Chapter 1329 Seeking inspiration from other people’s mistakes


    Although it suffered a huge impact during the process of disintegration and subsequent fall into the water, perhaps due to its location, the portion of the air inlet fragments made of lightweight alloy did not appear to be too much irreparable. bizarre deformations.


    After scanning its appearance into the database, the technicians basically restored its original appearance without much "rationalization".


    This is undoubtedly a huge benefit for subsequent analysis work -


    The rationalized deduction certainly has sufficient theoretical basis to support it, but the problem is that the American design may not be as reasonable as imagined.


    "Academician Chang, further analysis has proven that the reason why this thing can float on the sea for a long time, in addition to its suitable appearance, is that another important reason is that the inside of its wall is also designed as a hollow structure."


    Xing Muchun pointed to the 3D model of most of the air intake on the screen and introduced to Chang Haonan:


    "However, because there is no further specific information, it is impossible to judge whether these spaces are used for coolant flow channels or are designed purely for weight reduction."


    The latter moved closer to the monitor and stared at the series of triangular cross-sectional shapes on the cross-section diagram for a while:


    "Unlikely coolant..."


    Chang Haonan shook his head:


    "If the aircraft adopts liquid cooling, it will basically use fuel directly as the heat exchange medium. However, some water samples collected on the sea surface have been analyzed before. It is based on JP7 aviation fuel and mixed with some flammable metals. The...mixture made with metal oxide particles has poor fluidity. I''m afraid it needs a special fuel circulation system to maintain normal supply. It''s hard to imagine that we have to go through such a winding flow path again..."


    This analysis was quite reasonable and well-founded. Xing Muchun did not express any objection, but only showed a slightly confused expression:


    "But there is currently no evidence that the Americans have mastered the same plasma heat dissipation technology as we do... If no additional cooling methods are needed, the aerodynamic heating of hypersonic flight alone is enough to cause the flying body to collapse due to thermal expansion and contraction. Stretch a few centimeters or more..."


    Chang Haonan was quite tolerant about this. After all, he only had part of the wreckage in his hands. He couldn''t dig into such technical details and had to focus on the key parts.


    So I simply answered:


    "After all, the design speed of the X51A is only about Mach 6, and the aerodynamic heating is not particularly serious. If the distribution of aerodynamic heat can be calculated, then it can still be resisted by structural design... Anyway, don''t think so much, let''s The First Hospital quickly built a full-scale aerodynamic model according to these parameters and prepared the wind tunnel. "


    Xing Muchun immediately stood up and left the computer room to return to the office to make a call.


    And Jiang Zonglin, who was responsible for the operation of the wind tunnel and had been sitting silently on the side just now, also came up:


    "There are so many possibilities that could cause a test to fail. Which part are you going to start testing from?"


    Regarding this issue, Chang Haonan has already made plans in the past few days.


    Therefore, he analyzed it almost without thinking:


    "Judging from the characteristic flight parameters obtained by the radar, the X51A maintained normal flight for about 143 seconds, reached a final speed of Mach 5.45 and maintained it for about 9 seconds, and then almost without warning... at least not on the flight trajectory. Disintegrated suddenly without warning."


    "This situation is unlikely to be a cumulative problem. It is most likely that the working parameters of the scramjet engine were abnormal from the beginning. After accumulating to a critical point between Mach number 5.4-5.5, due to thermal congestion , or reasons such as a sudden intensification of the shock wave string, causing the working cycle to be completely disrupted and ultimately inducing structural damage. "


    "So, starting from the gas heating amount and inlet overflow resistance corresponding to different characteristic Mach numbers, if this is really the problem, the abnormality should be found quickly..."


    Jiang Zonglin stood up after hearing this:


    "Then I''ll get ready right away!"


    …


    It should be said that Chang Haonan''s luck is quite good.


    Although the most likely cause of the accident has been preliminarily analyzed, qualitative analysis and quantitative calculation are always two different levels of difficulty.


    Originally, he was only planning to personally see the entire testing process of the previous few days to gain a preliminary understanding of the design level of his American counterparts on the other side of the ocean, and then focus on the detailed design of the gliding waverider.


    As a result, just a few starts on the first day blew out a set of eye-catching data...


    "Are you sure...the airflow entering the combustion chamber can exceed the speed of sound?"


    Chang Haonan looked at the work cycle curve in front of him and asked the two people beside him doubtfully.


    This question was so basic that the air in the wind tunnel control room was silent for a moment.


    "Of course..." Jiang Zonglin nodded:


    "A single inlet compression surface cannot be used for complete wind tunnel testing, so we connected a standard kissing cone precursor and a standard equal-area-expansion series combustion chamber, which can theoretically meet the requirements of super combustion. Minimum conditions for ramjet start-up were simulated up to just above Mach 5.5 at which disintegration would occur..."


    As he described it, he called up the compiled wind tunnel operation log from the computer:


    "It can be seen that near the speed corresponding to the critical point of disintegration, the thermal congestion disappears, the intensity of the shock string in the isolation section decreases, the shock string in front of the combustion zone moves toward the entrance of the combustion chamber, and the airflow in the combustion chamber must have reached supersonic speed. "


    Indeed, there seems to be no problem from the running records.


    "But these phenomena can only show that the shock wave string exit has reached supersonic speed. Due to the influence of the boundary layer not being completely attached, the situation in the combustion chamber is not necessarily..."


    “…”


    Chang Haonan analyzed it while talking to himself. The expression on his face first became confused, and then quickly turned to understanding. He pointed to the work cycle on the report and said:


    "You see, at the critical point, the working cycle in the combustion chamber is 0-3-4*-9*. The airflow compressed through the inlet is first heated to congestion in an equal-area section, and then maintains Ma= in the expansion pipe 1 until the fuel heat is completely released and the congestion disappears, which is indeed consistent with the characteristics of the supersonic mode.”


    "But after crossing the critical point and reaching Mach 5.5, the working cycle in the combustion chamber instead became 0-3-3''-9''-9*, and the process from 3'' to 9'' is still a limit situation, and the actual pressure expansion The degree cannot reach the ideal value, that is, when the area is heated to the point of congestion, the fuel heat has not yet had time to be completely released..."


    There is no mistake in every song, one post, one content, one 6 one, one book, one book, take a look!


    In fact, as early as when he reached the end of the first half of the sentence, the other two people had already discovered something was wrong.


    "Is this a typical subsonic expansion process?"


    Xing Muchun exclaimed.


    Chang Haonan was also quite surprised by this conclusion, so he did not rush to a conclusion, but went back and checked it again.


    It was finally determined that there was nothing wrong with the analysis process just now.


    “So, as the speed gradually approached Mach 5.5, the scramjet engine of the X51A abnormally returned to the working state of sub-ramjet, causing the cycle to become abnormal, thermal congestion to reappear, and ultimately causing structural problems somewhere. disintegration…"


    He initially surmised the entire process.


    This is certainly not a traceable "cause" of the accident, but it''s pretty close.


    "If this is the case, it can explain why the aircraft was restricted by a speed wall of Mach 5.5 for such a long time under the premise that the scramjet engine was started normally."


    Xing Muchun''s tone gradually became confused:


    "But it''s so strange...how could this happen?"


    "This is something that can''t be inferred from the shape of a section of the air intake..."


    Chang Haonan gently threw the report on the table:


    "It is possible that the scramjet engine took some tricks during the design process and wanted to obtain the highest possible pressure ratio in the isolation section through the transition mode. As a result, due to a small error, the cycle stability was insufficient, and the scramjet engine eventually broke away from the scramjet engine. status, it is also possible that the engine starting speed did not reach the preset value, causing a problem at the beginning of the cycle, or..."


    Before saying the third possibility, his voice stopped abruptly.


    "What else could be possible?"


    Jiang Zonglin looked over curiously.


    "It''s not important."


    Chang Haonan pulled the report in front of him again, took a pen from the side, and drew a few arrows on the cycle parameter curve diagram:


    “I suddenly thought, if we reverse this process, that is, let the engine be in the subsonic cycle mode in the low-speed section, and enter the supersonic cycle mode in the high-speed section, can the ramjet engine have both sub-combustion and super-combustion? Two characteristics?”


    (End of chapter)