Wyniki wyszukiwania - BazTech

1

Centrifugal compressor performance improvement through multi splitter impeller

Malik Adil, Zheng Qun, Qureshi Shafiq R., Ahmed Salman A., Gambo D. KB

Polish Maritime Research

|

2019

|

nr 2

6--14

EN

In the paper, a back swept impeller of centrifugal compressor is experimentally studied and numerically validated and modified to increase its pressure ratio and improve efficiency, as well as to analyse the effect of splitter blade location between two main blades. The back swept multi splitter blade impeller was designed with a big splitter positioned close to the main blade suction surface and a smaller splitter close to the pressure surface. Adding this multi splitter improves the overall performance of the modified impeller due to less intensive flow separation and smaller pressure loss. In particular, the total pressure ratio was observed to increase from 4.1 to 4.4, with one percent increase in efficiency.

2

Study on the behavior of streamwise vortices formed between leading edge tubercles in a compressor cascade

Zheng Tan, Qiang Xiao-Qing, Teng Jin-Fang, Feng Jin-Zhang

Journal of Theoretical and Applied Mechanics

|

2019

|

Vol. 57 nr 3

617--629

EN

A study has been carried out to investigate the formation mechanism and development of streamwise vortices induced by leading edge tubercles in a high speed compressor cascade. The preliminary assessment of the cascade performance in terms of the total pressure loss coefficient shows that the loss reduction is achieved at high incidence angles. A smaller wavelength leads to higher additional losses at the design point, but gives rise to a greater loss reduction at high incidence angles. The modified cascade with a tubercle wavelength of 4% chord achieves the maximum loss reduction of 36.1% at i = 10◦ , as well as the stall angle improvement of 27.6%. The formation mechanism of streamwise vortices is elaborated on the basis of the streamwise vorticity equation, in which the streamwise turning terms may be responsible for the generation of streamwise vortices. Slices of streamwise vorticity at various streamwise locations, combined with vorticity strength distributions, have been presented to study the development of streamwise vortices. The counter-rotating vortices are divided into the crest-induced streamwise vortices (CSVs) and trough-induced streamwise vortices (TSVs). A streamwise vortex pair formed from a part of the CSV sheets behind troughs, is gradually entrained by the TSV pair along the streamwise direction. In addition, the tubercles with a smaller wavelength result in higher streamwise vorticity strength with which the streamwise vortices interact with the flow separation more sufficiently and delay the separation to a greater extent.

3

Numerical loss analysis in a compressor cascade with leading edge tubercles

Zheng T., Qiang X.-Q., Teng J.-F., Teng J.-Z.

Journal of Theoretical and Applied Mechanics

|

2018

|

Vol. 56 nr 4

1083--1095

EN

A numerical analysis of loss has been carried out to explore the loss mechanism of leading edge tubercles in a high speed compressor cascade. Taking the lead from flippers of the humpback whale, tubercles are passive structures of a blade for flow control. Evaluation of the overall performance in terms of entropy increase shows that the loss reduction is achieved both at high negative and high positive incidence angles, while a rise in the loss is obtained near the design point. And a smaller wave number as well as a smaller amplitude results in lower additional losses at the design point. Spanwise and streamwise distributions of pitchwise-averaged entropy increase combined with flow details have been presented to survey the loss development and, subsequently, to interpret the loss mechanism. The tubercle geometry results in the deflection flow and the consequent spanwise pressure gradient. This pressure gradient induces formation of counter-rotating streamwise vortices, transports away the low-momentum fluid near wall from crests towards troughs and leads to local high loss regions behind troughs as well as loss reduction behind the crests in comparison to the baseline. The interaction between these vortices and flow separation by momentum transfer leads to separation delay and the consequent loss reduction at the outlet.

4

Change in flow separation and velocity distribution due to effect of guide vane installed in a 90° pipe bend

Kumar Saha S., Nandi N.

Mechanics and Mechanical Engineering

|

2017

|

Vol. 21, nr 2

353--361

EN

Present paper makes an effort to study the flow separation and velocity distribution for incompressible turbulent flow through 90° pipe bend due to the effect of guide vane installed in the bend portion. It has been observed here how the normalized velocity distribution profile changes if the guide vane is provided. k-ɛ turbulence model has been adopted for simulation purpose. After validating with existing experimental results, a detailed study has been performed for a particular Reynolds number and four different positions of guide vane. The value of Curvature ratio (Rc/D) has been considered as 1 for present study. The results obtained from the present study have been presented in terms of graphical form. A flow separation region was found at bend outlet for flow through 90° pipe bend without guide vane. This secondary flow separation region was absent for the cases which deals with the flow through 90° pipe bend with guide vane. Velocity distribution at seven different downstream positions have been presented in graphical form. Position to get a fully developed velocity distribution profile for each cases has been estimated on the basis of presented results.

5

Analysis of wing-engine nacelle aerodynamic interference

Zalewski W., Stalewski W.

Journal of KONES

|

2017

|

Vol. 24, No. 3

339--344

EN

The article presents an analysis of the wing-engine nacelle flow interference phenomenon on the example of a light twin-engine commuter aircraft. The problems of propulsion system integration with the wing in airplanes are now frequently the subject of advanced optimization research performed by aircraft manufacturers. The shape of the engine nacelle and its connection with the wing determines the quality of the flow around the wing in that area. This is important for high-lift devices placed at the wing trailing edge behind engine nacelle used during the take-off and landing process. Additionally the flow is effected by the disturbances generated by working propellers, the presence of air inlets and an exhaust system of the engine. The article presents a process of numerical optimization of an engine nacelle rear part shape. The main goal of the process was to eliminate the flow disturbances caused by the engine nacelle-wing interference phenomenon. During analysis, the Adjoint Solver method was used to designate nacelle body areas where modification should have the most important impact on the flow quality. The results obtained from adjoint solver were used in the process of finding the optimum shape of the rear part of the nacelle using a parametric geometry generator powered by Ansys Design Modeler and PARADES software. Comparative computational analysis for selected geometries of the engine nacelle was performed using commercial Ansys Fluent solver. Ansys Fluent is an advanced computational solver based on the finite volume method for solving the Navier-Stokes flow equations. Several dozen of geometric shapes were analysed in the optimization process of the nacelle rear part. The final result was the shape of the engine nacelle with correct flow without separation and vortex structures. The article presents results of calculations and visualization of the flow pattern for analysed cases.

6

Lengthwise finning surface as the method of influence on the flow separation in diffusers

Zaryankin A., Rogalev A., Lisin E., Khudyakova V.

Journal of Applied Mathematics and Computational Mechanics

|

2017

|

Vol. 16, nr 1

127--138

EN

The paper deals with the analysis of power factors acting within the boundary layer for different types of flow: convergent, gradientless and diffuser. Based on the considered formation mechanism of boundary layer separation, a hypothesis about the possible influence on structure and character of a separated flow by changing the gradient of the tangential stresses in the boundary layer was proposed. This impact is proposed to realize by means of the longitudinal finning of diffuser. Verification of the concept is performed on the basis of numerical flow investigation and available experimental data.

7

CFD analysis of aerofoil using dimples and prevent radar signals using stealth technology

Maheswaran R., Manikandan R.

Archives of Materials Science and Engineering

|

2016

|

Vol. 77, nr 2

72--77

EN

Purpose: The main objective of aircraft aerodynamics is to enhance the aerodynamic characteristics and maneuverability of the aircraft. This enhancement includes the reduction in drag and stall phenomenon. The airfoil which contains dimples will have comparatively less drag than the plain airfoil. Introducing dimples on the aircraft wing will create turbulence by creating vortices which delays the boundary layer separation resulting in decrease of pressure drag and also increase in the angle of stall. In addition, wake reduction leads to reduction in acoustic emission. The overall objective of this paper is to improve the aircraft maneuverability by delaying the flow separation point at stall and thereby reducing the drag by applying the dimple effect over the aircraft wing. Design/methodology/approach: This project includes computational analysis of dimple effect on aircraft wing, using NACA 0018 airfoil. Dimple shapes are circular which locates the inward, outward are selected for the analysis; airfoil is tested under the inlet velocity of 30m/s at different angle of attack (-5°, 0°, 5°, 10°, and 15°). Findings: This analysis favors the dimple effect by increasing L/D ratio and thereby providing the maximum aerodynamic efficiency, which provides the enhanced performance for the aircraft. Practical implications: Stealth technology is based on the principle of reflection and absorption that makes the objects’ observability lower and stealthy. A 'stealth' vehicle will generally have been designed from the motive to reduce RCS (Radar Cross Section) of aircrafts i.e. radar signature of aircrafts.

8

Influence of membrane amplitude and forcing frequency on synthetic jet velocity

Kurowski M., Doerffer P.

TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk

|

2015

|

Vol. 19, No 2

111-120

EN

This paper presents the results of numerical investigations of a synthetic jet actuator for an active flow control system. The Moving-Deforming-Mesh method as a boundary condition is used to capture the real physical phenomenon. This approach allows precise investigation of the influence of the membrane amplitude, the forcing frequency and cavity effect on the jet velocity. A synthetic jet actuator is simulated using a membrane perpendicular to the surface arrangement. Two cases are investigated to maximize the jet velocity – an actuator with one and two membranes in a cavity. Two main forcing frequencies can be specified in the synthetic jet actuator application. One corresponds to the diaphragm natural frequency and the other corresponds to the cavity resonant frequency (the Helmholtz frequency). This study presents the results of actuators operating at the two abovementioned forcing frequencies. The simulation results show an increase in the jet velocity as a result of an increase in the membrane peak-topeak displacement. This study was a preliminary study of the synthetic jet actuator for single and double membrane systems. The optimization process of the synthetic jet actuator geometry and parameters is ongoing. Numerical results obtained in these investigations are to be validated in the experimental campaign.

9

Development of active composite aerofoil for assessment of novel flow control concepts

Koschichow R., Holeczek K., Koschichow D., Rüdiger F., Kostka P., Langkamp A., Fröhlich J., Modler N.

Composites Theory and Practice

|

2015

|

R. 15, nr 3

146--151

EN

In this paper, an investigation of the dynamic effects of the low-amplitude, high-frequency excitation of a composite aerofoil by means of integrated actuators on the flow is presented. For this purpose, a well-established elastic NACA 64-418 profile was manufactured from a glass fibre reinforced epoxy resin with integrated active elements. The modal properties of the profile were optimized during the design process in such a way that the spatial distribution of nodes and antinodes of the profile is potentially advantageous for the influence of the flow behaviour around the profile. Additionally, the respective eigenfrequency of the profile should be high enough to efficiently influence the flow. The first numerical and experimental results confirm that the aimed modal properties could be obtained. The optimized profile design has been implemented in the resin transfer moulding manufacturing process and selected low-profile actuating elements were applied after fibre-reinforced plastics consolidation on the inner surface of the NACA profile. The applicability of the proposed flow control approach will be evaluated in detail in a specially developed flow channel in further investigations.

PL

W pracy przedstawiono badania dynamicznego wpływu niskoamplitudowego, wysokoczęstotliwościowego pobudzenia za pomocą zintegrowanych w kompozytowy profil lotniczy elementów wykonawczych na opływające profil medium. W tym celu dobrze poznane profile typu NACA 64-418 zostały wytworzone z materiału kompozytowego na bazie żywicy epoksydowej wzmocnionej włóknami szklanych i wyposażone w zintegrowane elementy wykonawcze. Parametry modalne profili zoptymalizowano w procesie projektowania w taki sposób, iż przestrzenne rozmieszczenie węzłów i strzałek profilu ma potencjalnie korzystny wpływ na opływające go medium. Dodatkowo, odpowiadająca tej postaci częstotliwość własna profilu musi być wystarczająco wysoka, aby efektywnie wpływać na przepływ. Pierwsze numeryczne i eksperymentalne wyniki potwierdzają możliwość uzyskania zamierzonych parametrów modalnych. Do wytworzenia zoptymalizowanej konstrukcji profilu wykorzystano technologię RTM (ang. Resin Transfer Moulding). Po skonsolidowaniu profilu wybrane cienkie elementy wykonawcze zostały zaaplikowane na wewnętrznej powierzchni profilu NACA. Możliwość zastosowania proponowanego podejścia do kontroli przepływu medium będzie określana szczegółowo w dalszych badaniach w specjalnie skonstruowanym kanale przepływowym.

10

Transonic axial compressor active boundary layer control concept and its evaluation

Ziegler B.

Zeszyty Naukowe Politechniki Rzeszowskiej. Mechanika

|

2014

|

z. 86 [290], nr 1

143--150

EN

The article presents a concept of boundary layer control in transonic axial compressors. Two methods for obtaining boundary layer control are presented. It is proposed that by combining those two methods, an efficient way of preventing turbulent boundary layer separation in transonic compressor passages can be obtained without the loss of the compressor flux. The concept, is based on the idea of removing boundary layer flows at one stage, and using this removed flux as a blowing type boundary layer control, at previous stage where lower pressures occur. This creates a loop of secondary flow between those stages preventing the boundary layer separation (especially the shock induced separation) on both stages. Two dimensional numerical analyses are performed to assess the possible passage performance (especially the diffusion factor). On the basis of two dimensional analyses, the possible performance of such compressor stage is estimated. The aerodynamic possibility of greatly increasing the axial compressing stage loadings and pressure ratios without increasing blade velocities and passage flow Mach numbers is shown. This possibility has a growing importance as the overall pressure ratio of turbojet engines and tends to rise with every next engine generation. Main conclusions are drawn, showing the possibilities for further research in the scope of this concept.

PL

Artykuł prezentuje koncepcję dwóch metod kontroli warstwy przyściennej w kanałach transonicznych sprężarek. Zaproponowano aby przez połączenie tych dwóch metod, skuteczny sposób zapobiegania turbulentnego oddzielenia warstwy granicznej w transonicznych kanałach sprężarek można uzyskać bez straty strumienia sprężarki. Koncepcja opiera się na idei usuwania przepływów w warstwie brzegowej w jednym etapie oraz wykorzystaniu strumienia jako kontroli warstwy brzegowej we wcześniejszym etapie, gdy występuje niższe ciśnienie. To tworzy wtórną pętlę przepływu pomiędzy tymi etapami uniemożliwiających rozdzieleniu warstwy granicznej (zwłaszcza rozdzieleniu wywołanemu wstrząsem) na obu etapach. Dwuwymiarowa analiza numeryczna została przeprowadzona w celu oceny możliwej wydajności przejściowej (zwłaszcza współczynnika dyfuzji). Na podstawie dwuwymiarowej analizy określono możliwość wykonania takiego stopnia sprężarki. Przedstawiono aerodynamiczną możliwość znacznego zwiększenia obciążeń stopnia sprężania osiowego i wskaźników ciśnienia bez zwiększania prędkości łopat i liczb Macha podczas przepływu. Możliwośćta ma coraz większe znaczenie jako wskaźnika całkowitego ciśnienia silników turboodrzutowych i wykazuje tendencję do wzrostu w każdej następnej generacji silnika. Nakreślono główne wnioski, pokazując możliwości dalszych badań w tym zakresie.

11

Badania modelowe powolnych przepływów w przewodach za pomocą cyfrowej anemometrii obrazowej oraz modelowania matematycznego

Gawor M., Sławomirski M. R., Sobczyk J., Tichoruk M.

Prace Instytutu Mechaniki Górotworu PAN

|

2012

|

Vol. 14, no. 1-4

223--238

PL

Wykonano pomiary profi li prędkości przepływu powietrza w przewodach o ściankach wykonanych z przeźroczystego materiału (model). Ze względu na zastosowaną technikę pomiarową (cyfrowa anemometria obrazowa) przewody miały prostokątne przekroje. Przepływy były wymuszane za pomocą tunelu aerodynamicznego z dodatkowymi elementami kształtującymi płaski profi l prędkości na wejściu do modelu. Analizie zostały poddane w szczególności okolice zakrzywień („kolana”) i rozgałęzień przewodów. W przyjętym zakresie prędkości (do 0.2 m/s) nie zaobserwowano jakichkolwiek objawów niestateczności ruchu płynu prowadzących do powstawania turbulencji. Rezultaty doświadczalne porównano z wynikami symulacyjnych obliczeń numerycznych opartych na rozwiązywaniu równania Naviera-Stokesa, otrzymując zadziwiającą zgodność. Wyniki pomiarów i symulacji komputerowych mogą być przydatne podczas analizy rozpływu gazów w kopalnianej sieci wentylacyjnej, a także ewentualnie przepływów w układzie krwionośnym i oddechowym.

EN

The authors performed empirical research concerning air velocity profile for flows through tube systems made of transparent materias. Owing to the appointed measurement technique (numerical image anemometry) tube systems of rectangular cross-sections have been applied. Air flows were initiated by the aerodynemic tunnel. In order to obtain homegeneous stream extra forms were mounted at the entrance to tube systems. The elements of the tube systems of high curvature (e.g. ‘knees’) as well as braches of tube systems were the subject of detailed investigations. For the appointed flow velocities any symptms of flow instability and the development of turbulence have not been observed. The results of empirical measurements represented high compatibility with results obtained by means of the computer simulations based on solutions of the Navier-Stokes equation for comprebble flows. The results of empirical reseach and computer simulations may be applied for the analysis of air flows though mining ventillation systems and for analysis of fl uid motions in human and animal respiratory and circulatory systems.

12

Analiza powstawania przepływu wstecznego przy opływie ciał sztywnych

Sławomirski M. R.

Prace Instytutu Mechaniki Górotworu PAN

|

2011

|

Vol. 13, no. 1-4

267--290

PL

Przedstawiono analizę ruchu płynu rzeczywistego w pobliżu sztywnych ścianek ciała w warunkach przepływu akcelercyjnego i deceleracyjnego. Przepływ w warstwie granicznej rozważany jest w oparciu o równania Prandtla. Korzystając z numerycznych rozwiązań samopodobnych równań przepływu wykazano, że przepływ akceleracyjny jest ruchem regularnym, natomiast w przepływie deceleracyjnym występują osobliwości odpowiadające liniom i punktom oderwania. Obszarom oderwania odpowiada rodzina konkurencyjnych rozwiązań, z których tylko nieliczne posiadają sens fizykalny. Jako kryterium fizykalnej poprawności przyjęto warunek zanikania rotacji prędkości w miarę oddalania się od sztywnej ścianki. Przedstawiono złożone rozważania oparte na metodach sami-perturbacyjnych dotyczące przepływu w sąsiedztwie punktu oderwania. Analiza równań przepływu dla funkcji prądu Ψ przed i za punktem oderwania wykazała, że ścisłe rozwiązania równań Prandtla które poprawnie opisują ruch płynu w warstwie granicznej przed punktem oderwania nie posiadają swojej kontynuacji w obszarze oderwania, tj. za punktem oderwania.

EN

The analysis of accelerating and decelerating flows of real fluids in the vicinity of fixed walls has been presented. Fluid motions in the laminar boundary layer have been considered by means of the Prandtl equations. Applying numerical solutions of self-similar flow equations it has been demonstrated that that the accelerating flows is represented by regular fluid motions whereas for decelerating flows there are singularities corresponding with separation points and separation lines. For the separation zones there are families of various solutions, and rare of them possess physical meaning. The vanishing of fluid vorticity in the distance from fixed wall has been applied as the condition of physical correctness of the formal solution. Elaborate considerations based on the semi-perturbation methods and concerning the flow in the vicinity of the separation point have been presented. The analysis of flow equations for the stream function Ψ for upstream and downstream zones with respect to the separation point have demonstrated that exact solutions of the Prandtl equations which desctibe correctly the fluid motion in the laminar boundary layer upstream the separation point do not possess a prolongation in the separation zone, i.e. downstream the separation point.

13

Protodiastole and vessel damage in atherosclerosis

Beraia M., Todua F., Khomeriki I.

Biocybernetics and Biomedical Engineering

|

2006

|

Vol. 26, no. 3

65-75

EN

Hemodynamic forces are now known to be the localizing factors in atherogenesis, but conclusions as to the causes of the vessel wall damage are inconsistent. The purpose of the study was examination of the blood flow features in the aortic arch and establishment of the initial factors of atherogenesis. 15 men (age from 27 to 35 years) have been examined by magnetic resonance angiography on Siemens-Sonata-Cardio unit. Blood flow peak systolic velocity changes at the opposite walls of the aortic arch have been revealed. During protodiastole, the flow was found to form opposite directed streams, and a flow arrest with a flat flow profile was noted in discrete sites of the aorta. At these specified places, the peak systolic velocity was found to be low. Blood protodiastolic acceleration was 6 times higher than in the systole, and the shear stress was found to exceed the verge of the endothelial endurance. The circular blood flow at the aortic arch in protodiastole is characterized by a high acceleration, and the gradient pressure in the flat profile can damage the internal layers of the vessel.

14

Streamwise vortices induced by semi-circular rods submerged in turbulent boundary layer.

Szumowski A., Wojciechowski J.

Archive of Mechanical Engineering

|

2005

|

Vol. LII, nr 4

353-360

EN

Two semi-circular rods set up in V-shape form were used to generate streamwise vortices in a turbulent boundary layer. The vortices, due to induced helical flow, supplement the streamwise momentum of retarded air particles at the body surface with the momentum of the external flow. In this experimental study it was found that vortices are at their most intensity if the Reynolds number of the flow over generator, based on the diameter of rods is within the range 10 to the 4 - 1.5 x 10 to the 4. Several semi-circular rods set up in a tooth line were examined in delaying the separation of the turbulent boundary layer at a convex cylindrical surface. It has been noted that delay of separation is at its most efficient when the height of the generator is equal to at least half of the boundary layer thickness.

PL

Wiry, których oś wirowania pokrywa się z głównym kierunkiem przepływu (wiry wzdłużne) powodują ruch śrubowy elementów płynu. Tym samym, jeżeli wiry te generowane są w warstwie przyściennej, powodują intensyfikację transportu pędu w kierunku ścianki, a przez to uzupełnianie strat pędu warstwy przyściennej i opóźnianie jej oderwania. W pracy badano na drodze eksperymentalnej wiry wzdłużne generowane przez pręty półwalcowe zestawione w kształcie litery V, umieszczone na płaskiej ściance. Stwierdzono, że intensywność wirów jest największa dla liczb Reynoldsa w zakresie 10 do potęgi czwartej - 1.5 x 10 do potęgi czwartej i kąta rozwarcia między prętami ok. 60 stopni. Efekt działania wytworzonych w ten sposób wirów na opóźnienie oderwania warstwy przyściennej badano przy opływie wypukłej powierzchni walcowej. Uzykane wyniki świadczą, że skuteczność generatora wirów rośnie ze zwiększeniem promienia półwalca aż do wartości tego promienia równego w przybliżeniu połowie grubości warstwy. Dalsze zwiększenie promienia nie powoduje istotnego wzrostu opóźnienia oderwania.

15

Niektóre zagadnienia poprawy struktury przepływu w elementach układów gazowo-parowych typu utylizacyjnego

Gribin V. G., Paramonov A. N., Jesionek K. J.

Systems : journal of transdisciplinary systems science

|

2004

|

Vol. 9, Sp. 2/1

354-359

PL

Ograniczenie osiągów aerodynamicznych szeregu elementów systemów przepływowych należy od możliwości wystąpienia oderwania strumienia od ścianki kanału. To oderwania spowodowane jest oddziaływaniem dodatniego wzdłużnego gradientu ciśnienia statycznego, opóźniającego ruch płynu w obszarze warstwy przyściennej. Przedstawiono różne sposoby zapobiegania oderwaniu strumienia w kanałach, ich skuteczność i zakresy stosowalności. Szczególną uwagę, zwrócono na rolę tzw. komór wyrównawczych.

EN

Limiting of aerodynamical performance many elements of flow systems is depend on possibility of stream separation. This separation is caused by the action of adverse pressure gradients, retarding in the fluid in the boundary layer. This paper describes previous and new methods for flow separation prevention, their effectiveness and ranges of application. A special attention was paid on meaning of equalization chamber.

16

Numerical investigation of flow in mixed-flow pump with volute

Sedlar M.

TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk

|

2001

|

Vol. 5, No 4

595-602

EN

The work considers the modelling of flow in a complete mixed-flow pump with volute, including tip leakage flows, using both quasi-steady and true transient models of rotor/stator interaction. The CFX-TASCflow CFD package from AEA Technology is applied to calculate flows for a wide range of flow rates from about 0.2 to 1.4 Q/sub 0pt/. Fairly detailed flow structures have been predicted based on the flow rates, especially impeller inlet recirculation and separation on the suction side of the blades for suboptimal rates of flow, as well as strong secondary flows and separation in the volute for off-design conditions. The rotor/stator interaction influence on flow phenomena both in the impeller and volute have been investigated with very interesting results, providing good insight into the dynamics of flow close to the volute tongue. Based on the computational results, pump performance curves (Q-H, Q- eta /sub h/ and Q-P, eta /sub h/ being the hydraulic efficiency) have been obtained. The data from this numerical investigation have been used to improve the inlet part of the impeller blades, especially close to the tip. The geometry modifications have resulted in reduced cavitation in the impeller as well as noise at suboptimal rates of flow.

17

The Analysis of separation and methods of three-dimensional flow structure detection in the boundary layer shock wave interaction

Czerwińska J.

TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk

|

1999

|

Vol. 3, No 1

53-140

EN

The normal shock wave turbulent boundary layer interaction still draws a great deal of attention as a flow phenomenon. This is due to its profound importance to numerous applications. The understanding of phenomena is crucial for future aims connected with the interaction control. Experimental investigations of the interaction have been carried out since the 1940s. They were aimed however at the determination of such general flow features as: pressure distribution, shock wave configuration or oil visualization of separation structures. In order to better understand the phenomenon, measurements of the entire field are required. At present, such measurements do not exist. A great help is expected from numerical simulations in this respect. There is enough experimental data to check the general features of the flow obtained from calculations. This thesis presents numerical simulations of flow that is assumed: steady, three-dimensional, compressible, viscous and turbulent. Its general aim is to present to what extend the modern numerical methods are able to predict the flow in shock wave turbulent boundary layer interaction including shock induced separation structures. These structures are very sensitive to channel geometry and may be useful in the understanding of separation's development. In order to illustrate the abilities of numerical simulations, one aim of the presented thesis is to investigate the effect of the span-wise depth of the nominally two-dimensional test section. The presented results cast some light on the common problems experienced by typical comparisons of two-dimensional simulations to wind tunnel tests having a three-dimensional nature. The first Chapter presents the basic theory of elementary structures. Considerations of elementary structures of the flow along with their dependencies are necessary for a better understanding of the separation flow structures induced by the boundary layer shock wave interaction. The classification of elementary structures will be presented. In addition, the possible occurrence of bifurcation will also be studied. The second Chapter will be devoted to studying specific cases of transonic turbulent flow. The analysis of numerical results will be bounded to the shock wave structure. Studies shall include: the influence of the numerical scheme, three-dimensional effects connected with the changing width of the channel, a comparison to experiment and the influence of the symmetric boundary condition on the flow prediction in the channel. Finally, the boundary layer influence on the 1-foot structure will also be presented. Chapter three will present the separation structures. Here too a comparison to experiments will be done. Changes in separation structures connected with the width of the channel will be studied. The influence of the symmetry boundary condition will be shown. Finally, the specification of the basic flow structures will be done.

18

Numerical study of leading edge separated flow over wing-canard configuration, with emphasis on aerodynamic coefficients estimation.

Ghmmam A., Goraj Z.

Archive of Mechanical Engineering

|

1998

|

Vol. XLV, nr 1

43-57

EN

A numerical investigation for wing-canard configuration, based on potential flow, and non-linear panel methods, is performed. Flow emanating from leading edges is allowed to separate, with every vortex line represented by a number of segments with the last segment extending to infinity. Effect of canard vertical position, and deffection on the wing loading are investigated. Tapered swept wing, with rectangular canard and cropped delta wing with swept canard are considered. The model assumes a simplified geometry with no tickness or camber. Results indicate considerable influence onto the main lifting surface in the presence of the canard. At low to moderate angles of attack, canard effect could be positive or negative, depending on canard position and degree and direction of deflection. A comparison with experiment shows a good agreement in sectional lift distribution over the wing.

PL

W pracy przedstawiono model obliczeniowy i wykonano symulację opływu wokół konfiguracji 'Kaczka'. Do wyznaczania obciążeń aerodynamicznych zastosowano nieliniową metodę panelową. Uwzględniono, że w ostrych krawędziach natarcia płatów (przedniego o głównego) przy większych kątach natarcia następuje oderwanie przepływu. Założono, że włókna wirowe schodzące z krawędzi spływu i natarcia są styczne lokalnie do linii prądu i rozciągają się do nieskończoności. Zbadano wpływ pionowego przesunięcia płata przedniego oraz jego wychylenia na obciążenie aerodynamiczne płata głównego. Rozważono skośne płaty główne z prostokątnym płatem przednim oraz ścięte płaty delta wraz ze skośnym płatem przednim. Założono, że model ma geometrię uproszczoną (płaty cienkie i niewysklepione). Obliczenia wykonano dla tzw. Europejskiego modelu standardowego, dla którego znane są charakterystyki otrzymane eksperymentalnie w tunelach aerodynamicznych. Na małych i umiarkowanych kątach natarcia wpływ płata przedniego na płat główny może mieć zarówno dodatni (zwiększający siłę nośną) jak i ujemny efekt, w zależności od położenia płata przedniego i kierunku jego wychylenia. Porównanie otrzymanych wyników obliczeń z wynikami eksperymentalnymi wskazuje na dobrą zgodność odnośnie rozkładu siły nośnej wzdłuż rozpiętości płata głównego.