Über die Turbulenzfleckenbildung

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Paradigma zur Anwendung der irreversiblen Thermodynamik auf die Turbulenz, insbesondere auf die der ebenen Kanalströmung

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Design and Investigation of a Contra-Rotating Centrifugal Fan

Centrifugal fans are common in many fields of application. A centrifugal fan consists of a drive, an impeller, and a volute. The volute casing is designed to turn the dynamic pressure at the outlet of the fan impeller into static pressure and to guide the flow towards a connected geometry, e.g. a flange. However, centrifugal fans without a volute are being used more and more often. A common application is the installation in an air conditioning unit, where typically the dynamic pressure at the outlet is dissipated. In this way, both manufacturing costs and installation space can be saved. On the other hand it must be noted that the air at the outlet of the fan is strongly swirled, which may lead to inadequate acoustic and aerodynamic behaviour of the flow in subsequent devices. These two disadvantages of a fan without casing led to the consideration of a contra-rotating fan. The opportunities of a contra-rotating fans are well known and examined for axial fans, but rarely investigated for centrifugal fans. In this approach we present the design and the measurement of a contra-rotating radial fan comprising two concentrically rotating impellers and two drives. The fan is designed for a volume flow of 150 m³ h-1 and 125 Pa (static pressure). The diameter is 150 mm and the rotational speed of the inner impeller (impeller A) and the outer impeller (impeller B) is 3000 min-1 and 1500 min-1, respectively. The impeller were designed by means of CFturbo latest approach for the calculation of contra-rotating fans. This design's prototype was created by means of 3d printing and measured on a test-rig as well as examined by means of CFD. The results indicate that the simulations are in good agreement with the experiment and provide more detailed insights into the internal flow structure of the impellers. Based on these findings, investigations were made at the leakage point between the two impellers. The results of the test rig measurements and the laser optical measurements demonstrate the influence of different sealing geometries on the leakage. It has been shown that, compared to a centrifugal fan without volute, a contra-rotating fan can significantly reduce the power loss due to swirl at the outlet and increases the power transfer to the fluid compared to a diffuser with guide vanes at the same time

Characteristic Fields of the Natural Transitional Boundary Layer on the Flat Plate

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Bestimmung des Turbulenzfeldes bei Einrichtung der flammenlosen Oxidation von Brennstoff durch hohe Abgas-Luft-Vormischung Abschlussbericht

The aim of this research project which is supported by the Federal Ministry of Research and Technology is to determine the turbulence field during jet mix according to direct flameless oxidation (without local reaction). The fields of turbulence energy and dissipation can be estimated so far as to approach application of the k-#epsilon#-model. For practical application the number of air nozzles, the outlet diameter of the nozzles, the nozzle ring radius, burner output, fuel, air preheating temperature and material data will be varied as parameters. This study describes a calculation method for the estimation of the mix-turbulence field for the thermal inhomogeneious jet system, a calculation programme and first results of its application. Comparative data are available from published results of a study with a ''D5-model'' (four air outlet nozzles and one fuel outlet nozzle). These data are used for verification. (orig./GL)In diesem Forschungsprojekt, gefoerdert vom BMFT, wird das Turbulenzfeld im Mischzustand der Strahlen entsprechend der direkten FLOX-Verbrennung (Flammenlose Oxidation) (ohne lokale Reaktion) bestimmt. Damit lassen sich die Felder von Turbulenzenergie und Dissipation soweit abschaetzen, dass eine erste Naeherung fuer die Anwendung des k-#epsilon#-Modells vorliegt. Hinsichtlich der praktischen Anwendung sollen die Anzahl der Luftduesen, die Austrittsdurchmesser der Duesen, der Duesenkranzradius, die Brennerleistung, der Brennstoff, die Luftvorwaermtemperatur und die Stoffdaten selbst als Parameter variiert werden koennen. In folgender Arbeit werden ein Rechenverfahren zur Abschaetzung des Misch-Turbulenzfeldes fuer das thermische inhomogene Strahlensystem, ein diesbezuegliches Berechnungsprogramm und erste Ergebnisse der Anwendung beschrieben. Als erste Vergleichsdaten liegen veroeffentlichte Versuchsergebnisse an einem ''D5-Modell'' (vier Luftaustrittsduesen und eine Brennstoffaustrittsduese) vor, welche zur Verifikation herangezogen werden. (orig./GL)SIGLEAvailable from TIB Hannover: F94B2155+a / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Forschung und Technologie (BMFT), Bonn (Germany)DEGerman

Sound Level Control for Air Handling Units

People react very differently to the background noise of their environment depending on the activity they are performing. If the background noise is excessive, the sounds are perceived as unwanted noise. Focused intellectual work, for example, regularly requires a lower noise or background sound level than physical activity. The background sound emission of air handling units (AHU) is also perceived as either disturbing or acceptable, depending on the situation. This is particularly problematic in rooms with highly variable human activity, i.e. rooms in which phases of focused, noise-emphasising work and physical activity alternate. An example of such spaces are school classrooms, where noise pollution - also from air handling units - has to be avoided during lessons, while background noise is likely to be submerged and negligible during break times. The use of air handling units is often essential in order to maintain hygienic standards. In common rooms with several people in them, these devices can be perceived as disturbing during quiet periods. Therefore, there is a risk that they are switched off for the sake of convenience. However, as soon as the level of activity in the room increases, the unit is not necessarily put back into operation, which ultimately means that a pathogen-reducing air exchange then no longer exists: This situation has to be avoided. In this presentation, a concept is introduced with the objective of suppressing or reducing the sound emission of air handling units during idle periods (without putting the air handling unit out of operation) and allowing it during active periods. The sound level emitted by the air handling units shall be adapted to a desired background noise in the respective room depending on the situation. Such sound level adjustment has long been applied to devices and systems with loudspeakers. With this technology, also known as automatic volume control, the volume of a loudspeaker is increased or decreased depending upon the volume of the ambient noise. Unlike this well-known principle, the concept presented here permits the adaptation of a noise source (e.g. AHU) to the sound level present in a room. It consists of a microphone, an analyser and a controller and can be used in all common ventilation units (mobile air purifiers, central ventilation and air conditioning systems, etc.). The first findings will be presented at this presentation. The focus lies on the operating principle and the results of the measurements in a room with adjustable reverberation time and different positions of the noise sources and the sound sources due to the ventilation equipment

Test Procedures of Mobile Air Cleaning Devices - First Experiences and Results

The pandemic spread of the SARS-CoV2 viruses is leading to the use of new ventilation concepts in Europe. One of these options is the usage of Mobile Air Cleaning Devices. These are used as an alternative to central HVAC-systems (Heating-, Ventilation- and Air Conditioning-systems) and reduce the load of pathogens in the room. However, there are still no consistent methods for evaluating the performances of such devices. Thatswhy the effect on the pathogens, the benefit to the room, and the influence thereof on the room occupants are nearly unknown.This paper presents the measurements and results of different devices in the range of 500 m³/h to 1500 m³/h and beyond. Attention is given to the applied methods to define the different characteristics. Specifically, the parameters of volumetric flow rate, electrical power consumption, sound power, separation efficiency, effect on pathogens, room air flow, draught risk, and effects in the room show the need for development