This paper addresses the design of swirl recovery vanes for propeller propulsion in tractor configuration at cruise conditions using numerical tools.Amultifidelity optimization framework is formulated for the design purpose, which exploits low-fidelity potential flow-based analysis results as input for high-fidelity Euler equation-based simulations. Furthermore, a model alignment procedure between low- and high-fidelity models is established based on a shapepreserving response prediction algorithm. Two cases of swirl recovery are examined. The first is the swirl recovery by the trailing wing, which leads to a reduction of the lift-induced drag. This is achieved by the optimization of the wing twist distribution. The second case is swirl recovery by a set of stationary vanes, which leads to production of additional thrust. In the latter case, four configurations are evaluated by locating the vanes at different azimuthal and axial positions relative to the wing. An optimum configuration is identified where the vanes are positioned on the blade-downgoing side downstream of the wing. For the configuration and conditions examined, the wing twist optimization reduces the induced drag by 3.9 counts (5.9% of wing-induced drag), whereas the optimized 4-bladed SRVs lead to an induced-drag reduction of 6.1 counts (9.2% of wing-induced drag). ... Read more

A numerical investigation of a propeller with swirl recovery vanes, for which experimental data exist, is performed. A second swirl recovery vane geometry, with shorter vanes to avoid the impingement of the propeller tip vortices, is also investigated. For the baseline swirl recovery vanes, the efficiency of the propulsive system increases by 2.4% with respect to the isolated propeller. This is obtained by converting angular momentum in axial momentum. A reduction of the swirl angle in the near wake by 48% is found. Most of the thrust is generated at the root of the vanes. Leading-edge impingement noise is the dominant source. The vanes cause noise to increase by 20 dB with respect to the isolated propeller in the axial direction, where noise from the propeller vanishes. In the axial direction, sound pressure level spectra show tonal peaks at harmonics of the second blade passing frequency, while in the other directions, peaks are present at harmonics of the first blade passing frequency. However, the overall isolated propeller noise is 23 dB higher than the noise generated by the swirl recovery vanes. Shortening the vane length causes a 13% reduction of the thrust generated by the vanes with respect the baseline case but no variation of the far-field noise. ... Read more

In a propeller propulsion system, due to the torque working on the propeller, a rotational motion of the fluid is generated. This rotational motion, expressed as a swirl component in the slipstream, does not result in any useful propulsive power, but causes a decrease in propeller efficiency. By recovering the momentum in the crosswise direction with other aerodynamic components located in the slipstream, either extra thrust can be produced or the overall drag of the aircraft can be reduced with the same power input from the propeller. This dissertation provides aerodynamic design and investigation of swirl recovery for both uninstalled and installed propeller propulsion systems. Swirl recovery vanes (SRVs) are a set of stationary vanes located behind a propeller, by which the angular momentum contained in the propeller slipstream can be recovered and thereby extra thrust can be generated. In this thesis, a design framework of SRVs is developed based on a lifting line model. The design method features a fast turnaround time, which makes it suitable for system level design and parameter studies. As a test example, a set of SRVs was designed for an uninstalled six-bladed propeller at a high propeller loading condition. A parametric study was performed of the SRV performance as a function of the blade count and radius. In order to validate the design routine, an experiment was performed with a propeller and the SRVs in a low-speed open-jet wind tunnel. The thrust generated by the SRVs was measured at different propeller loading conditions. The experimental results show that the SRVs provided thrust at all the measured propeller advance ratios. Since the SRVs did not require any extra power input, the propulsive efficiency of the system (propeller + SRVs) has improved accordingly for all the loading conditions considered. For an installed tractor-propeller propulsion system, both the downstream wing and the SRV have the ability of recovering the swirl of propeller slipstream. In the first case of swirl recovery from the trailing wing, reduction of wing induced drag can be achieved. In order to determine the optimum wing shape for maximum drag reduction, a multi-fidelity optimization procedure is developed, where the low-fidelity method corresponds to the potential flow-based method, and the high-fidelity method is based on an analysis by solving Euler equations. As a test case, the twist distribution of the wing is optimized at the cruise condition of a typical turboprop aircraft. Compared to the baseline wing (untwisted), the induced drag of the optimized wing has decreased by 1.4% of the propeller thrust. In the second case of swirl recovery from the SRV, extra thrust can be generated by the vanes. Four different cases of SRVs installation positions are investigated (with assumption of inviscid flow) with different axial and azimuthal positions relative to the wing. An optimum configuration is identified where SRVs are positioned on the blade-downgoing side downstream of the wing. For the identified optimum configuration, a set of SRVs was designed taking the effect Summary II of viscosity into account. The SRV design is subsequently validated by RANS simulation. Good agreement is observed in the lift, circulation, and thrust distributions of the SRV between the lifting line prediction and the RANS result. A thrust of 1.6% of propeller thrust from SRVs was validated by the RANS simulation. Comparing the two ways of swirl recovery, further investigation has shown that for the installed propeller propulsion system, due to the different aerodynamic consequences of the two (drag reduction of the wing compared with thrust enhancement from the SRV), they can be algebraically added up. ... Read more

The swirl recovery vane (SRV) oriented in the slipstream of the propeller can in principle recover the swirl effect and thus would improve the propulsion performance in terms of thrust production and propulsive efficiency. The present study employs the design of experiments (DoEs) method to optimize the geometry of the specific SRV for Fokker 29 propeller for the sake of further enhancing the thrust generation and swirling recovery. First, orthogonal experiment was employed to identify the most significant factors, which directly influence the thrust production. Second, steepest ascent method was used to search the optimum range of target factors through climbing and factorial experiments. The resulting optimal solution was evaluated by the center composite experiment. Results show that the thrust generated by the SRV has been increased significantly (11.78%) after optimization at the design point, and a 0.66% increment in the total efficiency of the propeller-SRV system has been obtained. For the off-design point, an increment of the total efficiency (2.10%) can be observed at low rotating speed. Additionally, the optimized SRV is able to correct the out-flow behavior at the tip region of the vane, where the tip vortex and swirl kinetic energy loss is weaken, and the thrust distribution along the spanwise direction tends to be more uniform. ... Read more

This paper addresses the design of swirl recovery vanes for propeller propulsion in tractor configuration at cruise conditions using numerical tools. A multi-fidelity optimization framework is formulated for the design purpose, which exploits low-fidelity potential flow-based analysis results as input for high-fidelity Euler equation-based simulations. Furthermore, a model alignment procedure between low-and high-fidelity models is established based on the shape-preserving response prediction algorithm. Two cases of swirl recovery are examined, i.e. swirl recovery by the trailing wing which leads to a reduction of the lift-induced drag, and swirl recovery by a set of stationary vanes (SRVs) located inside the propeller slipstream which leads to production of additional thrust. In the first case, the optimization of the wing circulation distribution is achieved by twist optimization. The resulting reduction in induced drag is 5.9% out of 66.1 counts at the design cruise condition of C_L= 0.5. In the case of the SRV design, four configurations are evaluated by locating the vanes at different azimuthal and axial positions relative to the wing. The interactions between SRVs and wing are discussed and an optimum configuration is identified, where the vanes are positioned on the blade-downgoing side downstream of the wing. In this configuration, the wake and tip vortices of the vanes have negligible effect on the wing circulation distribution and consequently introduce no extra drag. With a blade count of 4, the total system drag has decreased by 6.1 counts, which is equivalent to 2.4% of propeller thrust. ... Read more

The momentum transferred to the fluid by a running propeller contains not only the desired axial component but also a rotational component that does not contribute to the propeller thrust. By introducing a set of swirl-recovery vanes (SRVs) downstream of the propeller, part of the rotational flow in the slipstream can be redirected into the streamwise direction, thereby producing extra thrust and enhancing the propulsive efficiency. The current study presents the development, application, and experimental validation of a low-order SRV design tool. The design method combines a short computational time with a detailed vane-shape representation. The procedure is presented together with a test example, consisting of a set of SRVs designed and manufactured for operation with a six-bladed propeller operating at thrust coefficient of CT;P _ 0.32. Results from the computations are subsequently validated by a wind-tunnel experiment with the propeller–SRV model. The SRVs were shown to provide extra thrust at all the considered propeller operating conditions. Because the installation of the SRVs does not lead to an increase in power consumption, it is thus shown that SRVs have the potential to increase the propulsive efficiency during all phases of the flight. ... Read more