| 1. |
- Murali, Damu, et al.
(författare)
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Flow Over Flat and Curved Plates: A Flow Visualization Study
- 2022
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Ingår i: Journal of Aerospace Engineering. - : ASCE. - 0893-1321 .- 1943-5525. ; 35:4
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Tidskriftsartikel (refereegranskat)abstract
- Visualization experiments are conducted in a water channel to investigate the wake vortex characteristics of a flat plate and convex and concave curved plates. Three parameters—vortex size (Sv��), vortex length (Lv��), and Strouhal number (St��)—are investigated in this study to deduce the effect of plate curvature and orientation. These parameters are estimated for both the upper and lower vortices by keeping the chord length (Lc��) fixed and changing the plate diameter (D). Various plate configurations are demonstrated by altering the Lc/D��/D ratio from 0 to 1; Lc/D=0��/D=0, 6/13, 3/4, and 1. The Reynolds number (Re) based on chord length remains unchanged at 5,878 throughout the analysis. For each case of the Lc/D��/D ratio, the angle of flow incidence of the plate (α�) is varied from 0° to 30° in steps of 5°. For the convex plate, the combined effect of curvature and orientation is found to enhance the vortex shedding frequency by 70.7%, whereas vortices shrink by 26.71%, and the vortex length is reduced by 25.38%. The manipulations achieved for concave plates reveal comparatively lesser enhancement in shedding frequency; however, concave surfaces are observed to be more suitable for stretching the vortices toward the downstream. The modifications thus achieved have significant practical relevance in various applications. A shedding mechanism that partially interrupts Gerrard’s mechanism is also found to operate with concave plate configurations.
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| 2. |
- Okda, Sherif, et al.
(författare)
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Testing of the Aerodynamic Characteristics of an Inflatable Airfoil Section
- 2020
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Ingår i: Journal of Aerospace Engineering. - 1943-5525 .- 0893-1321. ; 33:5
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Tidskriftsartikel (refereegranskat)abstract
- Inflatable structures are characterized by being light and easy to manufacture and deploy. Hence, they find many applications in aerospace and aeronautical engineering. In this paper, an inflatable segment with a The National Advisory Committee for Aeronautics (NACA) 0021 airfoil cross-section is designed, fabricated, and tested. The geometrical accuracy of the manufactured inflatable segment is measured using laser scanning. Measurements show that the average normalized error of the chord length and thickness are 2.97% and 0.554%, respectively. The aerodynamic behavior of the inflatable segment is then tested in a wind tunnel at different wind speeds and angles of attack. Lift forces are measured using a six-component balance, while the drag forces are calculated from the wake measurements. The lift and drag coefficients of the inflatable section are compared to those of a standard NACA 0021 airfoil. Finally, flow visualization is examined at different angles of attack using two methods: smoke and tufts. Both methods show that flow separation starts at 15° and full stall occurs at 25°. Results indicate that inflatables can find more applications in the design and construction of aerodynamic structures, such as wings.
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| 3. |
- Wei, X. F., et al.
(författare)
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Experimental Investigations of Screech Mitigation and Amplification by Beveled and Double-Beveled Nozzles
- 2022
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Ingår i: Journal of Aerospace Engineering. - : American Society of Civil Engineers (ASCE). - 0893-1321 .- 1943-5525. ; 35:4
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Tidskriftsartikel (refereegranskat)abstract
- An experimental study was conducted to investigate and compare the effects of beveled and double-beveled circular nozzles on supersonic jet screech at a nozzle pressure ratio of 5. In particular, near- and far-field microphone measurements and schlieren visualizations were utilized to look into selected acoustic and flow features associated with jet screech radiation. Results show that beveled nozzles eliminate jet screech by producing asymmetric shock structures and instability waves that are mismatched in phase and amplitude. In contrast, double-beveled nozzles produce symmetric shock structures and amplify screech intensity, even when jet mixing effects have been significantly enhanced. It is further observed that amplified jet screeches produced by double-beveled nozzles are highly unsteady and undergo nonperiodic and stochastic temporal variations. Last but not least, double-beveled nozzles also significantly impact screech peak noise locations and confer different changes along different measurement planes. The present study demonstrates that not all beveled-type nozzles are able to mitigate jet screech, with nonoptimal designs amplifying it instead.
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