Initial results from the NASA-Lewis wave rotor experiment

Wave rotors may play a role as topping cycles for jet engines, since by their use, the combustion temperature can be raised without increasing the turbine inlet temperature. In order to design a wave rotor for this, or any other application, knowledge of the loss mechanisms is required, and also how the design parameters affect those losses. At NASA LeRC, a 3-port wave rotor experiment operating on the flow-divider cycle, has been started with the objective of determining the losses. The experimental scheme is a three factor Box-Behnken design, with passage opening time, friction factor, and leakage gap as the factors. Variation of these factors is provided by using two rotors, of different length, two different passage widths for each rotor, and adjustable leakage gap. In the experiment, pressure transducers are mounted on the rotor, and give pressure traces as a function of rotational angle at the entrance and exit of a rotor passage. In addition, pitot rakes monitor the stagnation pressures for each port, and orifice meters measure the mass flows. The results show that leakage losses are very significant in the present experiment, but can be reduced considerably by decreasing the rotor to wall clearance spacing

Pulsed Ejector Thrust Amplification Tested and Modeled

There is currently much interest in pulsed detonation engines for aeronautical propulsion. This, in turn, has sparked renewed interest in pulsed ejectors to increase the thrust of such engines, since previous, though limited, research had indicated that pulsed ejectors could double the thrust in a short device. An experiment has been run at the NASA Glenn Research Center, using a shrouded Hartmann-Sprenger tube as a source of pulsed flow, to measure the thrust augmentation of a statistically designed set of ejectors. A Hartmann- Sprenger tube directs the flow from a supersonic nozzle (Mach 2 in the present experiment) into a closed tube. Under appropriate conditions, an oscillation is set up in which the jet flow alternately fills the tube and then spills around flow emerging from the tube. The tube length determines the frequency of oscillation. By shrouding the tube, the flow was directed out of the shroud as an axial stream. The set of ejectors comprised three different ejector lengths, three ejector diameters, and three nose radii. The thrust of the jet alone, and then of the jet plus ejector, was measured using a thrust plate. The arrangement is shown in this photograph. Thrust augmentation is defined as the thrust of the jet with an ejector divided by the thrust of the jet alone. The experiments exhibited an optimum ejector diameter and length for maximizing the thrust augmentation, but little dependence on nose radius. Different frequencies were produced by changing the length of the Hartmann-Sprenger tube, and the experiment was run at a total of four frequencies. Additional measurements showed that the major feature of the pulsed jet was a starting vortex ring. The size of the vortex ring depended on the frequency, as did the optimum ejector diameter

The Effect of Pulse Length and Ejector Radius on Unsteady Ejector Performance

The thrust augmentation of a set of ejectors driven by a shrouded Hartmann-Sprenger tube has been measured at four different frequencies. Each frequency corresponded to a different length to diameter ratio of the pulse of air leaving the driver shroud. Two of the frequencies had length to diameter ratios below the formation number, and two above. The formation number is the value of length to diameter ratio below which the pulse converts to a vortex ring only, and above which the pulse becomes a vortex ring plus a trailing jet. A three level, three parameter Box-Behnken statistical design of experiment scheme was performed at each frequency, measuring the thrust augmentation generated by the appropriate ejectors from the set. The three parameters were ejector length, radius, and inlet radius. The results showed that there is an optimum ejector radius and length at each frequency. Using a polynomial fit to the data, the results were interpolated to different ejector radii and pulse length to diameter ratios. This showed that a peak in thrust augmentation occurs when the pulse length to diameter ratio equals the formation number, and that the optimum ejector radius is 0.87 times the sum of the vortex ring radius and the core radius

Courtroom data and politeness research : a case for neo-Peircean semiotics in interpersonal pragmatics

In this article, we take a neo-Peircean semiotic approach to analyzing an interaction in which a routine bail hearing between a defendant and a judge goes awry. Neo-Peircean semiotics is steadily gaining recognition within linguistics for providing a new perspective on meaning. One neo-Peircean approach, referred to as Relationship Thinking (Enfield, 2009; 2013), has the potential to be influential for politeness research and linguistic pragmatics generally. In this article, we explore how the concept of relationship can be used to explore meaning on two dimensions: residential and representational (Kockelman, 2006 a;b). It is our contention that both of these dimensions are crucial to developing an understanding of what happens in the courtroom data on which this special issue focusses. We begin by providing a detailed overview of neo-Peircean semiotics in order to demonstrate its utility for researchers from different disciplines. We then show how a neo-Peircean analytical approach can illuminate elements of data that may not be accounted for in other analyses. This is as a consequence of the neo-Peircean framework’s scope and its capacity for coping with a range of interactionally significant phenomena, from individual linguistic tokens to institutional norms. In our analysis of the data at the heart of this special issue, the Penelope Soto case, we show that problems can arise when interactants have different understandings of what is a sign and what is an interpretant (Peirce, 1955). We make the case that it is a misunderstanding at this level (specifically the interpretations of the word “value”) that is ultimately what causes the interaction to conclude in the way that it does. Ultimately, we suggest that a neo-Peircean approach to the study of in/appropriate behaviour can facilitate links between the traditional (and sometimes disparate) methods of analysis used in politeness research

Tests of Sample-recovery Models of Cued Recall

Sample-recovery models are a predominant class of episodic memory models that seek to explain why sometimes the representation of an experienced event is not retrieved or retrieved incorrectly. In these models, a correct retrieval occurs if the correct target item was sampled among the alternative studied item, then recovered correctly. In cued recall, participants output the representation of a single experienced event, a target, given a presented test stimulus and some defined relationship between the stimulus and the target. This relationship depends on the kind of cued recall and can rely on either studied or pre-experimental relationships. Sample-recovery models of this task share common testable properties related to both sampling and recovery, which we do across two experiments. Experiment 1 tests the property that sampling in sample-recovery models of cued recall is one process: they combine information about test stimulus and its relationship to the target into a single value and sample in a way consistent with the Luce choice rule. We test this assumption by testing whether manipulating the strengths of these relationships generates differential influence on performance in kinds of cued recall where different relationships between test stimulus and response are probed. The pattern of data is inconsistent with one sample process but is consistent with a sampling procedure that separately samples for a cue given the stimulus and a target given a cue. Experiment 2 tests the assumption that recovery performance is independent of other studied items. We allow some cue and target words to be related to some other untested studied words. Targets with a related word on the study list were associated with more correct responses than targets without one. This suggests that recovery in some way uses the memory for the other studied items to help retrieve. We consider how various models of sample-recovery may be adapted to account for these findings, with a particular focus on the Retrieving Effectively from Memory model

Tests Of Sample-recovery Models Of Cued Recall

Sample-recovery models are a predominant class of episodic memory models that seek to explain why sometimes the representation of an experienced event is not retrieved or retrieved incorrectly. In these models, a correct retrieval occurs if the correct target item was sampled among the alternative studied item, then recovered correctly. In cued recall, participants output the representation of a single experienced event, a target, given a presented test stimulus and some defined relationship between the stimulus and the target. This relationship depends on the kind of cued recall and can rely on either studied or pre-experimental relationships. Sample-recovery models of this task share common testable properties related to both sampling and recovery, which we do across two experiments. Experiment 1 tests the property that sampling in sample-recovery models of cued recall is one process: they combine information about test stimulus and its relationship to the target into a single value and sample in a way consistent with the Luce choice rule. We test this assumption by testing whether manipulating the strengths of these relationships generates differential influence on performance in kinds of cued recall where different relationships between test stimulus and response are probed. The pattern of data is inconsistent with one sample process but is consistent with a sampling procedure that separately samples for a cue given the stimulus and a target given a cue. Experiment 2 tests the assumption that recovery performance is independent of other studied items. We allow some cue and target words to be related to some other untested studied words. Targets with a related word on the study list were associated with more correct responses than targets without one. This suggests that recovery in some way uses the memory for the other studied items to help retrieve. We consider how various models of sample-recovery may be adapted to account for these findings, with a particular focus on the Retrieving Effectively from Memory model