János Vad

János Vad
Budapest University of Technology and Economics · Department of Fluid Mechanics

PhD

About

55
Publications
31,188
Reads
How we measure 'reads'
A 'read' is counted each time someone views a publication summary (such as the title, abstract, and list of authors), clicks on a figure, or views or downloads the full-text. Learn more
620
Citations
Introduction
Skills and Expertise

Publications

Publications (55)
Conference Paper
Full-text available
The paper presents the further development of a combined acoustic-aerodynamic diagnostics method, suited to on-site investigation of industrial axial fans. The method, involving phased array microphone experiments, has been demonstrated in a case study. The acoustic data have been processed by means of a Rotating Source Identifier algorithm, and re...
Article
Full-text available
We describe a mechanical/acoustic study of a short-ducted axial flow fan. The purpose is to compare mechanical noise to that caused by flow phenomena. The eigenfrequencies of the fan are identified through measurement and finite element computations. The fan acoustics is evaluated by beamforming studies using the Phased Array Microphone technique....
Conference Paper
The paper presents a methodology for on-site investigation of short-ducted industrial axial flow fans, as an easily realizable and effective means for concerted diagnostics on fan aerodynamics and acoustics along the rotor radius. The methodology relies on the accessibility of the fan from the upstream direction only. It involves experiments such a...
Article
The paper aims at discovering the relationship between the spanwise gradient of blade circulation and the total efficiency gain due to forward sweep, in the case of low-speed axial flow fans, at the design point. For this purpose, an extensive set of literature data have been processed and evaluated by statistical means. A trend function has been e...
Conference Paper
Full-text available
In the case of axial flow fan rotors used for electric motor cooling, an axial clearance is present between the rotor shroud inlet and the perforated cover. The effect of axial clearance size on the operation of a case study fan has been investigated. The means of investigation were Computational Fluid Dynamics (CFD) and Computational Aero-Acoustic...
Conference Paper
An overview is given on the research maintained by the author about design aspects of three-dimensional blade passage flow in low-speed axial flow industrial fan rotors, affected by spanwise changing design blade circulation due to controlled vortex design (CVD), blade forward sweep (FSW), and their combination.It was pointed out that, comparing th...
Article
A new controlled vortex design (CVD) method has been presented herein, incorporating forward blade sweep (FSW) in the preliminary design phase of axial flow rotors. Supplementing the traditional quasi-two-dimensional (Q2D) technique applied to CVD rotors of notable radial flow, the new method enables a more accurate consideration and control of bla...
Article
This article studies the effect of changing the flow path length on development of total pressure loss in diffuser flows. The studies incorporate quasi-one-dimensional (conical diffuser), two-dimensional (linear blade cascade), and three-dimensional (annular blade cascade) flows. This article concludes that the consequence of decreasing the flow pa...
Conference Paper
Full-text available
The paper reports on the redesign of an electric motor cooling fan for reducing noise and moderating motor shaft power absorbed by the fan, while retaining the original cooling capacity. The datum fan was a radial flow rotor with radially aligned straight blades. The aerodynamic performance and acoustic behaviour of the datum fan have been measured...
Article
The article presents an analytical model for systematic investigation of the effects stimulating or retarding radial outward migration of fluid in the suction side (SS) boundary layer of the blades of axial flow rotors, contributing to increased near-tip loss and promoting tip stalling. With application of the model to an experimental case study, c...
Conference Paper
Full-text available
The aim of this investigation is the acoustical comparison of the broadband noise sources for two fans, the one being the datum unskewed case and the other a circumferentially forward skewed case, using computational fluid dynamics and broadband noise source models. In this way the acoustical advantages of forward skewed blades can be investigated...
Article
A computational investigation has been carried out on the effects of sweep and twist in stationary linear cascades. Circular arc sweep has been applied to the datum cascade of straight cylindrical blades, i.e. spanwise constant stacking line curvature was prescribed. Positive sweep was applied near the end-walls, and the sweep angle distribution wa...
Article
A detailed literature survey is presented herein in order to overview the aerodynamic impact of non-radial blade stacking techniques applied to axial flow fan and compressor rotors. The literature suggests a consensus that forward blade sweep and skew provides a means for the following advantages in the part load operational range of low-speed axia...
Conference Paper
Full-text available
The paper presents comparative studies on low-speed isolated rotors of free vortex design and controlled vortex design (CVD), in order to survey the impact of the vortex design method on the stall behavior of axial flow turbomachinery. The studies are based on 3D laser Doppler anemometer studies and global performance measurements, supplemented wit...
Article
Full-text available
Comparative studies have been carried out on two axial flow fan rotors of controlled vortex design (CVD), at their design flowrate, in order to investigate the effects of circumferential forward skew on blade aerodynamics. The studies were based on computational fluid dynamics (CFD), validated on the basis of global performance and hot wire flow fi...
Article
A fluid mechanical model was elaborated for the formation of mineral wool in the Junkers production technology. The model is based on an analytical approach. The future aim of the model is to establish guidelines for the following improvement in mineral wool quality: reduction of the diameter of mineral wool fibers, improvement of the homogeneity o...
Article
Full-text available
Experimental studies were carried out in order to survey the performance and efficiency aspects of spanwise constant forward and backward sweep in axial flow rotors of low aspect ratio (AR) blading for incompressible flow, for part-load, near-design, and overload operational ranges. The experiments involved overall performance tests, laser Doppler...
Article
Full-text available
Comparative acoustic and wind tunnel experiments were carried out on uncoated and coated isolated airfoils. The aim of the tests was to survey the airfoil noise reducing effect and the aerodynamic impact of the acoustically soft coating consisting of filaments, as a preliminary study in application of such coatings to axial flow turbomachinery blad...
Article
Full-text available
Reynolds averaged computation was carried out around an airfoil using the SST k-ω and the realizable k-ε turbulence model, to provide inlet and far field boundary condition for Large-Eddy Simulation planned in the future. The investigated airfoil was a RAF6 airfoil at angle of attack of 5° at a chord based Reynolds number of 1.22 . 10 5 . Streamwis...
Conference Paper
Full-text available
Comparative studies have been carried out on two axial flow fan rotors at their design flow rate in order to investigate the combined effects of controlled vortex design and circumferential forward skew on blade aerodynamics. The studies were based on Computational Fluid Dynamics, with composition and application of structured hexahedral grids taki...
Conference Paper
The paper presents an analytical model for qualitative prediction of physical effects stimulating or retarding the radial outward migration of high-loss fluid in the suction side boundary layer of the blades of isolated axial flow rotors. This fluid motion is considered as the main cause of tip stalling. In elaboration of the model, the radial acce...
Conference Paper
Full-text available
Pneumatic circuit protection valves are frequently used in the air supply systems of commercial vehicles. This paper presents a flexible computational simulation tool being applied in industrial research and development related to complex mechanical and fluid dynamical aspects in such devices. The numerical model has been created with AMESim, a com...
Article
Full-text available
The applicability of basalt fibers as reinforcing materials has been examined in a polypropylene (PP) matrix. The brittle basalt fibers have been mixed with the PP fibers by carding combined with needle punching and the composite sheets have been produced by pressing. SEN-T fracture mechanical specimens have been cut out of the sheets and the sensi...
Article
A synthetic method has been elaborated for the validation of a Computational Fluid Dynamics tool developed for the future investigation of the combined aerodynamic effects of sweep and spanwise changing stagger angle on stationary linear blade cascades. The validation method is based on specially selected experimental data available in the open tec...
Article
An experimental validation-based method is presented for qualification of CFD tools modelling stationary linear blade cascades. The method gives an aid on how to weight the discrepancy between certain measured and computed quantities when qualifying a CFD tool. The discrepancy between measured and computed data on each elemental cascade is expresse...
Article
Full-text available
Elkészítettünk egy félempirikus modellt, amely képes kisméretű elektropneumatikus (EP) szelepek átömlési karakterisztikájának visszaadására igen széles nyomásviszony-tartományban. Az átömlési karakterisztika alapjául egy egyszerűsített geometriára megalkotott analitikus modell szolgált. A valóságos geometria összetettebb voltából adódó korrekciókat...
Conference Paper
Experimental and computational studies were carried out in order to survey the energetic aspects of forward and backward sweep in axial flow rotors of low aspect ratio blading for incompressible flow. It has been pointed out that negative sweep tends to increase the lift, the flow rate and the ideal total pressure rise in the vicinity of the endwal...
Article
Isolated stationary airfoils of simple geometry were tested in incompressible flow in order to study the combined aerodynamic effects of sweep, spanwise changing circulation, and their combination. Endwall effects were excluded from the studies. The tool of study was computational fluid dynamics, supplemented with wind tunnel experiments involving...
Chapter
The goals in performance that are presently put forward for advanced turbomachines can only be achieved by a careful consideration of the three-dimensional (3D) geometric effects and secondary flows. The two-dimensional (2D) cascade concept for blade design is nowadays useful only as a first guess of the optimum geometry.
Book
Modelling Fluid Flow presents invited lectures, workshop summaries and a selection of papers from a recent international conference CMFF '03 on fluid technology. The lectures follow the current evolution and the newest challenges of the computational methods and measuring techniques related to fluid flow. The workshop summaries reflect the recent t...
Article
Full-text available
A semi-empirical model has been elaborated for analyzing and predicting the flow characteristics of small electro-pneumatic (EP) valves within a wide range of pressure ratio. As a basis for characterization of flow coefficient, an analytical model has been established for a simplified geometry. This model has been corrected corresponding to more co...
Article
Full-text available
A simplified one-dimensional (1D) simulation model has been elaborated in AMESim environment, which is capable of analyzing and predicting the flow characteristics of small electropneumatic (EP) valves within a wide range of pressure ratios. The flow coefficient in the model has been identified on the basis of experiments and was compared with the...
Conference Paper
Full-text available
The paper reports concerted experimental and numerical investigation on the dynamic behavior of a pneumatic pressure regulator valve. It has been pointed out that in case of leakage, laminar flow may develop in the orifice cross-section and thus, the isentropic or sonic orifice models applied in pneumatic simulation must be treated with criticism....
Conference Paper
Full-text available
A simplified one-dimensional (1D) simulation model has been elaborated in AMESim environment, which is capable of analyzing and predicting the flow characteristics of small electropneumatic (EP) valves within a wide range of pressure ratios. The flow coefficient in the model has been identified on the basis of experiments and was compared with the...
Conference Paper
Full-text available
A simplified one-dimensional (1D) simulation model has been elaborated in AMESim environment, which is capable for analyzing and predicting the flow characteristics of small electropneumatic (EP) valves within a wide range of pressure ratios in the sonic range. The flow coefficient in the model has been identified on the basis of experiments and wa...
Article
Full-text available
Abstract Comparative computational investigation has been carried out on two axial flow pump,rotors having identical basic geometrical and flow rate parameters but differing in the design methods. The two rotors were designed for free vortex (FV) and non-free vortex (NFV) operation. The global as well as pitchwise-averaged and pitchwise resolved bl...
Conference Paper
Full-text available
Electro-pneumatic (EP) components are frequently used in brake systems of commercial vehicles. The simulation of EP brake systems is of great importance in order to understand their dynamics for developing a control logic being robust but fulfilling the modern functional demands. On the other hand, the simulation aids the design of EP components be...
Conference Paper
Full-text available
Electro-pneumatic modulators (EPMs) are widely used in controlled pneumatic systems. Their aim is to ensure a controlled operating pressure modulated at a high accuracy and high temporal resolution. This paper reports a computational case study representing the influence of gas dynamic pipe flow effects on the operation of a pneumatic system to be...
Conference Paper
Full-text available
A generally applicable, synthetic simulation model and computational tool has been elaborated for dynamic simulation of solenoid valves (SV) applied as control elements in fast-response pneumatic fluid power systems. The SV of case study has been modeled as a system consisting of coupled magnetodynamic and mechanical subsystems. At the present stat...
Article
Full-text available
This paper presents the analysis of three-dimensional flow field developing through an industrial axial flow fan rotor of non-free vortex design carried out on the basis of concerted experimental and numerical investigations. The paper focuses on non-free vortex flow effects requiring consideration in rotor blade design theories. The distortion of...
Article
The paper presents a novel strategy for design of high-performance non-free vortex axial flow rotors with forward swept blades. The design methodology incorporates the determination of an optimum extent of forward blade sweep into the non-free vortex design methodology, considering the realistic three-dimensional blade-to-blade flow. The design met...
Article
This paper presents the principles of a novel laser optical method in the measurement of concentration distribution of air pollutants. It is based on a concerted application of panoramic annular lens (PAL) optical detection system and a laser sheet illumination equipment (PALLAS). The PAL optic provides full 360° angle of panoramic view information...
Article
Three-dimensional laser Doppler anemometer (LDA) measurements were carried out downstream of isolated axial fan rotors of non-free vortex design in order to investigate the role of radial velocity components in design. The structure of secondary flows due to non-free vortex operation was studied in detail. It is pointed out that the tangential grad...
Article
Full-text available
Large-eddy simulations were carried out in the vicinity of the RAF-6E airfoil at incidence of 5° at a chord based Reynolds number of 122 000. Hybrid RANS/LES method was employed on a zonal domain of the airfoil. Appropriate boundary conditions were investigated for the interface between RANS and LES on 2D RANS simulations. In order to determine the...
Article
Full-text available
A projekt során kialakítottunk AMESim környezetben egy olyan modellezési módszertant és egydimenziós szimulációs eszközt, amelynek révén szabályozott pneumatikus rendszerek, így pl. haszongépjármű-fékrendszerek dinamikai viselkedése vizsgálható, és az egyes fejlesztési módosítások, paraméter-változtatások hatása hatékonyan nyomon követhető. A szele...
Article
Az OTKA projekt keretében mérnöki támpontokat alapoztunk meg fokozott fajlagos teljesítményű - sugár mentén növekvő cirkulációra méretezett - axiális átömlésű forgógépek tervezése során a lapátnyilazás hatásainak figyelembevételére, hatásfokjavítás és széles leválásmentes üzemállapot-tartomány elérése érdekében. A támpontokat a lapátozásra jellemző...