Showing papers by "Vincenzo Dossena published in 2015"

Experimental Observation of Non-Ideal Nozzle Flow of Siloxane Vapor MDM

Abstract: The first experimental results from the Test-Rig for Organic Vapors (TROVA) at Politecnico di Milano are reported. The facility implements an Organic Rankine Cycle (ORC) where the expansion process takes place within a straight axis convergent-divergent nozzle, which is the simplest geometry representative of an ORC turbine blade passage. In order to reduce the required input thermal power, a batch operating mode was selected for the plant. Experimental runs with air allowed to verify the throttling valve operation and the measurement techniques, which include total pressure and temperature measurements in the settling chamber, static pressure measurements along the nozzle axis. A double-passage Schlieren technique is used to visualize the flow field in the nozzle throat and divergent section and to determine the position of shock waves within the flow field. The first experimental observation of non-ideal nozzle flows are presented for the expansion of siloxane fluid MDM (C8H24O2Si3, octamethyltrisiloxane) for vapor expansion in the close proximity of the liquid-vapor saturation curve, at relatively low pressure of operation. A supersonic flow is attained within the divergent section of the nozzle, as demonstrated by the observation of an oblique shock wave at the throat section, where a 0.1 mm recessed step is located. Schlieren visualizations are limited by the occurrence of condensation along the mirror side of the nozzle. Pressure measurements are compatible with the observed flow field.

Flow Evolution in a One and a Half Axial Steam Turbine Stage Under Different Operating Conditions

Abstract: In order to investigate in detail the performance of steam turbine stages the Low Speed Test Rig at Politecnico di Milano has been adapted. The setup consists of a one and an half turbine stage with an inlet guide vane. Two kind of experimental approaches are planned in the project: the first, denominated “performance”, has been carried out by the OGTL department of GE OilG this large amount of data will be used to validate the results of the CFD simulation carried out in the design stage. In this paper the preliminary findings of the steady flow-field will be presented as the basis for further analysis.© 2015 ASME

Design and Operation of a Low Speed Test Turbine Facility

Abstract: In order to investigate in detail the performance of steam turbine stages the Low Speed Test rig at Politecnico di Milano has been adapted. As different designs are going to be compared, very accurate measurement system is required. In order to reduce the performance measurement uncertainty, both thermodynamic and mechanic approach, respectively based on total temperature drop and torque measurement, will be applied. The setup consists of a one and an half turbine stage with an inlet guide vane. The idea is to replicate the condition of a stage for different operating points and the IGV is therefore applied to simulate the presence of an upstream rotor while the second stator provides the downstream potential field at the stage exit. The rig operates in close loop condition and the air is delivered by a centrifugal fan with a maximum pressure ratio of about 1.3; the mass flow is then measured by a Venturi tube and after passing through a plenum and a cooler, enters in the turbine section. The turbine shaft drives a two-stage axial compressor, operating as a brake and equipped with two variable pitch guide vanes (VGV). The compressor allows for an additional pressure ratio, while the fine tuning of the power shaft rotational speed is provided by an electrical motor. The maximum rotational speed for this study is limited to 3000 rpm. Depending on the operation mode and stage setup a maximum expansion ratio of about 1.5 and a maximum mass flow around 15 kg/s can be reached. Two kind of experimental approaches are planned on the rig: the first denominated “performance” will be carried out by the OGTL department of GE Oil&Gas Florence, due to their consolidated experience in global measurements. At the same time, Politecnico di Milano will perform detailed inter-stage measurement with steady probes and time resolved fast response pressure probes. Details of both measurements will be given in this paper. The paper will conclude with the presentation of the operability of the rig obtained with the flange to flange global measurement acquired in the commissioning phase of the project.

An Experimental Study of the Aerodynamics and Performance of a Vertical Axis Wind Turbine in Confined and Non-Confined Environment

Abstract: This paper presents the results of a wide experimental study on an H-type Vertical Axis Wind Turbine (VAWT) carried out at Politecnico di Milano in the frame of the national founded project PRIN 2009. The experiments were carried out in the large-scale wind tunnel of the Politecnico di Milano, where real-scale wind turbines for micro generation can be tested in full similarity conditions. Integral torque and thrust measurements were performed, as well as detailed aerodynamic measurements to characterize the flow field generated by the turbine downstream of the rotor.The machine was tested in both confined and non-confined environment, to highlight the effect of wind tunnel blockage on the aerodynamics and performance of the VAWT under investigation. The experimental results, compared with the blockage correlations presently available, suggest that specific correction models should be developed for VAWTs. The experimental thrust and power curves of the turbine, derived from integral measurements, exhibit the expected trends with a peak power coefficient of about 0.28 at tip-speed ratio λ = 2.5. Detailed flow measurements, performed in three conditions for λ equal to 1.5, 2.5 and 3.5, show the fully three-dimensional character of the wake, especially in the tip region where a non-symmetrical wake and tip vortex are found. The unsteady evolution of the velocity and turbulence fields further highlight the effect of aerodynamic loading on the wake unsteadiness, showing the time-dependent nature of the tip vortex and the onset of a non-symmetric dynamic stall for λ lower than 2.Copyright © 2015 by ASME

Development of a Background-Oriented Schlieren Technique with Telecentric Lenses for Supersonic Flow

Abstract: Background oriented schlieren (BOS) is a quantitative optical technique which exploits light deflection occurring in non-homogeneous transparent media. It allows to indirectly measure the density gradients by analysing the apparent displacement of features of a background pattern when imaged through the investigated flow. Thanks to its simple set-up and to the consolidated data reduction technique based on cross-correlation algorithms the BOS technique has progressively attracted the interest of the researchers. In this work a BOS system using a telecentric lens system has been set up in order to improve measurement accuracy and to avoid 3D effects arising from using conventional entocentric lenses. The design of the telecentric lens system is reported along with an analysis of its performance in term of spatial resolution. Some preliminary tests on a supersonic flows are also reported.