Abstract:In general, the blades of a multistage turbomachine move through a row of wakes shed from the blades of the preceding stage. This interaction between blade rows results in a transient fluctuation of the pressure distributions, which in turn can be expected to have an important effect on the drag, the maximum lift coefficient and, in the case of hydraulic machines, on the cavitation characteristics of the affected blades. In the paper, the time-dependent pressure gradient and the velocity are determined for the… Show more
“…On the other hand, when the low-pressure region of R2 is aligned with the R1 trailing edge and the high-pressure region of R2 points to the pressure surface of R1, the highest blade loading can be observed on the R1 blades (Figure 10(b)). The blade loading and static pressure distribution on the R1 blades surface vary periodically as the R2 blades pass across the R1 blades.Figure 9.The definition of “negative jet,” after Meyer et al 41 Figure 10.Static pressure contours at 90% blade span at different loading conditions (a) minimum loading (b) maximum loading.…”
Section: Resultsmentioning
confidence: 99%
“…More specifically, the effect of negative jet on the static pressure distribution of R2 is not significant as no local change can be observed in the impinging location of the wake segments. The "negative jet" is firstly proposed by Meyer et al 41 in 1958, and is utilized to describe the transportation process of upstream wake in the following blade passage, as shown in Figure 9. As illustrated in the following section, in the perturbation velocity flow field, the wake appears as a "jet" which sucks off air from the lower side of the blade and impinges on the upper side.…”
Section: Unsteady Static Pressure Of Swept and Baseline Configurationsmentioning
Counter-rotating (CR) compressor is a potential configuration to increase the thrust-to-weight ratio of aero-engines. The present study numerically investigated a dual-stage CR compressor by solving unsteady Reynolds-averaged Naiver–Stokes equations. The unsteady flow mechanisms were analyzed and compared for swept and baseline (radially stacked) CR rotors. Both of these rotor configurations were numerically simulated for the entire design speed line. The unsteady flow field near the mid-span and blade tip characterized by tip leakage vortex (TLV) was analyzed in detail for both near peak efficiency (NPE) and near stall (NS) conditions. According to the results, blade loading of the second rotor (R2) was much higher than that of the first rotor (R1). Moreover, the blade loading was higher in the swept rotors in comparison with the baseline CR rotors. In both baseline and swept CR compressors, the potential effect of R2 on the static pressure distribution of R1 was more significant compared to the opposite effect. Under the NS condition, the potential effect was confined in the rear zone of R1 where the potential flow of R2 passed. Despite the obvious impact of wake-induced negative jet on the flow field of R2 blade passage, the static pressure of R2 blade exhibited no evident variation except at 90% spanwise position. Although the blade loading of the swept CR compressor was increased, the potential effect of R2 on R1 was considerably reduced due to growth of axial gap between R1 and R2. Since the blade sweep improved the flow field, the wake passing effect on R2 was more moderate compared to that of the baseline CR compressor. The perturbation velocity magnitude of the swept CR compressor was approximately half of that of the baseline CR compressor. The TLV of R2 was periodically disturbed, and therefore, low axial velocity patches were observed on the TLV trajectory of R2. In addition, the swept CR compressor exhibited smaller low axial velocity patches of TLV due to weaker aerodynamic interaction between R1 and R2.
“…On the other hand, when the low-pressure region of R2 is aligned with the R1 trailing edge and the high-pressure region of R2 points to the pressure surface of R1, the highest blade loading can be observed on the R1 blades (Figure 10(b)). The blade loading and static pressure distribution on the R1 blades surface vary periodically as the R2 blades pass across the R1 blades.Figure 9.The definition of “negative jet,” after Meyer et al 41 Figure 10.Static pressure contours at 90% blade span at different loading conditions (a) minimum loading (b) maximum loading.…”
Section: Resultsmentioning
confidence: 99%
“…More specifically, the effect of negative jet on the static pressure distribution of R2 is not significant as no local change can be observed in the impinging location of the wake segments. The "negative jet" is firstly proposed by Meyer et al 41 in 1958, and is utilized to describe the transportation process of upstream wake in the following blade passage, as shown in Figure 9. As illustrated in the following section, in the perturbation velocity flow field, the wake appears as a "jet" which sucks off air from the lower side of the blade and impinges on the upper side.…”
Section: Unsteady Static Pressure Of Swept and Baseline Configurationsmentioning
Counter-rotating (CR) compressor is a potential configuration to increase the thrust-to-weight ratio of aero-engines. The present study numerically investigated a dual-stage CR compressor by solving unsteady Reynolds-averaged Naiver–Stokes equations. The unsteady flow mechanisms were analyzed and compared for swept and baseline (radially stacked) CR rotors. Both of these rotor configurations were numerically simulated for the entire design speed line. The unsteady flow field near the mid-span and blade tip characterized by tip leakage vortex (TLV) was analyzed in detail for both near peak efficiency (NPE) and near stall (NS) conditions. According to the results, blade loading of the second rotor (R2) was much higher than that of the first rotor (R1). Moreover, the blade loading was higher in the swept rotors in comparison with the baseline CR rotors. In both baseline and swept CR compressors, the potential effect of R2 on the static pressure distribution of R1 was more significant compared to the opposite effect. Under the NS condition, the potential effect was confined in the rear zone of R1 where the potential flow of R2 passed. Despite the obvious impact of wake-induced negative jet on the flow field of R2 blade passage, the static pressure of R2 blade exhibited no evident variation except at 90% spanwise position. Although the blade loading of the swept CR compressor was increased, the potential effect of R2 on R1 was considerably reduced due to growth of axial gap between R1 and R2. Since the blade sweep improved the flow field, the wake passing effect on R2 was more moderate compared to that of the baseline CR compressor. The perturbation velocity magnitude of the swept CR compressor was approximately half of that of the baseline CR compressor. The TLV of R2 was periodically disturbed, and therefore, low axial velocity patches were observed on the TLV trajectory of R2. In addition, the swept CR compressor exhibited smaller low axial velocity patches of TLV due to weaker aerodynamic interaction between R1 and R2.
“…In Figure 15b, the dotted line represents the position of the wake. The flow transport caused by the wake negative jet [35] makes the fluid at the SS flow towards the pressure side, and the transverse transport makes the pressure field along the wake direction consistent. In Figures 15b and 16, when at t1, the slip velocity of the wake is relatively large, and the high-pressure fluid transported to the PS significantly increases the pressure enhancing the pressure rise gradient.…”
This paper investigates the effect of rotor-stator spacing and operating conditions on compressor performance and the rotor-stator interaction mechanism. We focus on the interaction between the rotor wake and the stator’s flow field through several unsteady numerical simulations aiming at a transonic compressor stage in the equal radius flow path with two-axial spacing at three operating conditions. The simulation results indicate that the time-averaged efficiency almost declined by 0.6 points due to mixing loss in the spacing ranging from close to far at nominal and low load operating conditions. The deep upstream wake leads to corner separation at high load conditions due to close spacing, imposing a fluctuating efficiency at the frequency where the stator wake near the shroud oscillates, as found by the dominant frequency screening method. Under all conditions, the wake transport can reduce the static pressure on the pressure surface and weaken the hub leakage flow afterward.
“…In low speed fans, the effect of potential interaction is insignificant for an axial spacing more than 30% of blade pitch, while for the wake interaction, the trailing edge produces a velocity deficit in the flow field that convects downstream (Parker and Watson 1972). Meyer (1958) conducted the first study of wake blade interaction. He has described that as the wake arrives near the leading edge of the downstream blade the front part accelerates along the suction side away from the rear part that remains close to leading edge, and due to higher velocity on the suction side the wake exits the passage concentrated alongside with a tail reaching back to the pressure side.…”
The Counter-Rotating Fan (CRF) offers higher aerodynamic performance, in terms of pressure head and aerodynamic efficiency, compared to the single rotor fan, thus making it an attractive solution for equipment cooling and ventilation of mines and tunnels. Nevertheless, further investigations are required to understand the flow interactions between the front rotor (FR) and the rear rotor (RR), as these interactions are sources of noise emission. This numerical study used the Unsteady Reynolds Average Navier-Stokes (URANS) flow simulations and the Fast Fourier transformation (FFT) to analyse the rotor-rotor interactions and consequences on the aero-acoustic performance. The static pressure fluctuations were recorded at several locations and analysed by FFT to reveal the mechanisms of flow interactions and the effects of axial inter-distance between the two rotors. The inter-distance seems to influence the aerodynamic loading of RR more than that of FR and the total-to-static isentropic efficiency tends to drop. Over one chord distance, the noise level decreases but at the expense of isentropic efficiency. The balanced performance does not seem to improve for an inter-distance greater than 1.5 chords, considered the optimum distance in this study. Finally, a graphical correlation which can be used to estimate the Sound Pressure Level (SPL) is developed for this category of CRF.
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