Factors Affecting the Performance of the Supersonic Parallel Diffuser

1966 ◽  
Vol 8 (1) ◽  
pp. 62-69 ◽  
Author(s):  
B. W. Martin
Keyword(s):  
Static Pressure ◽  
Pressure Ratio ◽  
Area Ratio ◽  
Stagnation Pressure ◽  
Pressure Recovery ◽  
Cross Sectional ◽  
Factors Affecting ◽  
Single Shock ◽  
Wide Range

Following the work of Baker and Martin (1), this paper provides further information about static pressure recovery in axi-symmetric supersonic parallel diffusers of fixed length and the same upstream generating nozzle when the diffuser cross-sectional area is varied over a wide range. Correlations based on these and associated experiments by Martin and Baker (2) indicate an area ratio for maximum possible static pressure recovery. At breakdown of the single shock, the diffuser stagnation pressure ratio corresponds to that for normal shock pressure recovery, while the outlet Mach number becomes independent of area ratio as the latter increases. The factors which influence the development and stability of the single shock regime are considered in some detail, from which the role of the boundary layer is shown to be predominant.

Business Aviation in Russia: Specific Features and Prospects of Development

2020 ◽  
Vol 26 (1) ◽  
pp. 86-93
Author(s):  
D. V. Slivinsky ◽  
I. A. Fomina ◽  
D. G. Menshikh
Keyword(s):  
Systems Approach ◽  
National Policy ◽  
Civil Aviation ◽  
Economic Growth Rate ◽  
Factors Affecting ◽  
Organization And Management ◽  
Transport Services ◽  
Business Aviation ◽  
Wide Range

The presented study determines the role of business aviation in the modern economy and examines the specific features of its development in Russia.Aim. The study aims to analyze the development of business aviation in Russia and its correlation with economic development in general.Tasks. The authors determine the benefits of business aviation as a business tool, examine the specific features of the Russian business aviation market and problems of its development, and identify factors that affect the development of business aviation in Russia.Methods. This study uses the methods of comparative and retrospective analysis, cross-country comparison, systems approach, and expert analytics.Results. Business aviation is a new segment of civil aviation for Russia. Therefore, it is advisable to rely on foreign practices in the management of its development. In many countries, business aviation is a separate industry that specializes in providing transport services to a wide range of corporate clients and/or individuals. The development of this industry is associated with the economic growth rate and the development level of the national economy, and also depends on the national institutional specifics. This study describes the specific features of development of business aviation in Russia and problems arising in the organization and management of this type of business.Conclusions. The authors develop a system of factors affecting the development of business aviation in Russia, describe the major problems of this industry, and propose solutions. The results of this study can be used in the development (adjustment) of business aviation development strategies in Russia both at the industrial and corporate level, and in the implementation of the national policy in this field.

Effect of the turning angle on the flow and performance characteristics of long S-shaped circular diffusers

2003 ◽  
Vol 217 (1) ◽  
pp. 29-41 ◽  
Author(s):  
R B Anand ◽  
L Rai ◽  
S N Singh
Keyword(s):  
Total Pressure ◽  
Static Pressure ◽  
Area Ratio ◽  
Secondary Flows ◽  
Performance Characteristics ◽  
Pressure Recovery ◽  
Recovery Coefficient ◽  
Turning Angle ◽  
And Performance ◽  
Pressure Recovery Coefficient

The effect of the turning angle on the flow and performance characteristics of long S-shaped circular diffusers (length-inlet diameter ratio, L/Di = 11:4) having an area ratio of 1.9 and centre-line length of 600 mm has been established. The experiments are carried out for three S-shaped circular diffusers having angles of turn of 15°/15°, 22.5°/22.5° and 30°/30°. Velocity, static pressure and total pressure distributions at different planes along the length of the diffusers are measured using a five-hole impact probe. The turbulence intensity distribution at the same planes is also measured using a normal hot-wire probe. The static pressure recovery coefficients for 15°/15°, 22.5°/22.5° and 30°/30° diffusers are evaluated as 0.45, 0.40 and 0.35 respectively, whereas the ideal static pressure recovery coefficient is 0.72. The low performance is attributed to the generation of secondary flows due to geometrical curvature and additional losses as a result of the high surface roughness (~0.5 mm) of the diffusers. The pressure recovery coefficient of these circular test diffusers is comparatively lower than that of an S-shaped rectangular diffuser of nearly the same area ratio, even with a larger turning angle (90°/90°), i.e. 0.53. The total pressure loss coefficient for all the diffusers is nearly the same and seems to be independent of the angle of turn. The flow distribution is more uniform at the exit for the higher angle of turn diffusers.

Influence of Turbulent Flow Characteristics and Coherent Vortices on the Pressure Recovery of Annular Diffusers: Part A — Experimental Results

2015 ◽  
Author(s):  
Marcus Kuschel ◽  
Bastian Drechsel ◽  
David Kluß ◽  
Joerg R. Seume
Keyword(s):  
Boundary Layer ◽  
High Pressure ◽  
Static Pressure ◽  
Turbulent Transport ◽  
Axial Flow ◽  
Pressure Recovery ◽  
Turbulence Structure ◽  
Reynolds Stresses ◽  
Wide Range ◽  
Operating Points

Exhaust diffusers downstream of turbines are used to transform the kinetic energy of the flow into static pressure. The static pressure at the turbine outlet is thus decreased by the diffuser, which in turn increases the technical work as well as the efficiency of the turbine significantly. Consequently, diffuser designs aim to achieve high pressure recovery at a wide range of operating points. Current diffuser design is based on conservative design charts, developed for laminar, uniform, axial flow. However, several previous investigations have shown that the aerodynamic loading and the pressure recovery of diffusers can be increased significantly if the turbine outflow is taken into consideration. Although it is known that the turbine outflow can reduce boundary layer separations in the diffuser, less information is available regarding the physical mechanisms that are responsible for the stabilization of the diffuser flow. An analysis using the Lumley invariance charts shows that high pressure recovery is only achieved for those operating points in which the near-shroud turbulence structure is axi-symmetric with a major radial turbulent transport component. This turbulent transport originates mainly from the wake and the tip vortices of the upstream rotor. These structures energize the boundary layer and thus suppress separation. A logarithmic function is shown that correlates empirically the pressure recovery vs. the relevant Reynolds stresses. The present results suggest that an improved prediction of diffuser performance requires modeling approaches that account for the anisotropy of turbulence.

scholarly journals Stabilizing electrodeposition in elastic solid electrolytes containing immobilized anions

2016 ◽  
Vol 2 (7) ◽  
pp. e1600320 ◽  
Author(s):  
Mukul D. Tikekar ◽  
Lynden A. Archer ◽  
Donald L. Koch
Keyword(s):  
Elastic Solid ◽  
Present Theory ◽  
Metal Electrode ◽  
Mitigation Strategies ◽  
Factors Affecting ◽  
Wide Range ◽  
Current Densities ◽  
Morphological Instabilities ◽  
The Stability

Ion transport–driven instabilities in electrodeposition of metals that lead to morphological instabilities and dendrites are receiving renewed attention because mitigation strategies are needed for improving rechargeability and safety of lithium batteries. The growth rate of these morphological instabilities can be slowed by immobilizing a fraction of anions within the electrolyte to reduce the electric field at the metal electrode. We analyze the role of elastic deformation of the solid electrolyte with immobilized anions and present theory combining the roles of separator elasticity and modified transport to evaluate the factors affecting the stability of planar deposition over a wide range of current densities. We find that stable electrodeposition can be easily achieved even at relatively high current densities in electrolytes/separators with moderate polymer-like mechanical moduli, provided a small fraction of anions are immobilized in the separator.

Some Studies on Low Solidity Vaned Diffusers of a Centrifugal Compressor Stage

2005 ◽  
Author(s):  
T. Ch. Siva Reddy ◽  
G. V. Ramana Murty ◽  
Prasad Mukkavilli ◽  
D. N. Reddy
Keyword(s):  
Centrifugal Compressor ◽  
Static Pressure ◽  
Pressure Ratio ◽  
Pressure Recovery ◽  
Compressor Stage ◽  
Recovery Coefficient ◽  
Vaned Diffuser ◽  
Flow Angle ◽  
Centrifugal Compressor Stage ◽  
Pressure Recovery Coefficient

Numerical simulation of impeller and low solidity vaned diffuser (LSD) of a centrifugal compressor stage is performed individually using CFX- BladeGen and BladeGenPlus codes. The tip mach number for the chosen study was 0.35. The same configuration was used for experimental investigation for a comparative study. The LSD vane is formed using standard NACA profile with marginal modification at trailing edge. The performance parameters obtained form numerical studies at the exit of impeller and the diffuser have been compared with the corresponding experimental data. These parameters are pressure ratio, polytropic efficiency and flow angle at the impeller exit where as the parameters those have been compared at the exit of diffuser are the static pressure recovery coefficient and the exit flow angle. In addition, the numerical prediction of the blade loading in terms of blade surface pressure distribution on LSD vane has been compared with the corresponding experimental results. Static pressure recovery coefficient and flow angle at diffuser exit is seen to match closely at higher flows. The difference at lower flows could be due to the effect of interaction between impeller and diffuser combinations, as the numerical analysis was done separately for impeller and diffuser and the effect of impeller diffuser interaction was not considered.

Unravelling SMEs’ participation and success in public procurement

2020 ◽  
Vol 20 (4) ◽  
pp. 377-401 ◽  
Author(s):  
Carmela Di Mauro ◽  
Alessandro Ancarani ◽  
Tara Hartley
Keyword(s):  
Small And Medium Enterprises ◽  
Public Procurement ◽  
Sample Selection ◽  
Cross Sectional ◽  
Content Type ◽  
Factors Affecting ◽  
The Public ◽  
Ex Post ◽  
Medium Enterprises

Purpose This paper aims to investigate the role of micro, small and medium enterprises (MSMEs) within the Canadian public procurement, by seeking to identify barriers and supporting factors of MSMEs’ participation and success in public tenders. Design/methodology/approach The empirical analysis builds on a unique survey run by the Canadian federal government, which addressed firms either participating or not participating in public tenders. Model estimation on the survey data relies on sample selection methodologies, which allow separating determinants of MSMEs’ decision to participate from determinants of success. Findings Results provide evidence that costs stemming from asset specificity and uncertainty (e.g. costs of bidding, requirements for participation, bundling of contracts and award rules based on minimum price) affect participation in public procurement. Within MSMEs, micro-firms are the most discouraged from participating. However, after controlling for factors affecting participation, micro-firms emerge as having a higher success rate, possibly because of high specialization and joint participation with larger firms. Research limitations/implications Because of the cross-sectional nature of the data used for hypotheses testing, endogeneity may arise if ex post variables affect ex ante decisions. This may apply if participation in procurement feeds on success in past tenders. Social implications Findings may inform policies for the inclusion of smaller firms in the public marketplace. Originality/value To the best of the authors’ knowledge, this study is the first attempting to disentangle determinants of participation in public tenders from determinants of success. Separating the two aspects helps fine-tune SME-friendly public procurement policies, by identifying actions that effectively facilitate success of MSMEs in public tenders.

Experimental Study of an Exhaust Ejector With Entraining Diffuser

2005 ◽  
Author(s):  
Qi Chen ◽  
A. M. Birk
Keyword(s):  
Gas Turbine ◽  
Exhaust System ◽  
Industrial Applications ◽  
Area Ratio ◽  
Pressure Recovery ◽  
Entrainment Ratio ◽  
Wide Range ◽  
Inlet Swirl ◽  
Air Ejector ◽  
Velocity Pressure

Air-air ejectors are used in a wide range of industrial applications. In gas turbine installations, ejectors are typically used for entraining ventilation air or cooling of exhaust ducting. In some gas turbine applications, the exhaust system must be cooled to limit temperatures inside the structure or to manage heat signatures. The ducts are usually cooled by ejectors with film or effusion cooled diffusers. Entraining diffusers typically have poor pressure recovery and as a result, the ejector performance is affected. This paper presents experimental results on the performance of an air-air ejector with an entraining diffuser. The effects of inlet swirl, and primary nozzle area ratio on the diffuser pressure recovery and ejector pumping were studied. The ejector experiments were carried out on a cold flow wind tunnel that can provide primary air flow rates up to 2.2 kg/s at ambient temperature. Velocity, pressure and temperature measurements were taken in the annulus upstream of the primary nozzle, at the nozzle exit, at the diffuser inlet, on the diffuser walls, and at the diffuser exit. The results show that swirl strongly improves flow non-uniformity at the diffuser exit. The peak pumping performance and the strongest diffuser gap flows was observed with 20° of swirl in the primary nozzle flow. At the no swirl condition, the nozzle area ratio slightly affected the overall entrainment ratio. However, the large nozzle area ratio resulted in the best pumping when swirl was applied.

Impact of corporate governance, financial and regulatory factors on firms’ acquisition ability

2020 ◽  
Vol 20 (3) ◽  
pp. 461-484
Author(s):  
Tahira Awan ◽  
Syed Zulfiqar Ali Shah ◽  
Muhammad Yar Khan ◽  
Anam Javeed
Keyword(s):  
Corporate Governance ◽  
Stock Exchange ◽  
Corporate Control ◽  
Chief Executive ◽  
Cross Sectional ◽  
Content Type ◽  
Factors Affecting ◽  
Regulatory Influence ◽  
Financial Strength

Purpose The capital markets witness phenomenal shifts of corporate control. With the shift of world economy into a global one, there has been a rapid increase in the volume of acquisitions. The previous studies shed light on the motives behind acquisition and impact of acquisition on both bidding and target firms. The purpose of this study is to bridge a gap in literature by exploring the factors affecting the acquisition ability (AA) of the firms. The study has analyzed the role of financial strength, corporate governance and regulatory influence on AA of acquiring firm. Design/methodology/approach Cross-sectional data has been analyzed with respect to Pakistan stock exchange for a period of 2004-2017 by using logit regression. Findings Analysis indicates that firm-specific variables are important determinants in firm’s decision to acquire. Chief Executive Officer duality and presence of institutional shareholders on the board contribute to this important phenomenon in the life of the acquiring firms. Bidding firm’s financial strength is also another important consideration while going for corporate control transfer transactions. The empirical results indicate the better AA for firms characterized by minimum capacity usage, lower level of intangible assets, lower debt levels and lower advertising expenses. However, the regulatory factor has no significant role in firms’ AA. The findings of the study are helpful for managers, regulators and policymakers. Originality/value Analyzing the role of financial strength, corporate governance and regulatory influence on AA of acquiring firm is a rare study, especially in an emerging country such as Pakistan.

Numerical investigation of the role of hyper-mixers in supersonic mixing

2010 ◽  
Vol 114 (1161) ◽  
pp. 659-672 ◽  
Author(s):  
S. L. N. Desikan ◽  
K. Kumaran ◽  
V. Babu
Keyword(s):  
High Speed ◽  
Static Pressure ◽  
Numerical Study ◽  
Mie Scattering ◽  
Stagnation Pressure ◽  
Reacting Flow ◽  
Qualitative Comparison ◽  
Supersonic Mixing ◽  
High Speed Flows

Abstract In this numerical study, the role of hyper-mixers on supersonic mixing is investigated for six different strut configurations. To this end, 3D, compressible, turbulent, non-reacting flow calculations with air as the secondary injectant have been carried out. A qualitative comparison of the predictions with experimental results is made through Schlieren and Mie scattering images. A quantitative evaluation of the predictions is made by comparison with experimentally measured exit stagnation pressure, wall static pressure and the degree of unmixedness. Based on these results, three strut configurations have been selected for carrying out simulations with hydrogen as the injectant. Results from the hydrogen simulations are compared with the predictions using air and also across the strut configurations. The results clearly demonstrate that castellated strut configurations are very effective in enhancing mixing in such high speed flows.

Entrance Aspect Ratio Effect on S-Duct Inlet Performance at High-Subsonic Flow

2016 ◽  
Author(s):  
Asad Asghar ◽  
Robert A. Stowe ◽  
William D. E. Allan ◽  
Derrick Alexander
Keyword(s):  
Aspect Ratio ◽  
Total Pressure ◽  
Static Pressure ◽  
Three Dimensional ◽  
Area Ratio ◽  
Pressure Recovery ◽  
Exit Plane ◽  
Clear Trend ◽  
Parametric Investigation ◽  
Aspect Ratios

This paper reports the internal performance evaluation of S-duct diffusers with different entrance aspect ratios as part of an ongoing parametric investigation of a generic S-duct inlet. The generic S-duct diffusers were a rectangular-entrance (aspect ratio 1.5 and 2.0) transitioning S-duct diffuser in high subsonic (Mach number > 0.8) flow. The test section was manufactured using rapid prototyping for facilitating the parametric investigation of the geometry. Streamwise static pressure and exit-plane total pressure were measured in a test-rig using surface pressure taps and a 5-probe rotating rake, respectively and the baseline and a variant was simulated through computational fluid dynamics. The investigation indicated the presence of streamwise and circumferential pressure gradients leading to a three dimensional flow in the S-duct diffuser and distortion at the exit plane. The static pressure recovery increased for the diffuser with higher aspect ratio. Total pressure losses and circumferential and radial distortions at the exit plane were higher than that of the podded nacelle type of inlet. The increase in the total pressure recovery was observed for the increase in the aspect ratio for the baseline area ratio (1.57) S-ducts, but without a clear trend for the other area ratio (1.8) ducts. The work represents the beginning of the development of a database for the performance of a particular type of generic inlet. This database will be useful for predicting the performance of aero-engines and air vehicles in high subsonic flight.

Sign in / Sign up

Export Citation Format

Share Document