Low Aspect Ratio Transonic Rotors: Part 2—Influence of Location of Maximum Thickness on Transonic Compressor Performance

1993 ◽  
Vol 115 (2) ◽  
pp. 226-239 ◽  
Author(s):  
A. R. Wadia ◽  
C. H. Law
Keyword(s):  
Aspect Ratio ◽  
Test Data ◽  
Three Dimensional ◽  
Leading Edge ◽  
Chord Length ◽  
Design Parameters ◽  
Transonic Compressor ◽  
Low Aspect Ratio ◽  
Maximum Thickness ◽  
Design Speed

Transonic compressor rotor performance is sensitive to variations in several known design parameters. One such parameter is the chordwise location of maximum thickness. This article reports on the design and experimental evaluation of two versions of a low aspect ratio transonic rotor that had the location of the tip blade section maximum thickness moved forward in two increments from the nominal 70 percent to 55 and 40 percent chord length, respectively. The original hub characteristics were preserved and the maximum thickness location was adjusted proportionately along the span. Although designed to satisfy identical design speed requirements, the experimental results reveal significant variation in the performance of the rotors. At design speed, the rotor with its maximum thickness located at 55 percent chord length attains the highest peak efficiency among the three rotors but has lowest flow rollback relative to the other two versions. To focus on current ruggedization issues for transonic blading (e.g., bird and ice ingestion), detailed comparison of test data and analysis to characterize the aerodynamic flow details responsible for the measured performance differences were confined to the two rotors with the most forward location of maximum thickness. A three-dimensional viscous flow analysis was used to identify the performance-enhancing features of the higher efficiency rotor and to provide guidance in the interpretation of the experimental measurements. The computational results of the viscous analysis show that the difference in performance between the two rotors can be attributed to the higher shock losses that result from the increased leading edge “wedge angle” as the maximum thickness is moved closer to the leading edge. The test data and the three-dimensional viscous analysis also reveal that the higher efficiency rotor achieves the same static pressure rise potential and loading at a higher flow level than its less efficient counterpart and this is responsible for its resulting lower flow rollback and apparent loss in stall margin. Comparison of the peak efficiencies attained by the two rotors described in this article with the baseline ruggedized rotor performance presented in part 1 of this paper suggests the existence of an optimum maximum thickness location at 55 to 60 percent chord length for such low aspect ratio transonic rotors.

scholarly journals Low Aspect Ratio Transonic Rotors: Part 2 — Influence of Location of Maximum Thickness on Transonic Compressor Performance

1992 ◽  
Author(s):  
A. R. Wadia ◽  
C. H. Law
Keyword(s):  
Aspect Ratio ◽  
Test Data ◽  
Three Dimensional ◽  
Leading Edge ◽  
Chord Length ◽  
Design Parameters ◽  
Transonic Compressor ◽  
Low Aspect Ratio ◽  
Maximum Thickness ◽  
Design Speed

Transonic compressor rotor performance is sensitive to variations in several known design parameters. One such parameter is the chordwise location of maximum thickness. This article reports on the design and experimental evaluation of two versions of a low aspect ratio transonic rotor that had the location of the tip blade section maximum thickness moved forward in two increments from the nominal 70 percent to 55 and 40 percent chord length, respectively. The original hub characteristics were preserved and the maximum thickness location was adjusted proportionately along the span. Although designed to satisfy identical design speed requirements, the experimental results reveal significant variation in the performance of the rotors. At design speed, the rotor with its maximum thickness located at 55 percent chord length attains the highest peak efficiency amongst the three rotors but has lowest flow rollback relative to the other two versions. To focus on current ruggedization issues for transonic blading (e.g. bird, ice ingestion), detailed comparison of test data and analysis to characterize the aerodynamic flow details responsible for the measured performance differences was confined to the two rotors with the most forward location of maximum thickness. A three-dimensional viscous flow analysis was used to identify the performance enhancing features of the higher efficiency rotor and to provide guidance in the interpretation of the experimental measurements. The computational results of the viscous analysis shows that the difference in performance between the two rotors can be attributed to the higher shock losses that result from the increased leading edge “wedge angle” as the maximum thickness is moved closer to the leading edge. The test data and the three-dimensional viscous analysis also reveal that the higher efficiency rotor achieves the same static pressure rise potential and loading at a higher flow level than its lesser efficient counterpart and this is responsible for its resulting lower flow rollback and apparent loss in stall margin. Comparison of the peak efficiencies attained by the two rotors described in this article with the baseline ruggedized rotor performance presented in part 1 of this paper suggests the existence of an optimum maximum thickness location at 55 to 60 percent chord length for such low aspect ratio transonic rotors.

Review of self-induced roll oscillations and its attenuation for low-aspect-ratio wings

2019 ◽  
Vol 233 (16) ◽  
pp. 5873-5895 ◽  
Author(s):  
Tianxiang Hu
Keyword(s):  
Aspect Ratio ◽  
Flight Control ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Leading Edge ◽  
Micro Aerial Vehicles ◽  
Reynolds Number Flow ◽  
Low Aspect Ratio ◽  
Aerial Vehicles ◽  
Low Aspect Ratio Wings

Micro aerial vehicles are currently receiving growing interest because of their broad applications in many fields. In their flight tests, the onset of unwanted large amplitude roll oscillations was reported, which resulted in difficulties with flight control, and this has become one of the major challenges of current micro aerial vehicles design. In this review type of article, the low Reynolds number flow characteristics of a low-aspect-ratio wing are reviewed, and the self-induced roll oscillations are discussed with special attention being payed to the interaction between the three-dimensional flow structure and wing in reciprocatively rolling motion. The roll attenuation methods are introduced via flow control approaches, which can suppress the roll oscillations effectively by manipulating the leading-edge flow separation and tip vortices of the low-aspect-ratio wings.

scholarly journals Time Resolved Measurements in a Low Aspect Ratio Transonic Compressor Stage

1982 ◽  
Author(s):  
A. H. Epstein ◽  
W. T. Thompkins ◽  
J. L. Kerrebrock ◽  
W. F. Ng
Keyword(s):  
Aspect Ratio ◽  
High Frequency ◽  
Three Dimensional ◽  
Compressor Stage ◽  
Test Rig ◽  
Time Resolved ◽  
Transonic Compressor ◽  
High Frequency Response ◽  
Low Aspect Ratio ◽  
Conventional Test

The time resolved flowfield in a low aspect ratio transonic compressor stage has been studied using a high frequency response sphere probe with a bandpass of D.C. to 20 kHz in a blowdown compressor facility. Averaged over the compressor annulus, the data agree well with those measured with standard pilot type probes on the same stage in a conventional test rig. Not all the spanwise distributions agree, however. These differences are explained as errors in the pilot probe readings due to fluctuations in the flow. The experimental data are compared to the results of a three-dimensional inviscid Euler calculation.

scholarly journals Interplay of the leading-edge vortex and the tip vortex of a low-aspect-ratio thin wing

2020 ◽  
Vol 61 (9) ◽  
Author(s):  
Lei Dong ◽  
Kwing-So Choi ◽  
Xuerui Mao
Keyword(s):  
Aspect Ratio ◽  
Angle Of Attack ◽  
Three Dimensional ◽  
Separated Flow ◽  
Leading Edge ◽  
Tip Vortex ◽  
Leading Edge Vortex ◽  
Low Aspect Ratio ◽  
Thin Wing ◽  
Edge Vortex

Abstract Three-dimensional vortical structures and their interaction over a low-aspect-ratio thin wing have been studied via particle image velocimetry at the chord Reynolds number of $$10^5$$ 10 5 . The maximum lift of this thin wing is found at an angle of attack of $$42^\circ$$ 42 ∘ . The flow separates at the leading-edge and reattaches to the wing surface, forming a strong leading-edge vortex which plays an important role on the total lift. The results show that the induced velocity of the tip vortex increases with the angle of attack, which helps reattach the separated flow and maintains the leading-edge vortex. Turbulent mixing indicated by the high Reynolds stress can be observed near the leading-edge due to an intense interaction between the leading-edge vortex and the tip vortex; however, the reattachment point of the leading-edge vortex moves upstream closer to the wing tip. Graphic abstract

scholarly journals Secondary Flow Control in Low Aspect Ratio Vanes Using Splitters

2016 ◽  
Author(s):  
Christopher Clark ◽  
Graham Pullan ◽  
Eric Curtis ◽  
Frederic Goenaga
Keyword(s):  
Kinetic Energy ◽  
Aspect Ratio ◽  
Secondary Flow ◽  
Current Practice ◽  
Leading Edge ◽  
Horseshoe Vortex ◽  
Secondary Flows ◽  
Optimization Approach ◽  
Flow Strength ◽  
Low Aspect Ratio

Low aspect ratio vanes, often the result of overall engine architecture constraints, create strong secondary flows and high endwall loss. In this paper, a splitter concept is demonstrated that reduces secondary flow strength and improves stage performance. An analytic conceptual study, corroborated by inviscid computations, shows that the total secondary kinetic energy of the secondary flow vortices is reduced when the number of passages is increased and, for a given number of vanes, when the inlet endwall boundary layer is evenly distributed between the passages. Viscous computations show that, for this to be achieved in a splitter configuration, the pressure-side leg of the low aspect ratio vane horseshoe vortex, must enter the adjacent passage (and not “jump” in front of the splitter leading edge). For a target turbine application, four vane designs were produced using a multi-objective optimization approach. These designs represent: current practice for a low aspect ratio vane; a design exempt from thickness constraints; and two designs incorporating splitter vanes. Each geometry is tested experimentally, as a sector, within a low-speed turbine stage. The vane designs with splitters geometries were found to reduce the measured secondary kinetic energy, by up to 85%, to a value similar to the design exempt from thickness constraints. The resulting flowfield was also more uniform in both the circumferential and radial directions. One splitter design was selected for a full annulus test where a mixed-out loss reduction, compared to the current practice design, of 15.3% was measured and the stage efficiency increased by 0.88%.

Calculation of the Rise and Pitch of a Three-Dimensional Low-Aspect-Ratio Flat Ship

1991 ◽  
Vol 35 (04) ◽  
pp. 314-324
Author(s):  
Todd McComb
Keyword(s):  
Aspect Ratio ◽  
Three Dimensional ◽  
Static Case ◽  
Equilibrium Flow ◽  
Low Aspect Ratio ◽  
Fast Speed ◽  
Flow Past

Using low-aspect-ratio flat ship theory, this paper defines a procedure to determine the position of a hull which is in equilibrium at some "fast" speed in terms of a given hull shape for the same hull at rest. This procedure is then used to find the equilibrium flow past a moving ship, when given the shape of the hull at rest. The method is then extended to find the hull configuration at various speeds based on either the configuration in the static case or at some other equilibrium speed, leading to a calculation of drag versus speed. Some general formulas and some simple examples are given.

scholarly journals Aeroelastic Behavior of Low Aspect Ratio Metal and Composite Blades

1986 ◽  
Author(s):  
James F. White ◽  
Oddvar O. Bendiksen
Keyword(s):  
Aspect Ratio ◽  
Opposite Effect ◽  
Design Parameters ◽  
Aeroelastic Stability ◽  
Low Aspect Ratio ◽  
Supersonic Flutter ◽  
Type Mode ◽  
The Stability ◽  
Composite Blades ◽  
Plate Type

The aeroelastic stability of titanium and composite blades of low aspect ratio is examined over a range of design parameters, using a Rayleigh-Ritz formulation. The blade modes include a plate-type mode to account for chordwise bending. Chordwise flexibility is found to have a significant effect on the unstalled supersonic flutter of low aspect ratio blades, and also on the stability of tip sections of shrouded fan blades. For blades with a thickness of less than approximately four percent of chord, the chordwise, second bending, and first torsion branches are all unstable at moderately high supersonic Mach numbers. For composite blades, the important structural coupling between bending and torsion cannot be modeled properly unless chordwise bending is accounted for. Typically, aft fiber sweep produces beneficial bending-torsion coupling that is stabilizing, whereas forward fiber sweep has the opposite effect. By using crossed-ply laminate configurations, critical aeroelastic modes can be stabilized.

Improving the Performance of a Turbine With Low Aspect Ratio Stators by Aft-Loading

2004 ◽  
Vol 128 (3) ◽  
pp. 492-499 ◽  
Author(s):  
Graham Pullan ◽  
John Denton ◽  
Eric Curtis
Keyword(s):  
Aspect Ratio ◽  
Three Dimensional ◽  
Secondary Flows ◽  
Loss Reduction ◽  
Low Aspect Ratio ◽  
Surface Pressure Distribution ◽  
Loaded Surface ◽  
Nozzle Guide ◽  
Nozzle Guide Vanes ◽  
Stage Efficiency

Experimental data and numerical simulations are presented from a research turbine with low aspect ratio nozzle guide vanes (NGVs). The combined effects of mechanical and aerodynamic constraints on the NGV create very strong secondary flows. This paper describes three designs of NGV that have been tested in the turbine, using the same rotor row in each case. NGV 2 used three-dimensional design techniques in an attempt to improve the performance of the datum NGV 1 blade, but succeeded only in creating an intense vortex shed from the trailing edge (as previously reported) and lowering the measured stage efficiency by 1.1% points. NGV 3 was produced to avoid the “shed vortex” while adopting a highly aft-loaded surface pressure distribution to reduce the influence of the secondary flows. The stage with NGV 3 had an efficiency 0.5% points greater than that with NGV 1. Detailed comparisons between experiment and computations, including predicted entropy generation rates, are used to highlight the areas where the loss reduction has occurred and hence to quantify the effects of employing highly aft-loaded NGVs.

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