Oskar Szulc - Academia.edu (original) (raw)

Papers by Oskar Szulc

Archives of Mechanics, 2021

The paper describes an innovative idea of Thickness Noise Control (TNC) based on adoption of a fl... more The paper describes an innovative idea of Thickness Noise Control (TNC) based on adoption of a flow control strategy (i.e. surface ventilation) for acoustic attenuation of helicopter rotor periodic noise. The TNC method is relying on incorporation of multiple cavities (closed by perforated panels and linked to low- and high-pressure reservoirs) located in a symmetrical manner at front and rear portions of the blade tip. The efficiency of the new approach is verified using a two-bladed model rotor of Purcell (untwisted variant of the blade of Bell UH-1H Iroquois helicopter) in low-thrust hover conditions. The results of numerical simulations, obtained with CFD solver (Spalart–Allmaras turbulence and Bohning–Doerffer transpiration models), indicate that in the near-field of the blade tip, both the amplitude and spectral contents of pressure impulses of emitted thickness noise are significantly improved. The TNC method, in the proposed unsteady mode of operation, turns out to be a suit...

Journal of Thermal Science, 2016

The application of an efficient flow control system on helicopter rotor blades may lead to improv... more The application of an efficient flow control system on helicopter rotor blades may lead to improved aerodynamic performance. Recently, our invention of Rod Vortex Generators (RVGs) has been analyzed for helicopter rotor blades in hover with success. As a step forward, the study has been extended to forward flight conditions. For this reason, a validation of the numerical modelling for a reference helicopter rotor (without flow control) is needed. The article presents a study of the flow-field of the AH-1G helicopter rotor in low-, medium- and high-speed forward flight. The CFD code FLOWer from DLR has proven to be a suitable tool for the aerodynamic analysis of the two-bladed rotor without any artificial wake modelling. It solves the URANS equations with LEA (Linear Explicit Algebraic stress) k-ω model using the chimera overlapping grids technique. Validation of the numerical model uses comparison with the detailed flight test data gathered by Cross J. L. and Watts M. E. during the Tip Aerodynamics and Acoustics Test (TAAT) conducted at NASA in 1981. Satisfactory agreements for all speed regimes and a presence of significant flow separation in high-speed forward flight suggest a possible benefit from the future implementation of RVGs. The numerical results based on the URANS approach are presented not only for a popular, low-speed case commonly used in rotorcraft community for CFD codes validation but preferably for medium- and high-speed test conditions that have not been published to date.

Journal of Physics: Conference Series, 2016

A strong, normal shock wave, terminating a local supersonic area located at the tip of a helicopt... more A strong, normal shock wave, terminating a local supersonic area located at the tip of a helicopter blade, not only limits the aerodynamic performance, but also constitutes an origin of the High-Speed Impulsive (HSI) noise. The application of a passive control device (a shallow cavity covered by a perforated plate) just beneath the interaction region weakens the compression level, thus reducing the main source of the HSI noise. The numerical investigation based on the URANS approach and Bohning/Doerffer (BD) transpiration law (SPARC code) confirms a large potential of the new method. Two exemplary implementations, adapted to model helicopter rotors tested at NASA Ames facility in transonic conditions: Caradonna-Tung (lifting, transonic hover) and Caradonna-Laub-Tung (non-lifting, high-speed forward flight), demonstrate the possible gains in terms of the reduction of acoustic pressure fluctuations in the near-field of the blade tip. The CFD results are validated against the experimental data obtained for the reference configurations (no control), while the analysis of the passive control arrangement is based on a purely numerical research. The normal shock wave is effectively eliminated by the wall ventilation exerting a positive impact on the generated level of the HSI noise.

Journal of Thermal Science, 2003

The flow in transonic diffusers as well as in supersonic air intakes becomes often unsteady due t... more The flow in transonic diffusers as well as in supersonic air intakes becomes often unsteady due to shock wave boundary layer interaction. The oscillations may be induced by natural separation unsteadiness or may be forced by boundary conditions. Significant improvement of CFD tools, increase of computer resources as well as development of experimental methods have again.drawn the attention of researchers to this topic. To investigate the problem forced oscillations of transonic turbulent flow in asymmetric two-dimensional Laval nozzle were considered. A viscous, perfect gas flow, was numerically simulated using the Reynolds-averaged compressible Navier-Stokes solver SPARC, employing a two-equation, eddy viscosity, turbulence closure in the URANS approach. For time-dependent and stationary flow simulations, Mach numbers upstream of the shock between 1.2 and 1.4 were considered. Comparison of computed and experimental data for steady states generally gave acceptable agreement. In the case of forced oscillations, a harmonic pressure variation was prescribed at the exit plane resulting in shock wave motion. Excitation frequencies between 0 Hz and 1024 Hz were investigated at the same pressure amplitude. The main result of the work carried out is the relation between the amplitude of the shock wave motion and the excitation frequency in the investigated range. Increasing excitation frequency resulted in decreasing amplitude of the shock movement. At high frequencies a natural mode of shock oscillation (of small amplitude) was observed which is not sensitive to forced excitement.

Journal of Thermal Science, 2006

Normal shock wave, terminating a local supersonic area on an airfoil, limits its performance and ... more Normal shock wave, terminating a local supersonic area on an airfoil, limits its performance and becomes a source of high speed impulsive noise. It is proposed to use passive control to disintegrate the shock wave. Details of the flow structure obtained by this method are studied numerically. A new boundary condition has been developed and the results of its application are verified against experiments in a nozzle flow. The method of shock wave disintegration has been confirmed and detailed analysis of the flow details is presented. The substitution of a shock wave by a gradual compression changes completely the source of the high speed impulsive noise and bears potential of its reduction.

Lecture Notes in Computer Science, 2014

One of the achievements of the PLGrid Plus project is development of new services and tools desig... more One of the achievements of the PLGrid Plus project is development of new services and tools designed for numerical prediction of aerodynamic performance and aero-acoustic signature of helicopter rotor blades. A novel approach is based on the integration and automation of all stages of a numerical simulation pre-processing, processing and post-processing within a single tool available in the HPC environment of the PL-Grid Infrastructure. A well-established set of professional commercial software packages developed by Numeca Int. and Tecplot Inc., combined with knowledge and experience, ensure high quality of the overall service. Two initial "demonstrators" are designed to deliver aerodynamic performance Aero-H and aero-acoustic data Aku-H for the High-Speed Impulsive HSI noise generated by the two-bladed model of a helicopter rotor in high-speed, transonic hover conditions. An Euler or RANS structured approach to numerical simulation of the flow past ai¾źhovering rotor poses many challenges for Computational Fluid Dynamics CFD. Still, the predictions of Aero-H and Aku-H correspond well with the experimental databases of Caradonna-Tung and Purcell.

International Journal of Engineering Systems Modelling and Simulation, 2011

Strong, normal shock wave, terminating a local supersonic area on an airfoil (or helicopter blade... more Strong, normal shock wave, terminating a local supersonic area on an airfoil (or helicopter blade), not only limits aerodynamic performance but also becomes a source of a high-speed impulsive (HSI) noise. The application of a passive control system (a cavity covered by a perforated plate) on a rotor blade should reduce the noise created by a moving shock. This article covers details of the numerical implementation of the Bohning/Doerffer transpiration law into the SPARC code and includes a validation against the experimental data obtained for the ONERA transonic nozzle with a flat wall. The passive control device is then applied numerically on a helicopter blade in high-speed transonic hover conditions to weaken the shock wave-the main source of HSI noise.

Aerospace Science and Technology, 2004

This paper presents experimental investigations and the results of numerical simulations concerni... more This paper presents experimental investigations and the results of numerical simulations concerning the flow structure in the area where three shock wave interact, that is in the area of the triple point. The topology of shock waves presented in literature and obtained by assuming the equality of static pressure and flow direction downstream of the triple point is not compliant with experimental observations for low Mach numbers. The aim of the investigations described in this paper was to examine the phenomenon of the triple point, in which three shock waves come together in the shape of a λ-foot, and also to verify the present view generally held on this subject.

A numerical simulation of the flow past a complete helicopter poses many challenges for the Compu... more A numerical simulation of the flow past a complete helicopter poses many challenges for the Computational Fluid Dynamics. The rotor blades not only rotate and move forward with a flight speed, but also undergo a complicated motion due to the strong asymmetry of the inflow conditions between the retreating and advancing sides. This articulation consists of the pitch, flap and lead-lag motions designed to maintain the stability of the helicopter in flight. Usually, the first approximation is to abandon the influence of the fuselage and tail rotor and isolate the main rotor blades. The elastic deformation due to airloads is neglected in the overall picture as well. Still, the remaining task is computationally very demanding.

Abstract: The flow in transonic diffusers and supersonic air intakes often becomes unsteady due t... more Abstract: The flow in transonic diffusers and supersonic air intakes often becomes unsteady due to shock wave-boundary layer interaction. Oscillations may be induced by natural separation unsteadiness or forced by boundary conditions. Significant improvements of CFD tools, increased computer resources and the development of experimental methods have again drawn the attention of researchers to this topic. Forced oscillations of a transonic turbulent flow in an asymmetric two-dimensional Laval nozzle have been considered to investigate the problem. A viscous, perfect gas flow was numerically simulated using SPARC, a Reynolds-averaged compressible Navier-Stokes solver, employing a two-equation, eddy viscosity, turbulence closure in the URANS approach. For time-dependent and stationary flow simulations, Mach numbers upstream of the shock between 1.2 and 1.4 were considered. Comparison of computed and experimental data for steady states generally gave acceptable agreement. In the case of...

Abstract: The article presents details of a URANS simulation of the flow field near a hovering mo... more Abstract: The article presents details of a URANS simulation of the flow field near a hovering model of the Caradonna and Tung (1981) helicopter rotor [1]. The CFD code SPARC [2] proves to be capable of capturing the aerodynamics of a two-bladed rotor in high-speed transonic hover conditions. A comparison of the simulation results with the experimental data is acceptable, hence the described methodology might be used with confidence in future numerical studies of application of noise-reducing devices on helicopter blades.

Abstract: A peniche is designed to offset a half-span aircraft model from the wind tunnel wall bo... more Abstract: A peniche is designed to offset a half-span aircraft model from the wind tunnel wall boundary layer. This strategy of model mounting results in large influence on the measured aerody-namic coefficients, compared with full-span data. The negative influence is especially important in high-lift conditions leading to incorrect maximum lift behaviour. A very time-consuming set of python scripts was constructed to allow automatic meshing of the wing-body configuration of the DLR F11 high-lift model placed in the European Transonic Wind tunnel (ETW, Germany). Variations due to different concepts of model mountings (peniches) were included. A block-structured FLOWer solver (DLR, Germany) was used for all flow simulations, simplifying the mesh generation process by using the chimera overlapping grids technique. Preliminary results are available for a full-span configuration obtained with a symmetry condition at the mirror plane. Computations of the half-span model placed directly a...

Flow separation control by Vortex Generators (VGs) has been analyzed over the last decades. The m... more Flow separation control by Vortex Generators (VGs) has been analyzed over the last decades. The majority of the research concerning this technology has been focused on subsonic flows where its effectiveness for separation reduction has been proven. Less complex configurations should be analyzed as a first step to apply VGs in transonic conditions, commonly present in many aviation applications. Therefore, the numerical investigation was carried out for a Shock Wave-Boundary-Layer Interaction (SWBLI) phenomenon inducing strong flow separation at the suction side of the NACA 0012 profile. For this purpose, two kinds of VGs were analyzed: well documented Air-Jet Vortex Generators (AJVGs) and our own invention of Rod Vortex Generators (RVGs). The results of the numerical simulations based on the RANS approach reveal a large potential of this passive flow control system in delaying stall and limiting separation induced by a strong, normal shock wave terminating a local supersonic area.

This chapter describes the possible application of Rod Vortex Generators (RVGs) on helicopter rot... more This chapter describes the possible application of Rod Vortex Generators (RVGs) on helicopter rotor blades. Two different flight conditions are considered: hover and forward flight. The numerical model is validated with the available experimental data of the Caradonna–Tung model helicopter rotor blade (hover conditions) and the AH-1G helicopter (forward flight conditions). The application of RVGs on both rotor blades leads to an increment of the thrust coefficient with a power consumption penalty

A numerical study of air jet vortex generator (AJVG) to delay or suppress flow separation is pres... more A numerical study of air jet vortex generator (AJVG) to delay or suppress flow separation is presented in this paper. The main goal of vortex generators is to change the properties of the boundary layer in order to control the flow and reattach it to the wall. The proposed technology has been studied for a long time. Wallis and Stuart presented this new concept [1, 2] in 60’s. Furthermore, different researchers around the world have compared measurements in wind tunnels with numerical simulations [3-5]. It is well known that the efficiency of AJVG is highly dependence on a lot of parameters such as: skew and pitch angle, mass-flow or main velocity. Many researchers agree with the effectiveness of AJVG on airfoils for low Mach numbers (up to M=0.30.4). For these flow conditions there is an increase of lift coefficient and critical angle of attack with minimal drag penalty. When the Mach number is increased some publications [5] claim a very effective influence of AJVG but some [6] cl...

One of the main achievements of the PLGrid Plus project is the implementation of new tools and se... more One of the main achievements of the PLGrid Plus project is the implementation of new tools and services designed for the numerical prediction of the aerodynamic performance of wind energy turbines. An innovative and unique integration tool (Aero-T) is aiming at automating all stages (pre-, solution and post-processing) of the numerical simulation of the flow around wind turbine rotor blades using commercial CFD software based on the RANS approach and block-structured computational grids. The FINE/Turbo package (Numeca Int.) is applied in the structured grid generation process and solution phases, while the analysis of results is left to the Tecplot 360 (Tecplot Inc.) software. A demonstrator based on the NREL Phase VI rotor experiment (conducted at NASA Ames) is introduced to prove the excellent prediction capabilities of Aero-T.

The paper presents result of the numerical simulation of the flow and acoustic field generated by... more The paper presents result of the numerical simulation of the flow and acoustic field generated by the PZL W-3A “Sokół” (Falcon) helicopter main rotor in high-speed forward flight based on the URANS approach and chimera overlapping grids technique. A refined CFD model (40+ million of volumes, 600+ blocks chimera grid) was designed to resolve the flow-field together with the low-frequency content of the acoustic pressure spectrum in the near-field of the rotor blades to allow for the high-speed impulsive (HSI) noise prediction. The detailed, 3d data was recorded for one rotor revolution (approx. 3 TB) allowing exceptional insight into physical mechanisms initiating the occurrence and development of the HSI noise phenomenon.

The flow in transonic diffusers and supersonic air intakes often becomes unsteady due to shock wa... more The flow in transonic diffusers and supersonic air intakes often becomes unsteady due to shock wave-boundary layer interaction. Oscillations may be induced by natural separation unsteadiness or forced by boundary conditions. Significant improvements of CFD tools, increased computer resources and the development of experimental methods have again drawn the attention of researchers to this topic. Forced oscillations of a transonic turbulent flow in an asymmetric two-dimensional Laval nozzle have been considered to investigate the problem. A viscous, perfect gas flow was numerically simulated using SPARC, a Reynolds-averaged compressible Navier-Stokes solver, employing a two- equation, eddy viscosity, turbulence closure in the URANS approach. For time-dependent and stationary flow simulations, Mach numbers upstream of the shock between 1.2 and 1.4 were considered. Comparison of computed and experimental data for steady states generally gave acceptable agreement. In the case of forced o...

Journal of Physics: Conference Series, Oct 1, 2018