Relaminarization of pipe flow by means of 3d-printed shaped honeycombs

Based on a novel control scheme, where a steady modification of the streamwise velocity profile leads to complete relaminarization of initially fully turbulent pipe flow, we investigate the applicability and usefulness of custom-shaped honeycombs for such control. The custom-shaped honeycombs are used as stationary flow management devices which generate specific modifications of the streamwise velocity profile. Stereoscopic particle image velocimetry and pressure drop measurements are used to investigate and capture the development of the relaminarizing flow downstream these devices. We compare the performance of straight (constant length across the radius of the pipe) honeycombs with custom-shaped ones (variable length across the radius). An attempt is made to find the optimal shape for maximal relaminarization at minimal pressure loss. The maximum attainable Reynolds number for total relaminarization is found to be of the order of 10.000. Consequently the respective reduction in skin friction downstream of the device is almost by a factor of 5. The break-even point, where the additional pressure drop caused by the device is balanced by the savings due to relaminarization and a net gain is obtained, corresponds to a downstream stretch of distances as low as approx.\ 100 pipe diameters of laminar flow

Experimental investigation of transitional flow in a toroidal pipe

The flow instability and further transition to turbulence in a toroidal pipe (torus) with curvature (tube-to-coiling diameter) 0.049 is investigated experimentally. The flow inside the toroidal pipe is driven by a steel sphere fitted to the inner pipe diameter. The sphere is moved with constant azimuthal velocity from outside the torus by a moving magnet. The experiment is designed to investigate curved pipe flow by optical measurement techniques. Using stereoscopic particle image velocimetry, laser Doppler velocimetry and pressure drop measurements, the flow is measured for Reynolds numbers ranging from 1000 to 15000. Time- and space-resolved velocity fields are obtained and analysed. The steady axisymmetric basic flow is strongly influenced by centrifugal effects. On an increase of the Reynolds number we find a sequence of bifurcations. For Re=4075 a supercritical bifurcation to an oscillatory flow is found in which waves travel in the streamwise direction with a phase velocity slightly faster than the mean flow. The oscillatory flow is superseded by a presumably quasi-periodic flow at a further increase of the Reynolds number before turbulence sets in. The results are found to be compatible, in general, with earlier experimental and numerical investigations on transition to turbulence in helical and curved pipes. However, important aspects of the bifurcation scenario differ considerably

Culture, Self-construal and Social Cognition: Evidence from Cross-Cultural and Priming Studies

Members of different cultures vary in basic social psychological processes, such as value orientation, attitudes, attitude-behavior relations, person perception and attribution of observed behavior. Previous researchers have traced back these differences to the respective culture members’ self-construal: Westerners define their self primarily in independent terms, whereas Asians are more likely to define their selves in interdependent ways. This difference in construing the self in turn affects the above mentioned judgmental processes. However, when relying on cross-cultural studies alone, the critical role of the self cannot directly be tested. In this chapter I argue that the accessibility of either independent or interdependent self-knowledge plays a critical role, because judgments are assimilated to either autonomous –or social– contents to the degree that independent –or interdependent– self-knowledge is accessible in the judgmental situation. If so, making self-knowledge of one kind or the other temporarily accessible, should mirror cross-cultural differences. I will review a series of studies confirming this assumption. These studies will be discussed with regard to their implications a) for the role of the self in judgment formation and b) for the flexibility of cultural differences

Subcritical versus supercritical transition to turbulence in curved pipes

Transition to turbulence in straight pipes occurs in spite of the linear stability of the laminar Hagen--Poiseuille flow if the amplitude of flow perturbations as well as the Reynolds number exceed a minimum threshold (subcritical transition). As the pipe curvature increases centrifugal effects become important, modifying the basic flow as well as the most unstable linear modes. If the curvature (tube-to-coiling diameter $d/D$) is sufficiently large a Hopf bifurcation (supercritical instability) is encountered before turbulence can be excited (subcritical instability). We trace the instability thresholds in the $Re-d/D$ parameter space in the range $0.01\leq\ d/D \leq0.1$ by means of laser-Doppler velocimetry and determine the point where the subcritical and supercritical instabilities meet. Two different experimental setups were used: a closed system where the pipe forms an axisymmetric torus and an open system employing a helical pipe. Implications for the measurement of friction factors in curved pipes are discussed

Cross-Cultural Variations in Identifying Embedded Figures : Comparisons from the United States, Germany, Russia, and Malaysia

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.Previous studies have found cross-cultural variation in field dependence. In this study, cross-cultural differences were expected depending on the degree of individualism or collectivism of the respective cultures. Samples were taken from two prototypically individualist cultures, the United States and Germany, and two collectivist cultures, Russia and Malaysia. As predicted, field dependence did not differ between those samples that represented the same type of culture, either collectivist or individualist. However, a clear difference could be found between the two types of cultures; that is, U.S. and German participants were more field independent than were Russian and Malaysian participants

Relaminarising pipe flow by wall movement

Following the recent observation that turbulent pipe flow can be relaminarised by a relatively simple modification of the mean velocity profile, we here carry out a quantitative experimental investigation of this phenomenon. Our study confirms that a flat velocity profile leads to a collapse of turbulence and in order to achieve the blunted profile shape, we employ a moving pipe segment that is briefly and rapidly shifted in the streamwise direction. The relaminarisation threshold and the minimum shift length and speeds are determined as a function of Reynolds number. Although turbulence is still active after the acceleration phase, the modulated profile possesses a severely decreased lift-up potential as measured by transient growth. As shown, this results in an exponential decay of fluctuations and the flow relaminarises. While this method can be easily applied at low to moderate flow speeds, the minimum streamwise length over which the acceleration needs to act increases linearly with the Reynolds number.Comment: 13 pages, 9 figure

Do consumer choices augment narcissism? The role of self-referent processing

Drawing on the choice and self-referent processing literatures, we hypothesized that the act of making consumer choices will augment narcissism, because it directs attention to the self (i.e., increases selfreferencing). Results of three experiments provided support for the proposed path from choice to narcissism via self-referencing (indirect effect), but not for the path from choice to narcissism (total effect). This pattern, first reported in Experiment 1, held only for agentic choices (e.g., products for personal use), which prompt thoughts about the self, and not for communal choices (e.g., charitable organizations), which prompt thoughts about others (Experiment 2). Also, this pattern generalized across agentic choices of public and private products (Experiment 3). We consider theoretical and practical implications

Cultural Diversity in Meta-Cognitive Beliefs about Learning: Within-European Similarities and Differences?

Previous work on cross-cultural differences in the domain of education, has primarily studied Western (European) and Asian cultures or comparisons thereof. Current internationalization trends in higher education however call for a greater understanding of possible within-European cultural differences in the domain of learning. The current paper therefore addresses the question how culture influences the beliefs of Western and Eastern European students. The studies are based on the theory that the beliefs of students and faculty in the Western cultural context can be characterized as primarily ‘mind oriented’, whereas previous research has indicated that the beliefs of East-Asian academics has a stronger ‘virtue orientation’. In the mind orientation, the development of one’s cognitive thinking skills is at the heart of the concept of learning. In the virtue orientation, learning is primarily seen as a process of social and moral development of the person. Since the psychological literature has not yet reached a consensus on the degree and domains in which cultural differences emerge across the Eastern and Western European regions, a two-fold survey study was conducted in the Eastern European countries of Poland and Russia; and the Western European countries of the Netherlands and Germany. Students from both European regions were found to endorse mind oriented beliefs about learning more strongly than virtue oriented ones on the level of both attitudes and behavioral intentions, pointing to a striking cross-cultural similarity across the European region in the domain of beliefs about learning