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This study aims to clarify the mechanism of film hole location at the span-wise direction of an internal cooling channel with crescent ribs on the adiabatic film cooling…
This study aims to clarify the mechanism of film hole location at the span-wise direction of an internal cooling channel with crescent ribs on the adiabatic film cooling performance, three configurations are designed to observe the effects of the distance between the center of the ellipse and the side wall(Case 1, l = w/2, Case 2, l = w/3 and for Case 3, l = w/4).
Numerical simulations are conducted under two blowing ratios (i.e. 0.5 and 1) and a fixed cross-flow Reynolds number (Rec = 100,000) with a verified turbulence model.
It is shown that at low blowing ratio, reducing the distance increases the film cooling effectiveness but keeps the trend of the effectiveness unchanged, while at high blowing ratio, the characteristic is a little bit different in the range of 0 = x/D = 10.
These features could be explained by the fact that shrinking the distance between the hole and side wall induces a much smaller reserved region and vortex downstream the ribs and a lower resistance for cooling air entering the film hole. Furthermore, the spiral flow inside the hole is impaired.
As a result, the kidney-shaped vortices originating from the jet flow are weakened, and the target surface can be well covered, resulting in an enhancement of the adiabatic film cooling performance.
In this study, numerical simulations are performed to compare the adiabatic film cooling effectiveness and reveal the difference of film cooling mechanisms of two models…
In this study, numerical simulations are performed to compare the adiabatic film cooling effectiveness and reveal the difference of film cooling mechanisms of two models with the same geometries and cross-section areas of film holes’ exits at three typical blowing ratios (M = 0.5, 1 and 1.5). The two models are an elliptical model and a cylindrical model with 90° compound angle, respectively.
Three different cases are considered in this work and the baseline is the model with a cylindrical film hole. The same boundary conditions and a validated turbulence model (realizable k-ε) are adopted for all cases.
The results show that both the elliptical and cylindrical models with 90° compound angle can enhance the film cooling effectiveness compared with the baseline. However, the elliptical model performs well at lower blowing ratios and in the near region at each blowing ratio because of the wider width of the film hole’s exit. The cylindrical model with 90° compound angle provides better film cooling effectiveness in the further downstream area of the film hole at higher blowing ratio because of the less lift-off and better coolant coverage in the larger x/D region along the mainstream direction.
Overall, it can be concluded that although the elliptical and cylindrical models with 90° compound angle have identical hole exits, the different inlet direction and cross-sectional geometry affect the flow structures when the coolant enters, moves through and exits the hole and finally different film cooling results appear.
In a parachute canopy the combination comprises a fabric structure of inverted bowl‐like configuration developed from a plurality of individual pieces of material. The structure is further characterized in that portions thereof define a peak opening, and a lower peripheral edge and the inner surface thereof, in the developed shape of the structure, constitutes a spherical surface. The structure includes an annular skirt portion and at least one annular upper portion each portion having upper and lower spaced parallel edges, canopy reinforcing means. The adjacent edges of the skirt and upper portions being connected to the reinforcing means only at spaced circumferential points with the lower edge of the upper portion abutting the upper edge of the skirt portion on the reinforcing means without overlap of the portions. As assembled the upper edge of the upper portion and the lower edge of the skirt portion define the peak opening and lower peripheral edge, respectively, and the length of the lower edge of the upper portion exceeds the length of the upper edge of the skirt portion between the spaced points, whereby when the canopy is inflated, the lower edge of the upper portion and upper edge of the lower portion define crescent‐shaped openings.
The Thirteenth Wright Brothers Lecture delivered by Mr A. E. Russell of The Bristol Aeroplane Co. Ltd. before the Institute of the Aeronautical Sciences in New York on…
The Thirteenth Wright Brothers Lecture delivered by Mr A. E. Russell of The Bristol Aeroplane Co. Ltd. before the Institute of the Aeronautical Sciences in New York on December 17, 1949. The problem of flutter is one of the earliest associated with flying but has, until comparatively recent times, been solved merely by solving the problem of strength coupled with the tactical distribution of lead weights. We are now becoming quite proficient at solving the problem of strength and are disturbed if our test structures do not fall within 1 or 2 per cent of the design loads (however arbitrary these loads may be). At the same time this steady refinement of design has resulted in a reduction of structure weight for given design loads. Refinement of structural design has reduced the stiffness of the structure and this, coupled with a steady increase of cruising speeds, has brought the flutter problem into its present prominence.
In a compression‐ignition engine of the type in which substantially the whole of the air charge is forced into a spherical offset combustion chamber F during the…
In a compression‐ignition engine of the type in which substantially the whole of the air charge is forced into a spherical offset combustion chamber F during the compression stroke, the fuel is discharged by an injector H in a compact stream which passes through the centre of the chamber and impinges on an uncooled plug G, which forms the lower portion of the combustion chamber, at a spot adjacent to a tapering passage G4 through which the air is forced tangentially into the chamber; the circumferential portions of the rotating air charge are thus brought progressively into contact with the fuel spray as it impinges on the plug so that the air and fuel are thoroughly mixed immediately before the charge reaches the inner end of the passage G4, and the tendency for unconsumed air to be driven out of the chamber is reduced. No fuel is injected directly into the end of the passage. The passage may be of circular cross section throughout, or it may change to a crescent or kidney shape towards its inner end, the area of the latter end being preferably three‐fifths that at the outer. Instead of the passage traversing the plug, it may be formed by a groove cut in the outer cylindrical surface of the plug, the direction of rotation of the charge thus being opposite to that obtaining in Fig. 1. The plug G is made of a heat‐resisting metal of low heat conductivity; it is fitted loosely in the mouth of a water‐cooled pocket so that it is surrounded by a heat insulating air‐space F1. A retaining ring G2 may be optionally provided, the off‐set of the plug ensuring sufficient overlap between the cylinder end and plug to retain the latter if the ring is omitted. In the modified construction shown in Fig. 3, the upper portion of the combustion chamber is provided with a liner K which is insulated from the water‐cooled pocket by an air gap; the liner is supported by an integral boss K1 which passes through a bore in the wall of the pocket and is secured by a ring K2. An electrically heated hot wire J is employed at starting. The injector socket passes through the water jacket chamber of the cylinder head to ensure adequate cooling. Specification 371,025 is referred to.
EACH September the eyes of the aeronautical World turn towards the S.B.A.C. Air Display and Exhibition with interest unequalled by any other event. It is fitting that the…
EACH September the eyes of the aeronautical World turn towards the S.B.A.C. Air Display and Exhibition with interest unequalled by any other event. It is fitting that the Display is now held each year at the airfield of the Royal Aircraft Establishment, one of the world's most prominent aeronautical research centres. This interest becomes increasingly keen too, as the preview day comes closer, because new prototypes of unorthodox designs often appear a short time before the Show to illustrate the results of years of careful planning, development and research of the particular company. These designs often mould the path of progress for smaller countries without the economic resources to forge the way ahead alone. Most British citizens are very proud of their country's place in aviation today, both in the military and civil fields. This is understood by most foreigners because it is clear that Britain has won a place in aeronautical development second to none.
HAVING discussed in the standard longhand notation the main ideas and methods for the calculation of redundant structures on the basis of forces as unknowns we now turn…
HAVING discussed in the standard longhand notation the main ideas and methods for the calculation of redundant structures on the basis of forces as unknowns we now turn our attention to the matrix formulation of the analysis. Consider a system consisting of s structural elements with a total number n of redundancies which may be forces (stresses), moments or any generalized forces. We select a basic system by ‘cutting’ a number r of redundancies where r<n. Thus, the simple idea of a statically determinate basic system (r=n) is but a particular case of our investigations.
Construction companies have several possible growth paths to follow in their effort to develop. Studies show that the appropriate approach depends on the features of the…
Construction companies have several possible growth paths to follow in their effort to develop. Studies show that the appropriate approach depends on the features of the company and the prevailing economic conditions, and support measures and incentives. This paper reports the results of a study on the paths which construction enterprises in Singapore have adopted since 1980. The main basis of the study was a mailed questionnaire survey. It was found that most local contractors have grown by working at home, either as main contractors or as specialist subcontractors. Some theoretical implications of the findings are outlined. Recommendations are offered on appropriate growth paths for Singaporean contractors under various circumstances.
SOCIAL scientists have not yet been able to formulate any general laws about behaviour in industry that are capable of broad application. In recent years, however, they have made many useful case studies of which the one just published by the Department of Scientific and Industrial Research is typical. It is an approach to the problem which can do much to increase the understanding of the way in which people react to common industrial situations.