Romeo Resiga

Politehnica University Timișoara · Research Centre for Complex Fluid Systems Engineering & Hydraulic Machinery Dpt.

Nowadays the renewable energy plays an key role in the development of safe and clean energy. Worldwide and especially in Europe the development of renewable energy is focused on development of new wind and solar power plants. Accordingly, these energy technologies introduce high power fluctuations in the electrical system, which are necessary to co...

The current requirements of industrialized countries require the use of as much renewable energy as possible. One significant problem with renewable energy is that the produced power fluctuates. Currently, the only method available for energy compensation in the shortest time is given by hydroelectric power plants. Instead, hydroelectric power plan...

This paper represents a welcome synthesis of the results obtained by the authors over more than a decade. The reason why such an approach is perfectly justified is found in the novelty of the control techniques of decelerated swirling flows from the conical diffuser of hydraulic turbines. The results presented in this paper refer strictly to the ne...

The paper presents a novel approach for analytical representation of specific energy E and torque T curves versus discharge Q and speed N , for centrifugal pumps operated at variable speed both in pump and turbine mode. An enhanced polynomial expression valid for both E ( Q,N ) and T(Q,N) is introduced and validated against experimental data.

Current requirements of the industrialized countries impose to use as much renewable energy as possible. One meaningful problem of the renewable energy is that the produced power is fluctuating. Currently the only available method for energy compensation in the shortest time is given by hydroelectric power plants. Instead, the hydroelectric power p...

The main purpose of the paper is to investigate experimentally a new concept by using a free runner downstream of the main hydraulic runner turbine to increase the flexibility in operation. The free runner concept supposes that rotates at the runaway speed with vanishing mechanical torque. The main purpose is to redistribute between the shaft and t...

Within the framework of the classical turbine design setup, we present a numerical investigation of unsteady cavitating flow in tandem cascades of guide vanes and rotor blades. The practical relevance of the present investigation is ensured by choosing real blade profiles and domain geometry for the large Kaplan turbines (9.5 m rotor diameter) from...

The present study examines the possibility of using an industrial stirred chemical reactor, originally employed for liquid–liquid mixtures, for operating with two-phase liquid–solid suspensions. It is critical when obtaining a high-quality chemical product that the solid phase remains suspended in the liquid phase long enough that the chemical reac...

The paper explores a tandem configuration of three-blade impellers in a stirred reactor. The working fluid is a liquid-solid mixture and the stirring mechanism fitted with the two impellers must prevent the sedimentation of solid particles while homogenously dispersing them in the bulk liquid. The present numerical investigation, performed with the...

The self-induced instabilities developed in decelerated swirling flows lead to pressure fluctuations. The swirling flows generated under variable speeds of the rotor of a swirl generator using a magneto-rheological brake are numerically and experimentally investigated. Three-dimensional turbulent flow computation is performed for several rotor spee...

The induced flow instabilities are developed in the draft tube cone of the hydraulic turbines leading to the pressure fluctuations with negative impact on the mechanical components lifetime. Usually, two components (rotating and plunging) are discriminated in the unsteady pressure field induced by the swirling flow in the draft tube cone. The rotat...

The decelerated swirling flow in the discharge cone of Francis turbines operated at partial discharge, far from the best efficiency point, develops self-induced instabilities featuring a precessing helical vortex (so-called vortex rope) which hinders the stable and safe turbine operation. This is an intrinsic characteristic of the swirl exiting the...

When converting a baffled stirred reactor to work with a different fluid, usually the original impeller must be replaced with a customized one. If the original impeller was designed for mixing liquids, its performance for liquid–solid suspensions may not be satisfactory. A case study is presented, where a two-blade original impeller is replaced wit...

The fixed blade turbines, e.g. Francis, operating at part load, present a high level of swirl flow at the inlet of draft tube cone. When swirling flow is decelerating, it becomes unstable, giving rise at spiral vortex (or vortex rope). Vortex rope is the main cause for the occurrence of pressure fluctuations in draft tube of hydraulic turbines oper...

In this paper, we introduce a novel passive control method to mitigate the unsteadiness effects associated to the swirling flows with self-induced instabilities. The control method involves a progressive throttling cross-section flow at the outlet of the conical diffuser. It adjusts the cross-section area with a diaphragm while maintaining all posi...

We introduce a new benchmark test case for assessing the robustness and accuracy of various numerical methodologies for simulating swirling flows in pipes and step diffusers. First we present the design and detailed geometry of the swirl generator and downstream test section. The swirl is generated with fixed plane blades, parallel to the symmetry...

Hydraulic turbines operating at off-design regimes inherently have a large residual swirl at runner outlet. This swirling flow is further ingested by the draft tube and its deceleration in the discharge cone results in self-induced instabilities (e.g. precessing vortex rope, low frequency pressure pulsations, power swing) that may hinder the turbin...

Bypass graft patency is strongly influenced by geometric parameters such as anastomosis angle or the presence of competitive flow. Low values of Wall Shear Stress are associated to regions with flow disturbance, a main cause for intimal hyperplasia development and therefore graft failure. This paper analyzes the influence of anastomosis angle and c...

The paper focuses on numerical analysis of temperature field into a magneto-rheological clutch. The magneto-rheological fluid is used for a clutch operated at different speeds. The magneto-rheological clutch application was developed due to the magnetic control and fast response. The two dimensional axi-symmetric computational domain corresponds to...

The swirling flow exiting the runner of a hydraulic turbine is further decelerated in the discharge cone of the draft tube to convert the excess of dynamic pressure into static pressure. When the turbine is operated far from the best efficiency regime, particularly at part load, the decelerated swirling flow develops a self-induced instability with...

The unsteady pressure at the wall of the conical diffuser without and with a 74° heel elbow is examined. The self-induced instability is experimentally investigated on the swirl generator test rig. As a result, the asynchronous (rotating) pressure pulsation associated with the vortex rope and it second harmonic are discriminated. The discriminated...

Currently there is a growing demand for renewable energy in the industrialized countries. However, these sources (e.g. solar, wind) introduce a fluctuating component within the electrical grid. Therefore, the hydraulic turbines have to operate far away from the best efficiency point (BEP) covering a wide range. As a result, the self-induced instabi...

We present a swirl apparatus with lean straight blades in a convergent pipe. An axisymmetric swirling flow model, with blade body force and blade blockage, is used for numerical flow simulation. Numerical results are validated against LDV measurements for axial and circumferential velocity profiles.

The fluid engineering problems require tailored numerical computation algorithms and deep mathematical insight. The computation of swirling flows has been an intense field of investigation during the last three decades. Swirling flows may develop stagnant regions separated from the main flow by an interface that is not a-priori known. The interface...

The hydraulic turbines operated at partial discharge (especially hydraulic turbines with fixed blades, i.e. Francis turbine), developing a swirling flow in the conical diffuser of draft tube. As a result, the helical vortex breakdown, also known in the literature as "precessing vortex rope" is developed. A passive method to mitigate the pressure pu...

The decelerated swirling flow in the discharge cone of Francis turbines operated at partial discharge develops a self-induced instability with a precessing helical vortex (vortex rope). In an axisymmetric geometry, this phenomenon is expected to generate asynchronous pressure fluctuations as a result of the precessing motion. However, numerical and...

Modern hydraulic turbines require optimized runners within a range of operating points with respect to minimum weighted average draft tube losses and/or flow instabilities. Tractable optimization methodologies must include realistic estimations of the swirling flow exiting the runner and further ingested by the draft tube, prior to runner design. T...

Operating Francis turbine at part load is hindered by the flow instabilities developed downstream the runner, in the draft tube cone. The unsteady pressure field induced by the flow instabilities leads to vibrations. The paper presents the experimental investigations of the unsteady pressure field generated by the so-called vortex rope and its asso...

Bypass graft failure is mainly caused by intimal hyperplasia (IH) that occurs at the graft anastomosis after coronary artery bypass grafting (CABG) surgery. It has been shown that local hemodynamics influences the process of IH initiation and progression. A main concern at this type of surgery is to increase the graft patency, respectively to impro...

A weighted proper orthogonal decomposition method (wPOD) is proposed for analyzing the evolution of the swirling flow exiting the hydraulic turbine runner, strongly influenced by the turbine discharge coefficient. Through orthogonal decomposition, the leading modes of the axial and circumferential velocity profiles can be identified with respect to...

The flow unsteadiness generated in a swirl apparatus is investigated experimentally and numerically. The swirl apparatus has two parts: a swirl generator and a test section. The swirl generator which includes two blade rows, one stationary and one rotating, is designed such that the emanating flow at free runner rotational speed resembles that of a...

Operating hydraulic turbines over an extended range of discharge values requires an optimized runner that minimizes the weighted-average draft tube losses. It is shown that the draft tube losses can be minimized before actually designing the (new or refurbished) runner blades by optimizing the runner outlet flow. For this, a new runner surrogate mo...

The energy market imposes new requirements in hydraulic turbines operation. Usually, the old hydraulic turbines are not designed to meet these new requirements. Therefore, the refurbished solutions for hydraulic turbines are expected to be robust and flexible in operation in order to regulate the grid. A methodology is developed for a hydropower pl...

This paper analyses the influence of helical turn numbers to helicity values and axial velocity profile at the outlet sections of constant circular cross-section helical tubes. Five different tubes with one, two, four, six and eight turns and constant total length and amplitude, were considered for analyses in steady and laminar conditions at three...

The paper focuses on numerical analysis of temperature field into a magneto-rheological break. The magneto-rheological fluid is used for a brake operated at different speeds. The magneto-rheological brake application was developed due to the magnetic control and fast response. The two dimensional axi-symmetric computational domain corresponds to th...

Decelerated swirling flows in conical diffusers can develop self-induced instabilities for some configurations of incoming flow. As a result, an upstream steady and axis-symmetrical flow becomes unsteady and three-dimensional with associated pressure fluctuations that hinder the operation of tubomachines. This paper introduces a new approach for mi...

The paper presents an example of applying the theory for pipe swirling flow with stagnant region to the axial expansion turbines. It is shown that for most operating points examined the hub radius exceeds the stagnant region radius, thus the flow detachment from the hub is avoided. However, for the full-load operating points (large discharge and he...

The paper introduces a mathematical model for computing the swirling flow exiting the Francis turbine runner without actually computing the three-dimensional flow in the inter-blade channels. Such models are useful for a-priori assessment of the draft tube hydrodynamics, as well as for runner outlet optimization to achieve a best match with a given...

The paper attempts to elucidate a rather unexpected feature of the unsteady pressure field resulting from the self-induced instability of the decelerated swirling flow in a straight diffuser. We perform a numerical experiment using an axisymmetric surrogate draft tube, with inlet swirl corresponding to the flow exiting a Francis turbine runner when...

The flow in the draft tube cone of Francis turbines operated at partial discharge is a complex hydrodynamic phenomenon where an incoming practically steady axi-symmetric swirling flow evolves into a three-dimensional unsteady flow field with precessing helical vortex (also called vortex rope) and associated pressure fluctuations. The paper addresse...

In this paper we employ the method of Proper Orthogonal Decomposition (POD) in conjunction with the radial basis functions interpolation (RBF) for characterization of the swirling flow at the inlet of the draft cone of hydraulic turbines by modal decomposition. The efficiency of the reduced order model is tested by employing different kernels for R...

We introduce a variational formulation for computing swirling flow states with stagnant regions in a pipe. The new extended flow force functional is maximized with respect to the location of the stagnant region boundary, leading to a swirling flow state with minimum swirl number. By allowing a jump in velocity across the vortex sheet that bounds th...

Aorto-coronary by-pass graft anastomosis geometry is complex, which causes strong secondary flow formation inside the region. Critical flow regions (recirculation regions and particle deposition) inside to the anastomosis zone are found in the current model. Experimental results show high secondary flow along the occluded artery and good fluid mixi...

By-pass graft failure is mainly caused by progressive intimal hyperplasia at graft anastomosis and restenosis. A helical graft induces a swirl flow pattern at the outlet section of the graft, and that can reduce the effects that cause the graft failure. This paper analyses the efficiency of helical geometries in terms of helicity and vorticity. Twe...

We introduce and validate a mathematical model, derived from the turbomachinery throughflow theory, for computing the swirling flow exiting a Francis turbine runner operated within a range of discharge values. This swirling flow, further ingested by the draft tube, is used as inlet condition for numerically assessing the draft tube performance for...

In the present work, numerical analysis is performed in a helically sinuous tube with circular cross-section and a finite pitch under laminar flow conditions. The evolution of flows in three helically sinuous tubes at Re = 500 was studied taking into account the effects of torsion and curvature. Results show that in terms of axial velocity, the cur...

This paper discusses the comparison of the flow fields downstream of two different swirl generators. Both swirl generators are used to imitate the flow at the exit of the hydraulic turbine runner and study spatio-temporal behaviour of the swirling flow in the draft tube (i.e. outlet diffuser part of the hydraulic turbine), which undergoes breakdown...

The decelerated swirling flow in the draft tube cone of hydraulic turbines (especially turbines with fixed blades) is responsible for self-induced instabilities which generates pressure pulsations that hinder the turbine operation. An experimental test rig was developed in order to investigate the flow instabilities. A new method was implemented to...

The decelerated swirling flow in the discharge cone of hydraulic turbine develops various self-induced instabilities and associated low frequency phenomena when the turbine is operated far from the best efficiency regime. In particular, the precessing helical vortex ("vortex rope") developed at part-load regimes is notoriously difficult and expensi...

We introduce a quasi two-dimensional (Q2D) methodology for assessing the swirling flow exiting the runner of hydraulic turbines at arbitrary operating points, within a wide operating range. The Q2D model does not need actual runner computations, and as a result it represents a surrogate runner model for a-priori assessment of the swirling flow inge...

The flow unsteadiness generated in the draft tube cone of hydraulic turbines affects the turbine operation. Therefore, several swirling flow configurations are investigated using a swirling apparatus in order to explore the unsteady phenomena. The swirl apparatus has two parts: the swirl generator and the test section. The swirl generator includes...

PiiF, (PiiF stands for "Fluid Engineering Informatics Platform" which in Romanian is: "Platforma Informatica de Ingineria Fluidelor") is a new web-based platform, developed by a consortium of 6 Romanian Technical Universities, aimed to use the collective experience in Fluids Engineering Education. The platform, available on www.piif.ro, has the fol...

The paper presents a methodology for reducing the hydraulic losses in the draft tube of hydraulic turbines within a wide operating range, from part-load to full-load. The velocity field at the draft tube inlet is parameterized by taking into account the runner blade geometry at the trailing edge via the so called swirl-free velocity. It is shown th...

We investigated the flow field within a rigid-walled numerical model of 30°, 45°, and 60° degree bypass graft in order to attempt to identify different type of vortices developed in distal part of the bypass graft. In steady laminar flow, the presence of branching generates a secondary flow in the form of a pair of counter-rotating symmetrical vort...

The paper presents preliminary results of a work in progress addressing the hydrodynamic stability of swirling flows problems in ducts with variable radius which imply mathematical modeling, dynamic and stability investigations. The proposed quasi-analytical method aims to obtain the velocity profiles with a low order approximation method of which...

The paper presents the optimization procedure of a pump inducer taking into account the cavitation criterion. The pump inducer optimization procedure is based on inverse design method where the inflow and outflow conditions are known. Axial flow is considered as upstream condition while the downstream swirling flow is suited for the pump impeller i...

Operating Francis turbines over extended range is often hindered by the flow instabilities developed downstream the runner, in the draft tube cone. The unsteady pressure field induced by flow instabilities leads to pressure fluctuations. The paper presents the experimental investigations of the unsteady pressure field generated by flow instabilitie...

Developments of model reduction techniques for fluid dynamics applications have been widely analyzed, motivated mainly by the need to develop low costs effective computational models capturing as much of the flow physics as possible. In this paper, we investigate the efficiency of the proper orthogonal method's application in the reconstruction of...

The paper focuses on numerical analysis of hydrodynamic behavior in a discharge cone from a swirling flow generator when is operated at lower runner speeds. The swirl generator is used in laboratory instead of a turbine model in order to investigate different swirling flow configurations into a straight draft tube. The purpose for reducing the spee...

We examine the application of a polynomials based spectral technique to approximate the ordinary differential equation with non-constant coefficients defining the eigenvalue problem governing the stability of the basic flow is a swirling flow problem with applications in turbomachinery. The method is based on Laguerre functions expansions on semi-i...

When reaction hydraulic turbines are operated far from the design operating regime, particularly at partial discharge, swirling flow instability is developed downstream of the runner, in the discharge cone, with a precessing helical vortex and its associated severe pressure fluctuations. Bosioc et al. (2012, “Unsteady Pressure Analysis of a Swirlin...

Coronary angiogram (CA) is the gold standard diagnostic tool for coronary artery stenosis. Restenosis after balloon angioplasty is the major limitation of the technique. The goal of the paper is to evaluate the way in which the wall shear stress (WSS) distribution is affected by the blood flow evolution during the cardiac cycle in re-stenosed arter...

Atherosclerosis creating a constriction can significantly alter the local blood flow dynamics. From a biological aspect, the changes that take place in the flow have a profound effect on the structure and function of the arterial wall and the development of the disease. The purpose of this paper was to non-invasively assess hemodynamic parameters s...

The paper presents a novel mathematical model for a-priori computation of the swirling flow at Kaplan runners outlet. The model is an extension of the initial version developed by Susan-Resiga et al [1], to include the contributions of non-negligible radial velocity and of the variable rothalpy. Simple analytical expressions are derived for these a...

The previous experimental and numerical investigations of decelerated swirling flows in conical diffusers have demonstrated that water injection along to the axis mitigates the pressure fluctuations associated to the precessing vortex rope [1]. However, for swirling flows similar to Francis turbines operated at partial discharge, the water jet beco...

In this paper the hydraulic stresses induced in a Francis turbine runner blade by steady fluid flow were investigated. Based on the one-way coupled simulation, the approach consists of a fluid flow analysis which provides the distribution of the fluid pressure on the blade, followed by the structural finite element analysis. The three dimensional t...

We evaluate the sensitivity of the draft tube losses to the velocity field entering a given Francis turbine draft tube while this turbine is operated within a range of discharge values including part-load and full-load regimes. Within the present methodology, the velocity field at the draft tube inlet is determined prior knowing the runner by solvi...

Cavitating flows are notoriously complex because they are highly turbulent and unsteady flows involving two species (liquid/vapor) with a large density difference. These features pose a unique challenge to numerical modeling works. The study briefly reviews the methodology curently employed for industrial cavitating flow simulations using the two-p...

This paper presents the collaborative work that, the fluid mechanics, hydraulics or hydraulic machineries departments, from 6 Romanian universities, have put together in order to build up a web based platform to be used, by students as well as by teachers, in the study of fluid engineering. The different components of the platform are presented and...