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Languages : en
Pages : 13
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Since the need for improvements in high angle-of-attack maneuverability of aircraft's in transonic flight was of concern, a model was rotated around its longitudinal body axis with a dimensionless rolling rate of pi = 0.0762 (10 Hz), resulting in flow conditions with extensive vortical behavior and strongly non-linear, wing/vortex interference effects. This paper deals with validation experiments performed at the DLR Goettingen. The objective of this activity was to provide experimental data for comparison with numerical calculations performed within the international WEAG TA 15 group: Alenia (Italy), DERA (United Kingdom), DLR and EADS (Germany), and NLR (The Netherlands). A special 65 delta wing, the DLR PSP-model, was designed, manufactured and finally tested in the transonic 1mx 1m wind tunnel DNW-TWG in Goettingen. A rolling apparatus was built up to enable roll rates up to 10 Hz. A new sting concept was developed as elastic simulations showed dangerous problems associated with the rolling model exposed to the periodic aerodynamic load. The experiments were carried out at angles of attack alpha=10 and 17, M=0.8, Reynolds number of 5.3 Mio in the case of steady and 2.2 Mio for unsteady conditions. The model was equipped with only a few pressure taps for PSI and Kulite sensors, as surface pressure distributions of the model should be obtained using the pressure sensitive paint (PSP) technique, to measure the pressure all over the whole surface of the model. As the model was rotating an unsteady PSP technique had to be applied. Several steps had to be considered in order to finally use the measured pressure distributions for comparison with numerical predictions. In the case of steady conditions the results compare quite well with the conventional pressure taps and numerical calculations, in the case of the spinning model discrepancies between Kulite values and PSP as well as numerical results could be stated.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 13
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Book Description
Since the need for improvements in high angle-of-attack maneuverability of aircraft's in transonic flight was of concern, a model was rotated around its longitudinal body axis with a dimensionless rolling rate of pi = 0.0762 (10 Hz), resulting in flow conditions with extensive vortical behavior and strongly non-linear, wing/vortex interference effects. This paper deals with validation experiments performed at the DLR Goettingen. The objective of this activity was to provide experimental data for comparison with numerical calculations performed within the international WEAG TA 15 group: Alenia (Italy), DERA (United Kingdom), DLR and EADS (Germany), and NLR (The Netherlands). A special 65 delta wing, the DLR PSP-model, was designed, manufactured and finally tested in the transonic 1mx 1m wind tunnel DNW-TWG in Goettingen. A rolling apparatus was built up to enable roll rates up to 10 Hz. A new sting concept was developed as elastic simulations showed dangerous problems associated with the rolling model exposed to the periodic aerodynamic load. The experiments were carried out at angles of attack alpha=10 and 17, M=0.8, Reynolds number of 5.3 Mio in the case of steady and 2.2 Mio for unsteady conditions. The model was equipped with only a few pressure taps for PSI and Kulite sensors, as surface pressure distributions of the model should be obtained using the pressure sensitive paint (PSP) technique, to measure the pressure all over the whole surface of the model. As the model was rotating an unsteady PSP technique had to be applied. Several steps had to be considered in order to finally use the measured pressure distributions for comparison with numerical predictions. In the case of steady conditions the results compare quite well with the conventional pressure taps and numerical calculations, in the case of the spinning model discrepancies between Kulite values and PSP as well as numerical results could be stated.
Author: National Aeronautics and Space Administration (NASA)
Publisher: Createspace Independent Publishing Platform
ISBN: 9781722125998
Category :
Languages : en
Pages : 30
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A conical Euler code was developed to study unsteady vortex-dominated flows about rolling, highly swept delta wings undergoing either forced motions or free-to-roll motions that include active roll suppression. The flow solver of the code involves a multistage, Runge-Kutta time-stepping scheme that uses a cell-centered, finite-volume, spatial discretization of the Euler equations on an unstructured grid of triangles. The code allows for the additional analysis of the free to-roll case by simultaneously integrating in time the rigid-body equation of motion with the governing flow equations. Results are presented for a delta wing with a 75 deg swept, sharp leading edge at a free-stream Mach number of 1.2 and at 10 deg, 20 deg, and 30 deg angle of attack alpha. At the lower angles of attack (10 and 20 deg), forced-harmonic analyses indicate that the rolling-moment coefficients provide a positive damping, which is verified by free-to-roll calculations. In contrast, at the higher angle of attack (30 deg), a forced-harmonic analysis indicates that the rolling-moment coefficient provides negative damping at the small roll amplitudes. A free-to-roll calculation for this case produces an initially divergent response, but as the amplitude of motion grows with time, the response transitions to a wing-rock type of limit cycle oscillation, which is characteristic of highly swept delta wings. This limit cycle oscillation may be actively suppressed through the use of a rate-feedback control law and antisymmetrically deflected leading-edge flaps. Descriptions of the conical Euler flow solver and the free-to roll analysis are included in this report. Results are presented that demonstrate how the systematic analysis of the forced response of the delta wing can be used to predict the stable, neutrally stable, and unstable free response of the delta wing. These results also give insight into the flow physics associated with unsteady vortical flows about delta wings undergoing forced m...
Author: Alexander H. Hsia
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Author: Thomas G. Gainer
Publisher:
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Category : Aerodynamic measurements
Languages : en
Pages : 82
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Author: Harry J. Kowal
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Category :
Languages : en
Pages :
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Author:
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Category :
Languages : en
Pages : 23
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Author:
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ISBN:
Category :
Languages : en
Pages : 14
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This paper presents the results of research conducted by Alenia (Italy), Dasa (Germany), DERA (United Kingdom), NLR (The Netherlands), and DLR (Goettingen, Germany) as part of the Western European Armaments Group (WEAG) TA15 program, Common Exercise V. The WEAG TA15 program was a collaborative program concerned with the investigation of steady and unsteady vortical flows over military aircraft configurations. An important component of the program were the Common Exercises (CE), which promoted the exchange of knowledge between the participating nations and aided the development of computational methods to predict vortical flows. As the analysis of flow fields about rolling delta wings is of high interest, the last CE of this group concentrated on the numerical and experimental investigation of unsteady flow over a 65 degree swept delta wing in rolling motion at transonic speed. Guided by previous work on unsteady motions, the numerical investigation was again restricted to unsteady Euler methods. Each participant for the numerical calculations was asked to perform unsteady Euler calculations for given test cases using a mandatory grid and a given number of physical time steps per period. Numerical calculations with different unsteady Euler methods using a common grid were performed at a constant rolling rate of omega(r)=0.0762 for different angles of incidence: alpha(sub 0)=0 degrees, alpha(sub 0)=10 degrees, and alpha(sub 0)=17 degrees. The numerical results reveal that the different spatial discretizations lead to characteristic differences mainly in the magnitudes of the vortex-induced suction peaks in the unsteady pressure distributions and in the prediction of vortex breakdown. The results should finally result in the development of a data base for further code validation. (13 figures, 14 refs.).
Author: Mohammad-Ameen M. Jarrah
Publisher:
ISBN:
Category : Aerodynamics
Languages : en
Pages : 352
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Author: X. Z. Huang
Publisher:
ISBN:
Category :
Languages : en
Pages : 24
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This data set is selected from an extensive set of experimental results obtained for configurations with a 650 delta wing under static as well as large-amplitude high-rate rolling or pitching conditions at high incidence. The experiments were performed under a joint research program on "Non-Linear Aerodynamics under Dynamic Maneuvers" by the National Research Council of Canada (NRC (IAR)), the U.S. Air Force (USAF (AFOSR, AFRL)) and the Canadian Dept. for National Defence (DND). NASA Ames informally participated in the program through its substantial CFD work on specific test conditions. The experimental results provide both detail pressure measurements and a wide range of flow conditions covering from simple attached flow, through fully developed vortex and vortex burst flow, up to fully-stalled flow at very high incidence. Since this data set includes different levels of physical difficulty, the computational researchers wording in unsteady aerodynamics can use it as a staircase approach to the problem of validating their corresponding code Four schematic and representative configurations' were selected in the experiments (Fig. 1 to Fig. 3).
Author: Ismael Heron
Publisher:
ISBN:
Category : Electronic dissertations
Languages : en
Pages : 285
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An experimental investigation was undertaken at Wichita State University in order to quantify the vortex burst behavior of a pitching 70-degree sweep delta wing subjected to a variable freestream velocity (accelerating or decelerating flow), as well as to an impinging von Kármán vortex street generated by a cylinder placed ahead of the apex. The experiments were inspired by flow features present in the flow field of an aircraft executing a 0́−Cobra0́+ maneuver. A total of 222 test runs were conducted which resulted in the analysis of 6481 video frames for the von Kármán experiments and 8566 video frames for the variable velocity experiments. It was found that at different a8́2ranges and velocity ratios, accelerating the flow produced a mild to strong negative effect (i.e., an acceleration of the forward propagation velocity) on the burst location. This negative effect was almost independent of the actual acceleration or range of a over which it occurred. Deceleration, on the other hand, was found to delay the forward burst movement along the vortex core. This was consistent for the pitch rates tested, and in all cases resulted in a momentary reduction of the forward propagation of the burst location. In the more extreme cases where the velocity ratio was large (Vstart/Vfinal =2) a complete stop to the forward burst movement was possible. The most important result from the von Kármán experiments was that the burst could be observed by the 0́−jumping0́+ of the burst location forward towards the wing0́9s apex in response to the convection of the von Kármán wake filament. This was accomplished at both a regular frequency of approximately 3 Hz, and at higher non-uniform frequency centered around 5 Hz, the only difference between the two being the degree of change in the burst location. The experiments performed here represent an initial step towards a more complex Cobra maneuver experiment.
