8 research outputs found
Modeling deposit formation in diesel injector nozzle
No full textThesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2009.Includes bibliographical references (leaves 75-77).Formation of deposit in the diesel injector nozzle affects the injection behavior and hinders performance. Under running condition, deposit precursors are washed away by the ensuing injection. However, during the cool down process after engine shut down, fuel, detergent chemistry, and fluid transport (evaporation) compete to determine the magnitude of deposit. This project involves numerical modeling and simulation of these processes.by Chintoo Sudhiesh Kumar.S.M
Experimental Investigation Of Aerodynamic Interference Heating Due To Protuberances On Flat Plates And Cones Facing Hypersonic Flows
No full textWith the age of hypersonic flight imminent just beyond the horizon, researchers are working hard at designing work-arounds for all the major problems as well as the minor quirks associated with it. One such issue, seemingly innocuous but one that could be potentially deadly, is the problem of interference heating due to surface protuberances. Although an ideal design of the external surfaces of a high-speed aircraft dictates complete smoothness to reduce drag, this is not always possible in reality. Control surfaces, sheet joints, cable protection pads etc. generate surface discontinuities of varying geometries, in the form of both protrusions as well as cavities. These discontinuities are most often small in dimension, comparable to the local boundary layer thickness at that location. Such protuberances always experience high rates of heat transfer, and therefore should be appropriately shielded. However, thermal shielding of the protrusions alone is not a full solution to the problem at hand. The interference caused to the boundary layer by the flow causes the generation of local hot spots in the vicinity of the protuberances, which should be properly mapped and adequately addressed. The work presented in this thesis aims at locating and measuring the heat flux values at these hot spots near the protrusions, and possibly formulating empirical correlations to predict the hot spot heat flux for a given set of flow conditions and protrusion geometry.
Experimental investigations were conducted on a flat plate model and a cone model, with interchangeable sharp and blunt nose tips, with attached 3D protuberances. Platinum thin-film sensors were placed around the protrusion so that the heat fluxes could be measured in its vicinity and the hottest spot located. These experiments were carried out at five different hypersonic free stream flow conditions generated using two shock tunnels, one of the conventional type, and the other of the free-piston driven type. The geometry of the protrusions, i.e., the height and the deflection angle, was also parametrically varied to study its effect on the hot spot heat flux. The results thus obtained for the flat plate case were compared to existing correlations in the open literature from a similar previous study at a much higher Reynolds number range. Since a mismatch was observed between the results of the current experiments and the existing correlations, a new empirical correlation has been developed to predict the hot spot heat flux, that is valid within the range of flow conditions studied here. A similar attempt was made for the case of the cone model, for which no previous correlations exist in the open literature. However, a global correlation covering the entire range of flow conditions used here could not be formed. A correlation that is valid for just one out of the five flow conditions used here is presented for the cones with sharp and blunt nose tips separately.
Schlieren flow visualization was carried out to obtain a better understanding of the shock structures near the protuberances on both models. For most cases, where the protrusion height and deflection angle were large enough to cause flow separation immediately upstream of the protuberance, a separation shock was manifested which deflected some part of the boundary layer above the protuberance, while the rest of the fluid in the boundary layer entered a recirculating region in the separated zone before escaping to the side. Some preliminary computational analysis was conducted which confirmed this qualitatively. However, the quantitative match of surface heat flux between the simulations and experiments were not encouraging. Schlieren visualization revealed that for the flat plate case, the foot of the separation shock was located at a distance of 10.5 to 12 times the protrusion height ahead of it, whereas in the case of the sharp cone, it was at a distance of 9 to 10.5 times the protrusion height. The unsteady nature of the separation shock was also captured and addressed. Some preliminary experiments on boundary layer tripping were also conducted, the results of which have been presented here.
From this analysis, it has become evident that a single global correlation cannot be formed which could be used for a wide range of flow conditions to predict the hot spot heat flux in interference interactions. The entire range of conditions that may be encountered during hypersonic flight has to be broken down into sections, and the interference heating pattern should be studied in each of these sections individually. By doing so, a series of different correlations can be formed at the varying flow conditions which will then be available for high-speed aircraft designers
Application of KRR, K-NN and GPR Algorithms for Predicting the Soaked CBR of Fine-Grained Plastic Soils
No full textCalifornia bearing ratio (CBR) test is one of the comprehensive tests used for the last few decades to design the pavement thickness of roadways, railways and airport runways. Laboratory-performed CBR test is considerably rigorous and time-taking. In a quest for an alternative solution, this study utilizes novel computational approaches, including the kernel ridges regression, K-nearest neighbor and Gaussian process regression (GPR), to predict the soaked CBR value of soils. A vast quantity of 1011 in situ soil samples were collected from an ongoing highway project work site. Two data divisional approaches, i.e., K-Fold and fuzzy c-means (FCM) clustering, were used to separate the dataset into training and testing subsets. Apart from the numerous statistical performance measurement indices, ranking and overfitting analysis were used to identify the best-fitted CBR prediction model. Additionally, the literature models were also tried to validate through present study datasets. From the results of Pearson’s correlation analysis, Sand, Fine Content, Plastic Limit, Plasticity Index, Maximum Dry Density and Optimum Moisture Content were found to be most influencing input parameters in developing the soaked CBR of fine-grained plastic soils. Experimental results also establish the proficiency of the GPR model developed through FCM and K-Fold data division approaches. The K-Fold data division approach was found to be helpful in removing the overfitting of the models. Furthermore, the predictive ability of any model is considerably influenced by the geological location of the soils/materials used for the model development. © 2023, The Author(s)
Experiments in hand-operated, hypersonic shock tunnel facility
No full textExperiments were conducted using the newly developed table-top, hand-operated hypersonic shock tunnel, otherwise known as the Reddy hypersonic shock tunnel. This novel instrument uses only manual force to generate the shock wave in the shock tube, and is designed to generate a freestream flow of Mach 6.5 in the test section. The flow was characterized using stagnation point pressure measurements made using fast-acting piezoelectric transducers. Schlieren visualization was also carried out to capture the bow shock in front of a hemispherical body placed in the flow. Freestream Mach numbers estimated at various points in the test section showed that for a minimum diameter of 46 mm within the test section, the value did not vary by more than 3 % along any cross-sectional plane. The results of the experiments presented here indicate that the device may be successfully employed for basic hypersonic research activities at the university level
Hypersonic flow past a spherically blunted nose cone: a computational study
No full textThe present study investigates the aerodynamic characteristics of spherically blunted nose cone at a hypersonic Mach number of 5.8, numerically. The studies are conducted for different combinations of bluntness ratios and semi-cone angles, at zero angle of attack, in order to ascertain the nose cone parameters which provide minimum aerodynamic drag coefficient. The velocity vector shows the flow deceleration near the nose, re-acceleration through the sides as well the formation of recirculation zones. The structure of bow shock formed ahead of the nose as well as shock detachment distance is depicted by the Mach number contours. It is observed that the shock detachment distance follows linearly increasing behaviour with increase in bluntness ratios for all semi-cone angles studied. An empirical expression is developed for the shock detachment distance using the regression analysis, which reveals that it is mainly a function of bluntness ratio. It is observed that the aerodynamics drag coefficient attains a minimum value for smaller, bluntness ratios and semi-angle. Further, the aerodynamic drag coefficient is observed to be a strong function of bluntness ratios for smaller semi-cone angles
Synthesis and application of porous oil-sorbent microspheres: Characterization retention capacity and sorption kinetics
No full textThe article focuses on the study of oil spill cleanup in an aquatic media by comparing the oil sorption capacities of three polymeric sorbents. Styrene - dodecyl methacrylate - DVB with toluene as porogen (P3) showed a highest removal ability of 5 times its weight. However, key aspect of this research is associated with the retention capacities of the sorbents. The loss in weight measured over time was found to be numerically insignificant for all the three sorbents. Water contact angle for the sorbents i.e., P1, P2, P3 were found to be 113.3 degrees, 107.2 degrees and 97.5 degrees respectively. SEM results confirmed the entrapment of oil between the polymer molecules thereby confirming the phenomenon of sorption. The sorption kinetics of oil over the sorbent surface was followed the pseudo-second order model. The prepared sorbents can be successfully employed for the recovery of oil spills from water sources
