R. Sangras

Bio: R. Sangras is an academic researcher from University of Michigan. The author has contributed to research in topics: Plume & Turbulence. The author has an hindex of 6, co-authored 6 publications receiving 148 citations.

Self-Preserving Properties of Unsteady Round Nonbuoyant Turbulent Starting Jets and Puffs in Still Fluids

Abstract: The self-preserving properties of round nonbuoyant turbulent starting jets, puffs, and interrupted jets were investigated both experimentally and theoretically for flows in still and unstratified environments. The experiments involved dye-containing fresh water sources injected into still fresh water within a large windowed tank. Time-resolved video images of the flows were obtained using a CCD camera. Experimental conditions were as follows: jet exit diameters of 3.2 and 6.4 mm, jet exit Reynolds numbers of 3000-12,000, jet passage lengths in excess of 50 injector passage diameters, volume of injected fluid for puffs and interrupted jets up to 191 source diameters, and streamwise penetration lengths up to 140 source diameters. Near-source behavior varied significantly with source properties but the flows generally became turbulent within 5 source diameters from the source and self-preserving behavior was generally observed at distances greater than 20-30 source diameters from the source

Self-Preserving Properties of Unsteady Round Buoyant Turbulent Plumes and Thermals in Still Fluids

Abstract: The self-preserving properties of round buoyant turbulent starting plumes and starting jets in unstratified environments. The experiments involved dye-containing salt water sources injected vertically downward into still fresh water within a windowed tank. Time-resolved images of the flows were obtained using a CCD camera. Experimental conditions were as follows: source diameters of 3.2 and 6.4 mm, source/ambient density ratios of 1.070 and 1,150, source Reynolds numbers of 4,000-11,000, source Froude numbers of 10-82, volume of source fluid for thermals comprising cylinders having the same cross-sectional areas as the source exit and lengths of 50-382 source diameters, and stream-wise flow penetration lengths up to 110 source diameters and 5.05 Morton length scales from the source. Near-source flow properties varied significantly with source properties but the flows generally became turbulent and then became self-preserving within 5 and 20-30 source diameters from the source, respectively. Within the self-preserving region, both normalized streamwise penetration distances and normalised maximum radial penetration distances as functions of time were in agreement with the scaling relationships for the behavior of self-preserving round buoyant turbulent flows to the following powers: time to the 3/4 power for starting plumes and to the 1/2 power for thermals. Finally, the virtual origins of thermals were independent of source fluid volume for the present test conditions.

Mixing Structure of Plane Self-Preserving Buoyant Turbulent Plumes

Abstract: Measurements of the structure of plane buoyant turbulent plumes are described, emphasizing conditions in the fully developed (self-preserving) portion of the flow. Plumes were simulated using helium/air sources in a still and unstratified air environment. Mean and fluctuating mixture fractions were measured using laser-induced iodine fluorescence. Present measurements extended farther from the source (up to 155 source widths) and had more accurate specifications of plume buoyancy fluxes than past measurements and yielded narrower plume widths and different scaled mean and fluctuating mixture fractions near the plane of symmetry than previously thought. Measurements of probability density functions, temporal power spectra, and temporal integral scales of mixture fraction fluctuations are also reported

Mixture Fraction Statistics of Plane Self-Preserving Buoyant Turbulent Adiabatic Wall Plumes

Abstract: Measurements of the mixture fraction properties of plane buoyant turbulent adiabatic wall plumes (adiabatic wall plumes) are described, emphasizing conditions far from the source where self-preserving behavior is approximated. The experiments involved helium/air mixtures rising along a smooth, plane and vertical wall. Mean and fluctuating mixture fractions were measured using laser-induced iodine fluorescence. Self-preserving behavior was observed 92-155 source widths above the source, yielding smaller normalized plume widths and near-wall mean mixture fractions than earlier measurements. Selfpreserving adiabatic wall plumes mix slower than comparable free line plumes (which have 58 percent larger normalized widths) because the wall prevents mixing on one side and inhibits large-scale turbulent motion. Measurements of probability density functions, temporal power spectra, and temporal integral scales of mixture fraction fluctuations are also reported

Aero-tactile integration in speech perception

Abstract: When we listen to human speech we use a combination of the senses: the ears, obviously, and the eyes to see how a speaker's face changes the perception of consonant sounds. Experiments seeking to add the sense of touch to the mix have until now been inconclusive. Many languages use an expulsion of air to change vowel or consonant sounds — in English to distinguish a sound like 'da' from the microphone-popping 'pa'. Bryan Gick and Donald Derrick take that 'puff of air' as the starting point for a study of whether the sense of touch can contribute to what we 'hear'. They applied small, inaudible air puffs to the skin of volunteers who were simultaneously listening to a series of consonant sounds. Air puffs aimed at either the hand or neck made it more likely that aspirated sounds would be heard. So 'b' was misheard as 'p' following an air puff. This work could prove useful in the future development of audio and telecommunication aids for the hearing impaired. Auditory perception can be enhanced or interfered with by visual information from a speaker's face, but previous studies looking at whether tactile information influences speech perception have been limited. Here, by applying inaudible air puffs on participants' skin and thereby mimicking the tiny bursts of aspiration produced by certain speech sounds, it is found that syllables are more likely to be heard as aspirated, demonstrating that tactile information is also integrated in auditory perception. Visual information from a speaker’s face can enhance1 or interfere with2 accurate auditory perception. This integration of information across auditory and visual streams has been observed in functional imaging studies3,4, and has typically been attributed to the frequency and robustness with which perceivers jointly encounter event-specific information from these two modalities5. Adding the tactile modality has long been considered a crucial next step in understanding multisensory integration. However, previous studies have found an influence of tactile input on speech perception only under limited circumstances, either where perceivers were aware of the task6,7 or where they had received training to establish a cross-modal mapping8,9,10. Here we show that perceivers integrate naturalistic tactile information during auditory speech perception without previous training. Drawing on the observation that some speech sounds produce tiny bursts of aspiration (such as English ‘p’)11, we applied slight, inaudible air puffs on participants’ skin at one of two locations: the right hand or the neck. Syllables heard simultaneously with cutaneous air puffs were more likely to be heard as aspirated (for example, causing participants to mishear ‘b’ as ‘p’). These results demonstrate that perceivers integrate event-relevant tactile information in auditory perception in much the same way as they do visual information.

Speech can produce jet-like transport relevant to asymptomatic spreading of virus

Abstract: Many scientific reports document that asymptomatic and presymptomatic individuals contribute to the spread of COVID-19, probably during conversations in social interactions. Droplet emission occurs during speech, yet few studies document the flow to provide the transport mechanism. This lack of understanding prevents informed public health guidance for risk reduction and mitigation strategies, e.g., the "6-foot rule." Here we analyze flows during breathing and speaking, including phonetic features, using orders-of-magnitude estimates, numerical simulations, and laboratory experiments. We document the spatiotemporal structure of the expelled airflow. Phonetic characteristics of plosive sounds like "P" lead to enhanced directed transport, including jet-like flows that entrain the surrounding air. We highlight three distinct temporal scaling laws for the transport distance of exhaled material including 1) transport over a short distance (<0.5 m) in a fraction of a second, with large angular variations due to the complexity of speech; 2) a longer distance, ∼1 m, where directed transport is driven by individual vortical puffs corresponding to plosive sounds; and 3) a distance out to about 2 m, or even farther, where sequential plosives in a sentence, corresponding effectively to a train of puffs, create conical, jet-like flows. The latter dictates the long-time transport in a conversation. We believe that this work will inform thinking about the role of ventilation, aerosol transport in disease transmission for humans and other animals, and yield a better understanding of linguistic aerodynamics, i.e., aerophonetics.