Enthalpy Measurements in the Rent Facility Using the AEDC Transient Enthalpy Probe.

摘要

The heat transfer rates experienced by models in the Re-Entry Nose Tip (RENT) Leg of the Air Force Flight Dynamics Laboratory (AFFDL) 50 Megawatt (MW) Facility are significantly higher than that predicted by stagnation point heating theory, if the bulk (heat balance) enthalpy is used. This could be a result of (1) some of the assumptions in the stagnation point heating theories (i.e., laminar flow, equilibrium air, Newtonian pressure distribution around stagnation point) being violated, (2) a stagnation enthalpy distribution, (3) a stagnation pressure distribution in the free stream, or (4) any combination of these. Null point calorimeters have been used in the past to measure stagnation point heating rate on hemispherical quarter inch nose radius models. It was found that the stagnation point heating rate is a function of both radial position and time which indicates that there exist radial gradients as well as timewise fluctuations in free stream properties. Measurements to date indicate that local stagnation pressure does not vary significantly either spatially or with time within the free stream core and hence, does not appear to be the primary cause of the stagnation point heating fluctuations and profile shapes. Hence, there is a need to make independent measurements of stagnation enthalpy profiles and fluctuations to determine their relationship to the measured stagnation point heating rates.