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Experimental analysis on unsteady characteristics of sheet/cloud cavitating Venturi flow under the effect of dissolved air

Malekshah Emad Hasani, Wróblewski Włodzimierz, Bochon Krzysztof, Majkut Mirosław, Rusin Krzysztof

Archives of Thermodynamics

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2022

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Vol. 43, no 3

63--84

EN

The highly dynamic and unsteady characteristics of the cavitating flow cause many negative effects such as erosion, noise and vibration. Also, in the real application, it is inevitable to neglect the dissolved air in the water, although it is usually neglected in the previous works to reduce the complexity. The novelty of the present work is analysing the impact of dissolved air on the average/unsteady characteristics of Venturi flow by conducting sets of experimental tests. For this purpose, two different amounts of dissolved air at five pressure levels (i.e. five different sets of cavitation numbers) were considered in the study of cavitating flow inside a Venturi nozzle. The fast Fourier transform analysis of pressure fluctuations proved that the shedding frequency reduces almost by 50% to 66%, depending on the case, with adding the amount of dissolved air. However, the reduction of 14% to 25% is achieved by the vibration transducers. On the other hand, the cavity enlarges as well as bubbly flow is observed in the test chamber at a higher level of dissolved air. Furthermore, it is observed that the re-entrant jet, as the main reason for the cavity detachment, is more effective for the detachment process in cases with a lower level of dissolved air, where the re-entrant jet front penetrates more toward the leading edge.

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Selection of a numerical model to predict the flow in a fan with a cycloidal rotor

Staśko Tomasz, Majkut Mirosław, Dykas Sławomir, Smołka Krystian

Archives of Thermodynamics

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2021

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Vol. 42, no 4

3--15

EN

A fan with a cycloidal rotor (CRF) is a promising design for application in HVAC (heat, ventilation and air conditioning) systems. Despite the widespread use of the CRF design as a form of propulsion, there are practically no scientific publications examining the possibility of using it as the HVAC fan. The choice of the cycloidal rotor facilitates the operating procedure and widens the range of operating conditions. The paper focuses on the use of the CRF in HVAC, especially as a blowing machine integrated with rectangular ducts, presenting, and discussing the search for the most efficient numerical model. The way of discretizing the computational domain, the turbulence models and the time integration method were tested. A four-blade open rotor fan with a cycloidal impeller was used both in the numerical and in the experimental model. The 2D and 3D CRF models created in the Ansys CFX package were adopted. After a mesh-independence study, different turbulence models were tested for the selected mesh. In the case of the 2D model, various turbulence models such as the SST and the RNG k-ε options were tested and compared with each other. The computational fluid dynamics simulations were compared with in-house experimental results of the velocity field measurements performed by means of laser Doppler anemometry and thermoanemometry. It turned out that the considered numerical models did not reflect the experimental measurements quantitatively. This may be due to the small differences in the shapes of the cycloids of the rotor blades in the numerical model and in real geometry.

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Identification of unsteady effects in the flow through a centrifugal fan using CFD/CAA methods

Pritz Balazs, Probst Matthias, Wiśniewski Piotr, Dykas Sławomir, Majkut Mirosław, Smołka Krystian

Archives of Thermodynamics

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2021

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Vol. 42, no 4

169--181

EN

Besides centrifugal pumps, centrifugal fans are the most common turbomachines used in technical applications. They are commonly used in power engineering systems, such as heat engines and chillers, heating, ventilation, and air conditioning systems, supply and exhaust air systems. They are also used as machines consuming final energy (electricity). Therefore, any improvement in their efficiency affects the efficiency of energy generation and the level of electricity consumption. Many efforts have been made so far to find the most efficient numerical method of modelling flows in fans. However, only a few publications focus on the unsteadiness that may have an impact on device efficiency and noise generation. This paper presents an attempt to identify unsteadiness in the flow through a centrifugal fan by means of computational fluid dynamics and computational aeroacoustics methods. The works were performed using the Ansys CFX commercial software and the results of numerical studies are compared with experimental data.

4

Light extinction and ultrasound method in the identification of liquid mass fraction content in wet steam

Majkut Mirosław, Dykas Sławomir, Smołka Krystian

Archives of Thermodynamics

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2020

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Vol. 41, no 4

63--92

EN

Recently, significant progress has been made in experimental studies on the flow of wet steam, measuring techniques based on recording the phenomenon of extinction of light and ultrasound have been elaborated or improved. The basic value experimentally determined in the final stage was the content of the liquid phase defined as the wetness fraction. The methodology of tests and experimental investigations was presented, as well as the applied and developed measurement systems. Next, some developed designs of new ultrasonic and light extinction measuring probe and their modifications are described. The article presents also some examples of applications of the developed measurement techniques in application to experimental research conducted on wet steam. Examples of comparison between experimental and numerical tests for the extinction method are also provided.

5

Research on unsteady cavitating flow around a Clark-Y 11.7% hydrofoil

Homa Dorota, Wróblewski Włodzimierz, Majkut Mirosław, Strozik Michał

Journal of Theoretical and Applied Mechanics

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2019

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Vol. 57 nr 3

765--777

EN

The paper concerns experimental and numerical investigations focused on the cloud cavitation phenomenon over a hydrofoil. The results of flow visualization by means of a high- -speed camera are presented. The cavitation cycles including vapour structures occurrence, development and collapse were recorded and described. Within the numerical investigation, transient calculations of cavitating flow were performed. OpenFOAM software was used. To model mass transfer between phases, the Kunz cavitation model was chosen. Turbulences were modelled by means of k-ω SST model. The vapour areas appearance, their shapes and changes in time were described and compared with experimental results. The characteristic features of cavitating flow were observed, however further adjustment of the cavitation model was advised.