Performance of Low-Aspect-Ratio Diffusers With Fully Developed Turbulent Inlet Flows: Part II—Development and Application of a Performance Prediction Method

1973 ◽  
Vol 95 (3) ◽  
pp. 393-400
Author(s):  
O. J. McMillan ◽  
J. P. Johnston
Keyword(s):  
Aspect Ratio ◽  
Performance Prediction ◽  
Analytical Method ◽  
Prediction Method ◽  
Two Dimensional ◽  
Integral Type ◽  
Inlet Flow ◽  
Low Aspect Ratio ◽  
Performance Trends ◽  
Wide Range

An analytical method of the integral type is developed to allow prediction of performance in unstalled, straight, two-dimensional rectangular diffusers of aspect ratio less than approximately 0.5. The inlet flow is fully developed and turbulent. The results predicted by this method compare favorably to the data of Part I and to other relevant cases. The method has been applied to extrapolate performance trends to a relatively wide range of related, but untested, geometries and conditions.

Performance Prediction for High Turning Low Aspect Ratio Stator Cascades in the Transonic Regime

1970 ◽  
Vol 92 (4) ◽  
pp. 390-398
Author(s):  
H. F. L. Griepentrog
Keyword(s):  
Boundary Layer ◽  
Aspect Ratio ◽  
Flow Field ◽  
Performance Prediction ◽  
Transonic Flow ◽  
Secondary Flows ◽  
Compressor Stage ◽  
Low Aspect Ratio ◽  
Aspect Ratios ◽  
Boundary Layer Interaction

This paper describes a method for the prediction of the transonic flow field in a high solidity, high turning cascade, suitable for use as stator of a shock-in-rotor supersonic compressor stage. Effects of shock boundary layer interaction is taken into account by empirical correlation, valid for blade aspect ratios below unity. Use of partial slots for reduction of the secondary flows is briefly discussed and a correlation on slot efficiency is presented.

The Spinning Ellipse Speed Illusion

2017 ◽  
Author(s):  
Gideon Paul Caplovitz ◽  
Po-Jang Hsieh ◽  
Peter J. Kohler ◽  
Katharine B. Porter
Keyword(s):  
Aspect Ratio ◽  
Relative Motion ◽  
Characteristic Form ◽  
Low Aspect Ratio ◽  
Wide Range ◽  
Form Features ◽  
Illusory Percept ◽  
Perceived Speed ◽  
Contour Curvature

The Spinning Ellipse Speed Illusion is an illusion of perceived speed in which a low-aspect ratio “fat” ellipse will appear to rotate more slowly than a higher-aspect ratio “skinny” ellipse that is rotating at the same speed. This illusory percept can be observed when the ellipses are defined by luminance, color, relative motion, and dotted contours and across a wide range of rotational speeds and eccentricities. The illusion is not limited to rotating ellipses and can be observed with different-shaped contours as well. The Spinning Ellipse Speed Illusion illustrates that the perceived speed of a rotating object depends in part on the form and form features of the object. Objects without characteristic form features such as regions of high or discontinuous contour curvature will appear to rotate more slowly than objects that have these features.

A Method to Predict Rudder Stall Inception from Two-dimensional Airfoil Data

2014 ◽  
Vol 58 (01) ◽  
pp. 1-19
Author(s):  
Michael J. Hughes ◽  
Young T. Shen
Keyword(s):  
Aspect Ratio ◽  
Three Dimensional ◽  
Two Dimensional ◽  
Theoretical Formulation ◽  
Stall Inception ◽  
Low Aspect Ratio ◽  
Aspect Ratios ◽  
Flow Similarity ◽  
Naca 0015 ◽  
Naca 0012

The behavior of the force on a rudder changes significantly after the inception of stall, requiring different mathematical formulae to compute rudder forces prior-and poststall. Determining the inception angle at which stall occurs is important for predicting the rudder force on a maneuvering ship. A method to compute the inception angle of stall on a rudder is presented in this article. The theoretical formulation is based on a flow similarity approach, which relates three-dimensional rudder stall inception with two-dimensional airfoil data. Rudders are low-aspect ratio wings, and the three-dimensional lift is based on the low-aspect ratio wing theory. The two-dimensional airfoil stall data are obtained from National Advisory Committee for Aeronautics (NACA) reports. The derived theory is first validated with wind tunnel data from foils with a NACA 0015 profile of aspect ratios 1, 2, and 3. The theory is also validated with data from foils with a NACA 0012 profile and an aspect ratio of 2, 3, and 6.

Estimation of Stability Derivatives and Indices of Various Ship Forms, and Comparison With Experimental Results2

1966 ◽  
Vol 10 (03) ◽  
pp. 135-163
Author(s):  
W. R. Jacobs
Keyword(s):  
Aspect Ratio ◽  
Analytical Method ◽  
Flow Theory ◽  
Experimental Results ◽  
Class Model ◽  
Low Aspect Ratio ◽  
Stability Derivatives ◽  
Course Stability ◽  
The Right

The analytical method of reference [1]3 for estimating stability derivatives, and hence stability on course, which combines Albring's empirical modifications of simplified flow theory with low aspect-ratio wing theory, is extended to take into consideration the effects on course stability of higher aspect-ratio fins as well. The method, which has been applied in the earlier report to a family of eight hulls of 0.5 block coefficient, is tested further by application to eight Series 60 forms differing in block coefficient as well as in beam, draft, and displacement—with and without rudders; to an extreme vee modification of a Series 60 model; and to three other forms—a Mariner Class model, a destroyer, and a hopper dredge. Comparison with experimental results shows that the values of stability derivatives and indices determined by the analytical method are of the right orders of magnitude and indicate correct trends. Application to a variety of ship forms has demonstrated that the method can predict relative effects of changes in the geometry of a ship form, as well as the effects of changes in skeg and rudder area.

A study of laminar flow in low aspect ratio lid-driven cavities

2002 ◽  
Vol 29 (3) ◽  
pp. 436-447 ◽  
Author(s):  
Y Yang ◽  
A G Straatman ◽  
R J Martinuzzi ◽  
E K Yanful
Keyword(s):  
Reynolds Number ◽  
Laminar Flow ◽  
Aspect Ratio ◽  
Numerical Solutions ◽  
Cavity Flow ◽  
Momentum Equation ◽  
Laser Doppler Velocimeter ◽  
Countercurrent Flow ◽  
Two Dimensional ◽  
Low Aspect Ratio

The evolution to fully developed laminar flow in low aspect ratio, two-dimensional, lid-driven cavities has been studied experimentally and numerically. Velocity measurements were made in water in a moving-lid apparatus using a laser Doppler velocimeter (LDV). Numerical solutions for the cavity flow were obtained by solving the two-dimensional mass-momentum equation set in a finite-volume framework. The measured and predicted results were in excellent agreement. Fully developed cavity flow is said to exist when the main regions of the flow field become independent of the aspect ratio. When fully developed conditions prevail, a region of countercurrent flow (CCF) separates the end structures, which are decoupled. The extent of the end regions is shown to grow linearly with increasing Reynolds number Re, based on the lid speed and the cavity height. Consequently, the critical aspect ratio for the onset of fully developed flow is also linearly dependent on Re. Above a critical Reynolds number, Re [Formula: see text] 300, the flow becomes unsteady, and a lower-wall, tertiary vortex appears, which is thought to be associated with the onset of hydrodynamic instability.Key words: lid-driven cavity, laminar flow, shallow water cover, countercurrent flow.

Effects of Wall Shape on Flow Regimes and Performance in Straight, Two-Dimensional Diffusers

1967 ◽  
Vol 89 (1) ◽  
pp. 151-159 ◽  
Author(s):  
J. J. Carlson ◽  
J. P. Johnston ◽  
C. J. Sagi
Keyword(s):  
Flow Regime ◽  
Performance Prediction ◽  
Prediction Method ◽  
Flow Regimes ◽  
Two Dimensional ◽  
Simple Class ◽  
And Performance

Three diffuser sets (N/W1, held constant in each set) were built and tested for performance and flow regime over a range of total area ratios, AR, which yielded unstalled and stalled flows. At each AR and N/W1, a simple class of convex-inward (trumpet-shaped), straight, and convex-outward (bell-shaped) wall shapes were tested. It is concluded that there is little advantage to be gained by contouring the walls of two-dimensional diffusers. A corollary result shows that the performance prediction method of reference [1] gives good results for unstalled diffusers.

Performance of Low-Aspect-Ratio Diffusers With Fully Developed Turbulent Inlet Flows: Part I—Some Experimental Results

1973 ◽  
Vol 95 (3) ◽  
pp. 385-392 ◽  
Author(s):  
O. J. McMillan ◽  
J. P. Johnston
Keyword(s):  
Experimental Investigation ◽  
Aspect Ratio ◽  
Boundary Layers ◽  
High Aspect Ratio ◽  
Total Pressure ◽  
Turbulent Boundary Layers ◽  
Two Dimensional ◽  
Low Aspect Ratio ◽  
Performance Curves ◽  
Existing Data

An experimental investigation of the effects of incompressible, fully developed, turbulent inlet flow on the performance of straight, two-dimensional rectangular diffusers of low aspect ratio is presented. Results presented include flow regime information, performance curves, and total-pressure loss data for a series of diffusers of moderate non dimensional length and low aspect ratio. The results are compared to existing data and correlations and important differences are noted between the diffusers of this study and diffusers of high aspect ratio with thin to moderately thick turbulent boundary layers at inlet.

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