highly loaded aspirated compressor outlet vane. Three-dimensional numerical simulations were carried out to validate its effectiveness with different inlet boundary layer distributions. Both flow fields in the outlet vane and its loss characteristics were analyzed. The results show that, by applying the compound flow control, the outlet vane could not only achieve an aggressive loading without incurring large-scale separation at the design point but also have a considerable available incidence range. Due to the implement of the endwall boundary layer suction, the tandem blade can bring out its full potential in the two-dimensional flow control. Moreover, owing to the flow through the gap of the forward and rear blades, the aspiration flow rate required for the suppression of the three-dimensional corner stall can be reduced.
“…The shear stress transport turbulence model (SST) with Gamma-Theta transition model is selected for simulation due to its superiority in the predictions of the onset and the amount of flow separation under adverse pressure gradients. 28 Although some quantitative variations exist, the predicted trends and the control mechanisms of the CFC are basically in consistent with the previous findings. Taking the outlet loss distribution as an example, as can be seen from Figure 21 that, similar to the Figure 12, the endwall loss is also reduced with the increased incidence due to the enhanced gap flow (note that no large-scale corner stall is detected in the passage either), and the control effect of the gap flow seems more prominent for the results predicted by CFX (the inflection point close to the endwall is more evident).…”
Section: Discussion On the Cfc And Future Worksupporting
Aspirated compressor is a promising design concept to enhance the power density of the compression system; however, with regard to the rear stages of multistage aspirated compressor, the blade is fairly thin. Limited by the mechanical constraints, it seems impractical to implement the boundary layer suction on the blade suction surface. So the question arising is can we replace the blade suction surface with other feasible flow control methods without implementing extra device on the blade? To address this issue, a compound flow control method, composed of the endwall boundary layer suction and tandem blade, is proposed. The design philosophy is to utilize the EBLS to suppress the three-dimensional corner stall while to use the tandem blade to control the two-dimensional airfoil flow separation. The endwall boundary layer suction is barely implemented in the forward blade, whereas the corner flow in the rear blade is restrained by the flow through the gap between the forward and rear blades. The preliminary implement strategy of the compound flow control was presented and then applied in the design of a highly loaded aspirated compressor outlet vane. Three-dimensional numerical simulations were carried out to validate its effectiveness with different inlet boundary layer distributions. Both flow fields in the outlet vane and its loss characteristics were analyzed. The results show that, by applying the compound flow control, the outlet vane could not only achieve an aggressive loading without incurring large-scale separation at the design point but also have a considerable available incidence range. Due to the implement of the endwall boundary layer suction, the tandem blade can bring out its full potential in the two-dimensional flow control. Moreover, owing to the flow through the gap of the forward and rear blades, the aspiration flow rate required for the suppression of the three-dimensional corner stall can be reduced.
“…Two-dimensional numerical simulation was performed using the commercial CFD software ANSYS CFX. The SST turbulence model was used for the closure of the discretized Navier-Stokes equations which was fit for highly loaded compressor and boundary layer calculation (Yao et al, 2011;Zander et al, 2013). The O4H mesh topology was generated by grid generation tool MUMECA AutoGrid 5.…”
“…In the current study, a Rolls-Royce Deutschland low-speed compressor stator cascade 14,22,25 characterized with low aspect ratio and overcritical turning is investigated. The blade cascade is depicted in Figure 1(a).…”
Section: Computational Proceduresmentioning
confidence: 99%
“…Main design parameters of the cascade are summarized in Table 1 and detailed descriptions could be found in the literature. 14,22,25 Figure 1.Sketch of blade cascade and synthetic jet actuator: (a) Three-dimensional model of the cascade and (b) Geometrical definitions of the actuator.…”
Section: Computational Proceduresmentioning
confidence: 99%
“…To verify the accuracy of the above mentioned numerical methods, numerical simulation was carried out for the cascade without flow control. The comparisons of the experimental 25 and numerical results are presented in Figure 3. According to the limiting streamlines, where the inflow is from top to bottom, the numerical prediction could accurately detect both the onset of flow separation in the corner region and the boundary layer detachment at midspan near the trailing edge.…”
This paper presents flow separation control conducted on a highly loaded compressor stator cascade using endwall synthetic jets. Numerical methods are employed and mechanisms of endwall synthetic jets in improving the cascade performance are discussed in detail. The influence of several actuation parameters is also investigated. Results show that endwall synthetic jets are able to improve the flows in the blade passage significantly, a maximum loss reduction of 21.63% and a pressure rise increment of 5.60% are obtained at design condition. Apart from energizing the low momentum fluid inside endwall boundary layer by streamwise momentum addition, endwall synthetic jets could induce a streamwise jet vortex and impede the transverse movement of endwall boundary layer through upwash and downwash. Hence, at the expense of slightly degraded near-wall flows, the formation and further evolution of passage vortex would be delayed and flows in the midspan region would be improved notably. The effectiveness of endwall synthetic jets relies on the proper selection of actuation position and jet angle. Flow control turns out to be the most efficient when the actuator is positioned at just upstream of corner separation region with a relatively small jet angle, and a large enough injected momentum is also necessary. Additionally, the adaptability of the actuation at off-design conditions is validated in the present study.
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